Studies point to omega-6 / omega-3 imbalance as a greater factor in skin cancer deaths; excessive sun avoidance may raise overall cancer risk
by Craig Weatherby
We've reported on the increasing body of evidence indicating that overall, cancer risks are curbed by more sun exposure, not less.
There is no longer significant doubt that moderate sun exposure—short of suffering frequent, substantial sunburns— actually reduces cancer risk overall.
In fact, the reverse seems to be the case, as we report in elsewhere in this issue. New research affirms prior indications that many Americans—especially darker skinned people—lack sufficient vitamin D-generating (hence cancer-curbing) sun exposure.
The hypothesis that moderate sun exposure curbs cancer risks rests on abundant evidence that vitamin D probably ranks among the most powerful anti-cancer factors in the human body. (For more on that, see "Vitamin D versus cancer," below.)
Ads paid by sunscreen maker distort reality
Sadly, a summer-season ad campaign from the American Cancer Society defies the growing consensus concerning the causes of fatal skin cancers.
Sunscreen is certainly useful for preventing sunburn, which may be responsible for a small percentage of the relatively small number of fatal skin cancers that occur annually in the US.
Only fair-skinned people seem to run a substantial risk of developing skin cancer in response to the kind of daylong sun exposure hunting, gathering, and farming humans experienced throughout millennia of evolution, until very recently.
But it is not clear that sun exposure is a huge risk even for them, and there's much less that sun is a major risk factor among non-fair folks.
The latest outrage against reason comes in the form of an advertising campaign from the American Cancer Society (ACS) that's sponsored… silently… by Neutrogena: a major sunscreen maker.
This regrettable venture—whose anti-sun, pro-sunscreen message is intended, ostensibly, to reduce the risk of fatal skin cancers—could actually increase its largely female targets' overall cancer risk.
Fortunately, medical reporters at many major media outlets interviewed leading skin cancer researchers, who disputed the misleading message being foisted on millions of women by the Cancer Society's ads.
Cancer researchers excoriate anti-sun cancer ad
Under a headline that reads ““My sister accidentally killed herself. She died of skin cancer”, the American Cancer Society's new public service ad shows a young woman holding up a photograph of a smiling blonde.
Appearing this summer in more than a dozen women's magazines, the ad says that “left unchecked, skin cancer can be fatal,” and urges its female targets to “use sunscreen, cover up and watch for skin changes.”
But as The New York Times said about the ad, “The woman in the picture is a model, not a skin cancer victim. And the advertisement's implicit message—that those who die of skin cancer have themselves to blame—has provoked a sharp response from some public-health doctors, who say the evidence simply does not support it.”
The two key points made by experts interviewed by The New York Times, ABC News, and others were these:
- While most cases of skin cancer (carcinomas) may be caused by sun overexposure, almost all of these cancers are innocuous and not life-threatening.
- Even obsessive use of sunscreen may not prevent the most dangerous kind of skin cancers, called melanomas.
In truth, by reducing blood levels of vitamin D, constant use of sunscreen outdoors could raise the risk of many common, dangerous malignancies, including ovarian, breast, kidney, and colon cancers.
These are the basic facts, gleaned from the American Cancer Society, the National Cancer Institute (NCI), the National Institutes of Health (NIH), the World Health Organization (WHO), and leading academic researchers:
- Skin cancer is responsible for less than two percent of all cancer deaths, accounting for about 11,000 of the 565,000 American cancer deaths recorded in 2006.
- Nearly all skin cancer deaths stem from relatively rare malignant melanomas, which constitute only six percent of all skin-cancer cases.
- Sunscreen does not appear to prevent melanomas—the rarest but most lethal skin cancers by far—in which genetic and nutritional factors appear to play greater roles than sun exposure. Evidence for a cause-and-effect link between excessive sun exposure and deadly melanomas is weak.
- Only one in five melanomas is estimated to be related to sun exposure. This estimate comes from Howard L. Kaufman, M.D., co-director of the Melanoma Center at Columbia University. In contrast, the WHO estimates that between 50 and 90 percent of cases stem from sun exposure. However, clinical and lab studies don't support the epidemiological data behind the WHO's estimate.
