The functions of vitamin D are pleiotropic affecting all body organs and systems in some way. Its adequacy depends principally on sunshine for UV light to stimulate its synthesis in skin and on foods which contain it, either animal-derived or obtained from fungi or mushrooms, with the UV-responsive substrates dehydrocholesterol for vitamin D-3 or ergosterol for vitamin D-2, respectively. Thus, vitamin D health is very environmentally dependent. With ecosytem degradation, whether by atmospheric pollution or food systems which do not derive UV irradiation, as with fish farming or mushroom processing, then this nutrient input into human biology may falter. Vitamin D deficiency is now common and widespread in North-East Asia as elsewhere. When discovered early in the 20th century it was linked to rickets in children and osteomalacia in adults and, for a generation or so, children were given fish, usually cod, liver oil to prevent bone disease. Now cod as a species and many edible fish are threatened. Over-exposure to sun-light increases the risk of skin cancer. We may tackle this problem by vitamin D supplementation with an alternative to fish liver. But the demographic pressures of population size and ageing (when the skin is less UV responsive) make the clinical and public health decisions and strategies demanding. Vitamin D health has become indicative of food security whose usual indicator is food diversity; such diversity may allow lesser concentrations to be more effective in organ and system function, but we have little evidence to support this at present.