By Donna Feldman, MS, RD

You probably know that vitamin D is the “sunshine vitamin." Activated in our skin by the sun’s UVB rays, vitamin D is important for both calcium absorption and bone strength. But recently, thanks to modern urban lifestyles, vitamin D is becoming harder and harder to get. As we spend increasing amounts of time in cars and buildings, we’re getting less sun exposure…and this translates into less vitamin D production. To complicate matters, when we manage to get out in the sun we use lots of sunscreen to avoid the dangers of skin cancer. But sunscreen also blocks the vitamin D-producing rays. As a result, many researchers believe vitamin D deficiency is now widespread.

Health effects of a vitamin D deficiency?

What’s so dangerous about vitamin D deficiency? Well, a growing number of experts suspect that not only does it have a detrimental effect on bone strength, it also can be linked to many other diseases, including colon, breast and ovarian cancers; diabetes; and multiple sclerosis.

The new controversy: obtain vitamin D naturally and ditch your suncream?

Michael Holick, MD, at Boston University, is one of the most vocal vitamin D advocates. He goes so far as to claim that people should ditch their sunscreen altogether to get their vitamin D the natural way. While most dermatologists do not suggest this method, there is so much growing interest in the medical community that many new research projects are underway to evaluate just how far-reaching vitamin D’s health effects might be.

It will be years before the answers from these projects are available. What should you do while the experts sort through the research? If you live in a sunny climate and spend lots of time outside, your skin may be making enough. If not, be sure to get the minimum recommended intake. How much is that? According to official U.S. recommendations, 200 I.U. is considered an adequate daily intake, and that is increased to 400 for people over 50. Some scientists, including Holick, now claim 1000 I.U. is desirable.

Where to get vitamin D

There are few good natural food sources of D: mackerel, sardines, and fish livers are examples. Fortified milk and some fortified orange juice provide 100 I.U. per 8 ounce cup. If you take a multiple vitamin, you are likely getting 400 I.U. of vitamin D. You can also find vitamin D supplements, but always check the labels. Bottles labeled “Vitamin D” on the front may also list vitamin A on the back label as an additional ingredient, and excess vitamin A can cause toxicity.

And finally… get advice before taking supplements

With all the claims about the relationship of vitamin D deficiency to serious diseases, people diagnosed with those diseases may be tempted to take supplements. It’s never a good idea to self-medicate with vitamins in the hope of curing a disease. A discussion with your healthcare provider about your concerns is critical. For more information on adequate intake of vitamin D from food or supplements, consult a registered dietitian .