Sun Exposure 'Decreases' Risk of Skin Cancer

January 22, 2009 by Evelyn Vincent

Contrary to popular belief, exposing skin to the sun may stop certain cancers from growing, including skin cancer.
While previous studies have implied this protection comes from skin cells (damaged by the sun) committing suicide, cutting the risk of cancer, two studies propose the reduced cancer risk stems from an increased production of vitamin D made by sun-exposed skin. Here are excerpts from Dr. Mercola that I complied for your ease...

The two studies found:

• Sunshine helped beat the deadly skin cancer malignant melanoma: Melanoma patients with increased levels of sun exposure were less likely to die than other melanoma patients; also patients who already had melanoma and a lot of sun exposure were prone to a less aggressive tumor type.

• The sun helped with non-Hodgkin lymphoma: The risks of developing cancer was reduced by 30 percent to 40 percent when exposed to UV rays from the sun and sun lamps; findings were based on interviews with more than 3,000 lymphoma patients and 3,000 healthy members of the public.

In this video, Dr. John Cannell -- one of the leading authorities on vitamin D and founder and Executive Director of the Vitamin D Council -- sheds additional light on what several studies have already confirmed: that appropriate sun exposure actually helps prevent skin cancer. In fact, melanoma occurrence has been found to decrease with greater sun exposure, and can be increased by sunscreens.

One such study discovered that melanoma patients with higher levels of sun exposure were less likely to die than other melanoma patients, and patients who already had melanoma and got a lot of sun exposure were prone to a less aggressive tumor type.

How can this be? Experts are still recommending caution when going out in the sun, and the science still points to the fact that skin cancer is caused by sun exposure. 

As Dr. Cannell explains, the sun does increase genetic damage in your skin and can cause skin cancer, but nature has designed a clever system to obviate this risk. And by staying out of the sun entirely, you avoid the system nature created to help prevent skin cancer.
  
As you probably know by now, vitamin D is formed in your skin from exposure to sunlight. The vitamin D then goes directly to the genes in your skin where it helps prevent the types of abnormalities that ultraviolet light causes. Hence, when you avoid the sun entirely, or slather on sun block whenever you go out, your skin is not making any vitamin D, and you’re left without this built-in cancer protection.

But you’re not only raising your risk of skin cancer by shunning the sun.

Optimizing your vitamin D levels can help you to prevent as many as 16 different types of cancer including pancreatic, lung, breast, ovarian, prostate, and colon cancers. And vitamin D does not have just a slight impact on your cancer risk. It can cut your risk by as much as 60 percent!

Its protective effect against cancer works in several ways, including:

• Increasing the self-destruction of mutated cells (which, if allowed to replicate, could lead to cancer)
• Reducing the spread and reproduction of cancer cells
• Causing cells to become differentiated (cancer cells often lack differentiation)
• Reducing the growth of new blood vessels from pre-existing ones, which is a step in the transition of dormant tumors turning cancerous 

To Prevent Skin Damage You Have to Protect Against the Most Damaging Rays

Ultraviolet light from the sun comes in two main wavelengths – UVA and UVB.  The difference between them is part of the equation, so it’s important for you to understand the difference between the two.

UVB can be considered the ‘good guy’ that helps your skin produce vitamin D.

UVA is considered the ‘bad guy’ because it penetrates your skin more deeply and causes more damage.  Not only that, but UVA rays are quite constant during ALL hours of daylight, throughout the entire year -- unlike UVB, which are low in morning and evening, and high at midday.

If you’ve ever gotten sunburned on a cloudy day, you now understand why; it’s from the deeply penetrating UVA!
The exposure you’re looking for is the exposure to UVB’s, which are at their greatest during midday, when the sun is at its highest in the sky. This is what Dr. Cannell refers to in this interview when he says you need to expose your skin to the high-noon sun -- which is contrary to conventional advice, which says to avoid tanning during “peak” hours.

You also need to be aware that you need far less sun exposure than you might think to reap its beneficial effects.
Most people with fair skin will max out their vitamin D production in just 10-20 minutes, or when your skin starts turning the lightest shade of pink. Some will need less, others more. The darker your skin, the longer exposure you will need to optimize your vitamin D production.

The first large-scale, randomized, placebo-controlled study on vitamin D and cancer has shown that vitamin D can cut cancer risks by as much as 60 percent.

In response, the Canadian Cancer Society is now recommending vitamin D for all adults, the first time a major public-health organization has endorsed the vitamin as a cancer-prevention therapy.

The study looked at almost 1,200 women, aged 55 and older, over the course of four years. Those in a group that was given supplemental calcium and vitamin D had a 60 percent lower risk for all cancers than those who received a placebo.

American Journal of Clinical Nutrition, 85(6):1586-91 June 2007

GlobeAndMail.com June 8,2007

Reduce Cancer Risk with Sunlight Exposure
By William B. Grant, Ph.D.

With all of the publicity that UV radiation (UVR) is an important cause of skin cancer, premature skin aging and cataract formation, one might think that avoidance of UVR would be the best policy. Not so fast. If protection against UVR were the most important thing, all humans would have very dark skin, since the melanin in dark skin protects against skin cancer and premature skin aging.

