The search for environmental factors associated with autism has extended to the diet where certain deficiencies have been causally associated. We discuss the basis for the association below.

Vitamin D Deficiency

Vitamin D is a potent neurosteroid essential for proper brain development. Mice with deficient levels of active vitamin D produce offspring with neuroanatomical abnormalities similar to those observed in children with autism.¹ The hypothesis that vitamin D deficiency (resulting from the increased awareness of skin cancer and avoidance of direct sun exposure) causes autism was first proposed in 1998.² In support of this hypothesis, recent clinical studies of children with autism and their mothers report deficiencies in active vitamin D in both groups.^3,4  A 2016 study found that children whose mothers were deficient in vitamin D both mid-way through pregnancy and at birth had more behavioral traits associated with autism than those whose mothers either had no deficiency or were only deficient at one point in time.⁹  

Folic Acid Deficiency

Twenty years ago, supplementation of folic acid, a B vitamin, was recommended during pregnancy to prevent the occurrence of neural tube defects.^5,6 The observation that autism rates have risen dramatically since the implementation of folic acid supplementation has led some to hypothesize a causative relationship.⁶ In fact, mutations in the enzyme that activates folic acid have been observed in children with autism.⁷ Active folic acid, a DNA methylation agent, regulates gene expression, and a lack of this folic acid activity could constitute an autism risk factor. The evidence for this was provided in a 2004 study found that methylation capacity was significantly impaired in children with autism. Consequently, supplementation with folinic acid, which mimics the activity of folic acid, ameliorated the altered methylation metabolite profile in these children⁸.