A report came out recently showing that melanoma incidence has increased dramatically in the US since 1973, particularly among women. The authors suggested the rise could be due to increasing sun exposure, which I am highly skeptical of. The data he cites to support that idea are quite weak. I think the prevalence of vitamin D deficiency in this country suggests otherwise.
Melanoma is the most deadly form of skin cancer, and the only type that is commonly life-threatening. Its link to sun exposure is tenuous at best. For example, it often occurs on the least sun-exposed parts of the body, and its incidence is lower in outdoor workers.
What is the solution to rising melanoma incidence? Sunblock! Slather it on, ladies and gentlemen! No matter that we evolved outdoors! No matter that it may do nothing for melanoma incidence or mortality! No matter that you'll be vitamin D deficient! No matter that it contains known carcinogens! 30+ SPF, the more the better. Don't let one single deadly UV photon through.
The irony of all this is that if you believe the data on vitamin D, avoiding the sun would cause many more cancers than it would prevent, even if all melanoma were due to sun exposure.
Monday, July 14, 2008
Subscribe to:
Post Comments (Atom)
Posts
14 comments:
Sigh. As a pale redhead I'm so torn about this. I get as much sun as I can without sunblock, and I've generally bought the least toxic ones I can. But whether sunburn causes skin cancer or not, sunburn hurts. When the warm water in the shower hurts, when clothes hurt when they touch your body, sunburn is just not fun.
I'd like to find something more natural that reduces burning, but in the meantime I'll still spend some good, vitamin D soaking, sunblock-free time outdoors as much as I can, and I'll groan and wear sunblock when I'm in the hot sun for longer stretches.
Debs
Food Is Love
I just had a look at the Armstrong & Kricker review article that was cited as evidence for sun exposure and skin cancers. To me it seems to lay out a good case that melanoma is related to sun burn, but not really sun exposure (which does seem to be more the case for carcinoma).
There were several points of positive correlative data supporting this... the associations between melanoma and skin color, ability to tan vs burn/freckle, and age of immigration to Australia. The most common body parts to develop melanoma in the data set they used seemed to show an overall sun-exposure trend, although less striking than carcinoma. Still, the most common occurrences of melanoma were on the face, shoulders, neck, and back. Occurrence on buttocks was nearly non-existent. (Maybe it really does occur there but people are too embarassed to get it diagnosed? ;)
As far as the negative data, there are some possible explanations. When they looked within the same geographical population, melanoma was ~20x more prevalant among white people than black people, and ~10x more prevalent than in Hispanics! This alone could throw off surveys looking at different geographical populations, trying to correlate sun exposure w/ melanoma incidence. The non-association shown in fig 1 used Seattle (67% white) & Minneapolis (65% white) as low-sun cities. The most high sun areas used were Atlanta (59% black), New Orleans (67% black), and New Mexico (42% Hispanic, at least in year 2000). Given the major differences in risk of melanoma by race, and the geographical areas they used, I'm not surprised that this particular study failed to find an association with sunlight!
As far as the work exposure data, I have two ideas (which I'll admit are less compelling than the race effect.) People with fair skin would likely avoid outdoor jobs. And for those who can tan, then being outdoors for a consistent duration and frequency would make you pretty tan and resistant to burns. This was certainly my experience working one summer as a grounds crew member on a golf course. The problem with this idea, though, is that you only tan on exposed body parts but remain burn prone everywhere else. For me that summer I wore a t-shirt at work, so I had very dark arms but a normal torso.
Anyway, if melanoma really is related to sunburn then you could get the best of both worlds (vitamin D / no melanoma) by doing like Debs suggests and getting the right amount of sun.
We did evolve outdoors, but we evolved getting a fairly consistent amount of sun exposure daily. I suspect sunburns are rare or non-existent in native populations. They don't spend three weeks indoors in an office then one week on the beach in Hawaii.
Debs,
Of course you know I don't recommend burning.
Ross,
Well even if there is an association, it doesn't seem to be a very robust one, given that melanoma is often diagnosed on the soles of the feet. Also, the fact that melanoma accounts for ~5% of cancers in the US suggests that we're doing more harm than good by avoiding the sun. I think the baby has been thrown out with the bath water by these dermatologists who recommend putting on sunblock whenever you step outside. I don't recommend burning to a crisp, but I definitely think regular sun exposure is healthy.
Lisa,
Your point is well taken. I'm sure HGs did burn from time to time though. Some groups wore clothing in the winter, after all.
I didn't think you were suggesting burning, of course. I just meant that I get torn between my desire for vitamin D, my preference for avoiding unnatural, toxic compounds, and my desire to avoid the burn that comes all too quick. I wish sunblock were less problematic, and that we weren't told to believe we always need it.
About Lisa's comment, I've heard that our skin pigmentation has evolved/adapted pretty rapidly, relatively speaking. It makes sense, considering we wouldn't last very long without vitamin D, and people who migrated north had to get lighter to adapt. People from equatorial climates tend to be darker and less prone to burning. If I spent every day outside in Hawaii, I'd get some extent of a protective tan, but I'd still burn.
