ABSTRACT
Calcium is the fifth most abundant element in the earth's crust and is always found in relative excess in environments in which life exists or has evolved. Sea water, contains about 10 mmol calcium, and fresh water lakes and streams that support varied life forms typically exhibit 0.5–2 mmol concentrations. Vitamin D, like calcium, was also present in abundance for primitive humans. Its source was synthesis in the skin by photochemical conversion of a precursor molecule, 7-dehydrocholesterol, to cholecalciferol. It is a peculiar conceit of twentieth century biology that we look at contemporary low intakes of calcium and vitamin D as somehow the natural state of things. The vitamin D story is less clear. Rickets and osteomalacia were recognized pathologic entities long before their pathogenesis was known. While high intakes may ultimately prove not to be necessary for health, still they can hardly be considered as "treatment" for a disease, not even as nutritional "therapy." They are simply natural nutrition.
