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Sunlight and Cancer - Not What You Think

From Dr. Mercola's Website (

"For more than 50 years, there has been documentation in the medical literature suggesting that regular sun exposure is associated with substantial decreases in death rates from certain cancers and a decrease in overall cancer death rates. Recent research suggests that this is a causal relationship that acts through the body's vitamin D metabolic pathways. The studies reviewed here show that:

(a) sunlight activation is our most effective source of vitamin D;

(b) regular sunlight/vitamin D "intake" inhibits growth of breast and colon cancer cells and is associated with substantial decreases in death rates from these cancers;

(c) metabolites of vitamin D have induced leukemia and lymphoma cells to differentiate, prolonged survival of leukemic mice, and produced complete and partial clinical responses in lymphoma patients having high vitamin D metabolite receptor levels in tumor tissue;

(d) sunlight has a paradoxical relationship with melanoma, in that severe sunburning initiates melanoma whereas long-term regular sun exposure inhibits melanoma;

(e) frequent regular sun exposure acts to cause cancers that have a 0.3% death rate with 2,000 U.S. fatalities per year and acts to prevent cancers that have death rates from 20-65% with 138,000 U.S. fatalities per year;

(f) there is support in the medical literature to suggest that the 17% increase in breast cancer incidence during the 1991-1992 year may be the result of the past decade of pervasive anti-sun advisories from respected authorities, coinciding with effective sunscreen availability; and

(g) trends in the epidemiological literature suggest that approximately 30,000 U.S. cancer deaths yearly would be averted by the widespread public adoption of regular, moderate sunning. Advising the public to seek regular moderate sun exposure finds good support in the scientific literature as a means of lowering cancer mortality."

"In 1941, Apperly reported that overall cancer death rates increased with distance from the equator, and were further decreased in areas where a large percentage of the population was engaged in the sun-intensive occupation of farming...After reviewing his data, the author concluded: "A closer study of the action of solar radiation on the body might well reveal the nature of cancer immunity."

"Studies published during the past 20 years demonstrate that the link between sun exposure and cancer prevention acts through the vitamin D metabolic pathways."

"Vitamin D and Sunlight - In addition to its low cost and "high patient acceptance", sunlight activation of 7-dehydrocholesterol in the skin has significant advantages as a vitamin D source compared with diet and supplementation..."

"Breast Cancer - Support for the biochemical relationship between sun exposure and cancer inhibition came in 1979, when Eisman et al. of the University of Melborne reported that a human breast cancer cell line had receptor sites for 1,25-dihydroxyvitmain D3 (1,25-(OH)2-D3), the most active metabolite of vitamin D. ... in 1990, the Garland-Gorham team found that women from the areas of the United States with less available sunlight died 40-60% more frequently of breast cancer than women who lived in places like Honolulu and Tampa..."

"Colon Cancer - In 1980 Frank and Cedric Garland presented the first modern epidemiological research suggesting a direct protective effect of sunlight vitamin D on cancer, showing that colon cancer was decreased in areas of the United States with greater sun exposure. In 1985, further research by the Garlands showed decreased colon cancer rates with higher oral vitamin D and calcium intake in a prospective study..."

"Melanoma and Squamous-Basal Cancers of the Skin - The recent increases in melanoma and squamous-basal skin cancers have been used to justify advising everybody to either stay out of the sun or wear sunblock. However, as shown below, there is reason to believe that these recommendations are flawed. Koh et al. described squamous and basal cell skin cancers as most prevelant on the head-neck and forearms-hands where cumulative sun exposure is greatest, while melanoma is most prevalent on generally covered parts of the body. Boring et al. estimated 600,000 cases and 2,000 deaths (0.3% death rate) in 1991 from squamous-basal skin cancer. Melanoma, however, has a 20% fatality rate because of its typically early metastasis, producing 6,500 U.S. deaths in 1991 from 32,000 cases."

"The literature review and four studies that follow suggest a paradoxical relationship in which melanoma is initiated by severe sunburning, but inhibited by nonburning sun exposure. Koh et al., in their 1990 article on sunlight and melanoma, reviewed a substantial body of research indicating a causative relationship between "blister and peel" sunburning before the age of 20 and melanoma onset later. However, a 1981 study by Colston et al. reported that melanoma cells have receptors for 1,25-(OH)2-D3 and that this vitamin D metabolite slows the doubling time of melanoma cells in vitro. Also, in 1987, Eisman et al. demonstrated growth suppression of melanoma cells in a laboratory environment using 1,25-(OH)2-D3. Consitent with the findings of Colston and Eisman, Vagero et al. have shown that people who work outdoors get more total sun exposure but have a lower incidence of melanoma than office workers. Additionally, Crombie observed that melanoma seldom occurs on area of the skin that get regular sun exposure, also suggesting the preventative effect of consistent sunning."

"Sun-Promoted vs Sun-Inhibited Cancers - For more than 10 years, U.S. health authorities have pervasively and effectively advised against all sun exposure, including regular moderate exposure. Since melanoma has been shown to be inhibited by vitamin D and regular sun exposure, these advisories against regular moderate exposure can only be correctly based on solar promotion of squamous-basal skin cancers, which have a death rate of 0.3% and cause only 2,000 U.S. deaths yearly. In contrast, about 138,000 people in the United States die each year of cancer with death rates of 20-65% which have been shown to be inhibited by vitamin D, its metabolites, and regular sun exposure. The epidemiological studies show trends suggesting that widespread public adoption of routine sunbathing would result in approximately a one-third lowering of breast and colon cancer death rates, or about 32,000 fewer U.S. cancer deaths yearly. An increase in squamous-basal skin cancer would be expected, but even a 100% increase, with 2,000 additional deaths per year, would still leave a net 30,000 fewer U.S. cancer deaths. A decrease in deaths from leukemia, lymphoma, and melanoma would also be expected, but lack the epidemiological studies makes this prediction more difficult to quantify."

