Extra-Skeletal Effects of Vitamin D.

There are very solid data to confirm that the vitamin D endocrine system is important not only for calcium transport or bone homeostasis but also for operational functions in most cells of the body. Preclinical studies convincingly demonstrated coherent actions of the vitamin D endocrine system on the proliferation/differentiation of most cells (and thus possibly on the evolution of cancer). The most plausible target tissues include skeletal and cardiac muscle, all immune cells, many cells involved in cardiovascular homeostasis, brain cells, and reproductive tissues. These data have been generated in models of (near) total absence of vitamin D action or when exposed to very high concentrations of the active hormone, 1,25-dihydroxyvitamin D or its analogs. In humans, observational data frequently demonstrate a link between poor vitamin D status and a large number of major human diseases such as cancer, muscle weakness and falls, infections or autoimmune diseases, hypertension and cardiovascular risks and events, obesity, diabetes and all aspects of the metabolic syndrome, and other health problems. Intervention studies so far have not convincingly demonstrated a positive effect on such extra-skeletal health outcomes. A very large number of ongoing studies (about 3,000), however, should help to clarify the role of vitamin D on the musculoskeletal system and on global health.