Table of Contents

Autism Spectrum Disorder (ASD) is a complex neurodevelopmental condition affecting approximately 78 million people globally. The prevalence of autism has risen sharply in recent years, with estimates suggesting that one in every 50 to 70 individuals may now be affected [1]. The number of children diagnosed with autism has nearly quadrupled in the past decade. Currently, 9.2 children with autistic traits are reported for every 1,000 neurotypical children [2]. This increase is largely attributed to greater awareness and understanding of ASD, improved diagnostic methods and tools, and the broader definition encompassed by the term “autism spectrum.” As a result, more children are being identified and diagnosed with ASD at increasingly younger ages.

It has been observed that children with ASD are more prone to ear infections and therefore receive antibiotics more frequently than their neurotypical peers. Consequently, alterations in the gut microbiome of individuals genetically predisposed to ASD are being studied as a potential risk factor. It is believed that these changes in the microbiome may influence immune and metabolic processes, thereby increasing the risk of ASD. Since ASD often runs in families, it is possible that the altered gut microbiome of a child with ASD may affect siblings or others in close proximity, potentially contributing to the development of the disorder in genetically susceptible children. [3]

ASD is not an illness or disease, but a lifelong condition, with both genetic and environmental factors playing a role in its development.

What is Autism Spectrum Disorder?

ASD is a neurological and developmental disorder classified as a “spectrum” because its symptoms can range from mild (e.g., poor eye contact, difficulty expressing emotions and feelings) to severe (e.g., an inability to speak or follow instructions). The disorder typically begins in early childhood, follows a chronic course and presents with a wide variety of biological backgrounds and clinical features, which differ greatly between individuals.

Symptoms are highly variable, but core characteristics include challenges in social and communication skills, along with restricted and repetitive behaviours and interests. Intellectual and language delays are common, as are gastrointestinal (GI) complaints.

In addition to psychiatric comorbidities, ASD has also been associated with gastrointestinal (GI) dysfunction, which may contribute to maladaptive behaviors, irritability, and social withdrawal. Children with ASD who suffer from abdominal pain, gas, diarrhoea, or constipation are more likely to exhibit irritability, hyperactivity, and social withdrawal. Argumentative, oppositional, defiant, and destructive behaviours are also more frequent in the presence of GI issues. Therefore, gastrointestinal disorders may play a significant role in the severity of behavioural symptoms in autistic individuals. [4]

What are the symptoms?

Symptoms and their severity vary widely in ASD. The following examples illustrate common behaviours. Not every individual with ASD will show all of these traits, but most will display more than one.

  1. Behavioural anomalies related to social communication and interaction:
  • limited or inconsistent eye contact;
  • a lack of emotional response (e.g., happiness, sadness) or reaction to verbal cues (such as their names) by 9 months of age;
  • lining up toys or objects and becoming distressed when they are moved;
  • playing with toys in repetitive ways;
  • focusing on specific parts of objects, such as wheels;
  • and engaging in obsessive interests
  • or repetitive movements like flapping hands, rocking, or spinning.
  • Children may appear not to listen or hear when spoken to
  • Rarely shares interest, emotion or pleasure in objects or activities (including rarely pointing or showing things to others).
  • By 12 months, many do not play interactive games (like pat-a-cake or other clapping games) and do not use gestures like waving.
  • by 24 months, they often show little interest in others’ emotions or distress.
  • Difficulties include engaging in two-way conversations,
  • Often talks at length about a favourite topic without noticing that others are not interested or without giving them a chance to respond.
  • Their facial expressions, movements, and gestures do not match what they are saying.
  • Unusual voice inflection, which may be melodic, monotone or robotic. Speech often has unusual intonation, melody or rhythm. [5]
  • They find it difficult to understand others’ perspectives or social cues, and often cannot predict what others are going to do.
  • Problems adapting behaviour to social situations. Not participating in other children’s play at 36 months of age.
  • Difficulties in participating in imaginative play or forming friendships. At 48-60 months, no role-playing, singing or dancing in front of others.

These characteristics may be present in varying degrees. Individual differences play a big role in how exactly ASD manifests itself. [6]

  1. Repetitive or restricted behaviours may include:
  • Repetition of certain behaviours or unusual behaviours such as repetition of words or phrases (echolalia).
  • Persistent, intense interest in certain topics, such as numbers, details, or facts.
  • Excessively focused interest, for example in moving objects or parts of objects.
  • Changes in routine can make them nervous and difficult to transition from one activity to another; small changes can be upsetting.
  • Certain routine tasks must be followed strictly.
  • More or less sensitive to sensory stimuli than others; may show unusual reactions to, for example, light, sounds, clothing or temperature, or to different forms of sensation.
  • and sleep disturbances.

What could their strengths be?

Around 20% of people with ASD have above-average abilities. While those with Asperger’s syndrome are often perceived as geniuses, exceptional talent can occur across the entire spectrum. Asperger’s typically involves no language delay and often comes with strong cognitive skills, while other forms may involve intellectual or language impairments—yet both can show extraordinary ability in specific areas. People with ASD are often highly detail-oriented, learn effectively and recall knowledge accurately over long periods of time, have excellent visual and auditory memory, and may excel in mathematics, science, music, or art. In many cases, the uniqueness of their behaviour is an advantage, and these individual talents can be developed in a special way. One neurological trait of ASD is difficulty adapting to continuous background stimuli, like noise, which may be overwhelming. However, this same trait allows them to enjoy repetition or routine tasks without boredom, often finding pleasure in repetitive experiences. [6–7]

Figure 1. Exceptional abilities of individuals on the autism spectrum

How is it diagnosed?

ASD is not diagnosed through a single medical test but through a comprehensive assessment process. Professionals observe the child’s behaviour, inquire about developmental milestones in social interactions, communication, and behavioural habits, and assess hearing, speech, and language abilities. The evaluation involves structured observations of social and communicative behaviour, assessed against the criteria set forth in the Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition (DSM-5). [8]

Diagnosis typically involves a multidisciplinary team, including paediatricians, speech and language therapists, and child psychologists. Genetic testing may also be recommended to rule out other conditions such as Rett syndrome or Fragile X syndrome. A precise diagnosis is based on developmental history, direct observation, and information gathered from parents and caregivers [9]. It is crucial that the diagnosis draws on multiple sources to ensure accuracy and guide the development of effective support strategies.

Although ASD is a lifelong condition, early detection, targeted treatment, and appropriate support can significantly enhance the quality of life for individuals with ASD.

What are the underlying causes?

The development of ASD is influenced by a complex interplay of genetic, environmental, immunological, and neurobiological factors. Genetic mutations, epigenetic changes, and prenatal stress or infections can increase the risk. Brain development issues, including impaired connectivity between neural networks and neurotransmitter imbalances, also contribute. Involvement of the immune system, chronic inflammation, metabolic disorders, and mitochondrial dysfunction are key areas of focus in both research and treatment.

Nearly three-quarters of individuals with ASD exhibit low thyroid function. Alarmingly, 60% of women with hypothyroidism are unaware of their condition and may become pregnant without treatment.

