Rickets has been cited as the commonest non-communicable disease of childhood worldwide. It is certainly a disease that has been well described over the last four centuries, initially by Glisson (1648), who differentiated it from infantile scurvy, Trousseau (p 38), who identified sunlight and cod liver oil as effective treatments, Mellanby (1919), who created an animal model of rickets that was cured by cod liver oil, and Hess and Unger (1921), who cured rickets in children by exposing them to sunlight on a rooftop in New York.

The epidemiology of rickets—lack of vitamin D from diet and/or the action of sunlight on exposed skin, or of the bone mineral substrates calcium and phosphate—is also well established. The contribution of such deficiencies to other human ill health problems is less clear. There is no doubt that vitamin D is important for function of the musculoskeletal and immune systems, neurological function, and possibly mental health. But how much vitamin D is necessary to support human health and should vitamin D supplementation be targeted or universal? How should vitamin D sufficiency be assessed? Are there critical periods during which attention should be concentrated? Two papers in this issue of Archives make useful contributions to the debate.

The first paper, by Robinson et al, examines the effects of vitamin D deficiency in infancy.¹ This is not new territory, but the message of increasing frequency of presentation over the period of a decade in a developed country makes salutary reading. The diagnosis of vitamin D deficiency in the paper by Robinson et …