ive heard folic acid is good. whats it good for?
b-complex is for stress.
What vitamans are harmful in excess doses , and how many mgs and above are harmful?
Folic acid is important for the synthesis of DNA, RNA, and proteins. It has been proven to prevent certain birth deffects (this is why in 1998, the FDA mandated the addition of folic acid to all enriched cereal grains). It has also shown significant protection against cadiovascular disease and some forms of cancer.
If you are supplementing a quality B-complex, the amounts supplied should be sufficient. I take a B-complex twice a day. On a side note, while B vitamins work great for reducing stress, they are very important for proper neurological transmissions.
To answer your question, various minerals contain metal ions, which can build up in the body, so you might want to avoid larger than normal dosages. I think Bioman also pointed a few out like vitamin K, selenium, molybdenum, ect. Unless deficient, the amounts supplied in a balanced diet should be sufficient.
All in all though, determine wether or not you have a problem that you can adress specifically, and then adress it with larger amounts of the target nutrient.