Thyroid hormones (T3 and T4), which regulate the proliferation and differentiation of nerve cells, are critical for fetal brain development—especially in the first trimester when the fetus relies entirely on the mother’s hormone supply. A deficiency can result in behavioural, cognitive, and developmental issues, affecting expression of thyroid hormone-dependent genes and elevated oxidative stress.

Toxins and gluten can impair thyroid function. Gluten has been associated with Hashimoto’s thyroiditis, a leading cause of hypothyroidism. A gluten-free diet may reduce autoimmune responses against the thyroid.

Anyone showing signs of ASD should consult a physician familiar with the thyroid-brain connection and initiates the necessary diagnostic tests. Women planning pregnancy are advised to undergo thyroid screening, particularly if they experience hair loss, depression, or infertility. Early intervention is essential to ensure the brain receives sufficient thyroid hormone. [10]

Dysregulated immune responses and inflammation are commonly observed in both allergic diseases and neurodevelopmental disorders. Maternal factors—such as anxiety, depression, gestational diabetes, allergies, dietary habits, exposure to environmental toxins, gut microbiome imbalances, and early sleep disturbances—may all contribute to these outcomes.

People with ASD have higher rates of atopic dermatitis, asthma, and allergic rhinitis compared to neurotypical individuals. Maternal asthma and allergic conditions are linked to increased ASD risk in offspring. [11]

Shared inflammatory and epigenetic mechanisms underlie both allergies and neurodevelopmental disorders, with maternal and environmental influences playing a critical role in their expression and severity. [11]

Children with ASD frequently exhibit food sensitivities, particularly to gluten and dairy. According to the “opioid excess theory,” the digestion of gluten and casein produces peptides with opioid activity. These can enter the bloodstream if intestinal permeability is high and may affect the central nervous system by binding to opioid receptors [12]. Leaky gut syndrome, in which the intestinal lining becomes excessively permeable, allows bacteria, toxins, and undigested food particles to enter the bloodstream, and is widely recognized as a frequent contributor to the development of food sensitivities. [13]

Dysfunction in the dopamine system may contribute to ASD symptoms. The mesocorticolimbic pathway regulates motivation and reward behaviour, while the nigrostriatal pathway influences goal-directed actions. In ASD, dopamine synthesis may be normal, but the availability of dopamine receptors is altered. Dopamine antagonists (which block dopamine receptors) can help reduce irritability and stereotypical behaviours.

The opioid system is also believed to play a role in ASD. This system governs emotional regulation, social bonding, and reward mechanisms. Disruption in this system can lead to social and emotional difficulties. Opioid antagonists can help alleviate symptoms such as hyperactivity and anxiety.

Dysfunction of the dopamine and opioid systems may play a significant role in the pathophysiology of ASD. Medications targeting these systems may offer therapeutic benefits for managing specific symptoms. [14]

The blood–brain barrier (BBB) protects the brain by restricting the entry of microbes and toxins into the central nervous system (CNS). This selective membrane helps regulate nutrient exchange, maintain homeostasis, and support optimal conditions for neuronal function [15]. The gut microbiome significantly influences BBB integrity. Short-chain fatty acids (SCFAs), such as butyrate produced by gut bacteria, strengthen the BBB [15]. However, dysbiosis in the gut can increase intestinal permeability, promote inflammation, and damage the BBB, allowing harmful substances and toxins to enter the brain [16]. This can trigger intracerebral inflammation, neurodegeneration, and inflammatory processes in the neurovascular unit, setting off a vicious cycle that exacerbates central nervous system damage and contributes to neurodevelopmental disorders. [15]

The vagus nerve is increasingly studied in connection with ASD due to its central role in gut-brain communication. The health of the gut microbiome can influence vagus nerve function, which transmits signals from the gut to the brain and back.

An imbalance in the gut microbiome (dysbiosis) often found in ASD may impair vagus nerve signalling, leading to worsening of symptoms such as anxiety and social difficulties. This complex neuronal-microbial relationship plays a key role in regulating brain function and modulating inflammatory processes.

Stimulating the vagus nerve has shown potential in reducing behavioural symptoms and inflammation in individuals with ASD. Vagus nerve stimulation can reinforce BBB integrity, reduce levels of inflammatory mediators, and improve brain function. Signals transmitted from the gut can activate the anti-inflammatory reflex via the BBB, prompting the release of acetylcholine and the modulation of immune cells [15]. This response helps reduce neuroinflammation and protects the BBB.

The BBB can also detect signals from intestinal bacteria, distinguishing between pathogenic and non-pathogenic microbes. Depending on the stimulus, this can lead to either anxiety-inducing or calming effects. This gut–brain–immune network plays a key role in emotional regulation and neurological health. [17]

Transcutaneous vagus nerve stimulation (tVNS), a non-invasive method that stimulates the vagus nerve through the skin, is a promising therapeutic approach for ASD. tVNS has been shown to improve social communication, reduce repetitive behaviours and aggression, and enhance social interaction in children with ASD. [18]

Perinatal infections—including bacterial, viral, or parasitic infections during pregnancy—can activate maternal immune responses that may influence ASD development in the fetus. For example, maternal influenza has been linked to a twofold increase in ASD risk, and a persistent high fever may triple the risk. Antibiotic use during pregnancy may also slightly raise the risk. [19]

In some cases, protein fragments (peptides) from food, bacterial toxins, and environmental chemicals (xenobiotics) can bind to immune cell receptors or enzymes, triggering autoimmune reactions in children with ASD. Certain pathogens, such as bacteria and viruses, can provoke inflammation that affects brain development. [20]

Children with ASD frequently show abnormalities in immune system function. Autoimmune reactions may occur, where the body produces antibodies that target its own nerve cells. Imbalanced inflammatory processes and a family history of autoimmune diseases are also common.

Some children with ASD have antibodies (IgG, IgM, IgA) in their blood that bind to nine different neuromuscular proteins—many of which structurally resemble casein, a milk protein. Pathogens such as Streptococcus (producing streptokinase) and dietary proteins like gliadin and casein may interact with the immune system to trigger the production of autoantibodies (e.g., anti-SK, anti-gliadin, anti-casein) [21]. In such cases, the immune system misidentifies these proteins as foreign and initiates immune responses that may target the child’s own neural structures. The resulting autoantibodies can bind to immune cell receptors or enzymes, thereby triggering an autoimmune process.

