Professor John McGrath is getting closer to proving his theory that schizophrenia is connected to vitamin D deficiency. He is, of course, saying that African Americans have higher rates of schizophrenia than do Whites, a fact every psychiatrist knows to be true but a fact that violates the politically inviolate “no racial differences in diseases above the neck” rule.
In this paper, he and his colleagues add to the evidence vitamin D is involved in schizophrenia, finding low vitamin D levels at birth increase risk in teenagers and young adults (14-27 years old). However, the dreaded U-shaped curve again reared its head. The authors found that levels of 16-20 ng/ml at birth afforded the best protection 14-27 years later. That’s right, 16-20 ng/ml, but levels above and below that were associated with increased risk decades later.
I smell cod liver oil. It turns out that most, but not all, of the U-shaped curves come from Nordic countries, like this study came from Denmark. When found, the U-shaped curve is usually more dramatic in Nordic countries. Again, ask yourself where did the mothers of these kids get their vitamin D? From the seasonal variation, we can estimate that the mothers got about, on the average, 400-600 IU/day from the sun. The rest had to be obtained from diet or supplements. In Denmark, during the 1980s and 90s, the supplement most likely to raise vitamin D levels would have been cod liver oil, which contains all that toxic vitamin A.
McGrath JJ, Eyles DW, Pedersen CB, Anderson C, Ko P, Burne TH, Norgaard-Pedersen B, Hougaard DM, Mortensen PB. Neonatal vitamin D status and risk of schizophrenia: a population-based case-control study. Arch Gen Psychiatry. 2010 Sep;67(9):889-94. http://www.ncbi.nlm.nih.gov/pubmed/20819982