Debs
Food Is Love
By the way, sunblock only reliably filters out UVB. That means you may actually be increasing your exposure to UVA by wearing it. There seems to be an association between wearing sunscreen and melanoma incidence (at least at some latitudes). This is after controlling for skin type and sun exposure:
http://www3.interscience.wiley.com/journal/112717902/abstract?CRETRY=1&SRETRY=0
http://www.ncbi.nlm.nih.gov/pubmed/18022535?ordinalpos=2&itool=EntrezSystem2.PEntrez.Pubmed.Pubmed_ResultsPanel.Pubmed_RVDocSum
Dr. Briffa has some pretty good commentary on this issue that is worth checking out: http://www.drbriffa.com/blog/2008/06/16/bmj-editorial-casts-doubt-on-the-notion-that-sunlight-causes-malignant-melanoma/
Rob
Thanks Rob; that's actually one of the things that got me thinking.
That piece about sunscreen and UVA/UVB is disturbing.
I guess I'll just keep getting some sun, eating a lot of butter, and hoping for the best.
Debs
Food Is Love
Stephan,
I was wondering if you had seen this article? Though I haven't read the actual study, the headline could be misleading because in the article it sounds like they lumped the meat and fat diet with processed and sugary foods.
Hey Reid,
I took a quick look. It's hard to draw any conclusions from the study (although the authors don't seem to think so!). The pattern high in meat and fat also eats more sugar, white bread and vegetable oil (as you pointed out). That's the problem with this kind of study, you can't draw any solid conclusions because there are so many variables. They also didn't address melanoma. Maybe the results weren't what they were hoping for?
debs, keep in mind that cloud cover and shade do not eliminate UV exposure but only (roughly) cut it in half. There are opportunities here for vitamin D without the burn.
Debs,
Have you considered sun protective clothing? Perhaps not the whole enchilada from the Sun Precautions Solumbra SPF fabric catalog as I see some elderly people wear in the resort-ish San Diego areas (super skinny seniors covered head to toe in SPF clothing, gloves, hats, and bathing suits, with enormous black wraparound sunglasses, not to mention parasols.
I use clothing instead of sunscreen a lot more frequently now when I know my exposure will go beyond my capacity (though I still sunscreen my nose fairly frequently). 3/4 length sleeves instead of cap sleeves or sleeveless, higher necklines (my upper check and neck seem to be reddish colored by capillaries year-round now so I really protect this area - should have done so sooner), cropped/capri pants instead of shorts, hats of course. This year I even bought the high-necked skirtini bathing suit from Lands' End, after years of wearing V-necked styles. I have a few specialty clothing items (mostly blouses) that are very lightweight and comfortable in warm weather, layer will without bulk and are especially useful for travel, as they pack easily, wash in a sink and dry fast, and have concealed or securely closed pockets as well (very usual on our recent trip to Italy). I stuffed a white blouse in Italy in my day pack to layer over t-shirts during the strong midday sun to protect my arms and neck back - it has zip open ventilated panels and I think it helped me stay cooler, too.
I don't cover up all the time, but I am very mindful of my limits with full sun and clothing has a lot of advantages over sunscreens. REI Outlet and Sierra Trading Post often have great bargains.
Of course, I'm quite a bit older than you and you might not like the styles of the SPF clothing. But I think protective coverage can be achieved with younger styled clothing without looking like a matron - like me :-).
Here's a paper I came acorss; great work you're doing, Geoff
1: Arch Environ Health. 1990 Sep-Oct;45(5):261-7.Links
Occupational sunlight exposure and melanoma in the U.S. Navy.Garland FC, White MR, Garland CF, Shaw E, Gorham ED.
Occupational Medicine Department, School of Medicine, University of California, San Diego.
Melanoma is the second most common cancer, after testicular cancer, in males in the U.S. Navy. A wide range of occupations with varying exposures to sunlight and other possible etiologic agents are present in the Navy. Person-years at risk and cases of malignant melanoma were ascertained using computerized service history and inpatient hospitalization files maintained at the Naval Health Research Center. A total of 176 confirmed cases of melanoma were identified in active-duty white male enlisted Navy personnel during 1974-1984. Risk of melanoma was determined for individual occupations and for occupations grouped by review of job descriptions into three categories of sunlight exposure: (1) indoor, (2) outdoor, or (3) indoor and outdoor. Compared with the U.S. civilian population, personnel in indoor occupations had a higher age-adjusted incidence rate of melanoma, i.e., 10.6 per 100,000 (p = .06). Persons who worked in occupations that required spending time both indoors and outdoors had the lowest rate, i.e., 7.0 per 100,000 (p = .06). Incidence rates of melanoma were higher on the trunk than on the more commonly sunlight-exposed head and arms. Two single occupations were found to have elevated rates of melanoma: (1) aircrew survival equipmentman, SIR = 6.8 (p less than .05); and (2) engineman, SIR = 2.8 (p less than .05). However, there were no cases of melanoma or no excess risk in occupations with similar job descriptions. Findings on the anatomical site of melanoma from this study suggest a protective role for brief, regular exposure to sunlight and fit with recent laboratory studies that have shown vitamin D to suppress growth of malignant melanoma cells in tissue culture. A mechanism is proposed in which vitamin D inhibits previously initiated melanomas from becoming clinically apparent.
PMID: 2256710 [PubMed - indexed for MEDLINE]
Post a Comment