Aside from causing sunburn, the sun’s ultraviolet (UV) rays can also cause wrinkles, sags, leathery skin, eye cataracts, and other generally non-fatal ills.
But, more importantly, UV rays are major perpetrators of DNA-distorting, cancer-promoting cell damage. And, ironically, the human immune system’s inflammatory response to UV-induced cell damage often makes matters worse.
According to a new report from the World Health Organization, up to 60,000 people worldwide die every year from skin cancers. Of these, the UN agency estimates that 48,000 succumb to malignancies called melanomas. The remaining 12,000 die from skin carcinomas.
While it appears likely that most of the 20 percent of skin cancer deaths related to carcinoma-type tumors are caused by excessive sun exposure, evidence for the alleged cause-and-effect link between excessive sun exposure and far deadlier melanomas seems increasingly shaky (See "Does excess sun really cause the worst kind of skin cancer?” below).
Sun exposure: The risk-reward equation
The key question concerning sun exposure is whether the likely benefits of moderate amounts outweigh the likely risks.
By "moderate” exposure, we mean the substantial levels that early humans and their immediate evolutionary ancestors probably evolved in response to receiving: amounts of sun exposure that would have been much higher than their modern, urbanized, descendents receive.
Given that humans evolved foraging for food outdoors, it seems reasonable to presume that our early ancestors received at least 90-120 minutes of sun exposure per day, including at least 15-30 minutes of exposure during the four peak sun hours from 10:00 AM to 2:00 PM. In contrast, most dermatologists say it is unsafe to get more than 10 to 20 minutes of sun exposure per day.
There are two key points to remember in the debate over sun exposure:
- Vitamin D, which the human body manufactures in response to sun exposure, is a potent anti-cancer agent.
- The sunscreens available today excel at blocking the short-wavelength "burning” UVB rays that stimulate production of vitamin D in the skin. (We lack highly effective sunscreens for longer-wavelength UVA rays, which penetrate much deeper into skin, and do not stimulate production of vitamin D in skin cells.)
Despite the vitamin D-generating power of sunlight, the answer to our risk-reward question remains uncertain. But recent research results suggest that worldwide, the numbers of deadly cancers likely prevented by the increase in vitamin D levels stimulated by sun exposure are several times greater than the relatively small number of deadly cancers caused by sun exposure.
And the "moderate-sun-is-beneficial” hypothesis also makes sense in the context of human evolution. It seems unlikely that high susceptibility to sun-induced skin cancers would have persisted, under the pressures of natural selection, as a common human characteristic.
One obvious exception would be pale-skinned people, whose lack of UV-blocking melanin pigment puts them at greater risk of premature skin-aging and skin cancers: especially if they work outdoors, sunbathe, or live in tropical latitudes. For them, it seems reasonable to limit sun exposure to levels closer to current medical recommendation (e.g., no more than 30-40 minutes per day, with most of it outside the peak midday hours).
Could omega-3s hold the key to safer sun exposure?
The risk of relatively easy-to-detect and highly treatable carcinoma-type skin cancers can be reduced by available sunscreens, which do a good job of blocking UVB rays, but the chore of constantly applying the stuff and washing it off discourages routine use.
Fortunately, the skin-protective benefits attributed to dietary omega-3s by the eminent authors of a new evidence review suggest that these fish fats could do two things that would make moderate sun exposure, as we've defined it, substantially safer:
- Provide the "foundational” level of protection needed to dampen cancer-promoting inflammation and the premature skin aging it induces.
- Reduce the risk of "shallow” squamous cell carcinomas: the category of skin cancers tied most credibly to greater lifetime sun exposure.
The new evidence review was published in the journal Cancer Detection and Prevention, and its authors summarized the field’s most reliable findings. The results indicate that the long-chain marine omega-3s obtainable from seafood or fish oil supplements offer substantial protection against sun-induced damage to skin cells (Black HS, Rhodes LE 2006).
