This was written a year ago. Has links and videos.
Brain Health: Vitamin D.
Did you know there are some people who desperately need higher levels of vitamin D than others? Some people genetically are different and don't have as good cell receptors for the hormone (vitamin D is actually a hormone). My doctor said the only way to know for sure if your level is enough is to know how much gets inside the cell. So before, we used to rely on serum level, and now there is an even better test to test the amount inside. He said there is a genetic test for it, too (VDR alleles). I didn't have the genetic test. I did have the test for whether I have enough vitamin D on the inside of my cells.