According to Jack Norris, Registered Dietitian and Executive Director of Vegan Outreach, we need vitamin D for healthy bones, as it can increase calcium absorption when the body signals that it needs calcium. Research has shown that in populations with calcium intakes similar to omnivores in the United States, vitamin D is more important than calcium for preventing osteoporosis. For instance, an adequate vitamin D intake is associated with a lower risk of osteoporotic hip fractures in postmenopausal women. Neither milk nor a high-calcium diet appears to reduce risk.
Recently, low levels of vitamin D have been linked to many other diseases such as multiple sclerosis, respiratory disorders, various types of cancers, and cardiovascular disease. Some researchers have suggested that the recommended vitamin D levels are too low. However, the Institute of Medicine has reviewed the research and concluded that is not the case. The controversy has resulted in many people thinking they are deficient in vitamin D when they are not.
Most people get a significant amount of their vitamin D from the action of UV rays on their skin. However, aging decreases the capacity of human skin to produce vitamin D3. Moreover, although the body can store vitamin D made in the sunnier months for use during less sunny times, this does not work for everyone. In fact, some people, even those living in sunny climates, develop extremely low levels of vitamin D. This can manifest itself through fatigue and bone pain.
Most Americans get their dietary vitamin D through fortified milk and fortified margarine. The only significant, natural, dietary sources of vitamin D are fatty fish, eggs (if chickens have been fed vitamin D), and mushrooms (if treated with UV rays). The vegan diet contains little, if any, vitamin D without fortified foods or supplements. On average, vegans’ vitamin D levels are adequate, but somewhat lower than non-vegans.
There are two forms of supplemental vitamin D: ergocalciferol (D2) and cholecalciferol (D3). Vitamin D2 is always vegan, made from exposing fungi to UV rays. Vitamin D3 normally comes from fish oil or sheep’s wool, but there is a vegan version made by Vitashine. A great deal of research has compared vitamin D2 to D3. Vitamin D2 is effective at increasing bone mineral density (when given to people who are deficient). Vitamin D2 can also increase vitamin D levels temporarily but is not as effective as vitamin D3 at keeping vitamin D levels raised when taken only weekly. Thus, if you take vitamin D on a daily basis, D2 should be fine, whereas if you’re only going to take it sporadically, without getting sun in the interim, or find that your vitamin D levels will not increase on D2, then you should opt for D3.