If you take vitamin D supplements, a research study in the American Journal of Clinical Nutrition has confirmed previous studies that showed taking vitamin D3 is twice as effective as vitamin D2 for raising your blood levels of vitamin D. After some checking, I found that (luckily) most of the vitamin D supplements you buy online or on store shelves contain just D3. However, there are some D2 supplements available for sale, such as on CVS’s website. Keep in mind that this research study does not say D2 supplements are useless; it simply says that they are not as useful in raising levels of active vitamin D in the body.
So you may wonder why are there two supplements masquerading as vitamin D, and don’t we also make a lot of vitamin D on sunny days? Here’s some answers.
- First, let’s look at the vitamin D in foods. Plant foods (such as some mushrooms) contain vitamin D2, and animal foods (egg yolks and oily fish) contain vitamin D3. It is not unusual to have one form of a vitamin in plant foods and a slightly different form in animal foods. But it is a little unusual to have so few sourcesof a vitamin in foods.
- That’s why vitamin D is added to some foods. In fact, most Americans get their dietary vitamin D from food and beverages fortified with vitamin D – particularly milk and breakfast cereals (usually the vitamin is in the D3 form). If we didn’t have foods fortified with vitamin D, even more Americans would be deficient.
- During warmer months, you can make a lot of vitamin D because the ultraviolet light from the sun makes previtamin D3in your skin and the body turns it into vitamin D3.
- You get a mix of D2and D3 in your body from foods, supplements, and sunshine. Both forms are activated in the liver and the kidneys and then, finally, we have active vitamin D.
Active vitamin D is, of course, very important because it maintains normal blood levels of calcium and phosphorus so they are available to build and maintain strong bones. Not only is this vitamin important for bones, but recent research seems to show that it is important for muscle health as well. Researchers are also looking to see if vitamin D is related in some way to other conditions such as heart disease and cancer.
Vitamin D supplements may be sensible for many Americans who get very little from their diet and/or from sun exposure, especially during the winter months. Older adults are especially at risk because, even if they are regularly outside all year long, they make a lot less previtamin D3 in their skin. So, if you take vitamin D supplements, look for D3 on the label, and keep in mind that the RDA for men and women up to age 70 is 15 micrograms (20 micrograms if you are over 70). According to the Institute of Medicine, taking over 100 micrograms daily is very dangerous to your health, so stay below that number unless directed by a physician. And don’t forget to always tell your health care provider about the supplements you are taking.