Different species have very different essential nutrients. For example, Vitamin C is essential to humans but not to most other mammals.
Many essential nutrients are toxic in large doses (see hypervitaminosis or the nutrient pages themselves below). Some can be taken in amounts larger than required in a typical diet, with no apparent ill effects. Linus Pauling said of vitamin B3, (either niacin or niacinamide), "What astonished me was the very low toxicity of a substance that has such very great physiological power. A little pinch, 5 mg, every day, is enough to keep a person from dying of pellagra, but it is so lacking in toxicity that ten thousand times as much can [sometimes] be taken without harm." [1] A similar statement can be made about vitamin C and some other vitamins.
The body's requirements vary widely. At one extreme a 70 kg human contains 1.0 kg of calcium but only 3 mg of cobalt.[10]
Elements with speculated role in human health
Many elements have been implicated at various times to have a role in human health. For none of these elements has a specific protein or complex been identified:
^ Pauling, L. (1986). How to Live Longer and Feel Better. New York NY 10019: Avon Books Inc.. ISBN 0-380-70289-4. Page 24.
^ R. Bruce Martin “Metal Ion Toxicity” in Encyclopedia of Inorganic Chemistry, Robert H. Crabtree (Ed), John Wiley & Sons, 2006. DOI: 10.1002/0470862106.ia136