We should stress that most deaths caused by generally non-fatal carcinoma-type tumors (only 20 percent of all skin cancer fatalities) appear linked to excessive sun exposure.
This is why research indicates that sunscreen can reduce the risk of this least-dangerous category of skin cancers.
But one must weigh the best sunscreens' ability to reduce the already minuscule risk of death from skin carcinomas against three countervailing factors:
- The potential for increasing one's risk of non-skin cancers, due to reduced vitamin D production.
- The unknown risks of the insufficiently safety-tested additives in sunscreens.
- The substantial expense and hassle of doing what most dermatologists advise, which is to apply hefty amounts of sunscreen whenever one spends more than 20 minutes in the sun.
Dermatologists' advice regarding sunscreen use and sun avoidance makes the most sense for fair-skinned folks, who lack UV-blocking pigment (melanin) in their skin, who can make extra efforts to get ample dietary vitamin D.
(Note: the most useful form of vitamin D is the D3 form found in animal foods like fish, not the D2 form found in most vitamin D and multivitamin supplements.)
Even though an expert quoted by The New York Times noted that skin screenings are not proven to reduce skin cancer death rates, it seems wise to take reasonable early detection measures:
- Get regular physical checkups that include skin exams.
- See a dermatologist about mysterious skin lesions or changes in moles and blemishes.
Vitamin D versus cancer
To appreciate the excitement over vitamin D's powerful anti-cancer potential—and concern over Americans' general lack of the “sunshine and seafood” vitamin—read some of our prior stories on this subject, which explain why the Cancer Society's summer-season ad campaign could prove counterproductive:
- Vitamin D vs. Cancer
- Vitamin D and Cancer: A Sunny Follow-Up Story
- Vitamin D May Lower Risk of Ovarian, Breast, Kidney, and Colon Cancers
- Vitamin D's Anti-Cancer Potential Affirmed
Unfortunately, given Americans' increasingly indoor-oriented, sun-deprived lives, most don't consume enough vitamin D from foods or supplements. This is why most vitamin D researchers want to raise the US recommended daily allowance (RDA) from 400 IU to 1,000 or 2,000 IU, and urge people to eat fatty fish (the best food source) and take higher supplemental doses (See "Review Supports Much Higher Vitamin D Intake").
Wild Salmon top all whole food sources of vitamin D by far. And wild Sockeye Salmon are the richest source of all, providing more vitamin D in one 3.5 oz serving (687 IU) than you'd get from six glasses (588 IU) of milk: the fortified food that constitutes most people's main dietary source (See “Wild Salmon Affirmed as Top Vitamin D Source”).
Omega-6 / omega-3 intake imbalance seen as key risk factor
Last summer, we examined some compelling evidence concerning the role of America's all-too-common omega-6/omega-3 fatty acid intake imbalance in creating increased risk of skin cancers (see “Fish Fats Called Credible Foes of Skin Aging and Skin Cancer”).
We've just come across two more studies that support this idea.
Back in 2000, researchers at the American Health Foundation (AHF) in Valhalla, New York reported the results of a study using human skin cancer cells.
The AHF scientists introduced their findings by noting the growing consensus that prompted their revealing test tube research: “Epidemiological, experimental, and mechanistic data implicate omega-6 polyunsaturated fatty acids (PUFAs) as stimulators and long-chain omega-3 PUFAs as inhibitors of… a range of human cancers, including melanoma” (Albino AP et al 200).
They set out to test this hypothesis by exposing human melanoma cancer cells to omega-3 DHA from fish oil. While DHA had little braking effect on growth of some melanoma cell types, it curbed the growth of more types of melanoma.
As the AHF wrote, “After treatment with increasing concentrations of DHA, cell growth in a majority of melanoma cell lines (7 of 12) was inhibited, whereas in 5 of 12 cell lines, cell growth was minimally affected" (Albino AP et al 200).
