I was diagnosed with LOW Vitamin D recently, via blood test, 19 ng/ml. Supposedly, optimal is 40-70ng/ml. Needless to say, 19 is really low. I started taking this supplement. I'm happy with it thus far, but since my levels are so low, I was told by my doctor to purchase one with higher IU's. They are easy to swallow, tiny little gel pills, and the price is reasonable. After I finish taking these, I will opt for Vitamin D3 in liquid form with Calcium for maximum absorption.