Autism may be caused by deficiencies in several nutrients

During fetal development and childhood, the brain requires a range of nutrients to build the nervous system and support cognitive development. According to a new review article published in Nutrients, widespread deficiencies in vitamins C, D, and A, as well as iron, iodine, selenium, zinc, and other nutrients, may contribute to the development of autism.

Individuals with autism experience significant impairments in social imagination, behavior, communication, and interaction. The condition is thought to result from changes in brain development, with symptoms often appearing in childhood and leading to lifelong challenges of varying severity. The term autism spectrum disorder (ASD) is also used, which includes variants such as infantile autism and Asperger’s syndrome. Around 20 percent receive the diagnosis as adults, and many also suffer from co-occurring conditions such as ADHD, depression, anxiety, and eating disorders.
Although genes may play a role, environmental factors are believed to be the primary cause of the sharp rise in autism rates. In the U.S., the prevalence of autism has quadrupled over the past 20 years, and the same trend is seen in other countries. One contributing factor appears to be unbalanced diets and nutrient deficiencies. It has been reported that 89% of children with autism have restrictive eating habits, which makes them more vulnerable during development. Vitamin C deficiency has previously been linked to an increased risk, and the new meta-analysis aimed to examine whether deficiencies in other nutrients may also raise the risk.

Widespread nutrient deficiencies worsen the issue

Using the PubMed and ScienceDirect databases and relevant search terms, the researchers analyzed 27 articles involving children and adolescents (aged 2 - 18) with autism and their deficiencies in various nutrients. The study revealed widespread deficiencies in the following:

• Vitamin D (25%)
• Vitamin A (25%)
• B vitamins (18%)
• Calcium (11%)
• Iron (10%)
• Mild deficiencies in iodine, zinc, vitamin E, selenium, and others

The authors also found that all cases of calcium deficiency were accompanied by vitamin D deficiency, and all cases of iron deficiency were accompanied by vitamin C deficiency. Additionally, 25% of those with vitamin A deficiency also lacked vitamin B12. The authors highlight that these combined deficiencies are problematic, as nutrients interact and support each other’s absorption and function in the body.
Deficiency diseases such as rickets, goiter, pellagra, and xerophthalmia (an eye disorder) were also reported. Seventy percent of individuals with autism had multiple deficiencies, all of which were linked to poor or restrictive diets due to pickiness, sensitivities, or other aversions. These diets often consisted of refined carbohydrates and empty calories. Over 50% of the participants had a high BMI, and none were underweight.
The researchers conclude that children and adolescents with autism are at high risk of nutrient deficiencies - even if their growth and BMI appear to be normal. Therefore, further research is needed to understand how early intervention with proper nutrition can help prevent complications associated with autism.

