Occupational physical activity and risk of malignant melanoma: the Western Canada Melanoma Study.

The relationship between physical activity and cutaneous malignant melanoma has not been fully investigated; in particular, many previous studies have not controlled for sunlight exposure, which is an important environmental risk factor for melanoma. The aim of this study was to examine the relationship between occupational physical activity and melanoma risk. The data were collected for a population-based case-control study that consisted of 595 melanoma patients diagnosed between 1979 and 1981. Five hundred and ninety-five controls matched on sex, age and area of residence were selected from provincial government health insurance rolls. Lifetime job histories, sun exposure and other host factors were obtained from personal interviews with each individual. Logistic regression analysis was used to examine the relationship between melanoma risk and occupational activity levels, measured as total metabolic equivalent hours, with adjustment for occupational sun exposure, recreational sun exposure and host factors. Risk estimates were elevated above one for each occupational activity quintile compared with those with sedentary jobs. However, the pattern of risk ratios was irregular and statistical significance was reached only by the highest quintile (odds ratio: 1.59, 95% confidence interval: 1.02-2.47) and the second lowest quintile (odds ratio: 1.62, 95% confidence interval: 1.10-2.39). Our data showed an elevated risk for cutaneous malignant melanoma among those with higher levels of physical activity, although no clear dose-response relationship was observed. Further studies examining lifetime physical activity histories and sunlight exposure are required to explicate these findings.