Hi,
It seems like I remember hearing somewhere that it's a copper deficiency. Anyway, I wanted to share with you about a family from Russia called the Boutenkos. They have a website called http://www.rawfamily.com. I just went to her seminar & her husband's beard & hair is turning from grey to black again. She also doesn't have any grey hairs. She contributes it to drinking "green" smoothies mostly made from kale and the raw foods diet. I drink them & they are pretty good. As long as there is 60% fruit & 40% greens, they taste good.