The brain's nutritional needs during growth and development

The brain contains the highest concentration of vitamin C in the body. This is because vitamin C is essential for collagen production and numerous enzyme functions of importance to the nervous system. It also acts as a powerful antioxidant that protects nerve cells from damage caused by free radicals. Among individuals with autism, vitamin C deficiency is common due to low intake of fruits and vegetables.
The review article also discusses how vitamin D and calcium are essential for bone development. Moreover, most cells (including those in the brain and nervous system) have vitamin D receptors. The risk of developing autism is particularly high in boys whose mothers lacked vitamin D during pregnancy, according to a study from the University of Queensland in Australia.
Vitamin D deficiency is widespread due to limited sun exposure and excessive use of sunscreen, which blocks the skin's ability to produce the vitamin. Many pregnant women, children, and adolescents do not receive the recommended vitamin D supplements, and many require higher doses to optimize blood levels.
A study published in the Journal of Child Psychology and Psychiatry showed that vitamin D supplementation can improve autism symptoms such as hyperactivity, social withdrawal, and functional impairments.
Although vitamin A deficiency is rare in the general population, it is common among individuals with autism. Vitamin A is particularly important for eye health, mucous membranes, skin, and the immune system. Good sources of true vitamin A (retinol) include liver, liver pâté, eggs, fish, and full-fat dairy products - foods often avoided by people with autism. Carrots and green vegetables contain beta-carotene, a precursor to vitamin A (retinol).
B vitamins are a group of water-soluble vitamins crucial for energy metabolism, blood formation, and nervous system function. Good sources include whole grains and green vegetables, while vitamin B12 is only found in animal products.
It is recommended that pregnant women take higher doses of folic acid (vitamin B9) early in pregnancy to prevent neural tube defects. A Canadian study has shown that folic acid supplementation throughout pregnancy reduces the risk of the child developing neurological damage and autistic behaviors due to lead exposure.
Iron is vital for transporting oxygen in the blood to all cells, and it supports growth, vitality, and learning ability. Good sources include meat, eggs, and other animal-based foods. Iron absorption is vitamin C-dependent. Diets dominated by foods like pizza, bread, fries, and ultra-processed products contribute to widespread iron deficiency, especially in individuals with autism. Calcium supplements and excessive dairy intake can inhibit iron absorption.
Iodine, mainly found in fish, shellfish, and seaweed, is essential for the production of thyroid hormones. Selenium is needed to activate these hormones. It also supports brain function and helps detoxify heavy metals like mercury, which can harm the nervous system. Selenium is found in organ meats, meat, eggs, Brazil nuts, and grains, but deficiencies are common in Europe due to mineral-depleted soil, which affects the entire food chain.
Zinc plays a vital role in growth and mental balance. Researchers have now identified a connection between zinc, genes, and the abnormal neurological pathways associated with autism. Good sources of zinc include shellfish, liver, meat, eggs, dairy, nuts, seeds, and beans. Zinc from animal sources is more easily absorbed.
In short, the brain and nervous system require a broad spectrum of nutrients that work together in numerous biochemical processes. Therefore, widespread deficiencies in one or more nutrients can have serious consequences for the brain, nervous system, and overall health.
Although magnesium deficiency was not covered in this review, other studies suggest that it may also contribute to the development of autism and ADHD. It is also important to remember that the brain needs a substantial amount of cholesterol and other high-quality fats.

The role of omega-3 fatty acids in brain health

Oily fish and fish oil supplements contain the omega-3 fatty acids EPA and DHA, which are crucial for the brain, nervous system, and mental health throughout life. Deficiencies in EPA and DHA are widespread and increase the risk of numerous conditions, including autism, ADHD, depression, and bipolar disorder. Fish oil supplements may therefore hold promise in preventing and supporting the treatment of various mental health disorders, according to a previous review published in Nutrients.
Another review article published by Cambridge University Press has also shown that fish oil supplementation can reduce hyperactivity and incoherent speech in young children with autism.

References:

Kamsiyochukwu S Daniel et al. The Increasing Prevalence of Autism Spectrum Disorder in the U.S. and Its implications for Pediatric Micronutrient Status. A narrative Review of Case Reports and Series. Nutrients 2025

Joshua D et al. Combined Exposure to Folate and Lead during Pregnancy and Autistic-Like Behaviors among Canadian Children from the MIREC Pregnancy and Birth Cohort. Environmental Health Perspective, 2024

Ali, A. A. et al. Developmental vitamin D deficiency increases foetal exposure to testosterone. Molecular Autism. 2020

Khaled Sall et al. Randomized controlled trial of vitamin D supplementation in children with autism spectrum disorder. Journal of Child Psychology and Psychiatry. 2016

Anatoly v Skalny. Magnesium Status in Children with Atten-Deficit/hyperactivity Disorder and/or Autism Spectrum Disorder. Child and Adolescent Psychiatry. 2020

Hamid Abbasi et al. Impact of omega-3 fatty acid supplementation on clinical manifestations in autism spectrum disorder: an umbrella review of meta-analysis. Cambridge University Press. 2024

Pablo Roman et al. Exposure to Environmental Pesticides and the Risk of Autism Spectrum Disorders: A Population-Based Case Control Study. ResearchGate 2024