FOOD FOR THOUGHT:
There are at least ten different neurological functions that could be impaired in the fetus of women who are vitamin d deficient. It is certain that a greater number of people of equatorial genetic history (darker skin) will suffer impaired neurological functions in their children when they reside in the higher latitudes.
By contrast then, wouldn't it also make sense that people with lighter skins living close to the equator have other such problems? Like too much Vitamin D?