. This is due to the fact that Vitamin D plays a role in activating or shutting down as many as 100 genes, many of which have a role in fighting these diseases. Vitamin D's protective effects, according the the Vitamin D Council, lie in its conversion to calcitrol, which has activity against cancer and other disease. Here is how it works:
1) Vitamin D3 is transported to the liver and converted to calcidiol. This is the storage form of vitamin D and the form that helps regulate calcium levels in the body. Calcidiol then takes one of two pathways in the body.
2) Calcidiol is transported to the kidneys, where it is converted to calcitrol. Calcitrol circulates in the blood to maintain calcium levels
3) Or...excess calcidiol goes to the cells in your body which can then make calcitriol, which fight disease such as cancer in the cells. If you are deficient in vitamin D, this second step never happens and all of the available vitamin D goes toward regulating calcium levels.
So, if you do not have enough vitamin D, the important function of regulating blood calcium levels may be achieved, but many of the disease-fighting benefits will be lost.
How do I know if I am deficient in vitamin D? A simple blood test, now given by many doctors as part of routine physical exams, can determine vitamin D deficiency. The proper test is for 25-hydroxyvitamin D. The Vitamin D Council states that a proper level of vitamin D is between 50-70 ng/ml. Webmd.com recommends a lower range of 35-50 ng/ml. Your doctor may have a sense for where he or she would like you to be, but it is safe to say 35 ng/ml is a minimum.
How much vitamin D you should take depends on various things including your size, body fat, the latitude you live at, skin coloration, use of sunblock, the season, and whether or not you have any health conditions that could be helped by an increased intake of vitamin D. In general, you should take more the more you weigh, the more body fat you have, the further north you live, the darker your skin, the more sunblock you use and if you have a health issue. The current RDA for vitamin D is only 200 IU per day, 1000 times less than the amount you can get from direct exposure to UVB rays of the sun in just 20-30 minutes. The guideline is under review and most sources are now saying that the average person could safely take 1000-2000 IU's per day. Since most multivitamins have only 200-400 IU's in them and vitamin D is difficult to get in large amounts in the diet, it follows that most of us should be supplementing with vitamin D.
There has been some concern in the past about the potential toxicity of high levels of vitamin D, but the only known cases of toxicity relate to high dose pharmaceutical vitamin D (D2) and industrial accidents. In the case of the industrial accidents, the levels were in the range of 100,000 IU's and up. This is obviously a far cry from 2000 IU's per day. Some people also have a hypersensitivity to vitamin D, most notably those with hyperparathyroidism and granulomatous disease. These conditions can cause an over-calcification of the blood and additional supplementation in these should be recommended and closely monitored by a physician.
So get out there and get your vitamin D! If you are a part time sun worshipper, you probably will not need to supplement during the summer. While it is perfectly normal and natural to get some sun, the key is not to burn. Once you have gotten to 20-30 minutes of full sun exposure, switch to sunscreen. The use of sunscreens with antioxidants like green tea, vitamin C, grapeseed extract and carotenoids in them will reduce any oxidative stress to the skin that occurs from full sun exposure. Use a high quality sunscreen with a physical versus chemical blocker, and make sure there are not other harmful substances as well. I like the UV Natural brand in particular as it provides both a physical block as well as antioxidants to alleviate any harmful effects of the sun. Soak up the sun and enjoy!
Feature Article: The Big Deal About Vitamin D 
