Should vitamin D supplements be recommended to prevent chronic diseases?

#### The bottom line Vitamin D has gained much attention in research and clinical practice as a possible preventive factor for a wide array of chronic diseases, including cardiovascular disease, various cancers, type 2 diabetes, autoimmune diseases, and chronic obstructive pulmonary disease. Vitamin D3 (cholecalciferol) is a steroid hormone precursor and is synthesised when skin is exposed to ultraviolet B radiation. It is also found in a limited number of foods, especially oily fish. The other form of the vitamin, vitamin D2 (ergocalciferol), is found in dietary plant sterols exposed to ultraviolet B radiation and is somewhat less effective than vitamin D3.1 Vitamin D has well known effects on calcium metabolism and is traditionally linked to the prevention of rickets in children. It is also now clear that vitamin D deficiency causes bone loss through secondary hyperparathyroidism.2 Because vitamin D receptors are present in many organs and tissues, vitamin D may have extraskeletal effects.2 In addition, many observational studies have shown associations between 25-hydroxyvitamin D3 (25(OH)D3), the major circulating form of vitamin D, and the risk of chronic diseases.3 As a consequence of increased popularity, measurement of 25(OH)D3 to determine vitamin D status has become common, and vitamin D supplements, at doses far exceeding the recommended daily allowances or dietary reference values,4 5 6 are often given, despite limited evidence of an effect. ### What are the possible benefits? On the basis of the existing evidence, we can conclude that vitamin D …