Keeping diabetes under control or preventing it is the best solution, you don't want to end up blind or limbless by letting it get out of hand (or fingers). On an unrelated note, prescription vitamin D is amazing for health, is a necessary supplement for some who have low absorption rates, live in not-so-sunny areas and can't get enough sunlight, or are in at-risk groups, including the elderly (it's been shown to have possible buffering effects against memory-loss related diseases). Over the counter is usually not the same type and does not get processed by the body the same way.