Most people feel sad in the winter. This is evident by a higher suicide rate in countries where sunlight is void for many months like the Scandinavian areas of the world. Further, after testing most people through their doctors, many resulted in lower than average levels of vitamin D. I have read that low levels of this vitamin are responsible for breast cancer, immune problems and other conditions. Research indicates and links low circulating levels of vitamin D to seasonal affective disorder or SAD, as well as depression. In addition, the lack of vitamin D has also been associated with cancer, arthritis, high blood pressure osteoporosis, diabetes and multiple sclerosis.. With these conditions at hand, it is a good idea first of all to have a complete physical EVERY year, with a colonoscopy for those 45 and older. Your blood levels should be checked not only for cholesterol levels, but for oxidation to the vessels caused by high cholesterol levels.. Your vitamin D levels should be checked as well. Blood tests are warranted at least once a year and if insurance will pay, twice a year as problems like cancer, diabetes and an array of other problems can show up in blood and urine tests which are vitally important. I have had my share of doctors who have told me, “You don’t need this or that, but believe me, it’s your life and it’s your money and insurance so be well informed and let the doctor know that you want these tests regardless of his opinion. They are tests, not surgery! So get it done. With that said, vitamin D deficiency is a problem that needs to be checked and remedied at your earliest opportunity. Remember!! You only live once! So get going!.