Vitamin amino acids. Most vitamins are not single molecules, but groups of related molecules called vitamers. For example, vitamin E consists of four tocopherols and four tocotrienols. The thirteen vitamins required by human metabolism are: vitamin A (retinols and carotenoids), vitamin B (thiamine), vitamin B (riboflavin), vitamin B (niacin), vitamin B (pantothenic acid), vitamin B (pyridoxine), vitamin B (biotin), vitamin B (folic acid or folate), vitamin B (cobalamins), vitamin C (ascorbic acid), vitamin D (calciferols), vitamin E (tocopherols and tocotrienols), and vitamin K (quinones). Vitamins have diverse biochemical functions. Some forms of vitamin A function as regulators of cell and tissue
Vitamin C megadosage allowance of vitamin C is 90 milligrams. Although sometimes considered free of toxicity, there are known side effects from vitamin C intake, and it has been suggested that intravenous injections should require "a medical environment and trained professionals." Blood levels of vitamin C remain steady at approximately 200 mg per day. Although vitamin C can be well tolerated at doses well above what government organizations recommend, adverse effects can occur at doses above 3 grams per day. The common 'threshold' side effect of megadoses is diarrhea. Other possible adverse effects include increased oxalate excretion and kidney stones, increased uric-acid excretion,