Inflammatory and allergic mechanisms may contribute to the development of ASD. Certain immune cells, such as macrophages, can cross the blood–brain barrier and induce changes in the brain that influence behaviour and may be linked to psychiatric symptoms. These processes are often associated with elevated levels of inflammatory cytokines and increased activity of Th2 and Th17 cells.” [11]

Moreover, children with ASD often consume diets lacking in essential amino acids like glutamic acid, serine, tyrosine, and histidine. These are essential for the production of neurotransmitters in the nervous system, so their deficiency can also affect brain function. [22]

Children with ASD often show elevated levels of lead and mercury, which can negatively impact mitochondrial function—vital for cellular energy production [1]. Increased mercury exposure during pregnancy, such as from maternal amalgam dental fillings, has been linked to a higher risk of ASD in offspring [23]. Furthermore, children with ASD may have reduced efficiency in the detoxification of bisphenol A (BPA). The glucuronidation process, which helps eliminate toxins, is found to be 11% lower in children with ASD and 17% lower in those with ADHD compared to neurotypical peers. [24]

Mitochondrial dysfunction is frequently observed in children with ASD, resulting in reduced energy production and elevated oxidative stress. These disruptions can lead to cellular metabolic and bioenergetic abnormalities, which in turn contribute to inflammation, neurodevelopmental disorders and co-morbidities, immune dysregulation, and gastrointestinal problems. [11]

Research has shown diminished activity in the electron transport chain (ETC) and mitochondrial DNA mutations, especially in the frontal and temporal cortices of the brain in children with ASD [25], [11]. In some cases, ETC activity has been associated with increased sensitivity and neurodevelopmental regression. Elevated metabolic biomarkers such as pyruvate, lactate, and alanine further support the presence of mitochondrial issues. Interventions targeting mitochondrial dysfunction—such as L-carnitine and coenzyme Q10—have shown promise, particularly in cases involving gastrointestinal symptoms. Around 74% of individuals with ASD experience GI problems, which are often linked to mitochondrial dysfunction. [25]

A growing body of evidence suggests that certain environmental factors may contribute to the development of ASD. Nutrition is a fundamental component of overall health and well-being and plays a particularly important role in neurodevelopmental disorders, such as ASD and ADHD.

A high-fat maternal diet during pregnancy can negatively affect the fetal gut microbiome and increase the likelihood of ASD. In contrast, breastfeeding for at least six months appears to offer a protective effect. Formula feeding may disrupt the gut microbiome and increase the prevalence of harmful bacteria, such as Clostridium difficile. Children with ASD often exhibit reduced microbiome diversity, with fewer Firmicutes (beneficial bacteria) and more Bacteroidetes, which produce excess propionate—which may affect glucose metabolism and immune responses and have a detrimental effect on the gut-brain axis.

Elevated levels of advanced glycation end-products (AGEs) have also been found in the brains of individuals with ASD, often due to excessive carbohydrate intake. These compounds can promote oxidative stress, inflammation, and neurodegeneration.

In short, maternal diet, eating habits, and the composition of the gut microbiome play a crucial role in the development and manifestation of ASD symptoms. [3]

Children with ASD are five times more likely than their neurotypical peers to exhibit eating disorders, pickiness, refusal of certain foods, and inadequate food intake. They are also more than four times more likely to have gastrointestinal (GI) problems, constipation, diarrhoea and abdominal pain, which can contribute to worsening ASD symptoms.

Around 40% of children with ASD suffer from gastrointestinal symptoms. These problems are linked to dysbiosis—an imbalance in gut bacteria—often triggered by chronic inflammation. Gut microbiome abnormalities, especially in children with ASD, GI symptoms and inflammatory bowel disease, further confirm this connection. [3]

Deficiencies in essential nutrients for brain health—such as B vitamins, omega-3 fatty acids, zinc, magnesium, and selenium—are common in ASD. These deficiencies are often made worse by food selectivity and aversions, particularly regarding food texture. [13]

Underlying causes of autism

Figure 2. Underlying causes of autism

What is the relationship between Autism Spectrum Disorder and the gut microbiome?

Gastrointestinal issues are common in children with ASD and are frequently accompanied by alterations in the gut microbiome, also known as dysbiosis. Gut bacteria influence brain function and behaviour through the gut–brain axis. Research shows that children with ASD tend to have a higher abundance of Clostridium, Desulfovibrio, and Sutterella species, and lower levels of beneficial, anti-inflammatory, and neurotransmitter-producing bacteria such as Bifidobacterium and Lactobacillus. [3]

Frequent antibiotic use and repeated ear infections may contribute to an overgrowth of Desulfovibrio species, which produce pro-inflammatory lipopolysaccharides that can influence ASD-related behaviours. Additionally, certain Clostridium species produce toxins believed to play a significant role in the pathogenesis of ASD. [3]

Dysbiosis does not only lead to gastrointestinal problems but can also result in central nervous system symptoms such as irritability, aggression, sleep disturbances, and anxiety. Targeted modulation of the gut microbiome, for example with probiotics, has emerged as a promising treatment approach. These interventions may reduce inflammation and enhance cognitive functioning in individuals with ASD. [4]

Based on our observations and clinical experience, the gut microbiome of children with ASD differs significantly from that of children with healthy intestinal flora:

  1. Mucus-degrading bacteria (e.g., Ruminococcus gnavus, Ruminococcus torques) are present in unusually high numbers. While these bacteria play a role in renewing the protective mucus layer of the gut, excessive levels can strip and damage the intestinal wall, causing chronic inflammation and increased permeability. This allows bacterial toxins, bacteria, viruses, and undigested proteins to enter the bloodstream, triggering immune responses, intolerances, and allergies.
  2. There is a significant lack of bacteria producing beneficial short chain fatty acids (SCFAs), butyric acid, acetic acid and propionic acid. SCFAs are not only important in maintaining the balance of the gut microbiome, but are also essential for the healthy functioning of the central nervous system and other organs.
  3. As proteins degrade and ferment, pathogenic bacteria proliferate. This leads to abdominal pain, bloating, and protein deficiencies, negatively impacting growth, muscle development, hormone and enzyme production, immune function, and more. Additionally, the enzyme diamine oxidase (DAO), which breaks down histamine, functions only in a sufficiently acidic environment—so an alkaline environment in the small intestine can increase histamine-related symptoms.
  4. Sulfate-reducing bacteria, which thrive on undigested proteins, are overrepresented. This results in both sulfur deficiency (essential for protein synthesis) and an excess of hydrogen sulfide, a toxic compound that damages the gut lining, is toxic to the body and contributes to foul-smelling gas.
  5. We also observe overgrowths of Alistipes species, which metabolise tryptophan. This can disrupt serotonin balance. For instance, Alistipes putredinis produces putrescine, a compound similar to histamine that is also degraded by DAO and may lead to histamine-like symptoms.
  6. Some toxin-producing bacteria are also present, overloading the liver and immune system and impairing nervous system function.
  7. The unprotected gut lining, along with bacteria that produce lipopolysaccharides and other toxins, can activate mast cells (mastocytes). The resulting high levels of histamine increase the permeability of both the intestinal and blood–brain barriers, allowing inflammatory mediators, toxins, and even pathogens to enter the brain and impair neurological function.
  8. Several pathogenic bacteria, typically found in the urinary tract or absent in healthy individuals, have been observed in the gut microbiome of children with ASD. Their presence may indicate urinary tract infections or weakened immune function and can further contribute to intestinal inflammation.
  9. Overgrowth of antibiotic-resistant bacteria is also common, likely due to frequent antibiotic treatments for respiratory and other infections.

All these intestinal imbalances often lead to the overgrowth of bacteria that overload the immune system, keeping the body’s defenses in a state of chronic activation and sustaining a persistent, fluctuating level of inflammation.