Skin pigmentation becomes paler the closer one’s ancestors lived to the polar-regions, evidently to balance cutaneous production of vitamin D with protection against free radicals and DNA damage from UVR [Jablonski and Chaplin, 2000]. In addition, even a cursory look at the geographic variation in cancer mortality rates in the United States [Devesa et al., 1999] indicates that some environmental factor has to explain why mortality rates for a number of internal cancers are approximately twice as high in northeastern, highly-urbanized states than in southwestern, more rural states.

Diet and smoking are, of course, important risk factors for many types of cancer [Doll and Peto, 1981]. But in order for diet to explain the geographic variation in cancer rates, Americans would need to be eating drastically different diets by region. However, anyone who has travelled throughout the United States knows that the food choices do not vary much anywhere in the contiguous 48 states.

The Risk of Cancer Lessens With More Sun Exposure

The key to understanding this geographic pattern was provided by Cedric and Frank Garland in 1980 [Garland and Garland, 1980]. They reasoned that sunlight, through the production of vitamin D, reduced the risk of colon cancer in the sunny areas compared to that in the darker areas. They performed an ecologic study of annual solar irradiance versus colon cancer mortality rates and found a strong inverse correlation, i.e. the more sunlight, the less cancer. (An ecologic study treats entire populations defined geographically as entities, with values for disease outcome and environmental or dietary factors averaged for each entity.)

Their paper received little notice at first, perhaps because UVR was commonly associated with skin cancer, perhaps because the ecologic approach was falling out of favor [Doll and Peto, 1981]. Undaunted, they extended their work through the use of stored serum 25-hydroxyvitamin D (25(OH)D)--the common form of circulating vitamin D--values for another purpose along with a determination of colorectal cancer incidence among the serum donors, finding a significant inverse correlation between 25(OH)D and colorectal cancer rates [Garland et al., 1985]. The list of cancers for which ultraviolet B (UVB) (290-315 nm) and vitamin D is protective was extended through a variety of observational epidemiologic studies by the end of the 1990s to include breast, ovarian and prostate cancer and non-Hodgkin’s lymphoma [Grant, 2002b].

How Vitamin D Reduces the Risk of Cancer

The mechanisms by which vitamin D reduces the risk of cancer are fairly well understood. They include enhancing calcium absorption (in the case of colorectal cancer) [Lamprecht and Lipkin, 2003], inducing cell differentiation, increasing cancer cell apoptosis or death, reducing metastasis and proliferation, and reducing angiogenesis [van den Bemd and Chang, 2002]. In addition, 25(OH)D downregulates parathyroid hormone (PTH) [Chapuy et al., 1987]. Since IGF-I stimulates tumor growth and high quantities are a consequence of the standard American diet [Grant, 2002a; 2004], vitamin D can be considered one partial antidote to the American diet.

When I decided to investigate the role of UVB and vitamin D in reducing the risk of cancer, after I convinced myself that dietary factors could not explain the geographic variation of cancer mortality rates in the United States, I posed two questions to address:

• For how many cancers is UVB/vitamin D protective?
• How many Americans die prematurely each year due to inadequate levels of vitamin D?

I started with the maps of cancer mortality rates in the Atlas of Cancer Mortality [Devesa et al., 1999] and found the UVB irradiance/dose map for the United States for July 1992 made using data obtained by NASA’s Total Ozone Mapping Spectrometer (TOMS) to use as a proxy for vitamin D production. In this study, I determined that UVB was inversely correlated with mortality rates for 12 types of cancer, including five types of cancer already identified plus an additional seven, and estimated that 17, 000 to 23,000 Americans died prematurely each year due to insufficient vitamin D [Grant, 2002b].

While the study was generally accepted, critics pointed out that I had ignored a number of factors that affect the risk of cancer and which could, perhaps, explain much of the variation in mortality rates. To respond to these critics, I extended the analysis by including a number of cancer risk factors for which I could find state-averaged values.

These factors included lung cancer mortality rates (an index for the adverse health effects of smoking), fraction of the population considered of Hispanic heritage (Hispanics are counted as white Americans in the Atlas), alcohol consumption rates, degree of urbanization, and fraction of the population living below the poverty level.

Sun Exposure (UVB) Protects Against 16 Types of Cancer

The new study links UVB as protective to a total of 16 types of cancer, primarily epithelial (pertaining to the surface) cancers of the digestive and reproductive systems [Grant, submitted]. Six types of cancer (breast, colon, endometrial, esophageal, ovarian, and non-Hodgkin’s lymphoma) were inversely correlated to solar UVB radiation and rural residence in combination. This result strongly suggests that living in an urban environment is associated with reduced UVB exposure compared to living in a rural environment.

Another 10 types of cancer including bladder, gallbladder, gastric, pancreatic, prostate, rectal and renal were inversely correlated with UVB but not urban residence. Ten types of cancer were significantly correlated with smoking, six types with alcohol, and seven types with Hispanic heritage. Poverty status was inversely correlated with seven types of cancer. Since the results for alcohol, Hispanic heritage, and smoking for white Americans agree well with the literature [Trapido et al., 1995; Thun et al., 2002], they provide a high level of confidence in the approach and its results for UVB radiation.