Relationship between sun exposure and melanoma risk for tumours in different body sites in a large case-control study in a temperate climate

Abstract

Aim A melanoma case-control study was conducted to elucidate the complex relationship between sun exposure and risk. Methods Nine hundred and sixty population-ascertained cases, 513 population and 174 sibling controls recruited in England provided detailed sun exposure and phenotype data; a subset provided serum 25-hydroxyvitamin D 2 + D 3 levels. Results Phenotypes associated with a tendency to sunburn and reported sunburn at ⩾20 years of age were associated with increased melanoma risk (odds ratio (OR) 1.56, 95% confidence intervals (CI) 1.23–1.99). Holiday sun exposure was not associated with an increased melanoma risk although this may be in part because reported sun exposure overall was much lower in those with a sun-sensitive phenotype, particularly among controls. Head and neck melanoma was associated with less sun exposure on holidays at low latitudes (OR 0.39, 95% CI (0.23–0.68) for >13 h/year compared to <3.1). Overall the clearest relationship between reported sun exposure and risk was for average weekend sun exposure in warmer months, which was protective (OR 0.67, 95% CI 0.50–0.89 for highest versus lowest tertile of exposure). Serum vitamin D levels were strongly associated with increased weekend and holiday sun exposure. Conclusions Sun-sensitive phenotypes and reported sunburn were associated with an increased risk of melanoma. Although no evidence was seen of a causal relationship between holiday sun exposure and increased risk, this is consistent with the view that intense sun exposure is causal for melanoma in those prone to sunburn. A protective effect of regular weekend sun exposure was seen, particularly for limb tumours, which could be mediated by photoadaptation or higher vitamin D levels.