A small Swedish study suggests that, as a group, children with autism have significantly lower vitamin D levels at birth compared to their siblings who develop typically. The researchers call for clinical trials exploring whether taking prenatal vitamin D supplements can lower autism risk.
The findings add to a growing body of research suggesting that vitamin D may play a protective role against autism – or conversely, that low levels could predispose some children to developing the disorder.
The researchers looked at vitamin D levels in dried blood spots taken at birth from 58 pairs of Swedish-born siblings (116 children total). In each sibling pair, one child had autism.
The group included 22 children from Somali-immigrant families. In recent years, a number of reports have described unusually high rates of autism among Somali immigrant families in high-latitude regions such as northern Europe, North America and Australia. Low vitamin D levels have been among the proposed explanations.
The sunshine vitamin
The body produces vitamin D in skin exposed to sunlight, which is limited in winter at high latitudes. Dark pigment further lowers the skin’s production of vitamin D.
Among the children who developed autism, the study found an average vitamin D level at birth of 24.0 nM (nanomoles per liter). By contrast, vitamin D levels averaged 31.9 nM among their siblings who developed typically.
Vitamin D levels above 30 nM are considered normal. Those between 20 to 30 nM are considered “insufficient.” Vitamin D deficiency is defined as less than 20 nM.
Winter Babies at Risk
As might be expected, the researchers found lower vitamin D levels among the children born in winter than those born in summer. They also found vitamin D deficiency in all the children with African and/or Middle Eastern heritage – regardless of when they were born or whether they developed autism.
“These new results suggest that vitamin D may be another nutritional factor important in the development of autism spectrum disorder during pregnancy and early life,” comments developmental pediatrician Paul Wang, Autism Speaks head of medical research. Previous research has shown that prenatal supplements containing folate (vitamin B9) can lower the risk of autism if started before conception and continued through pregnancy.
Still, Dr. Wang cautions that more study is needed. “The researchers found a wide range of vitamin D levels among the children with autism and an overlap in vitamin D levels between those who developed the disorder and those who did not. So there’s still much we don’t understand,” he notes.
“It may be that the link between autism and prenatal nutrition is particularly relevant for certain subgroups of children who are more vulnerable due to differences in genetic predisposition, diet or other environmental factors,” Dr. Wang adds.
In addition to sunlight exposure, sources of vitamin D include vitamin-fortified milk, fatty fish and, to a lesser extent, eggs. Vitamin D is also included in most prenatal and children’s vitamins.
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