A study just published online in the peer-reviewed journal Dermato-Endocrinology found additional evidence that vitamin D reduces the risk of developing autism (Grant and Cannell, 2012). The study examined the variation of autism prevalence by state for those aged 6-17 years in 2010. It found that states with higher solar ultraviolet-B (UVB) doses in summer or autumn had half the rate of autism as states with the lowest doses. The study also found that in the states with the least solar UVB, black-Americans had a 40% higher rate of autism than white-Americans. Black-Americans have lower vitamin D or serum 25-hydroxyvitamin D [25(OH)D] concentrations due to their darker skin and since solar UVB is the primary source of vitamin D for most Americans.
Similar geographical variations have been noted for incidence and mortality rates for about 15 types of cancer in the United States (Grant and Garland, 2006). The UVB-vitamin D-cancer hypothesis was proposed in 1980 based on variations in colon cancer mortality rates in the United States and now has strong support from observational studies, laboratory studies of mechanisms, and limited support from randomized controlled trials. Those who have lower serum 25(OH)D concentrations have been found to have a greater risk of developing breast and colorectal cancer. In addition, those who have lower 25(OH)D concentrations at time of cancer diagnosis have a much lower survival rate for at least seven types of cancer.
Similar geographical variations in dental caries among white boys aged 12-14 years were also reported in the mid-1930s and linked to the amount of sunshine. Also, dental rank of men entering the Armed Forces for World War I and World War II also showed a similar variation with respect to solar UVB. Vitamin D reduces risk of dental caries through induction of cathelicidin, which has antibacterial effects. (Grant WB. 2011)
Thus, studies of geographical variation of disease with respect to solar UVB doses are important ways to identify a potential role of vitamin D in preventing a disease. No factor other than vitamin D production has been proposed to explain the findings for the inverse correlations between solar UVB and cancer or dental caries. Thus, the same conclusion seems very likely for autism.
This finding regarding autism leads to the question whether maternal vitamin D deficiency during pregnancy or vitamin D deficiency in early life is related to development of autism.
Regarding maternal vitamin D deficiency, other studies have found adverse effects on fetal brain development during the third trimester of pregnancy related to vitamin D deficiency, including increased risk of schizophrenia and language difficulties. Also, increased risk of autism related to springtime births has been reported in several studies.
One of the mechanisms whereby vitamin D might reduce the risk of autism is through reducing the risk of sporadic DNA mutations from influencing fetal development. Another is through reducing the risk of influenza and other infectious diseases during pregnancy, which have been linked to increased risk of schizophrenia. Also, vitamin D reduces inflammation by shifting cytokine production towards less inflammatory cytokines.