Vitamin D Explains Autism
Why are boys at higher risk?
The reason for the striking 4:1 sex difference is totally unknown. However, there is a clue or two. Estrogen and testosterone have very different effects on vitamin D metabolism. In mid-pregnancy, when brains are rapidly developing, boy brains bathe in testosterone and girl brains bathe in estrogen. The majority of studies have found estrogen has multiple enhancing effects on vitamin D metabolism while testosterone does not. For example, in Feldman's massive textbook on vitamin D, Dr. Epstein and Dr. Schneider report, "the majority of studies have found a positive effect of estrogen on activated vitamin D levels." Yet, after reviewing similar studies on testosterone they conclude that "it is unlikely that testosterone is a major controlling factor in vitamin D metabolism." If estrogen potentiates activated vitamin D, but testosterone does not, the differences in sex steroids during brain development may mean that estrogen protects developing female brains from vitamin D deficiencies, while testosterone exposes male brains to those same deficiencies. This is important because any good theory must be parsimonious (explain all known facts). Epstein S, Schneider AE. Drug and hormone effects on vitamin D metabolism. In Feldman D, Pike JW, Glorieux FH, eds. Vitamin D. San Diego: Elsevier, 2005.
The vitamin D theory of autism predicts that eating vitamin D-rich, fatty ocean fish during pregnancy would improve the offspring's mental abilities—that is, as long as that fish did not contain a lot of mercury. Higher fish consumption during pregnancy was associated with better infant cognition, with the greatest effect for infants whose mothers consumed the most fish. Very recently in a Lancet article, Dr. Joseph Hibbeln and colleagues at the National Institutes of Health found low maternal seafood consumption was associated with infants with an increased-risk of lower verbal IQs and poor outcomes for social behaviors, fine motor skills, communication, and social development—outcomes eerily similar to autism. We don't know what in ocean fish helped, omega-3 or vitamin D, but this evidence from a completely different source could support the vitamin D theory of autism. Oken E, et al. Maternal fish consumption, hair mercury, and infant cognition in a U.S. Cohort. Environ Health Perspect. 2005 Oct;113(10):1376–80. Hibbeln JR, et al. Maternal seafood consumption in pregnancy and neurodevelopmental outcomes in childhood (ALSPAC study): an observational cohort study. Lancet. 2007 Feb 17;369(9561):578–85.
If vitamin D played a role in autism, the disorder should be less common at latitudes closer to the equator, at least before modern sun-avoidance. Dr. William Grant of Sunarc found a strong positive association between latitude and the prevalence of autism in children born in various countries born before 1985, but not after. Recently, the Centers for Disease Control (CDC) in Atlanta reported the autism rates from 14 states. The state with the highest prevalence, New Jersey, is the second most northern state. Alabama, with the lowest prevalence, is the most southern of the 14 states surveyed. Studies of season-of-birth and autism are contradictory, as would be expected if activated vitamin D deficiencies can impair brain development during either pregnancy or in early childhood. However, most studies show excessive autism births in the winter—especially March—when vitamin D levels are at their lowest. Grant WB, Soles CM. Epidemiological evidence for supporting the role of maternal vitamin D deficiency as a significant risk factor for the development of infantile autism in those born prior to 1985. Unpublished manuscript. Centers for Disease Control and Prevention. Prevalence of autism spectrum disorders—autism and developmental disabilities monitoring network, 14 sites, United States, 2002. MMWR Surveill Summ. 2007 Feb 9;56(1):12–28. Stevens MC, Fein DH, Waterhouse LH. Season of birth effects in autism. J Clin Exp Neuropsychol. 2000 Jun;22(3):399–407.
If prenatal or postnatal vitamin D deficiency caused autism, then parents who rigorously used sun protection, both during pregnancy and for their children, would be more likely to have children with autism. Richer parents are more likely to apply sunscreen to their children, as are parents with a higher education. Although numerous studies—especially early ones—linked higher social class with autism, a certain kind of statistical problem (called ascertainment bias) confuses such associations. Despite identifying the source of the bias, Dr. Tanya Bhasin at the CDC recently again found wealthier parents and more highly educated parents were at higher risk for having an autistic child. It was not at all clear that ascertainment bias explained all her findings. It appears that people who bought into the sun-scare are more likely to have an autistic child. Robinson JK, Rigel DS, Amonette RA. Summertime sun protection used by adults for their children. J Am Acad Dermatol. 2000 May;42(5 Pt 1):746–53. Hall HI, et al. Protection from sun exposure in US white children ages 6 months to 11 years. Public Health Rep. 2001 Jul–Aug;116(4):353–61. Bhasin TK, Schendel D. Sociodemographic Risk Factors for Autism in a US Metropolitan Area. J Autism Dev Disord. 2007 Apr;37(4):667–77.
If children can develop autism after birth, and it's not entirely a genetic brain injury before birth, then autism should be rare before weaning as infant formula contains significant amounts of vitamin D when calculated on a per-pound basis and breast fed babies are supposed to be supplemented with vitamin D. The disease should rapidly progress after weaning, unless the child takes vitamin D supplements or drinks significant amounts of vitamin D-fortified milk. A recent prospective study (the only such prospective study in the medical literature) of 87 children, some at high-risk for autism and some not, found that the children who later developed autism appeared entirely normal at 6 months of age. However, around the age of weaning, the children who later developed autism first showed signs of the disease with rapid additional impairments occurring between 14 months and 24 months—the same age many toddlers stop drinking vitamin D-enriched formula or milk and begin consuming lots of sodas and juice, which usually contain no vitamin D. Landa R, Garrett-Mayer E. Development in infants with autism spectrum disorders: a prospective study. J Child Psychol Psychiatry. 2006 Jun;47(6):629–38. Northstone K, et al. Drinks consumed by 18-month-old children: are current recommendations being followed? Eur J Clin Nutr. 2002 Mar;56(3):236–44.» page: autism index 1 2 3 4 5 6 7 8 9 10 11