Study shows how autism-linked picky eating causes serious vitamin deficiencies

Hidden risks in plain sight: New research reveals how children with autism can suffer life-altering vitamin deficiencies despite appearing healthy, urging a rethink of routine nutritional screening.

Review: 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. Image Credit: Marko Novkov / Shutterstock

In a recent review article in the journal Nutrients, researchers in the United States explored micronutrient deficiencies (other than isolated vitamin C deficiency, though cases where vitamin C deficiency co-occurred with other deficiencies were included) in children with autism spectrum disorder (ASD).

They identified 44 cases discussed in 27 studies and found that deficiencies in vitamins A, B, and D, as well as iron and calcium, are most common. Vitamin E, zinc, and iodine (2.4% of cases) accounted for relatively few instances, though these often occurred alongside other deficiencies.

ASD and Micronutrient Deficiencies

Micronutrients are critical for brain development, immune function, and growth. Thus, deficiencies in these nutrients can cause neurodevelopmental issues, infections, and stunted growth. Estimates suggest that between 1% and 10% of children in the United States have micronutrient deficiencies, but children with ASD may be at higher risk.

This is because ASD, which is a neurodevelopmental disorder, is characterized by social and behavioral challenges, which include extreme food selectivity. As many as 89% of children with ASD have restricted diets and often reject food groups, especially vegetables and fruits, preferring processed and calorie-dense foods.

From 2000 to 2020, ASD prevalence increased from 0.7% to 2.8%, and public health experts have noted the need for improved nutritional assessments for this population. Vitamin D deficiency among children with ASD has been well-studied and documented, in part due to its routine testing in clinical practice, but other micronutrient deficiencies have received less attention.

In this study, researchers reviewed the medical literature for cases of micronutrient deficiency among American children with ASD, identifying 27 articles that documented 44 cases.

They focused on cases where laboratory tests confirmed inadequate nutrient levels. To focus on deficiencies caused by selective eating, they excluded cases involving medical conditions such as Crohn’s disease or cancer, poverty, eating disorders, or drug interactions. They also excluded cases where the only deficiency was vitamin C.

Percentage of vitamin and mineral deficiencies from a review of case reports and series on micronutrient deficiencies in children with autism spectrum disorder (ASD).

Documented Micronutrient Deficiencies

In half the documented cases, the children had a normal body mass index (BMI), while the other half were obese or overweight. However, no cases of underweight children with ASD were recorded. Vitamins A, B, and D, as well as iodine, calcium, and iron, were the most common deficiencies. Approximately 70% of cases showed two or more co-occurring deficiencies, often due to overlapping dietary gaps, highlighting the interactions between nutrients.

Due to restrictive eating habits, many children were found to have multiple deficiencies. Calcium and vitamin D were the most common deficiency and often occurred together. Children exhibiting these deficiencies often avoided dairy, an important source of vitamin D. Since these deficiencies cause bone disorders, five of the children had rickets, three had osteopenia (low bone density), and two required orthopedic surgery.

Children in 20 cases exhibited vitamin A deficiency; this nutrient is critical for immune health and vision. Common sources, such as leafy greens, eggs, fish, and liver, were missing from the children’s diet in these cases. While most recovered with supplementation, two children had permanent blindness as a result of the deficiency.

The most commonly deficient B vitamin was B12, followed by B6, B1, and B3. In one case, inadequate B12 levels were linked to vision loss, while in two severe cases, B3 deficiency led to a skin disorder, which was reversed after supplementation. In these cases, diets were high in processed foods such as crackers, pizza, and chicken nuggets.

In eight cases, iron deficiency was identified; however, only one child had anemia. Diets, in these cases, lacked iron-rich foods despite the consumption of fortified cereals. Researchers also noted that 75% of iron-deficient cases showed co-occurring deficiencies in vitamin C, which boosts iron absorption.

Two cases exhibited iodine deficiency, which led to thyroid gland swelling (goiter). Both cases lacked important sources of iodine, such as seafood and dairy. They were treated using supplementation, which, over time, resolved the goiter.

Some less common but reported micronutrients of concern included selenium, copper, folate, vitamin K, vitamin E (occurring with vitamin A in multiple cases), and zinc.

Conclusions

In the United States, micronutrient deficiencies are generally considered to be rare because of successful food fortification programs.

However, children with ASD are at high risk of multiple micronutrient deficiencies due to restrictive eating habits. Nearly half of the deficiencies involved fat-soluble vitamins such as A and D. Vitamin D was commonly tested for, contributing to its prominence in findings, but vitamin A deficiency was frequently found despite lower testing.

Micronutrient deficiencies can cause serious health complications, including bone disorders, vision loss, and immune issues. Progression varies across the nutrients, making early detection challenging; while vitamin C deficiencies manifest quickly, rickets or xerophthalmia take longer to show symptoms. Preventive screening and intervention are crucial to prevent severe outcomes, and selective supplementation may be inadequate when deficiencies co-occur.

The findings from this review highlight the importance of conducting routine assessments of micronutrients for children with ASD, especially as many may present with normal BMI. Since current pediatric guidelines do not recommend testing beyond 12 months of age, standardized tools combining dietary, biochemical, and anthropometric evaluations must be developed for assessment and treatment.