Sun avoidance will increase incidence of cancers overall
- Cedric F Garland (), professor
- University of California at San Diego, School of Medicine, 9500 Gilman Drive, La Jolla, CA 92093-0631, USA
EDITOR—Fry and Verne in their editorial concluded that sunscreens may create a false sense of security and encourage over-exposure to the sun.1 2 Sunscreens should not be relied on to prevent melanoma. Typical sunscreens only weakly absorb ultraviolet A light, which is 97% of ultraviolet radiation and is nearly as carcinogenic as ultraviolet B light. The typical protection factor for ultraviolet A is 2-4 for chemical sunscreens.3 Absorption of ultraviolet A is not included in calculation of the sun protection factor.
The authors' advice to avoid the sun would not be the best strategy for reducing overall incidence of cancer. Recommending moderate exposure to the sun would be more prudent.
Solar exposure is the main source of vitamin D. Vitamin D and its metabolites reduce the risk of cancers of the colon,4 5 w1 w2 breast,w3-w5 and prostate,w6-w8 and other cancers.w9 Since the United Kingdom is located at northern latitudes supplementation of the diet with vitamin D would be helpful, in addition to encouraging moderate exposure to the sun. People in the United Kingdom cannot synthesise vitamin D from November to the end of March, like residents of Boston.w9 The half life of the storage form of vitamin D is about three weeks, so Britons become deficient by December.
Residents of the United Kingdom should aim for 10-15 minutes a day in the sun when the weather allows, without sunscreen, to allow adequate synthesis of vitamin D. Vitamin D3 supplementation of children aged 1 year and older and adults at 400 IU per day (10 μg) would be appropriate and would avoid risk of toxicity.w10 Adults aged 71 and older should receive 600 IU (15 μg) daily.w11 Sunscreens should be used with caution until products are available that block ultraviolet A with the same degree of protection as ultraviolet B.
References w1-11 are available on bmj.com
Competing interests None declared.