The review’s positive conclusions carry unusual weight because they come from two prominent researchers in the field: Homer S. Black, Ph.D., who hails from the Baylor College of Medicine in Houston, Texas—one of the world’s leading cancer research centers—and Lesley E. Rhodes M.D., FRCP of England’s University of Manchester Hospital: a well-respected researcher in the field.
Their conclusions stem from a review of the most credible human and animal studies conducted over the past 15 years, whose positive results affirm and extend the encouraging findings of many prior studies in isolated cells.
Taken together, the evidence suggests that dietary omega-3s offer very substantial protection against the cell-damaging, wrinkle-promoting, sag-inducing effects of the sun’s ultraviolet rays: especially when a person’s average intake of omega-6 EFAs is two to three times their omega-3 intake.
If affirmed by future research results, the positive conclusions reached by Drs. Black and Rhodes concerning the meaning of the best current evidence would allow people who get adequate amounts of omega-3s from fish or supplements to breathe a bit easier when they’re out and about... whether wearing sunscreen or not.
New review praises omega-3s, damns omega-6 fatty acids
The lead sentence of the new review summarizes the current facts succinctly: "In toto, there is strong circumstantial evidence from both experimental and clinical studies to support a role for [long-chain] omega-3 FA [fatty acids] in the prevention of non-melanoma skin cancer...”
Drs. Black and Rhodes went on to enumerate the likely preventive benefits of diets rich in omega-3 EFAs from seafood or fish oil supplements:
Animal studies on marine omega-3s
- Dietary omega-3s inhibit the cancerous genetic changes produced by UV sunrays, while slowing the formation of skin tumors and limiting their numbers.
- Dietary omega-3s reduce blood and skin levels of a prostaglandin (messenger chemical) called PGE2, which promotes cancer-fueling inflammation and suppresses the immune response to pre-cancerous cell changes.
- Dietary omega-3s significantly reduce the damaging inflammatory response to UV exposure, when compared to an equivalent dietary level of omega-6 fatty acids.
Human studies on marine omega-3s
- Supplemental omega-3s from fish oil raise the amount of UV exposure required to produce the inflammation (skin redness or "erythema”) that accompanies and exacerbates sunburn.
- Supplemental omega-3s from fish oil significantly reduce the level of pro-inflammatory and immune-suppressive PGE2 produced in response to UV exposure.
The results of an earlier study co-authored by Dr. Rhodes suggest that omega-3s may exert part of their protective power by acting as an "oxidizable buffer”, whose self-sacrifice serves to protect genetic structures from the skin-aging, cancer-promoting effects of free radical damage caused by UV sunrays (Rhodes LE 1994).
The authors of the new evidence review also described the drawbacks of pro-inflammatory omega-6 essential fatty acids (EFAs), which Americans consume, unknowingly, in amounts 20 to 40 times too high in relation to their omega-3 intake.
While the body needs both omega-6 EFAs and omega-3 EFAs, it has evolved to perform optimally when they are consumed in close balance. Americans consume omega-6 fatty acids in great excess because they dominate the standard vegetable oils abundant in most packaged and prepared foods (canola, soy, corn, safflower, sunflower, cottonseed). The exceptions are olive oil, macadamia nut oil, and the "hi-oleic” oils pressed from the seeds of hybrid strains of safflower and sunflower.
In contrast, Drs. Black and Rhodes found that the current evidence shows that diets high in omega-6 EFAs yield negative effects in response to UV sunrays: Animal studies on omega-6 EFAs
- Dietary omega-6 EFAs raise blood and skin levels of prostaglandin PGE2, which promotes cancer-fueling inflammation and suppresses the immune response to pre-cancerous cell changes.
- Dietary omega-6 EFAs do not dampen the damaging inflammatory response to excessive UV exposure significantly, when compared to an equivalent dietary level of omega-3 fatty acids.
Unsurprisingly, much of the UV-damage-undoing power of omega-3s revealed by the research reviewed by Drs. Black and Rhodes appears to stem from these fatty acids’ well-documented anti-inflammatory actions.
