McCann & Ames point out that evidence for vitamin D's involvement in brain function includes the wide distribution of vitamin D receptors throughout the brain. They also discuss vitamin D's ability to affect proteins in the brain known to be directly involved in learning and memory, motor control, and possibly even maternal and social behavior. The review also discusses studies in both humans and animals that present suggestive though not definitive evidence of cognitive or behavioral consequences of vitamin D inadequacy. The authors discuss possible reasons for the apparent discrepancy between the biological and behavioral evidence, and suggest new, possibly clarifying avenues of research.
As you might know, it seems that most dark-skinned people at higher latitudes have a deficiency. Also, tests of natural selection seem to suggest that
humans have become far lighter over the past 10-20,000 years
. Why? Here's the citation: McCann, JC, Ames BN (2008) Review Article: Is there convincing biological or behavioral evidence linking vitamin D deficiency to brain dysfunction" FASEB J. 22: 982-1001. The paper is not online yet.... A word of caution: many nutrients are involved in thousands of biochemical pathways. The main reason I focus on Vitamin D is that the data for selection of lighter skin at northern latitudes is very powerful....