Points to Ponder Concerning Self-Prescribed Supplements:
In general - "We readily construct myths when we do not have data (or we suppress data in favor of legend when a truth strikes us as too common-place)." Stephen J. Gould, Ph.D. in Bully for Brontosaurus, p. 45, Norton paperback, London, 1992.
In particular - "Americans love hogwash. They think if a little is good, more is better." E.H. Rynearson, M.D. earlier director of the Mayo Clinic and past-president of the American Medical Association.
Nutrient Status Assessment vis-à-vis Supplement Use:
Clinical signs of insufficiency of a micronutrient, whether vitamin or trace element, may not appear until deficiency has advanced and may be difficult to interpret, especially where there are multiple insults. Biochemical index measurements are more specific for a particular micronutrient and they can detect mild, subclinical deficiency, which reflects suboptimal nutrition, the continuance of which leads to increased risk of future clinical deterioration. Hence, biochemical measurements can serve as early indicators of the need to increase intake of a given micronutrient, by supplementation when appropriate, and help to clarify the etiology of deficiency pathologies with multiple causation.
When there is neither biochemical nor clinical evidence for supplement need, the current US RDAs (or British RNIs) suffice for almost all people. This applies not only for avoidance of deficiency diseases but should be considered in the use of micronutrients to treat non-deficiency diseases where there is not secure evidence of benefit from randomized, controlled clinical trials in addition to epidemiological indications.