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US and Canadian health groups say the potential role of vitamin D in cancer prevention deserves more research. The American Cancer Society (ACS) joined the Canadian Cancer Society and six other health groups in issuing a statement of findings from the first North American conference on vitamin D, held in March.
The conference brought together experts in nutrition, epidemiology, dermatology, oncology, and other fields to discuss what is and is not known about vitamin D and its effect on human health.
The consensus: There is still much to learn about how much vitamin D people need for good health, how much might be too much, and—perhaps most importantly—the best way to get enough.
The statement is available on the Web site of the Canadian Cancer Society at http://www.cancer.ca/ccs/internet/mediareleaselist/0,3172_615815452_1056572174_langId-en.html. In addition to the Canadian and American Cancer Societies, other groups signing onto the statement include the American College of Rheumatology, Canadian Dermatology Association, Dietitians of Canada, National Council on Skin Cancer Prevention (US), Osteoporosis Canada, and the World Health Organization Collaborative Centre for the Promotion of Sun Protection.
"There is no dispute among medical professionals that vitamin D is beneficial for our health, and there is no dispute that sun exposure is the major source of vitamin D for most of us," said ACS deputy chief medical officer Len Lichtenfeld, MD, who participated in the conference. "But there is also no dispute that exposure to ultraviolet (UV) radiation from the sun and other sources can be harmful."
That is why making recommendations about vitamin D is problematic.
UV light in the form of UVA and UVB is known to raise the risk of melanoma and nonmelanoma skin cancers, as well as cataracts. But vitamin D is crucial to bone health, and there is growing evidence that it may have a role in preventing some cancers, especially colorectal cancers.
Because vitamin D occurs naturally in only a few foods and is added to just a handful of others, many experts worry that some Americans get too little vitamin D to reap these potential benefits. Yet few are willing to encourage sun exposure with its well-known dangers. UVB radiation is what spurs the skin to produce vitamin D.
The health groups' statement acknowledges this conundrum and concludes that a balance of some sun exposure and vitamin D supplementation may be the best answer for now.
"To minimize the health risks associated with UVB radiation exposure while maximizing the potential benefits of optimum vitamin D status, [dietary] supplementation and small amounts of sun exposure are the preferred methods of obtaining vitamin D," the consensus statement says.
Current intake recommendations for vitamin D, set by the Institute of Medicine, are 200 international units (IU) a day for children and adults up to age 50; 400 IU for adults age 51–70; and 600 IU for adults age 71 and older.
However, those levels are considered "adequate intake" to maintain bone health and normal calcium metabolism. They do not reflect the other potential health benefits of vitamin D. Indeed, many experts consider these levels too low for optimal health, and recommend as much as 1,000 IU daily.
The statement of findings from the health group does not go so far as to recommend that level of vitamin D. Rather, it calls for more research to determine the optimal amount and encourages the public to discuss supplementation with a health care professional.
The statement says those at greatest risk of having too little vitamin D include the following:
Lichtenfeld said people must also use common sense when deciding what constitutes a "small amount" of sun exposure. Five minutes may be enough for some, but not others.
"There is no ‘one size fits all’ recommendation for people to follow in determining how much sun exposure is adequate to obtain healthful vitamin D levels," he said.
How much sun any single person might need depends on many things: their age, the amount of vitamin D obtained from their diet, skin darkness, and sunshine intensity where they live. It will take more research to figure out specifics.
"Avoiding the sun at all costs, for most of us, simply doesn't make sense," Lichtenfeld acknowledged. "But that doesn't mean people should bake themselves outside or in a tanning booth. The ACS does not advocate seeking sun exposure for the purpose of obtaining vitamin D."
The ACS is in the process of updating its skin cancer prevention guidelines and currently recommends reducing sun exposure to reduce the risk of skin cancer. Although the guidelines note that vitamin D is important to good health, the ACS does not currently have a recommendation about vitamin D as a way to treat or prevent cancer.
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