I have gained most of my knowledge, by working in the Medical Field. Last week, they did have something on-line about Vitamin D 3. It's been on the News also. about 4 years ago, is when we noticed that People with low levels of the Vitamin, suffered a wide variety of complications because of the lack of it. With the use of Sun Block these days, we are all pretty low on the Vitamin. They recomend you send your Children out for 10 minutes without it, and then apply the Sun Screen. It's also known to help people with Chronic Fatigue, Depression, and even Fibromyalgia. The BEST source of this information, is your Doctor, like I said in the previous post. If you are really interested in this, Google it. When I had my level checked , it was 17. Optimum is in the high 30's. My Doc put me on a Prescription of it. I take it once a week, as per the Directions. I am a Smoker, who use to get 4, or more Colds a year. I haven't had a Cold in about 2 years. Knock on Wood!! Smokers get Colds a lot!!