I am a retired person who reads many "health" books each month. This is one of the three best health books I have read in the past six months, and that is saying a lot! I was diagnosed by my doctor as being low in Vitamin D (a 22, when we should be much higher). Aside from the stunning fact that a conventional doctor " actually caught a vitamin deficiency, I was shocked that I, a vitamin chomper of the first order, could be deficient in any nutrient. I got Dr. Dowd's book to check up on my own doctor's recommendation and realized she was more than right. In the bargain, I learned about this incredible steroid and its importance to our entire body. This information is crucial because most of us are very careful to "protect" ourselves from the sun. I did,--very successfully apparently. I am recommending this book to many friends and relatives for its relevance to cancer, diabetes, rheumatoid arthritis, and a host of medical conditions.