If you have a low level of vitamin D, taking this inexpensive supplement may help you prevent diabetic retinopathy, one of the most serious complications of diabetes. This is the most common reason why some people with diabetes lose their vision.
The optimal level
These three researchers analyzed data from 13 studies involving 9,350 people with diabetes who had been tested for both diabetic retinopathy and vitamin D deficiency, which is as a serum level less than 20 ng/ml. They defined the optimal vitamin D level as greater than 30 ng/ml. But as per my research it should be >50 ng/ml to work at optimal level.
Knowing your serum level of vitamin D is important. Now, those of us who have diabetes have an another important reason to make sure that we have the right level of vitamin D.
Pl see below link for more details. The site is also good to browse for diabetics.