Sun Avoidance Will Increase Overall Cancer Incidence

[Neon Beach]

SUN AVOIDANCE WILL INCREASE OVERALL CANCER INCIDENCE 19 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

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