Do you suffer from Autism Spectrum Disorder?

Examining the composition of the gut microbiome can help uncover the underlying root causes behind your symptoms.

What are the treatment options?

Currently, there is no medication that can cure ASD or address all of its symptoms. However, certain drugs can help manage specific symptoms—particularly behavioural challenges such as self-injury or aggression. By minimising these issues, individuals with ASD may be better able to focus on learning and communication. Antipsychotic and antidepressant medications are sometimes used to treat associated problems like hyperactivity or anxiety. These medications are often more effective when combined with behavioural therapy. [27]

Behavioural and communication therapies are central to ASD treatment. These interventions aim to improve social interaction and reduce problematic behaviours. Applied Behaviour Analysis (ABA) and specialised educational programmes offer intensive, individualised approaches. Parents can also be trained to support their children in developing daily living skills.

Speech, occupational, and physical therapy can help improve communication abilities, motor coordination, and balance.

Many individuals with ASD experience co-occurring medical conditions, including epilepsy, sleep disturbances, and gastrointestinal issues. Addressing these health concerns is essential and requires collaboration with healthcare providers. Adolescence and adulthood bring additional challenges—ranging from physical changes to social situations—which also require attention. Mental health issues such as anxiety and depression are common and can be effectively managed with support from mental health professionals. [8]

Macronutrient supplementation

Supplements such as omega-3 fatty acids, L-carnitine, and sulforaphane have shown promise in managing ASD symptoms. Omega-3 fatty acids have been found to improve repetitive behaviour, hyperactivity, social communication, and nutritional status. Acetyl-L-carnitine has improved nonverbal cognitive skills, especially when used alongside antipsychotic medications. Sulforaphane, which helps regulate oxidative stress and mitochondrial function, has been shown to reduce irritability and hyperactivity.

Allicin, a bioactive compound derived from garlic, may also benefit individuals with ASD. It possesses antioxidant and neuroprotective properties, helps balance neurotransmitters, and reduces oxidative stress and neuroinflammation. Additionally, it inhibits cholinesterase enzymes, which may support cognitive functions in neuropsychological conditions. [28]

Micronutrient supplementation

Vitamin A supports mucosal immunity and immune tolerance. Supplementation has significantly improved social responsiveness in children with ASD. Vitamin D also shows beneficial effects—especially when combined with omega-3—by reducing hyperactivity and irritability. The most promising outcomes have been seen with combined interventions: vitamins, minerals, essential fatty acids, and a gluten- and casein-free (GFCF) diet. [26]

The mechanism behind vitamin C supplementation lies in its ability to reduce oxidative stress. In children with ASD, vitamin C has been shown to significantly lower oxidative stress levels, as evidenced by improvements in the glutathione ratio. [29]

Coenzyme Q10, known for its antioxidant properties and its role in maintaining cell membrane integrity, may also contribute to managing oxidative stress in ASD. In children, a daily dose of 60 mg has been associated with improved sleep and gastrointestinal symptoms. Higher doses of Coenzyme Q10 (greater than 60 mg/day) may offer a quicker and more sustained antioxidant effect; however, further research is needed to determine the extent of its clinical benefits. [30]

Restoring the microbiome

Probiotics and prebiotics may have beneficial effects in individuals with ASD. Dietary interventions may help reduce symptom severity, improve gastrointestinal function, and alleviate behavioural problems.

Maternal obesity and high-fat diets during pregnancy (MHFD) can alter the gut microbiome and social behaviour of offspring, potentially leading to ASD-like symptoms. The balance in the intestinal tract can be restored by certain beneficial bacteria, which may have a positive effect on ASD symptoms. For instance, Bacteroides fragilis has been shown to restore gut barrier integrity, improve microbial balance, and reduce behavioural symptoms. Lactobacillus reuteri, another probiotic, may significantly alleviate social difficulties. This bacterium boosts oxytocin production, a hormone essential for social bonding and brain function, which is often dysregulated in ASD. [26]

Diet

A gluten- and casein-free diet (GFCF) is a popular intervention for ASD. Following this diet for several months can lead to improvements, especially in individuals with accompanying gastrointestinal symptoms. However, it’s important to avoid nutritional deficiencies, particularly since many individuals with ASD already have restrictive eating habits. [29]

People with ASD typically have lower levels of glutathione and S-adenosylmethionine—key substances in antioxidation and methylation. Testing for oxidative stress and methylation metabolites can distinguish individuals with ASD from neurotypical peers with up to 97% accuracy. Nutrients that support glutathione and S-adenosylmethionine production—such as cysteine, methionine, folic acid, and vitamins B6 and B12—are often essential in an ASD-friendly diet. [29]

Other interventions

Sleep disturbances are common in children with ASD and include trouble falling asleep, restlessness, and poor-quality sleep. Melatonin supplementation can improve sleep quality and reduce daytime symptoms, but should only be used if sleep issues are ASD-related. Light therapy is another helpful tool that can help restore circadian rhythms. Other helpful strategies include avoiding stimulants before bedtime, maintaining a consistent nighttime routine, limiting screen time, and using blackout curtains. [31]

Relaxation techniques—such as deep pressure massage, meditation, and yoga—can reduce agitation and help manage behavioural challenges. Yoga, in particular, has been shown to improve social interaction and overall behaviour, enhancing quality of life. [31]

A personalised approach to behavioural and communication therapy remains essential for managing ASD, supporting the development of social skills, and addressing behavioural challenges. [32]

Functional medicine approach of Autism

Figure 3. Functional medicine approaches to Autism Spectrum Disorder

Do you suffer from Autism Spectrum Disorder?

Examining the composition of the gut microbiome can help uncover the underlying root causes behind your symptoms.

References

[1] M. Ding, S. Shi, S. Qie, J. Li, and X. Xi, ‘Association between heavy metals exposure (cadmium, lead, arsenic, mercury) and child autistic disorder: a systematic review and meta-analysis’, Front Pediatr, vol. 11, p. 1169733, Jul. 2023, DOI: https://doi.org/10.3389/fped.2023.1169733

[2] ‘23.1.1.6. Sajátos nevelési igényű gyermekek, tanulók száma fogyatékosság-típus szerint’ https://www.ksh.hu/stadat_files/okt/hu/okt0006.html

[3] A. Fattorusso, L. Di Genova, G. B. Dell’Isola, E. Mencaroni, and S. Esposito, ‘Autism Spectrum Disorders and the Gut Microbiota’, Nutrients, vol. 11, no. 3, p. 521, Feb. 2019, DOI: https://doi.org/10.3390/nu11030521

[4] M. Madra, R. Ringel, and K. G. Margolis, ‘Gastrointestinal Issues and Autism Spectrum Disorder’, Psychiatr Clin North Am, vol. 44, no. 1, pp. 69–81, Mar. 2021, DOI: https://doi.org/10.1016/j.psc.2020.11.006

[5] R. Andersen, ‘Complications Among People With Autism’, Autism Parenting Magazine, Nov. 17, 2022 https://www.autismparentingmagazine.com/autism-people-complications/

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Table of Contents

Autism Spectrum Disorder (ASD) is a complex neurodevelopmental condition affecting approximately 78 million people globally. The prevalence of autism has risen sharply in recent years, with estimates suggesting that one in every 50 to 70 individuals may now be affected [1]. The number of children diagnosed with autism has nearly quadrupled in the past decade. Currently, 9.2 children with autistic traits are reported for every 1,000 neurotypical children [2]. This increase is largely attributed to greater awareness and understanding of ASD, improved diagnostic methods and tools, and the broader definition encompassed by the term “autism spectrum.” As a result, more children are being identified and diagnosed with ASD at increasingly younger ages.

