Vitamin D and risk of type 2 diabetes

Type 2 diabetes mellitus (T2DM) is a public health disaster; it affects approximately 480 million people worldwide, predicted to increase to 700 million by 2045.1 Another half a billion people have impaired glucose tolerance,2 an intermediate stage in T2DM development but amenable to interventions that halt disease progression and lead to remission.3

Weight loss and exercise decrease risk of progression to T2DM in people with impaired glucose tolerance.4567 However, lifestyle interventions are difficult to sustain.8 The possibility that a vitamin might prevent T2DM development is attractive to both healthcare professionals and patients. Interest in vitamin D is based on epidemiological evidence showing an association between low vitamin D status and increased risk for T2DM.9

A link is also biologically plausible: pancreatic β cells have vitamin D receptors, and animal studies show improved production of and sensitivity to insulin associated with vitamin D treatment1011; also, vitamin D has immunomodulatory effects and may modify risk of …