Natural and Synthetic Sources of Circulating 25-Hydroxyvitamin D in Man

Abstract

THE antiricketic sterols are both assimilated from the diet and endogenously produced by ultraviolet irradiation of cutaneous 7-dehydrocholesterol^1–3. Before the modern practice of supplementing foods with irradiated ergosterol (ergocalciferol, vitamin D₂), deficiency states were frequently observed in subjects whose dark skin colour and/or minimal exposure to sunlight minimized the natural endogenous production of cholecalciferol (vitamin D₃)⁴. It has been generally accepted that casual exposure to sunlight and average diets provide enough antiricketic sterol to prevent osteomalacia in the adult (American Academy of Pediatrics, 1963). Infants, however, are recognized to require vitamin D supplementation, for their maternally derived stores wane at a time when their natural foods are a poor source and their exposure to ultraviolet radiation unreliable. Supplementation of foods with vitamin D₂ has thus become a widespread and successful practice which has subsequently undergone quantitative revisions in several countries.