It has been observed that children with ASD are more prone to ear infections and therefore receive antibiotics more frequently than their neurotypical peers. Consequently, alterations in the gut microbiome of individuals genetically predisposed to ASD are being studied as a potential risk factor. It is believed that these changes in the microbiome may influence immune and metabolic processes, thereby increasing the risk of ASD. Since ASD often runs in families, it is possible that the altered gut microbiome of a child with ASD may affect siblings or others in close proximity, potentially contributing to the development of the disorder in genetically susceptible children. [3]

ASD is not an illness or disease, but a lifelong condition, with both genetic and environmental factors playing a role in its development.

What is Autism Spectrum Disorder?

ASD is a neurological and developmental disorder classified as a “spectrum” because its symptoms can range from mild (e.g., poor eye contact, difficulty expressing emotions and feelings) to severe (e.g., an inability to speak or follow instructions). The disorder typically begins in early childhood, follows a chronic course and presents with a wide variety of biological backgrounds and clinical features, which differ greatly between individuals.

Symptoms are highly variable, but core characteristics include challenges in social and communication skills, along with restricted and repetitive behaviours and interests. Intellectual and language delays are common, as are gastrointestinal (GI) complaints.

In addition to psychiatric comorbidities, ASD has also been associated with gastrointestinal (GI) dysfunction, which may contribute to maladaptive behaviors, irritability, and social withdrawal. Children with ASD who suffer from abdominal pain, gas, diarrhoea, or constipation are more likely to exhibit irritability, hyperactivity, and social withdrawal. Argumentative, oppositional, defiant, and destructive behaviours are also more frequent in the presence of GI issues. Therefore, gastrointestinal disorders may play a significant role in the severity of behavioural symptoms in autistic individuals. [4]

What are the symptoms?

Symptoms and their severity vary widely in ASD. The following examples illustrate common behaviours. Not every individual with ASD will show all of these traits, but most will display more than one.

  1. Behavioural anomalies related to social communication and interaction:
  • limited or inconsistent eye contact;
  • a lack of emotional response (e.g., happiness, sadness) or reaction to verbal cues (such as their names) by 9 months of age;
  • lining up toys or objects and becoming distressed when they are moved;
  • playing with toys in repetitive ways;
  • focusing on specific parts of objects, such as wheels;
  • and engaging in obsessive interests
  • or repetitive movements like flapping hands, rocking, or spinning.
  • Children may appear not to listen or hear when spoken to
  • Rarely shares interest, emotion or pleasure in objects or activities (including rarely pointing or showing things to others).
  • By 12 months, many do not play interactive games (like pat-a-cake or other clapping games) and do not use gestures like waving.
  • by 24 months, they often show little interest in others’ emotions or distress.
  • Difficulties include engaging in two-way conversations,
  • Often talks at length about a favourite topic without noticing that others are not interested or without giving them a chance to respond.
  • Their facial expressions, movements, and gestures do not match what they are saying.
  • Unusual voice inflection, which may be melodic, monotone or robotic. Speech often has unusual intonation, melody or rhythm. [5]
  • They find it difficult to understand others’ perspectives or social cues, and often cannot predict what others are going to do.
  • Problems adapting behaviour to social situations. Not participating in other children’s play at 36 months of age.
  • Difficulties in participating in imaginative play or forming friendships. At 48-60 months, no role-playing, singing or dancing in front of others.

These characteristics may be present in varying degrees. Individual differences play a big role in how exactly ASD manifests itself. [6]

  1. Repetitive or restricted behaviours may include:
  • Repetition of certain behaviours or unusual behaviours such as repetition of words or phrases (echolalia).
  • Persistent, intense interest in certain topics, such as numbers, details, or facts.
  • Excessively focused interest, for example in moving objects or parts of objects.
  • Changes in routine can make them nervous and difficult to transition from one activity to another; small changes can be upsetting.
  • Certain routine tasks must be followed strictly.
  • More or less sensitive to sensory stimuli than others; may show unusual reactions to, for example, light, sounds, clothing or temperature, or to different forms of sensation.
  • and sleep disturbances.

What could their strengths be?

Around 20% of people with ASD have above-average abilities. While those with Asperger’s syndrome are often perceived as geniuses, exceptional talent can occur across the entire spectrum. Asperger’s typically involves no language delay and often comes with strong cognitive skills, while other forms may involve intellectual or language impairments—yet both can show extraordinary ability in specific areas. People with ASD are often highly detail-oriented, learn effectively and recall knowledge accurately over long periods of time, have excellent visual and auditory memory, and may excel in mathematics, science, music, or art. In many cases, the uniqueness of their behaviour is an advantage, and these individual talents can be developed in a special way. One neurological trait of ASD is difficulty adapting to continuous background stimuli, like noise, which may be overwhelming. However, this same trait allows them to enjoy repetition or routine tasks without boredom, often finding pleasure in repetitive experiences. [6–7]

Figure 1. Exceptional abilities of individuals on the autism spectrum

How is it diagnosed?

ASD is not diagnosed through a single medical test but through a comprehensive assessment process. Professionals observe the child’s behaviour, inquire about developmental milestones in social interactions, communication, and behavioural habits, and assess hearing, speech, and language abilities. The evaluation involves structured observations of social and communicative behaviour, assessed against the criteria set forth in the Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition (DSM-5). [8]

Diagnosis typically involves a multidisciplinary team, including paediatricians, speech and language therapists, and child psychologists. Genetic testing may also be recommended to rule out other conditions such as Rett syndrome or Fragile X syndrome. A precise diagnosis is based on developmental history, direct observation, and information gathered from parents and caregivers [9]. It is crucial that the diagnosis draws on multiple sources to ensure accuracy and guide the development of effective support strategies.

Although ASD is a lifelong condition, early detection, targeted treatment, and appropriate support can significantly enhance the quality of life for individuals with ASD.

What are the underlying causes?

The development of ASD is influenced by a complex interplay of genetic, environmental, immunological, and neurobiological factors. Genetic mutations, epigenetic changes, and prenatal stress or infections can increase the risk. Brain development issues, including impaired connectivity between neural networks and neurotransmitter imbalances, also contribute. Involvement of the immune system, chronic inflammation, metabolic disorders, and mitochondrial dysfunction are key areas of focus in both research and treatment.

Nearly three-quarters of individuals with ASD exhibit low thyroid function. Alarmingly, 60% of women with hypothyroidism are unaware of their condition and may become pregnant without treatment.

