absorption of minerals, calcium, and phosphorus from the food we eat.
Unfortunately, these days many of us are finding ourselves more and more deficient of this necessary vitamin, due to a number of different factors. As we grow out of childhood we tend to drink less milk...if any at all, which provided a good source of the vitamin for us as children. With all the hours and hours that we spend in front of the our computers, tablets, blackberries, etc., we usually are not soaking it up from the sunshine- and as we have also constantly had drilled into our brains- since the UV rays that stimulate vitamin D can also cause skin cancer, the sun is not the recommended source. Even if you do spend a lot of time outside under the sun, with the proper sunscreen, experts say that unless you live farther north than LA, you can not truly get enough vitamin D from the sun only, during winter months. Finally, as vegetarian and vegan diets become more prevalent, we also lose ingesting the needed vitamin from certain animal products.
The good news is that if you have a fairly omnivorous diet and you find that you are deficient, which you most likely are, there are some ways to replenish your vitamin D. Foods such as fatty fish (salmon, tuna, mackerel, and sardines), fortified breakfast cereal, fortified orange juice, eggs (yolks) and fortified milk are the best sources. To give you an idea, a yolk contains roughly 20 IU (a small amount), a 3.5oz serving of salmon contains roughly 400 IU. However, since at least 400 to 800 IU are needed per day, supplements in the form of a daily multi-vitamin and vitamin D pills are the best way to quickly replenish your supply.
While I am in no way a doctor and so do not want to attempt to explain the multiple reasons for why we need vitamin D, all of the experts seem to agree that (all other variables held constant) people with proper amounts of vitamin D tend to starve off diseases (not to mention weak bones and weak muscles) much better than those with low levels. So unless you eat fish often, drink lots of fortified milk and cereal, and happen to soak up some rays every now and then, next time your grocery shopping check the label for vitamin D. And the next time you find yourself fasting for the past 12 hours and about to faint from hunger as you wait in line at the blood lab, put all that good fasting work to use and request a test.