Your body produces vitamin D when sunlight reaches the skin. Another way to get it is by eating foods that contain vitamin D. Though there are not a lot of foods that have it naturally, some foods like milk, orange juice and cereals are fortified with D. Additionally, you can take a supplement. There are several factors in determining levels of vitamin D. The following are some important ones.
Use of sunscreen. While sunscreen can prevent sunburn by blocking UVB light, does that mean using it will lower your vitamin D level? Practically speaking, most people don’t put on enough sunscreen to block all UVB light, or they use it sporadically. In an Australian study that is often cited, there was no difference in D levels between adults who used a placebo cream, and those who applied sunscreen.
Age. Older people have lower levels of the skin substance that UVB light converts into Vitamin D. Some evidence also suggests that as we age we are less efficient at producing it.
Where you live. We have shorter days in the winter and wear more clothing – limiting UVB exposure. The farther you live from the equator means less UVB light reaching us during the winter months.
Skin color. Melanin, the substance that makes skin dark “vies” for UVB with the substance in the skin that makes the body’s vitamin D. Because of this dark-skinned people may need more UVB exposure than light-skinned people to get comparable amounts of vitamin D.
Weight. Some studies have shown that being obese may be linked to low vitamin D levels. Other studies have found that body fat absorbs it, making it a good source of the vitamin when the body may be producing less of it in other ways.
Air quality. The burning of fossil fuels, wood and other materials produce carbon particles in the air. These particles absorb UVB rays, which limit the making of vitamin D. However, it’s also recognized that ozone absorbs UVB radiation – so that holes in the ozone layer may actually boost vitamin D levels.
Check with your doctor to find out how much vitamin D is right for you……. Healthbeat Harvard Medical School 1/10/13