Vitamin D3 better than metformin for insulin sensitivity

I had my levels checked about 6 months ago at a routine screening and was deficient at 21. I upped my intake to 6000 units a day (dr.'s office said to take 2500) and I am now up to 41 (in normal range, but could go higher). I am now taking 10,000 units of D3 a day.
Another benefit - it is a mood enhancer, frankly, I think it works better than prozac.