Sunlight and Vitamin D
by Roberta Lee, MD (topic expert: health)

In our frenzy to protect ourselves against skin cancer, we forget that sunlight can be beneficial, too - if taken in moderation. In fact, sunlight is natural and necessary for human health just as much as food, water and companionship. We need sunlight to establish the appropriate levels of vitamin D in our bodies.

While vitamin D helps maintain the health of your bones by absorbing calcium more efficiently, other benefits of the vitamin are becoming increasingly apparent. Evidence shows that vitamin D has some capacity to protect us against certain kinds of cancers.

Studies show that moderate exposure to the sun can help ward off prostate, breast and colon cancers. In 1940, Dr. Frank Apperly, a physician, observed that people living in sunny climates with latitudes between 10 and 30 degrees had lower rates of cancer than those living in the higher latitudes. Those living in latitudes above 30-40 degrees had 85% higher incidence of cancer, on average, compared to those people living 20 degrees closer to the equator. Subsequent studies have confirmed these observations.

A more recent 2001 study published in the Lancet, a peer-reviewed medical journal, correlated increased sun exposure to lower rates of prostate cancer [1]. The average age of the higher sun-exposure group diagnosed with prostate cancer was 72 years whereas the lower sun-exposure group was diagnosed at a mean age of 67.7. Similar positive correlations of increased sun exposure and lower cancer rates have been published with regard to breast and colon cancer [2].

How does vitamin D protect us? Experts suggest that vitamin D prevents the unhealthy cell growth that is a precursor to cancer. Cells and organs in the body, including immune cells, colon, prostate, breast, and skin cells, have the ability to make their own vitamin D to maintain health and inhibit abnormal cell growth. Measurement of vitamin D can be done in routine laboratory tests, but it is the 1,25 vitamin D level that is the important form of vitamin D to measure.  A result less than 20 ng/milliliter is considered deficient.

A patient would have to ask their doctor to measure vitamin D, as it is not done in a routine check-up. It is available in most commercial labs. As a practicing physician, I have been able to have my patients tested who are covered under insurance, but they have to ask for measurement of 1,25 vitamin D.

The current daily recommendations for vitamin D, according to most vitamin D experts, should be 800 IU-1,000 IU /day for adults, although the current recommended daily amounts are far below. There are discussions among nutrition experts to raise the recommended amounts because scientific data suggests that vitamin D can be tremendously helpful in fighting cancer [3].

Finding sources of vitamin D in the American diet is challenging. An 8-ounce glass of milk provides a meager 100 IU of vitamin D. Cod liver oil is one of the richest sources of vitamin D; one tablespoon of cod liver oil provides 1,360 IU of vitamin D. A three-ounce serving of salmon provides 360 IU of vitamin D, while a can of sardines provides 270 IU of vitamin D.

Two forms of vitamins exist: fat-soluble and water-soluble. Excesses of water-soluble vitamins are easily released via the kidneys through the urine, though they are hard to find for purchase. Fat-soluble vitamins simply accumulate in the body and are stored in the fat. Thus fat-soluble vitamins can reach toxic levels if taken in too high amounts. Such is the case of vitamin D, which is a fat-soluble vitamin.

So how much is sun is considered just enough to keep your vitamin D levels up? Expose 25% of your body to sun for approximately 10 minutes, three times a week and use sun blocker afterwards to minimize radiation damage to your skin.

Those who wish more details on vitamin D metabolism should consider reading The UV Advantage, by Michael Holick and Mark Jenkins. Dr. Holick is a world-renowned expert in vitamin D research at The Vitamin D, Skin and Bone Research Laboratory at Boston University Medical Center.

Sources:

1. Luscombe CJ, Fryer AA, French ME, Liu S, Saxby MF, Jones PW, Strange RC. Exposure to ultraviolet radiation: association with susceptibility and age at presentation with prostate cancer. Lancet.2001;358(9282):641-2.
2. Giovannucci E. The epidemiology of vitamin D and cancer incidence and mortality: a review ( United States). Cancer Causes Control. 2005;16(2):83-95.
3. www.cbsnews.com/stories/2007/06/07/earlyshow/contributors/emilysenay/main2897386.shtml, "Two New Vitamin D studies Reveal Powerful Cancer Protection."