One year later, researchers at the Hormel Institute—funded by the folks who make cocktail franks, among other meat products—reported similar results from a mouse study.
Their introductory overview echoed the AHF team's assessment of the evidence as it stood then: “Omega-3 fatty acids, including DHA and EPA, can effectively reduce the risk of skin cancer whereas omega-6 fatty acids such as arachidonic acid (AA) reportedly promote risk” (Liu G et al 2001).
The Hormel results affirmed the AHF group's findings. And they discovered that while one omega-3 in particular—DHA— had the greatest skin-cancer-inhibiting effect, omega-6 fatty acids blunt the ability of DHA to discourage growth of melanoma cells.
As they wrote, “The results of this study demonstrate that the inhibitory effects of omega-3 fatty acids on tumorigenesis [tumor development] are more significant for DHA than for EPA... Similarly, because [omega-6] AA abrogates the beneficial effects of DHA, the dietary ratio of omega-6 to omega-3 fatty acids may be a significant factor in mediating tumor development” (Liu G et al 2001).
Why should America's chronic fatty acid intake imbalance matter in terms of cancer risk?
The two kinds of long-chain fatty acids in human diets and cell membranes—omega-3 and omega-6—influence cellular switches called transcription factors, in ways that either promote or discourage inflammation and cancer growth.
As it happens, dietary omega-6 fatty acids exert cellular influences that tend to promote inflammation and cancer growth while omega-3s tend to discourage both.
This is why nutrition-savvy doctors like Andrew Weil, Nicholas Perricone, and many others now stress the importance reducing intake of omega-6 fatty acids.
Omega-6 fatty acids predominate in America's most common vegetable oils (corn, soy, canola, safflower, sunflower, cottonseed)—hence in most packaged and prepared foods—and in standard, grain fed meats and poultry.
Long-chain omega-3s—the most beneficial kind—are abundant only in fish and fish oils, while the valuable but less beneficial short-chain kind is abundant only in leafy green vegetables and flaxseed or flaxseed oil.
- Aschwanden C. Doctors Balk at Cancer Ad, Citing Lack of Evidence. The New York Times, July 10 2007. Accessed online July 20, 2007 at http://www.nytimes.com/2007/07/10/health/10skin.html.
- Menghrahani K. Scared Sun Safe: Melanoma Ad Under Fire. ABC News Internet Ventures, July 12, 2007. Accessed online July 20, 2007 at http://abcnews.go.com/Health/CancerPreventionAndTreatment/story?id=3364010&page=1
- Meyskens FL Jr, Farmer PJ, Yang S, Anton-Culver H. New perspectives on melanoma pathogenesis and chemoprevention. Recent Results Cancer Res. 2007;174:191-5. Review.
- Schwartz GG, Skinner HG. Vitamin D status and cancer: new insights. Curr Opin Clin Nutr Metab Care. 2007 Jan;10(1):6-11. Review.
- Albino AP, Juan G, Traganos F, Reinhart L, Connolly J, Rose DP, Darzynkiewicz Z. Cell cycle arrest and apoptosis of melanoma cells by docosahexaenoic acid: association with decreased pRb phosphorylation. Cancer Res. 2000 Aug 1;60(15):4139-45.
- Garbe C, Eigentler TK. Diagnosis and treatment of cutaneous melanoma: state of the art 2006. Melanoma Res. 2007 Apr;17(2):117-27. Review.
- Liu G, Bibus DM, Bode AM, Ma WY, Holman RT, Dong Z. Omega 3 but not omega 6 fatty acids inhibit AP-1 activity and cell transformation in JB6 cells. Proc Natl Acad Sci U S A. 2001 Jun 19;98(13):7510-5.
- Daily News Central. Major Health Milestone: Number of US Cancer Deaths Drops. February 6, 2006. Accessed online July 20, 2007 at http://health.dailynewscentral.com/content/view/0002106/49/.
- WHO. Global disease burden from solar ultraviolet radiation. Accessed online July 20, 2007 at http://www.who.int/mediacentre/factsheets/fs305/en/index.html.