A new study has found that most Americans are Vit. D deficient. A lot of women in particular, are very badly deficient. We use sunscreen and with clothing and busy schedules we do not get enough sun. So for a deficient person, Drs. are recommending 5000-10000 units or whatever it comes in per day. It will not hurt you! I started taking Vit. D3 from Sam's Club. I take 2 of the 5000 units per day & I do feel better. This also improves our immune system.