Nutrition

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The analysis by Brondum-Jacobsen and colleagues1 of skin cancer as a marker for sun exposure and its inverse association with all-cause mortality has been criticized for the immortal person-time bias.2,3 Inappropriately using prospective survival analysis for a retrospective study suggested a dramatic halving of the hazard ratio of all-cause death in individuals with non-melanoma skin cancer (NMSC) compared with the skin cancer-free population. The age- and sex-matched case-control study analysing the same dataset was not subject to this error however, and should not be overlooked. Here, the presence of a NMSC was shown to produce a small but significant reduction in all-cause death (0.97, 0.96-0.99) and a greater reduction in myocardial infarction (0.9, 0.88-0.92). These findings are consistent with the growing body of data suggesting that sunlight exposure, while increasing skin cancer incidence, reduces all-cause mortality. Two recent exemplary prospective Scandinavian cohort studies have both shown that increased sun-seeking behaviour reduces all-cause death.4,5 This effect was dose dependent and occurred after carefully correcting for major confounding factors, and despite the increased incidence of cases (not deaths) of melanoma in more sun-exposed individuals. These studies were designed to quantify the risk of sunlight exposure on the development of melanoma and the resultant deaths from this disease. The separate directions of association between sunlight and melanoma, and sunlight and death, are not what one imagines was anticipated.