Does sun exposure promote or prevent skin cancer?
The answer to both appears to be yes … depending on which kinds are in question.
So far, most evidence suggests that, by boosting vitamin D blood levels, reasonable sun exposure may reduce the risk of deadly skin melanomas.
On the other, lesser hand, sun worshipping seems to promote the far more common and benign kinds of skin cancer among fairer-skinned folks.
Vitamin D, Cancer, and the new RDA
Vitamin D helps control how quickly cells replicate … a process that often goes awry in cancer.
Many studies have linked higher vitamin D intakes and blood levels with lower risks of colon, breast, prostate, and other cancers.
Still, in November of 2010, a panel appointed by the U.S. Institute of Medicine (IOM) concluded that the largely epidemiological and lab evidence couldn't prove that vitamin D deters cancer.
For more on that, see “Vitamin D RDAs Raised Substantially”, which includes a sharp critique of the IOM's timid move by leading vitamin D researcher Michael Holick, M.D., Ph.D., of Boston University School of Medicine.
And we recommend reading the cogent comments by leading nutrition-oriented physician-educator Andrew Weil, M.D.
A new study indicates that the combination of supplemental calcium and vitamin D may halve the risk of melanoma among women at higher risk of this killer skin cancer.
And, based on earlier findings by these and other researchers, it appears likely that vitamin D is the critical component of the combo.
Scientists from Stanford University School of Medicine analyzed data from 36,282 postmenopausal women aged 50 to 79 who took part in the Women's Health Initiative (WHI) clinical trial (Tang JY et al. 2011).
Women in the WHI study were randomly assigned to take a combined calcium (1000mg) plus vitamin D (400 IU) supplement or a placebo pill, to see if the supplements would reduce the risk of hip fractures or colon cancer.
The Stanford team's new analysis zeroed in on women with a history of one of the more common non-melanoma skin cancers … mostly the basal cell or squamous cell kinds.
People with these generally non-fatal forms of skin cancer are more likely to develop the more lethal form called melanoma.
The new analysis of WHI data showed that women who once had a non-melanoma form of skin cancer and took the calcium-vitamin D combination developed 57 percent fewer melanomas than women with similar histories who did not take the supplements (Tang JY et al. 2011).
However, the study – led by dermatologist Jean Tang, M.D., Ph.D. – found that the daily dose of 1000 mg calcium plus 400 IU of vitamin D didn't protect everybody.
Women with no history of non-melanoma skin cancer showed no risk reduction, compared with their placebo-group counterparts.
Because men were not part of the WHI trial, it's not certain whether the protective effect of the supplements would also apply to males with a history of non-melanoma skin cancer.
However, a study published last year by Dr. Tan's group found that older men with higher blood levels of vitamin D had only about half the risk for any of the common non-melanoma skin cancers (Tang JY, Parimi N, Wu A, et al. 2010).
Fish fit the vitamin D bill; Sockeye salmon stand out
In addition to getting vitamin D from supplements, certain fish rank among the very few substantial food sources of vitamin D, far outranking milk and other D-fortified foods.
Among fish, wild Sockeye Salmon may be the richest source of all, with a single 3.5 ounce serving surpassing the US RDA of 400 IU by about 70 percent:
Vitamin D per 3.5 ounce serving*
Sockeye Salmon 687 IU
Albacore Tuna 544 IU
Silver Salmon 430 IU
King Salmon 236 IU
Sardines 222 IU
Sablefish 169 IU
Halibut 162 IU
*For our full test results, click here.
In that study, conducted among men aged 68 to 78, those with vitamin D blood levels ranking in the top one-fifth (i.e., above 30 ng/mL) were 47 percent less likely to have any kind of non-melanoma skin cancer, compared to those with the lowest blood levels.
Vitamin D dose called low, but still appeared effective
The lack of melanoma protection found among women in the WHI trial without a history of non-melanoma skin cancer might have been due to the low dose of vitamin D given.
According to co-author David Feldman, M.D., “The patients in the Women's Health Initiative were given vitamin D at a very low dose, based on today's knowledge — only 400 IU per day.” (Young S 2011)
Also, patients in the WHI trial's placebo group were allowed to take as much vitamin D as patients that were provided the calcium and vitamin D supplements, so the experimental difference between the two groups was small.
As Dr. Feldman said, in light of the fairly small difference in vitamin D intakes between the WHI's test and control groups, “It's somewhat surprising that [we detected] an effect on melanoma risk, and I think many potential benefits of vitamin D may not have been detected.” (Young S 2011)
Even in a large study like the WHI, the low frequency of melanomas means that the absolute number of cancers was small. Out of the 36,000 participants, only 176 cases of melanoma were reported.
