…be cautious on high-dose anything, natural supplement or not.
For some substances, uptake from food or ordinary supplements is self-limiting due to an in vivo conversion. An example is folic acid, where the active form is l-methylfolate (a/k/a Deplin), as mentioned in #msg-70926846. (Unlike folic acid, one can OD on l-methylfolate, and I know this from first-hand experience.)
“The efficient-market hypothesis may be the foremost piece of B.S. ever promulgated in any area of human knowledge!”