Last year the consultant endocrinologist I saw tested my Vit D levels and found them to be very low and started me on a supplement (it can be bought at the chemist for a £1 I have since found out). The consultant said that she tested all her diabetic patients for Vit D deficiency as it was common.
I’m pretty convinced that the increase in my levels has made a difference and there is circumstantial evidence and research of the link between Vit D and T2 diabetes and other conditions. Particularly of note is the fact that to absorb the Vit D we have to eat fat. This slide show gives some very brief info:
http://www.webmd.boots.com/healthy-eating/ss/slideshow-vitamin-d
A friend who asked for a Vit D test after cancer treatment was told by her GP that she couldn’t have one because it Was too expensive…go figure compared to the cost of her chemo, radio etc. however it is possible to get a test kit and do it yourself for £28 from this company: http://vitamindtest.org.uk/index.html