The expert doctors' conclusions, while not final, offer credible support for the hypothesis that higher intake of long-chain marine omega-3 fatty acids blunts the negative effects of the sun’s UV rays: especially the short-wave UVB rays believed responsible for most of the 12,000 skin-carcinoma fatalities that occur annually around the world.
Does excess sun really cause the worst kind of skin cancer?
The widely accepted assertion that melanoma risk rises in tandem with sun exposure rests on rather shaky evidentiary ground. In fact, the claim is undermined by a considerable amount of contrary evidence.
For example, the results of a recent substantial case-control study conducted at the Mayo Clinic (Kennedy C, 2003) indicate that greater lifetime sun exposure produced a lower risk of malignant melanoma among the participants, despite the fact that it did not reduce the frequency with which the subjects developed skin marks associated with higher melanoma risk (moles, beauty spots, etc.).
Instead, the Mayo study’s results showed that greater lifetime sun exposure is linked predominantly to an increased risk of squamous cell carcinoma and, to a lesser extent, with two common types of basal cell carcinoma. While carcinomas can kill if left untreated, most are much easier to detect and cure, compared with melanomas.
(Note: The available evidence does not support the oft-cited assertion that children who experience a serious sunburn are at greater risk of getting a more dangerous melanoma cancer in adulthood.)
In the early 1990’s, former NASA scientist William B. Grant, Ph.D. compared maps showing rates of various cancers with NASA’s satellite measurements of UVB radiation (a proxy for sun exposure) over the U.S.
In a discovery that made headlines, Dr. Grant uncovered a statistically significant correlation between lower average sun exposure and higher death rates from a number of common cancers, and he later joined with two leading researchers in the field—Dr. Cedric Garland at UCLA and Dr. Michael Holick at Boston University—to estimate that 50-63,000 Americans die prematurely from cancer annually due to insufficient sun (UVB radiation) exposure, versus about 9,800 who die of melanoma and skin cancer (Grant WB 2002, Grant WB et al 2006).
Dr. Grant also points out that while melanoma rates appear to rise with increasing proximity to the equator—a proxy for increasing degrees of lifetime sun exposure—research studies also show that in northern climes like Canada, Denmark and the Netherlands, greater exposure to UV sunrays yields a reduced risk of melanoma.
For more on the several critical, oft-ignored, but un-refuted discoveries regarding the ability of moderate sun exposure to reduce overall cancer risks, see "The Neglected Nutrient, Part 1: Vitamin D vs. Cancer.”
More recently, the link between greater sun-exposure and greater risk of melanoma was further undermined by the results of a case-control study from researchers at the National Cancer Institute (NCI). Their findings indicate that melanoma rates fall when diets are low in alcohol and rich in vitamin D and the carotenoid-class antioxidants that lend color to salmon (via dietary plankton), carrots, tomatoes, spinach, collards, watermelon, and certain other fruits and vegetables (Millen AE, 2004).
The NCI researchers’ finding that dietary vitamin D appears to protect against melanomas makes good sense, because this essential nutrient appears to constitute a highly effective anti-cancer agent in other contexts (see "Vitamin D May Diminish Breast Cancer Risk” and "Higher Vitamin D Intake Could Cut Cancer Risk in Half.”) And, as we’ll explain, there is good reason to believe that the vitamin D generated in the skin when it is struck by sunlight is equally protective.
Sunlight is the single biggest vitamin D "source” among Americans, with dietary sources a distant second. While, hypothetically, you could get all the vitamin D you need from foods and supplements, the experts’ current consensus recommendation of 1000-2000 IU/day for optimal health would be hard for anyone but a conspicuous consumer of sockeye salmon to get from food alone (see sidebar titled "Could sockeye curb skin cancer?" above).
What’s a confused, conflicted sun-lover to do?
On one side, a large majority of dermatologists still advise against more than 10 to 20 minutes of sun exposure per day, and all exposure in the midday, with their minds seemingly rather closed to a compelling body of contrary evidence.
