HEALTH UPDATES
Sunny Results for the Sunshine Vitamin
A review of multiple studies suggests a protective relationship between vitamin D and cancer risk
Most adults are familiar with vitamin D, which combined with calcium is essential for bone health. As reported in two recent studies, vitamin D also holds promise as a protective agent against cancer, the second leading cause of death in the U.S.
Vitamin D is a fat-soluble vitamin that is often referred to as the “sunshine” vitamin because skin cells are stimulated to manufacture vitamin D when exposed to ultraviolet light. The recommended dietary allowance (RDA) is 200 IUs for people under 50; 400 IUs for adults 51-70; and 600 IUs for adults over 70. Good dietary sources include: fish and shellfish (especially fatty fish such as salmon, sardines and mackerel), mushrooms, fortified cereals and low-fat or skim milk products.
Nevertheless, it is difficult to obtain sufficient levels of vitamin D from diet alone. In fact, for most people, sunshine and not food, is a major source of vitamin D. For those who get limited sun exposure, such as those living in northern climates in the winter, or seniors who don’t get outdoors, and individuals with darker skin (skin pigmentation reduces the ability to synthesize the vitamin), vitamin D deficiency is fairly common. Studies have suggested that half the elderly in the U.S. are vitamin D deficient as well as 35%-40% of the younger population.
Obtaining sufficient levels of vitamin D may be important not just for bone health. That’s because several studies suggest that vitamin D plays a protective role against some cancers whether intake is from diet, supplementation or exposure to sunlight. The strongest evidence has supported an inverse relationship between vitamin D intake and incidence of colon and colorectal cancers. Despite this evidence, researchers haven’t been able to identify the mechanism of vitamin D’s influence over cancer development. In particular, they are unsure of the amount of vitamin D necessary to provide cancer protection.
Researchers from the Moores Cancer Center at the University of California, San Diego, attempted to answer some of these questions. The researchers conducted a systematic review of 63 observational studies on the relationship between vitamin D and several neoplasms including, colon, breast, prostate, and ovarian cancer. Their findings will be published in the February 2006 issue of American Journal of Public Health.
Of the 30 colon cancer studies the researchers reviewed, 20 found a positive relationship between vitamin D levels, sunlight exposure or another marker of vitamin D status. Nine of the 13 breast cancer studies showed a positive relationship; 5 of the 7 ovarian cancer studies found higher death rates associated with lower sun exposure or decreased vitamin D intake. Of the 26 prostate cancer studies, 13 found a positive relationship with vitamin D intake.
The type of studies the UCSD
researchers reviewed was observational which rely on study participants
to estimate and record their behavior. Compared to a randomized, double-blind
study, observational studies can’t always control for other factors
such as nutrients in an individual’s diet, which might influence
the study results. However, clinical trials can take 20 years to complete.
In the meantime, Cedric Garland, co-author of the study, recommends that
adults take 1,000 IUs of vitamin D every day. This amount is well within
the 2,000 IU upper intake level established by the Institute of Medicine
and confirmed as safe. Oral supplementation of vitamin D can’t compete
for spending 10 to 15 minutes outdoors on a sunny day. But, with skin
cancer rates rising, many people are concerned about spending time outdoors
and prefer to obtain their intake from a nutritional supplement.
References:
Garland, C. F. et al, “The role of vitamin D in cancer prevention”,
American Journal of Public Health, 2006: 96: 2:9-18.
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