Being....Go to http://www.vitamindcouncil.org.
It is far more dangerous to be deficient in vitamin d than to supplement. And, if you don't happen to live on the equator, pretty darn hard to raise levels as the sun only is strong enough in the summer and most of us work in an office. You have to have most of the skin exposed (bathing suit or nude) to make enough vitamin D to raise levels without supplementing. I took 1,000iu D3 for years and was concerned about over doing it, but when I had my level tested, it was 12ng/ml -- severely deficient. Optimal ranges are 70-90ng/ml for most people, kids with autism it's even higher like 150ng/ml.