Thyroid hormones (T3 and T4), which regulate the proliferation and differentiation of nerve cells, are critical for fetal brain development—especially in the first trimester when the fetus relies entirely on the mother’s hormone supply. A deficiency can result in behavioural, cognitive, and developmental issues, affecting expression of thyroid hormone-dependent genes and elevated oxidative stress.

Toxins and gluten can impair thyroid function. Gluten has been associated with Hashimoto’s thyroiditis, a leading cause of hypothyroidism. A gluten-free diet may reduce autoimmune responses against the thyroid.

Anyone showing signs of ASD should consult a physician familiar with the thyroid-brain connection and initiates the necessary diagnostic tests. Women planning pregnancy are advised to undergo thyroid screening, particularly if they experience hair loss, depression, or infertility. Early intervention is essential to ensure the brain receives sufficient thyroid hormone. [10]

Dysregulated immune responses and inflammation are commonly observed in both allergic diseases and neurodevelopmental disorders. Maternal factors—such as anxiety, depression, gestational diabetes, allergies, dietary habits, exposure to environmental toxins, gut microbiome imbalances, and early sleep disturbances—may all contribute to these outcomes.

People with ASD have higher rates of atopic dermatitis, asthma, and allergic rhinitis compared to neurotypical individuals. Maternal asthma and allergic conditions are linked to increased ASD risk in offspring. [11]

Shared inflammatory and epigenetic mechanisms underlie both allergies and neurodevelopmental disorders, with maternal and environmental influences playing a critical role in their expression and severity. [11]

Children with ASD frequently exhibit food sensitivities, particularly to gluten and dairy. According to the “opioid excess theory,” the digestion of gluten and casein produces peptides with opioid activity. These can enter the bloodstream if intestinal permeability is high and may affect the central nervous system by binding to opioid receptors [12]. Leaky gut syndrome, in which the intestinal lining becomes excessively permeable, allows bacteria, toxins, and undigested food particles to enter the bloodstream, and is widely recognized as a frequent contributor to the development of food sensitivities. [13]

Dysfunction in the dopamine system may contribute to ASD symptoms. The mesocorticolimbic pathway regulates motivation and reward behaviour, while the nigrostriatal pathway influences goal-directed actions. In ASD, dopamine synthesis may be normal, but the availability of dopamine receptors is altered. Dopamine antagonists (which block dopamine receptors) can help reduce irritability and stereotypical behaviours.

The opioid system is also believed to play a role in ASD. This system governs emotional regulation, social bonding, and reward mechanisms. Disruption in this system can lead to social and emotional difficulties. Opioid antagonists can help alleviate symptoms such as hyperactivity and anxiety.

Dysfunction of the dopamine and opioid systems may play a significant role in the pathophysiology of ASD. Medications targeting these systems may offer therapeutic benefits for managing specific symptoms. [14]

The blood–brain barrier (BBB) protects the brain by restricting the entry of microbes and toxins into the central nervous system (CNS). This selective membrane helps regulate nutrient exchange, maintain homeostasis, and support optimal conditions for neuronal function [15]. The gut microbiome significantly influences BBB integrity. Short-chain fatty acids (SCFAs), such as butyrate produced by gut bacteria, strengthen the BBB [15]. However, dysbiosis in the gut can increase intestinal permeability, promote inflammation, and damage the BBB, allowing harmful substances and toxins to enter the brain [16]. This can trigger intracerebral inflammation, neurodegeneration, and inflammatory processes in the neurovascular unit, setting off a vicious cycle that exacerbates central nervous system damage and contributes to neurodevelopmental disorders. [15]

The vagus nerve is increasingly studied in connection with ASD due to its central role in gut-brain communication. The health of the gut microbiome can influence vagus nerve function, which transmits signals from the gut to the brain and back.

An imbalance in the gut microbiome (dysbiosis) often found in ASD may impair vagus nerve signalling, leading to worsening of symptoms such as anxiety and social difficulties. This complex neuronal-microbial relationship plays a key role in regulating brain function and modulating inflammatory processes.

Stimulating the vagus nerve has shown potential in reducing behavioural symptoms and inflammation in individuals with ASD. Vagus nerve stimulation can reinforce BBB integrity, reduce levels of inflammatory mediators, and improve brain function. Signals transmitted from the gut can activate the anti-inflammatory reflex via the BBB, prompting the release of acetylcholine and the modulation of immune cells [15]. This response helps reduce neuroinflammation and protects the BBB.

The BBB can also detect signals from intestinal bacteria, distinguishing between pathogenic and non-pathogenic microbes. Depending on the stimulus, this can lead to either anxiety-inducing or calming effects. This gut–brain–immune network plays a key role in emotional regulation and neurological health. [17]

Transcutaneous vagus nerve stimulation (tVNS), a non-invasive method that stimulates the vagus nerve through the skin, is a promising therapeutic approach for ASD. tVNS has been shown to improve social communication, reduce repetitive behaviours and aggression, and enhance social interaction in children with ASD. [18]

Perinatal infections—including bacterial, viral, or parasitic infections during pregnancy—can activate maternal immune responses that may influence ASD development in the fetus. For example, maternal influenza has been linked to a twofold increase in ASD risk, and a persistent high fever may triple the risk. Antibiotic use during pregnancy may also slightly raise the risk. [19]

In some cases, protein fragments (peptides) from food, bacterial toxins, and environmental chemicals (xenobiotics) can bind to immune cell receptors or enzymes, triggering autoimmune reactions in children with ASD. Certain pathogens, such as bacteria and viruses, can provoke inflammation that affects brain development. [20]

Children with ASD frequently show abnormalities in immune system function. Autoimmune reactions may occur, where the body produces antibodies that target its own nerve cells. Imbalanced inflammatory processes and a family history of autoimmune diseases are also common.

Some children with ASD have antibodies (IgG, IgM, IgA) in their blood that bind to nine different neuromuscular proteins—many of which structurally resemble casein, a milk protein. Pathogens such as Streptococcus (producing streptokinase) and dietary proteins like gliadin and casein may interact with the immune system to trigger the production of autoantibodies (e.g., anti-SK, anti-gliadin, anti-casein) [21]. In such cases, the immune system misidentifies these proteins as foreign and initiates immune responses that may target the child’s own neural structures. The resulting autoantibodies can bind to immune cell receptors or enzymes, thereby triggering an autoimmune process.

