Summer Health Tip Three: Make a little vitamin D.
Vitamin D is a fascinating vitamin. Well, it actually isn't a vitamin per-say, but is a fat-soluble (meaning stored in fat) steroid. It has two forms D2 and D3. It is often said that the sun "makes" vitamin D. Vitamin D precursors lie in our skin and are activated when the ultra-violet (UV) rays of the sun penetrate the skin.
Adequate levels of vitamin D in the body have been linked to protecting the body from all kinds of diseases, especially cancer. Unfortunately, anyone living far north of the equator is not exposed to enough sun in order to produce enough vitamin D naturally. That is why it is important to supplement vitamin D during the less-sunny months (roughly October to April).
When outside, with some exposed skin (think shorts and a t. shirt), without any sunscreen, and for a duration of fifteen minutes, the body can produce up to 10 000 IU (International Units) of vitamin D. Of course many people spend more than fifteen minutes a day in bright sunlight during the Summer and thus these people are making WAY more vitamin D (note: if you aren't outdoors a lot this Summer, try to at least be outside for fifteen minutes wearing as little clothes as possible to expose skin to sun contact). This amount (10 000 IU/15 min) shows how different the vitamin D levels of the bodies living far north of the equator are in Winter and Summer months. Well over 10 000 IU a day compared to 0 IU a day (honestly, how often is bare skin exposed to the sun during the Winter?). It is unknown how this huge change in vitamin D supply affects the human body in the long-term, but it strongly believed to have something to do with the higher prevalence of chronic diseases that exist today.
As for vitamin D in the diet, it really only exists in a handful of foods and many of these foods have been fortified (i.e. vitamin D has been added to them). Egg yolks contain some natural vitamin D, whereas cow's milk contains vitamin D only because it was added to it during the milk's processing.
As for vitamin D supplements, liquified versions are best absorbed and are best when taken with a meal containing fat because vitamin D is a fat-soluble vitamin (during the winter I took mine with my morning toast because the fatty nut butter I used helped with its absorption).