This study examines whether maternal vitamin D deficiency is a risk factor for infantile autism disease (IAD). We used epidemiologic data seasonal variation of birth rates and prevalence of IAD for cohorts born before 1985. For seven studies reporting spring-to-summer excess birth rates for IAD, the season progressed from broad near 30° N latitude, spring/summer in midlatitudes, to winter at the highest latitude. Also, using data from 10 studies, we found a strong effective latitudinal (related to wintertime solar ultraviolet B radiation) increase in IAD prevalence. These findings are consistent with maternal vitamin D deficiency's being a risk factor for IAD, possibly by affecting fetal brain development as well as possibly by affecting maternal immune system status during pregnancy. Further investigation of this hypothesis is warranted. IntroductionThe etiology of autism is still somewhat of an enigma. Autism is considered an autoimmune disease. 1 It also appears to have important risk factors in utero, as evidenced by a highly significant increased frequency of congenital malformations; 2 and those with autism have several characteristics associated with schizophrenia, 3 which is also linked to in utero risk factors. 4 Perinatal viral infection of mother or infant is a risk factor for both infantile autism and schizophrenia. 5 Also, several studies have reported seasonality in excess births of those with autism, with March being a peak month in Sweden, 6 Denmark 7 and Boston, 8 but without a good explanation for this seasonality.Schizophrenia is another disease that exhibits excess of births in winter and a deficit in summer. 9 This seasonality has sometimes been shown to be linked to influenza epidemics. 10,11 Infectious disease during pregnancy has been found to adversely affect rodent brain development in a manner that can lead to schizophrenia as well as autism. [12][13][14][15][16][17][18] The hypothesis that the seasonality was related to low levels of maternal serum 25-hydroxyvitamin D (calcidiol) was also advanced. 19 Support for the maternal vitamin D deficiency hypothesis has been reported based on rat studies. [20][21][22] It was recently proposed that the annual solar ultraviolet-B (UVB) and vitamin D cycles explained some of the seasonality of epidemic influenza, which peaks in winter. 23 This hypothesis received experimental support in a randomized, prospective, placebo-controlled vitamin D study involving 204 postmenopausal black women living in the state of New York. Those taking 2,000 IU of vitamin D3 per day got 10% as many colds or influenza as those taking the placebo. 24 More support came from a study of meteorological variables associated with incidence of respiratory syncytial virus that found an effect for solar UVB in addition to temperature and relative humidity, with greatest effect at lower latitude. 25 Thus, serum calcidiol levels can affect risk of maternal viral disease during pregnancy.This report examines the evidence supporting the hypothesis that maternal vitamin D deficien...

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