Just because low levels of vitamin D has been associated with the development of Type 2 diabetes does not mean that taking supplements would be advantageous. This may simply be just an association and could quite easily relate to lower vitamin D levels in people who are more overweight and by inference more prone to diabetes.

The way to sort this out is to review the results not of observational studies looking at associations but to examine randomised controlled trials. These have been published and the results so far do not support an effect of vitamin D on diabetes control. It is still possible that further studies will reveal more positive results but at the moment from a diabetes perspective there is no evidence that vitamin D supplementation is good.

A further interesting question is whether vitamin D supplements are bad for you. In this respect there is a fascinating piece of research work which shows that both low and high vitamin D levels are associated with a higher incidence of cardiovascular disease than so called normal levels. Also very high vitamin D levels just like very low levels have been shown to be associated with increased bone fractures