The promises and pitfalls of vitamin D deserve more research, according to the American Cancer Society (ACS) and 7 other health groups. The US and Canadian groups issued a statement of findings this week from the first North American conference on vitamin D, a nutrient most people get though exposure to sunlight.
The conference, held in March, brought together experts in nutrition, sun exposure, skin cancer, and other diseases to discuss what is and isn't 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.
"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) rays from the sun and other sources can be harmful."
Recommendations a Balancing Act
That is why making recommendations about vitamin D is problematic.
Ultraviolet 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 Americans get too little vitamin D to reap these potential benefits. Yet few are willing to encourage sun exposure with its well-known dangers.
"If vitamin D is good for you, and exposure to the sun is bad for you, what do you do?" Lichtenfeld explained.
The answer may lie in balancing sunshine with vitamin D supplements.
"Supplementation and small amounts of sun exposure are the preferred methods of obtaining vitamin D," the consensus statement says. "If you are concerned about adequate vitamin D levels, discuss supplementation with your health care practitioner."
The statement says those at greatest risk of having too little vitamin D include:
- elderly people
- babies who are exclusively breast-fed
- people with dark skin (darker-skinned people need more sun exposure to make vitamin D)
- people who don't get any sun exposure (those who are housebound or who cover their bodies with clothing for religious or cultural reasons)
- people who live in the northern US and Canada in winter (above 37 degrees latitude)
Common Sense Crucial
Until more research is done, the key is to use common sense when deciding what constitutes a "small amount" of sun exposure, Lichtenfeld said. Five minutes may be enough for some, but not others.
How much sun any single person might need depends on many things: how old they are, how much vitamin D they get from their diet, how dark their skin is, and how intensely the sun shines 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.
"What you do not do is seek the sun," Lichtenfeld cautioned. "That would be absolutely the wrong message to send, and that is what has so many of us in the skin cancer prevention community so concerned."
Any time spent in the sun must include sun protection, he added.
"Using sunscreen, wearing a hat, wearing long-sleeved shirts, and wearing sunglasses are all recommendations that I believe are prudent," he said. "It is also sensible to avoid the sun at the most intense times of day [generally 10 am to 4 pm], and if you must be outside during those times, try to seek the shade."
The American Cancer Society is in the process of updating its skin cancer prevention guidelines, and currently recommends reducing sun exposure to reduce the risk of skin cancer. While the guidelines note that vitamin D is important to good health, ACS does not have a recommendation about vitamin D as a way to treat or prevent cancer.
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