The only thing that does matter in here is that patients with diabetes, who are using Vitamin D, are minimizing the daily drug constantly, because of an improvement in their condition.
There are several doubts raising out regarding the usage of Vitamin D in patients with diabetes:
The first one is that the exact mechanism of actions is still not discovered.
The second thing is that, the possible side effects and drug interactions are not found.
This means that vitamin D is still not proved to be safe in patients with diabetes. According to this, I have to warn you not to use the Vitamin D by yourself and to talk to your physician about its eventual usage.
Just for your information, I will mention that there are several clinical trials regarding the effectiveness of Vitamin D and if you want to test its effectiveness, you can always participate in one of them.
Other thing, which I want you to keep in mind, is that the Vitamin D is playing very important role in the calcium metabolism and if you are having problems with it, avoid its usage and talk to your doctor about this.