Sun Avoidance Will Increase Overall Cancer Incidence

[Editor-in-Chief]

SUN AVOIDANCE WILL INCREASE OVERALL CANCER INCIDENCE19 January 2003 CEDRIC F. Garland,
PROFESSOR
UNIV OF CALIF SAN DIEGO SCH OF MEDICINE 9500 GILMAN DRIVE LA JOLLA CALIFORNIA 92093-0631 USA
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Re: SUN AVOIDANCE WILL INCREASE OVERALL CANCER INCIDENCE

The authors correctly conclude that sunscreens may create a false sense of security and encourage overexposure to the sun (1). Sunscreens certainly should not be relied upon for prevention of melanoma, as typical sunscreens have extremely poor absorption of UVA, which is 95% of UV radiation and is nearly as carcinogenic for melanocytes as UVB. The typical protection factor for UVA is 2-4 for the usual UVA-related compounds in sunscreens (2). This is true even if the SPF is 50 or higher, as UVA is not included in calculation of the SPF.

The author's advice to avoid the sun certainly would not be the best strategy for reducing overall incidence of cancer in the UK. A recommendation for moderate exposure to the sun would be far more prudent.

Solar exposure is the overwhelmingly main source of vitamin D. Vitamin D and its metabolites reduce the risk of cancers of the colon (3-6), breast (7-9), and prostate (10-11), and recent studies suggest that vitamin D may reduce the risk of other cancers (12). Since it was proposed in 1980 that vitamin D reduces risk of colon cancer, there have been 1,021 scientific papers indexed in the US National Library of Medicine MEDLINE database on the role of vitamin D in cancer control and prevention, including analysis of the mechanisms.

Since the UK is located at northern latitudes, supplementation of the adult diet with vitamin D would be helpful, in addition to encouraging moderate exposure to the sun. Individuals at the latitudes of the UK cannot synthesize vitamin D from November through March, like residents of the the US Northeast (13). The half-life of the storage form of vitamin D (25(OH)2D) is only 12-22 days, so people become deficient by December and become increasingly deficient until March, if not supplemented.

Residents of the UK should aim for 10-15 minutes a day in the sun when the weather allows, without sunscreen, to allow adequate synthesis of vitamin D. Such moderate exposures are unlikely to adversely influence the risk of melanoma or other skin cancers, but are likely to reduce the incidence of cancers of the colon, breast and prostate, among other non-cutaneous cancers. Vitamin D supplementation of children age one year and older and adults at a level of 400 IU per day (10 micrograms) would also be appropriate, and consistent with guidelines for avoidance of toxicity from the US National Academy of Sciences (15). Individuals aged 71 and older should receive 600 IU (15 micrograms) per day, due to poorer absorption and synthesis of vitamin D at older ages (15).

Sunscreens should be used with caution until products are available that block UVA with the same degree of protection as UVB, and SPF should not be relied upon as an indicator of the safety of sunscreens. Future sunscreens should perhaps contain a moderate amount of vitamin D to counteract their abolition of vitamin D synthesis

References
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2. Diffey BL, Farr PM. UVA filters in sunscreen preparationsLancet 1989; 2: 170-1.
3. Garland CF, Garland FC. Do sunlight and vitamin D reduce the likelihood of colon cancer? International Journal of Epidemiology 1980; 9: 227-31.
4. Garland CF, Shekelle RB, Barrett-Connor E, et al. Dietary vitamin D and calcium and risk of colorectal cancer: a 19-year prospective study in men. Lancet 1985; 1: 307-9.
5. Garland CF, Comstock GW, Garland FC, Helsing KJ, Shaw EK, and Gorham ED. Serum 25-hydroxyvitamin D and colon cancer: eight-year prospective study. Lancet 1989; 2: 1176-8.
6. Tangrea J, Helzlsouer K, Pietinen P, Taylor P, Hollis B, Virtamo J, Albanes D, Serum levels of vitamin D metabolites and the subsequent risk of colon and rectal cancer in Finnish men. Cancer Causes and Control 1997;8:615-25.
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8. Janowski EC, Lester GE, Weinberg CR, Millikan RC, Schildkraut JM, Garrett PA, Hulka BS. Association between low levels of 1,25-dihydroxyvitamin D and breast cancer risk. Publ Hlth Nutr 1999;2:283-91.
9. John EM, Schwartz GG, Dreon DM, Koo J. Vitamin D and breast cancer risk: The NHANES I epidemiologic follow-up study, 1971-1975 to 1992. Cancer Epidemiol Biomark Prev 1998;8:399-406.
10. Hanchette CL, Schwartz G. Geographic patterns of prostate cancer mortality: evidence for a protective effect of ultraviolet radiation. Cancer 1992;70:2681-9.
11. Ma J, Stampfer MJ, Gann PH, Hough HL, Giovanucci E, Kelsey KT, Hennekens CH, Hunder DJ. Vitamin D receptor polymorphisms, circulating vitamin D metabolites, and risk of prostate cancer in United States physicians. Cancer Epidemiol Biomarkers Prev 1998;7:385-90.
12. Grant WB. An estimate of premature cancer mortality in the U.S. due to inadequate doses of solar ultraviolet-B radiation. Cancer 2002: 94: 1867-75.
13. Webb AR, Kline L, Holick MF. Influence of season and latitude on the cutaneous synthesis of vitamin D3: exposure to winter sunlight in Boston and Edmonton will not promote vitamin D3 synthesis in human skin. J Clin Endocrinol Metab 1988; 67:373-8.
14. Haddad, JG, Jr., Rojanasathit S. Acute administration of 25-hydroxycholecalciferol in man. J Clin Endocrinol Metab 1976;42:284-90. 15. National Academy of Sciences–Institute of Medicine–Food and Nutrition Board. Dietary reference intakes for calcium, phosphorus, magnesium, vitamin D, and fluoride. Washington DC: National Academy Press, 1997. Competing interests: None declared


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