Great article: Most people in northern countries a low in vitamin d. This is because most people are aware of the cancer risk and aging effect of UV radiation from the sun, so they stay covered, indoors, or wear sunscreen. Get your vitamin d levels checked by your doctor, it is usually covered as preventative care. Chances are you are low. I was taking 5000 IU per day as a supplement for years. That is considered a high dose, but it was still low so now have increased it even more. It is one of the most important things you can do for your health - get it tested before you start popping too many though.