Vitamin D supplementation and type 2 diabetes: a substudy of a randomised placebo-controlled trial in older people (RECORD trial, ISRCTN 51647438)

SIR—Studies in animals show that vitamin D deficiency is associated with impaired insulin sensitivity, and that insulin secretion can be increased by vitamin D supplementation [ 1 ]. Epidemiological studies in man show associations between low vitamin levels and glucose intolerance [ 2 ]. Pittas et al . systematically reviewed the intervention trial evidence for the role of vitamin D and/or calcium in the prevention of metabolic syndrome and type 2 diabetes mellitus [ 2 ]. On the basis of evidence from small intervention trials or post hoc analyses of trials, they concluded that it was difficult to be definite whether or not vitamin D and/or calcium were important in the prevention of type 2 diabetes, and that effects might only be manifest in people who were particularly at risk of type 2 diabetes. As an adjunct to the RECORD trial [ 3, 4 ], a blinded, randomised, placebo-controlled trial of oral vitamin D 3 and/or calcium supplementation for the secondary prevention of osteoporotic fractures in older people, we examined whether vitamin D (with or without calcium) was associated with a reduction in self-reported development of diabetes, and starting tablets or insulin for diabetes as indicators of deteriorating glycaemic control.