"Sunscreen Use and Cancer Rates - American Cancer Society statistics show that estimated breast cancer incidence recently increased 17% in 1 year, from 150,000 new cases in 1990 to 175,000 in 1991. In a search for the cause of this dramatic increase, the following must be considered: (a) previously cited research showing that decreased sun exposure causes increased breast cancer; (b) research showing that the past decade of anti-sun advisories has resulted in decreased sun exposure with increased sunscreen use; (c) research linking chronic sunscreen use to decreased blood levels of 25-OH-D3, the necessary precursor to 1,25-(OH)2-D3; (d) research showing that decreased tissue levels of 1,25-(OH)2-D3 is associated with increased growth rates of breast cancer. From these research findings, it appears reasonable to speculate that the cause of this increase in breast cancer is that for more than a decade our population has been encouraged as never before to avoid sun exposure; meanwhile, because of the concurrent emergence of very effective topical sun blockers, effectively avoiding sun exposure has become very easy. Furthermore, a substantial body of knowledge provided in recent literature review suggests that regular sunscreen use is associated with higher risk of melanoma. Increased risk of basal cell cancer has been noted among women who use sunscreen."

"Conclusions and Recommendations - The benefits of regular sun exposure appear to outweigh substantially the risks of squamous-basal skin cancer, accelerated aging, and melanoma from burning, all of which can be mitigated. In contrast to Peller's and Apperly's time, we may, as a result of improved understanding, be able to use sun exposure now to dramatically lower our death rates from internal cancers and melanoma without suffering any consequent increased incidence in squamous-basal skin cancer. We are also in a position to be able to mitigate the accelerated aging and melanoma risks."

"Preventing melanoma is largely a matter of preventing sunburning, especially in children and adolescents. As the melanoma research has demonstrated, the best prevention is regular exposure, thereby maintaining a protective tan and high vitamin D blood and tissue levels. This is especially important in early spring preparation for the very intense sun of early summer. Sun exposure and burning potential are dramatically affected by the altitude of the location, the sun-reflective nature of the environment, the angulation of the sun in the sky, the purity or pollution of the air, the sensitivity of the skin, and the degree to which the skin is tanned. These variables must be considered carefully. Until further guidelines are available, it is probably best to start with a few minutes a day and increase this gradually according to individual response. It must be noted that a very few individuals have abnormal skin conditions that make any sun exposure harmful."

"The squamous-basal skin cancer and accelerated aging risks can be mitigated by spreading the exposure over the whole body, while selectively shading the thin, sensitive, and cancer-prone skin of the head and neck. It appears that hats should be used. The dramatic increase in skin cancers over the past decade has been extensively discussed with regard to ozone depletion. However, the change in styles of dress that has resulted in the almost complete abandonment of the hat as an article of clothing for the past 30 years offers a hypothetical timeframe of carcinogenesis more in line with our knowledge of skin cancer. In view of the recent suggested link between sunscreen use and increased melanoma incidence, physical shading appears to be the safest way to limit sun exposure."

"The research cited here demonstrates the need for regular exposure to the sun. Additionally, Webb and Holick have shown that vitamin D synthesis continues for 3 days after sun exposure. Therefore it seems prudent to recommend sunbathing at least every 3-4 days, if practical. Short daily exposure, perhaps during lunch time, would appear to be best."

"Studies of the geographical distribution of cancer deaths in general and certain cancers in particular show that sun exposure can be an ineffective source of vitamin D at the higher latitudes, colder climates, and regions of polluted air, especially during fall and winter. Personal supplementation or dietary alteration appears to be seasonally appropriate in these locales. Cross-cultural studies suggest that diet can be effective source of vitamin D for cancer prevention and that 400-800 IU daily is an effective safe dose. Sun exposure, if available, eliminates the risks of vitamin D toxicity and intestinal malabsorption."

"The research studies presented here suggest that dermal activation of vitamin D from regular, moderate sun exposure has a strong protective effect in the prevention of breast and colon cancer; has a weaker protective effect in melanoma, leukemia, and lymphoma; and acts to lower overall cancer death rates. These studies emphasize cancers with high death rates, rather than high-incidence, generally nonfatal dermal cancers. The combined findings of these studies suggest that advising the public to seek regular moderate solar exposure is supported by a broad view of the available scientific research as an effective means of lowering cancer mortality."[1]

Author's Note:

For years we have been told to avoid sun exposure and apply sun screen at all times. This advice was fatally flawed having not taken into account the multiple functions of sunlight and vitamin D. As a result, in part people are experiencing vitamin D deficiency that will in part be responsible for increases in breast and colon cancer. And since vitamin D is involved in bone formation, low amounts of vitamin D will also contribute to a greater amount of osteoporosis as well as less healthy gums and gum tissue. We need to all get moderate sunlight during the day and avoid the use of sunscreens that block that health giving light. In places where light is limited as in northern climates or during the winter we can return to the use of proper amounts of fish oils as a supplement and/or the use of full spectrum lights.

[1] H. Gordon Ainsleigh, DC, "Beneficial effects of sun exposure on cancer mortality", Preventive Medicine, 1993, Vol. 22, pp. 132-140
Last update on October 21, 2002

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