The following info from the Linus Pauling Institute is the best I've seen for biotin:
http://lpi.oregonstate.edu/infocenter/vitamins/biotin/
It seems that biotin has not been well studied, so we don't really know how much should be taken, daily, or what the upper tolerable limit is. The US government says about 30 mcg/day should be enough, but the truth is, not enough studies have been done. It seems that very high doses, far above 500, have been used in clinical trials of diabetic patients, because of its effect on how the body handles glucose.
The Institute says, "Although hair loss is a symptom of severe biotin deficiency, there are no published scientific studies that support the claim that high-dose biotin supplements are effective in preventing or treating hair loss in men or women."
Post Edited (njmom) : 4/24/2011 12:36:57 AM (GMT-6)