But as we've seen, a growing body of research suggests that in amounts more generous than dermatologists usually recommend, the sun is a preventive-health plus, with strong anti-cancer and anti-osteoporosis powers among others.
Vitamin D's apparent power to reduce the risks of cancers that are far more common than skin cancers—colon, breast, ovarian, and prostate cancers—and to prevent melanomas in an unknown proportion of people outweighs the fact that sun exposure probably does promote carcinomas: the least dangerous, relatively uncommon, infrequently fatal kinds of skin cancers.
And as we alluded, higher dietary intake levels of vitamin D than health authorities now recommend—1,000 IU per day versus the RDA of 400 IU—appear to reduce people’s risk of osteoporotic fractures. This benefit arises because higher tissue levels of vitamin D—which sun exposure create—aid absorption of calcium into bones.
We could say, "Consult your doctor,” but frankly, we think the evidence is pretty clear. Use common sense and avoid burning, but don’t avoid the sun too much, or you may be doing your health a disservice. And enjoy plenty of omega-3-rich fish to give your skin substantial additional protection.
- Black HS, Rhodes LE. The potential of omega-3 fatty acids in the prevention of non-melanoma skin cancer. Cancer Detect Prev. 2006 Jul 25; [Epub ahead of print]
- Kennedy C, Bajdik CD, Willemze R, De Gruijl FR, Bouwes Bavinck JN; Leiden Skin Cancer Study. The influence of painful sunburns and lifetime sun exposure on the risk of actinic keratoses, seborrheic warts, melanocytic nevi, atypical nevi, and skin cancer. J Invest Dermatol. 2003 Jun;120(6):1087-93.
- Millen AE, Tucker MA, Hartge P, Halpern A, Elder DE, Guerry D 4th, Holly EA, Sagebiel RW, Potischman N. Diet and melanoma in a case-control study. Cancer Epidemiol Biomarkers Prev. 2004 Jun;13(6):1042-51.
- Rhodes LE, O'Farrell S, Jackson MJ, Friedmann PS. Dietary fish-oil supplementation in humans reduces UVB-erythemal sensitivity but increases epidermal lipid peroxidation. J Invest Dermatol. 1994 Aug;103(2):151-4.
- Grant WB. An estimate of premature cancer mortality in the U.S. due to inadequate doses of solar ultraviolet-B radiation. Cancer. 2002 Mar 15;94(6):1867-75.
- Grant WB, Garland CF. The association of solar ultraviolet B (UVB) with reducing risk of cancer: multifactorial ecologic analysis of geographic variation in age-adjusted cancer mortality rates. Anticancer Res. 2006 Jul-Aug;26(4A):2687-99.
- Babcock TA, Novak T, Ong E, Jho DH, Helton WS, Espat NJ. Modulation of lipopolysaccharide-stimulated macrophage tumor necrosis factor-alpha production by omega-3 fatty acid is associated with differential cyclooxygenase-2 protein expression and is independent of interleukin-10. J Surg Res. 2002 Sep;107(1):135-9.
- Fischer MA, Black HS. Modification of membrane composition, eicosanoid metabolism, and immunoresponsiveness by dietary omega-3 and omega-6 fatty acid sources, modulators of ultraviolet-carcinogenesis. Photochem Photobiol. 1991 Sep;54(3):381-7.
- Kim HH, Cho S, Lee S, Kim KH, Cho KH, Eun HC, Chung JH. Photoprotective and anti-skin-aging effects of eicosapentaenoic acid in human skin in vivo. J Lipid Res. 2006 May;47(5):921-30. Epub 2006 Feb 7.
- Shahbakhti H, Watson RE, Azurdia RM, Ferreira CZ, Garmyn M, Rhodes LE. Influence of eicosapentaenoic acid, an omega-3 fatty acid, on ultraviolet-B generation of prostaglandin-E2 and proinflammatory cytokines interleukin-1 beta, tumor necrosis factor-alpha, interleukin-6 and interleukin-8 in human skin in vivo. Photochem Photobiol. 2004 Sep-Oct;80(2):231-5.