When I had my vitamin D checked it was 19 ng/ml which is deficient. The healthy range suggested to me was 30ng/ml to 96ng/ml. I started taking 5000 IU of vitamin D3 and in three months got my level up to 72.2 ng/ml. Most people are deficient in vitamin D because they do not get enough sun. Factors determining vitamin D levels are Sun Exposure, location, Age, Dark Skin, Weight, and Chronic Illness. Oil based vitamin D3 is the best form to take.