In addition to the current epidemic of vitamin D deficiency, say another epidemic—an epidemic of autism—was upon our children? What if the autism epidemic began at the same time the epidemic of vitamin D deficiency began? What if both epidemics had worsened in unison? What if one theory explained all the unexplained facts about autism?
What if both epidemics had the same root cause: sun avoidance? What if both were iatrogenic, that is, medical advice to avoid the sun had caused both epidemics? Be warned, what follows is not light reading—autism is not a light disease.
The theory that vitamin D deficiency, during pregnancy or childhood, causes autism is just a theory. However, the theory has a plausible mechanism of action, explains all the unexplained facts about autism, subsumes several other theories, implies simple prevention, and is easily disprovable—all components of a useful theory. A genetic lesion (abnormality) in some component of the vitamin D system—a lesion vitamin D's unique pharmacology could overcome—would explain why monozygotic (identical) twins are highly affected while fraternal twins are not. Varying brain levels of activated vitamin D during later life would explain why some identical twins get severe disease while others are barely affected. Falling vitamin D levels over the last 20 years due to sun-avoidance explain autism's rapid increase in incidence during that same time. The very different effects estrogen and testosterone have on vitamin D metabolism may explain why boys are much more likely to get it than girls are. Lower vitamin D levels in blacks may explain their higher rates of autism. The vitamin D theory has tenable explanations for all the epidemiological features of autism.