Inflammatory and allergic mechanisms may contribute to the development of ASD. Certain immune cells, such as macrophages, can cross the blood–brain barrier and induce changes in the brain that influence behaviour and may be linked to psychiatric symptoms. These processes are often associated with elevated levels of inflammatory cytokines and increased activity of Th2 and Th17 cells.” [11]

Moreover, children with ASD often consume diets lacking in essential amino acids like glutamic acid, serine, tyrosine, and histidine. These are essential for the production of neurotransmitters in the nervous system, so their deficiency can also affect brain function. [22]

Children with ASD often show elevated levels of lead and mercury, which can negatively impact mitochondrial function—vital for cellular energy production [1]. Increased mercury exposure during pregnancy, such as from maternal amalgam dental fillings, has been linked to a higher risk of ASD in offspring [23]. Furthermore, children with ASD may have reduced efficiency in the detoxification of bisphenol A (BPA). The glucuronidation process, which helps eliminate toxins, is found to be 11% lower in children with ASD and 17% lower in those with ADHD compared to neurotypical peers. [24]

Mitochondrial dysfunction is frequently observed in children with ASD, resulting in reduced energy production and elevated oxidative stress. These disruptions can lead to cellular metabolic and bioenergetic abnormalities, which in turn contribute to inflammation, neurodevelopmental disorders and co-morbidities, immune dysregulation, and gastrointestinal problems. [11]

Research has shown diminished activity in the electron transport chain (ETC) and mitochondrial DNA mutations, especially in the frontal and temporal cortices of the brain in children with ASD [25], [11]. In some cases, ETC activity has been associated with increased sensitivity and neurodevelopmental regression. Elevated metabolic biomarkers such as pyruvate, lactate, and alanine further support the presence of mitochondrial issues. Interventions targeting mitochondrial dysfunction—such as L-carnitine and coenzyme Q10—have shown promise, particularly in cases involving gastrointestinal symptoms. Around 74% of individuals with ASD experience GI problems, which are often linked to mitochondrial dysfunction. [25]

A growing body of evidence suggests that certain environmental factors may contribute to the development of ASD. Nutrition is a fundamental component of overall health and well-being and plays a particularly important role in neurodevelopmental disorders, such as ASD and ADHD.

A high-fat maternal diet during pregnancy can negatively affect the fetal gut microbiome and increase the likelihood of ASD. In contrast, breastfeeding for at least six months appears to offer a protective effect. Formula feeding may disrupt the gut microbiome and increase the prevalence of harmful bacteria, such as Clostridium difficile. Children with ASD often exhibit reduced microbiome diversity, with fewer Firmicutes (beneficial bacteria) and more Bacteroidetes, which produce excess propionate—which may affect glucose metabolism and immune responses and have a detrimental effect on the gut-brain axis.

Elevated levels of advanced glycation end-products (AGEs) have also been found in the brains of individuals with ASD, often due to excessive carbohydrate intake. These compounds can promote oxidative stress, inflammation, and neurodegeneration.

In short, maternal diet, eating habits, and the composition of the gut microbiome play a crucial role in the development and manifestation of ASD symptoms. [3]

Children with ASD are five times more likely than their neurotypical peers to exhibit eating disorders, pickiness, refusal of certain foods, and inadequate food intake. They are also more than four times more likely to have gastrointestinal (GI) problems, constipation, diarrhoea and abdominal pain, which can contribute to worsening ASD symptoms.

Around 40% of children with ASD suffer from gastrointestinal symptoms. These problems are linked to dysbiosis—an imbalance in gut bacteria—often triggered by chronic inflammation. Gut microbiome abnormalities, especially in children with ASD, GI symptoms and inflammatory bowel disease, further confirm this connection. [3]

Deficiencies in essential nutrients for brain health—such as B vitamins, omega-3 fatty acids, zinc, magnesium, and selenium—are common in ASD. These deficiencies are often made worse by food selectivity and aversions, particularly regarding food texture. [13]

Underlying causes of autism

Figure 2. Underlying causes of autism

What is the relationship between Autism Spectrum Disorder and the gut microbiome?

Gastrointestinal issues are common in children with ASD and are frequently accompanied by alterations in the gut microbiome, also known as dysbiosis. Gut bacteria influence brain function and behaviour through the gut–brain axis. Research shows that children with ASD tend to have a higher abundance of Clostridium, Desulfovibrio, and Sutterella species, and lower levels of beneficial, anti-inflammatory, and neurotransmitter-producing bacteria such as Bifidobacterium and Lactobacillus. [3]

Frequent antibiotic use and repeated ear infections may contribute to an overgrowth of Desulfovibrio species, which produce pro-inflammatory lipopolysaccharides that can influence ASD-related behaviours. Additionally, certain Clostridium species produce toxins believed to play a significant role in the pathogenesis of ASD. [3]

Dysbiosis does not only lead to gastrointestinal problems but can also result in central nervous system symptoms such as irritability, aggression, sleep disturbances, and anxiety. Targeted modulation of the gut microbiome, for example with probiotics, has emerged as a promising treatment approach. These interventions may reduce inflammation and enhance cognitive functioning in individuals with ASD. [4]

Based on our observations and clinical experience, the gut microbiome of children with ASD differs significantly from that of children with healthy intestinal flora:

  1. Mucus-degrading bacteria (e.g., Ruminococcus gnavus, Ruminococcus torques) are present in unusually high numbers. While these bacteria play a role in renewing the protective mucus layer of the gut, excessive levels can strip and damage the intestinal wall, causing chronic inflammation and increased permeability. This allows bacterial toxins, bacteria, viruses, and undigested proteins to enter the bloodstream, triggering immune responses, intolerances, and allergies.
  2. There is a significant lack of bacteria producing beneficial short chain fatty acids (SCFAs), butyric acid, acetic acid and propionic acid. SCFAs are not only important in maintaining the balance of the gut microbiome, but are also essential for the healthy functioning of the central nervous system and other organs.
  3. As proteins degrade and ferment, pathogenic bacteria proliferate. This leads to abdominal pain, bloating, and protein deficiencies, negatively impacting growth, muscle development, hormone and enzyme production, immune function, and more. Additionally, the enzyme diamine oxidase (DAO), which breaks down histamine, functions only in a sufficiently acidic environment—so an alkaline environment in the small intestine can increase histamine-related symptoms.
  4. Sulfate-reducing bacteria, which thrive on undigested proteins, are overrepresented. This results in both sulfur deficiency (essential for protein synthesis) and an excess of hydrogen sulfide, a toxic compound that damages the gut lining, is toxic to the body and contributes to foul-smelling gas.
  5. We also observe overgrowths of Alistipes species, which metabolise tryptophan. This can disrupt serotonin balance. For instance, Alistipes putredinis produces putrescine, a compound similar to histamine that is also degraded by DAO and may lead to histamine-like symptoms.
  6. Some toxin-producing bacteria are also present, overloading the liver and immune system and impairing nervous system function.
  7. The unprotected gut lining, along with bacteria that produce lipopolysaccharides and other toxins, can activate mast cells (mastocytes). The resulting high levels of histamine increase the permeability of both the intestinal and blood–brain barriers, allowing inflammatory mediators, toxins, and even pathogens to enter the brain and impair neurological function.
  8. Several pathogenic bacteria, typically found in the urinary tract or absent in healthy individuals, have been observed in the gut microbiome of children with ASD. Their presence may indicate urinary tract infections or weakened immune function and can further contribute to intestinal inflammation.
  9. Overgrowth of antibiotic-resistant bacteria is also common, likely due to frequent antibiotic treatments for respiratory and other infections.

All these intestinal imbalances often lead to the overgrowth of bacteria that overload the immune system, keeping the body’s defenses in a state of chronic activation and sustaining a persistent, fluctuating level of inflammation.

Do you suffer from Autism Spectrum Disorder?

