Study finds new evidence that vitamin D decreases risk of autism in children
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 (UVBlack Eye 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.
If vitamin D deficiency during pregnancy is a risk factor for autism, then risk could be reduced by having pregnant women take 4000 IU/d vitamin D3 and raising serum 25(OH)D concentrations to above 40 ng/ml (100 nmol/l). This amount has been shown to be both safe and necessary to increase concentrations of 1,25-dihydroxyvitamin D (calcitriol), the active metabolite of vitamin D, to optimal levels in a randomized controlled trial by Drs. Bruce Hollis, Carol Wagner and colleagues at the Medical University of South Carolina. Calcitriol can control the expression of more than 200 genes through interacting with vitamin D receptors, which would be very important during fetal development.
Vitamin D deficiency in early life could be a risk factor for autism, although this remains to be proved. The ways that vitamin D might reduce the risk of autism in early life are by strengthening the body's innate immune system and reducing inflammation. Vitamin D strengthens the body's innate immune system by inducing production of cathelicidin and defensins, which can combat bacterial and viral infections. Vitamin D also shifts cytokine production away from T-helper 1 (Th1) proinflammatory ones toward Th2 cytokines. Recent studies also show vitamin D increases neurotrophins, upregulates glutathione, increases DNA repair enzymes, and protects against mitochondrial damage.
Once autism develops, symptoms may be reduced by treating vitamin D deficiency in autistic children, although this remains to be shown in randomized controlled trials. The rationale for such a statement comes from several recent studies showing vitamin D deficiency is common among autistic children and from a recent study in the Journal of Neurodevelopment that showed vitamin D levels are inversely and strongly>
If vitamin D is a risk factor for autism, then autistic children should have their serum 25(OH)D concentration raised to above 30-40 ng/ml, which could take 1000-2000 IU/d vitamin D3, or more depending on such factors as genetics, weight and amount of time spent in the sun. |
发表于 2012-12-17 19:50
|