“That just highlights how large a trial needs to be to capture cancer as relatively rare as melanoma,” said Marcia Stefanick, Ph.D., the Stanford WHI principal investigator and senior author of the new analysis led by Dr. Tang.
Dr. Tang plans to examine the potential relationship between vitamin D and cancer prevention, including a study that will compare blood levels of vitamin D with melanoma outcomes.
Another line of research will examine the effect of larger doses of vitamin D on the behavior of skin cells in patients with high skin-cancer risk.
Sun exposure: A double-edged but live-saving skin cancer factor
Sunlight is the major “source” of vitamin D for most people … unless they take vitamin pills and/or eat lots of fatty fish such as wild salmon, sardines, tuna, and the like.
Unfortunately, abundant sun exposure early in life does raise the risk of non-melanoma forms – that is, generally non-fatal – of skin cancer.
But Michael Holick, M.D., Ph.D., of Boston University School of Medicine – one of the leading vitamin D researchers in the world – made a key point about the new study's encouraging results (HDN 2011):
“Melanoma is a different story. Being exposed to sunlight, [and] making some vitamin D may very well be protective of melanoma.”
“The thinking is, [by] improving your vitamin D status, whether by supplements or by exposure to sunlight, you are providing your skin cells with a mechanism to prevent them from becoming malignant.”
Interestingly, another study by Dr. Tang's group found that people who avoid sun exposure because they've been diagnosed with “basal cell nevus syndrome” – a group of inherited genetic defects that raises the risk of skin cancers – were woefully deficient in vitamin D and need to take supplements (Tang JY, Wu A, Linos E, et al. 2010).
And the role of calcium, if any remains unknown, said Holick: “We don't know whether vitamin D can have its effect in the absence of calcium or vice versa; there's rationale for both.” (HDN 2011)
Importantly, based on the earlier study by Dr. Tang and related research, Holick believes that her team's finding about women would likely apply to men.
People can get their vitamin D from diet, sun exposure, and supplements. Fatty fish are the richest food sources of vitamin D, by far, with wild salmon providing the highest levels: from about 230 IU to 690 IU per 3.5 oz serving. (Click here for our chart showing vitamin D levels in the top seafood sources.)
Professor Holick recommends 2000 IU of vitamin D a day for adults and 1000 IU for children, versus the IOM's recently updated recommended daily allowance (RDA) of 600 IU from birth through age 70.
The study was funded by the National Heart, Lung and Blood Institute, the U.S. Department of Health and Human Services, the National Institute of Arthritis and Musculoskeletal and Skin Diseases, the National Center for Research Resources, and the Stanford Medical School Medical Scholars Research Fellowship.
Chang AL, Fu T, Amir O, Tang JY. Association of facial skin aging and vitamin D levels in middle-aged white women. Cancer Causes Control. 2010 Dec;21(12):2315-6. Epub 2010 Sep 30.
HealthDay News (HDN). Vitamin D, Calcium Combo May Halve Melanoma Risk in Some Women. Tuesday, June 28, 2011. Accessed at http://www.nlm.nih.gov/medlineplus/news/fullstory_113691.html
Tang JY, Fu T, Leblanc E, Manson JE, Feldman D, Linos E, Vitolins MZ, Zeitouni NC, Larson J, Stefanick ML. Calcium Plus Vitamin D Supplementation and the Risk of Nonmelanoma and Melanoma Skin Cancer: Post Hoc Analyses of the Women's Health Initiative Randomized Controlled Trial. J Clin Oncol. 2011 Jun 27. [Epub ahead of print]
Tang JY, Parimi N, Wu A, Boscardin WJ, Shikany JM, Chren MM, Cummings SR, Epstein EH Jr, Bauer DC; Osteoporotic Fractures in Men (MrOS) Study Group. Inverse association between serum 25(OH) vitamin D levels and non-melanoma skin cancer in elderly men. Cancer Causes Control. 2010 Mar;21(3):387-91.
Tang JY, Wu A, Linos E, Parimi N, Lee W, Aszterbaum M, Asgari MM, Bickers DR, Epstein EH Jr. High prevalence of vitamin D deficiency in patients with basal cell nevus syndrome. Arch Dermatol. 2010 Oct;146(10):1105-10.
Young S. Vitamin D, Calcium Combo May Halve Melanoma Risk in Some Women. Stanford University School of Medicine. Tuesday, June 28, 2011. Accessed at http://med.stanford.edu/ism/2011/june/tang.html