Examining the composition of the gut microbiome can help uncover the underlying root causes behind your symptoms.

What are the treatment options?

Currently, there is no medication that can cure ASD or address all of its symptoms. However, certain drugs can help manage specific symptoms—particularly behavioural challenges such as self-injury or aggression. By minimising these issues, individuals with ASD may be better able to focus on learning and communication. Antipsychotic and antidepressant medications are sometimes used to treat associated problems like hyperactivity or anxiety. These medications are often more effective when combined with behavioural therapy. [27]

Behavioural and communication therapies are central to ASD treatment. These interventions aim to improve social interaction and reduce problematic behaviours. Applied Behaviour Analysis (ABA) and specialised educational programmes offer intensive, individualised approaches. Parents can also be trained to support their children in developing daily living skills.

Speech, occupational, and physical therapy can help improve communication abilities, motor coordination, and balance.

Many individuals with ASD experience co-occurring medical conditions, including epilepsy, sleep disturbances, and gastrointestinal issues. Addressing these health concerns is essential and requires collaboration with healthcare providers. Adolescence and adulthood bring additional challenges—ranging from physical changes to social situations—which also require attention. Mental health issues such as anxiety and depression are common and can be effectively managed with support from mental health professionals. [8]

Macronutrient supplementation

Supplements such as omega-3 fatty acids, L-carnitine, and sulforaphane have shown promise in managing ASD symptoms. Omega-3 fatty acids have been found to improve repetitive behaviour, hyperactivity, social communication, and nutritional status. Acetyl-L-carnitine has improved nonverbal cognitive skills, especially when used alongside antipsychotic medications. Sulforaphane, which helps regulate oxidative stress and mitochondrial function, has been shown to reduce irritability and hyperactivity.

Allicin, a bioactive compound derived from garlic, may also benefit individuals with ASD. It possesses antioxidant and neuroprotective properties, helps balance neurotransmitters, and reduces oxidative stress and neuroinflammation. Additionally, it inhibits cholinesterase enzymes, which may support cognitive functions in neuropsychological conditions. [28]

Micronutrient supplementation

Vitamin A supports mucosal immunity and immune tolerance. Supplementation has significantly improved social responsiveness in children with ASD. Vitamin D also shows beneficial effects—especially when combined with omega-3—by reducing hyperactivity and irritability. The most promising outcomes have been seen with combined interventions: vitamins, minerals, essential fatty acids, and a gluten- and casein-free (GFCF) diet. [26]

The mechanism behind vitamin C supplementation lies in its ability to reduce oxidative stress. In children with ASD, vitamin C has been shown to significantly lower oxidative stress levels, as evidenced by improvements in the glutathione ratio. [29]

Coenzyme Q10, known for its antioxidant properties and its role in maintaining cell membrane integrity, may also contribute to managing oxidative stress in ASD. In children, a daily dose of 60 mg has been associated with improved sleep and gastrointestinal symptoms. Higher doses of Coenzyme Q10 (greater than 60 mg/day) may offer a quicker and more sustained antioxidant effect; however, further research is needed to determine the extent of its clinical benefits. [30]

Restoring the microbiome

Probiotics and prebiotics may have beneficial effects in individuals with ASD. Dietary interventions may help reduce symptom severity, improve gastrointestinal function, and alleviate behavioural problems.

Maternal obesity and high-fat diets during pregnancy (MHFD) can alter the gut microbiome and social behaviour of offspring, potentially leading to ASD-like symptoms. The balance in the intestinal tract can be restored by certain beneficial bacteria, which may have a positive effect on ASD symptoms. For instance, Bacteroides fragilis has been shown to restore gut barrier integrity, improve microbial balance, and reduce behavioural symptoms. Lactobacillus reuteri, another probiotic, may significantly alleviate social difficulties. This bacterium boosts oxytocin production, a hormone essential for social bonding and brain function, which is often dysregulated in ASD. [26]

Diet

A gluten- and casein-free diet (GFCF) is a popular intervention for ASD. Following this diet for several months can lead to improvements, especially in individuals with accompanying gastrointestinal symptoms. However, it’s important to avoid nutritional deficiencies, particularly since many individuals with ASD already have restrictive eating habits. [29]

People with ASD typically have lower levels of glutathione and S-adenosylmethionine—key substances in antioxidation and methylation. Testing for oxidative stress and methylation metabolites can distinguish individuals with ASD from neurotypical peers with up to 97% accuracy. Nutrients that support glutathione and S-adenosylmethionine production—such as cysteine, methionine, folic acid, and vitamins B6 and B12—are often essential in an ASD-friendly diet. [29]

Other interventions

Sleep disturbances are common in children with ASD and include trouble falling asleep, restlessness, and poor-quality sleep. Melatonin supplementation can improve sleep quality and reduce daytime symptoms, but should only be used if sleep issues are ASD-related. Light therapy is another helpful tool that can help restore circadian rhythms. Other helpful strategies include avoiding stimulants before bedtime, maintaining a consistent nighttime routine, limiting screen time, and using blackout curtains. [31]

Relaxation techniques—such as deep pressure massage, meditation, and yoga—can reduce agitation and help manage behavioural challenges. Yoga, in particular, has been shown to improve social interaction and overall behaviour, enhancing quality of life. [31]

A personalised approach to behavioural and communication therapy remains essential for managing ASD, supporting the development of social skills, and addressing behavioural challenges. [32]

Functional medicine approach of Autism

Figure 3. Functional medicine approaches to Autism Spectrum Disorder

Do you suffer from Autism Spectrum Disorder?

Examining the composition of the gut microbiome can help uncover the underlying root causes behind your symptoms.

References

[1] M. Ding, S. Shi, S. Qie, J. Li, and X. Xi, ‘Association between heavy metals exposure (cadmium, lead, arsenic, mercury) and child autistic disorder: a systematic review and meta-analysis’, Front Pediatr, vol. 11, p. 1169733, Jul. 2023, DOI: https://doi.org/10.3389/fped.2023.1169733

[2] ‘23.1.1.6. Sajátos nevelési igényű gyermekek, tanulók száma fogyatékosság-típus szerint’ https://www.ksh.hu/stadat_files/okt/hu/okt0006.html

[3] A. Fattorusso, L. Di Genova, G. B. Dell’Isola, E. Mencaroni, and S. Esposito, ‘Autism Spectrum Disorders and the Gut Microbiota’, Nutrients, vol. 11, no. 3, p. 521, Feb. 2019, DOI: https://doi.org/10.3390/nu11030521

[4] M. Madra, R. Ringel, and K. G. Margolis, ‘Gastrointestinal Issues and Autism Spectrum Disorder’, Psychiatr Clin North Am, vol. 44, no. 1, pp. 69–81, Mar. 2021, DOI: https://doi.org/10.1016/j.psc.2020.11.006

[5] R. Andersen, ‘Complications Among People With Autism’, Autism Parenting Magazine, Nov. 17, 2022 https://www.autismparentingmagazine.com/autism-people-complications/

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Published On: July 17th, 2025 / Categories: Uncategorized / Tags: /

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