Question: Concerning your multivitamins, vitamin B12 significantly exceeds 100% of the daily value. Since the equilibrium concept is of paramount importance to any system well-being, both deficiency and excess of any sort are equally bad. Would you please explain?
Answer: The levels are not solely on RDA's but to offer amounts that attempt to complement a healthful diet and mimic blood levels shown to offer maximum disease reduction and longevity, in numerous studies, so that individual variances in absorption would enable even those with less than optimal absorption to achieve those levels. This is especially important for vitamin B12, because our ability to absorb B12 decreases with age. Also, since B12 is only present in animal foods, it is scarce in a Nutritarian diet. It is also not quite accurate to say there is an equilibrium, suggesting a fine line between optimal and toxic. Many water soluble vitamins are non-toxic in a wide range of dosages, for example, taking anywere from 2 to 2000 mcg of B12 would be non-toxic. The RDA is a suggested minimum and it is not an attempt to be optimal. For example, the RDA for vitamin C is ridiculously low; if you ate healthfully you would consume more than 10 times the RDA from food. However, in those nutrients that have a narrow range of optimal intake and the potential for toxicity or other harmful effects, I am very careful to exclude them (such as vitamin A, beta carotene or iron) or to use smaller amounts on the lower side (such as iodine). Every nutrient is a judgment though there is certainly a degree of agreement with many researchers and others reviewing the nutritional literature.