In October of 2007, a paper, Autism and Vitamin D, authored by Dr. John Cannell, was published on line in Medical Hypotheses. In the article, Dr. Cannell presented his theory that the rising incidence of autism was due to the then relatively recent trend toward sun avoidance and the resulting drop in vitamin D3 levels, particularly in babies and young children.
My link to his original paper no longer goes to the full paper, but as of today (late 2020) you can read a later August 2010 paper by Dr. Cannell, On the aetiology of autism, in which he discusses in layman's terms aspects his theory and some additional studies done since his original paper was published in 2007. It's well worth reading. (He cites his original paper in the footnotes for those who have access beyond the abstract.)
Scientific American magazine, in 2009, also published an article hypothesizing a possible link between autism and a vitamin D deficiency. The author failed to credit Dr. Cannell for originating the theory but did give him the privilege of adding the first comment.
The attempt to link a vitamin D deficiency to autism was thus a new development. Dr. Cannell's paper got me wondering about a similar connection between Vitamin D and dyslexia because both autism and dyslexia diagnoses tend to be based primarily on symptoms, many of which overlap between the two conditions.
Back in 2009 or so, an internet search on "vitamin d and autism" yielded two relevant results, Dr. Cannell's original paper and the Scientific American article. A similar search a decade later yields results in support of his theory from many credible sources.
A Parsimonious Theory - The Simplest Explanation Is Often the Best
In his original paper, Dr. Cannell explained how the spread of autism, including the specific populations most affected, are explained by his vitamin D theory. He also explains how common symptoms, including how widely they vary, are covered in his theory. And finally, he explains how most of the other suspected causes of autism, such as mercury contamination or oxidative stress, are also subsumed by his theory. In short, he has come up with a parsimonious theory of autism, a simple explanation that explains all facets of the epidemic. If you chance to read his original paper, you will find that his theory addresses each of the following aspects of autism.
- The Rise in Cases: Around the early 1990's school administrators began to note an increase in the number of autistic students they had to accommodate. Dr. Cannell points out that in 1989 the medical community began advising women to avoid direct sun when pregnant and also to keep their newborns out of the sun unless using sun blockers. Since most of the vitamin D3 we produce is the result of being out in the sunshine, this advice was bound to result in more mothers and young children becoming deficient in Vitamin D.
- Higher Prevalence in Well Off Families: Because families of means were more likely to see their doctors regularly during pregnancy, the pregnant women among them were also more likely to get the above-mentioned advice about avoiding direct sun. They were also quite likely to take their doctor's advice and therefore more likely to become deficient in vitamin D.
- Higher Prevalence in Northern States: Studies have found that the further we go from the equator, the higher the incidence of autism. Similarly, the further we are from the equator, the less sun exposure we are likely to get, and therefore the less vitamin D our bodies will manufacture.
- Higher Incidence in Dark-Skinned Immigrants in the North: The higher melanin concentration in dark skin prevents blacks who have moved to more northern climates from absorbing the amount of sunlight they need to create sufficient vitamin D3 stores. The result is that blacks in northern climates are more likely to be vitamin D3 deficient than are lighter-skinned people.
- Relation to Maternal Fish Consumption: From Dr. Cannell's original paper: "...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." He states that it's not known whether it was due to the vitamin D3 in the fish or the Omega 3's or something else, but there was an association found.
- More Autistic Boys than Girls: Approximately three to four times as many boys are diagnosed autistic than are girls. Dr. Cannell has written that estrogen improves the functioning of vitamin D3 in the system, whereas testosterone has no impact, hence the reason girls are less likely to be autistic.
- Relation to Birth Order and Time Between Births: A second child is more likely to have autism that the first, especially if born soon after. The developing baby draws down the mother's vitamin D levels during gestation. If the mother is low on vitamin D initially, or is avoiding sunshine, a second baby born just a year after is more likely to find that the mother's vitamin D stores are depleted, leading to a vitamin D deficiency in the baby.
- The Genetic Component: A mother who has had one autistic child is more likely to have another one if she has additional children, compared to a mother whose prior children were not autistic. While there probably is a specific gene or genes involve in autism, the role of a vitamin D deficiency could be to activate or deactivate certain genes, rather than causing autism directly.
In 2009 Dr. John Cannell proposed a theory that a vitamin D deficiency could explain the rising incidence of autism seen since the late 1980's. Since then, evidence has accumulated that that he was on the right track. Also since that time, the interest in both vitamin D supplementation and in getting sufficient sun exposure has grown immensely. And government agencies have even raised the recommended daily allowances for vitamin D by significant amounts.
I believed then, and believe more strongly now, that his theory is correct. Upon reading it for the first time, I wondered if there could be a similar relationship between a vitamin D deficiency and reading problems experienced by children considered dyslexic. The next page, Vitamin D and Dyslexia, examines that potential relationship.