Recreational physical activity and the risk of adult leukemia in Canada.

OBJECTIVE: To examine the association between adult onset leukemia and recreational physical activity. METHODS: We analysed data obtained from a population-based case-control study conducted in seven Canadian provinces. Risk estimates were generated by applying multivariate logistic regression methods to 653 incident histologically confirmed leukemia cases and 3,106 controls aged 20-74. RESULTS: We observed a 25% risk reduction for adult leukemia associated with the highest category of vigorous physical activity (adjusted odds ratio (OR) = 0.75; 95% confidence interval [CI] = 0.57-0.99). This reduction was stronger among men (OR = 0.64; 95% CI = 0.41-0.95), than among women (OR = 0.82; 95% CI = 0.52-1.29). For women, reduced risk estimates were observed for all levels of vigorous activity; for men, reduced risk estimates were restricted to the highest category of vigorous activity High levels of vigorous activity were associated with some degree of risk reduction for each of the five histological subtypes except chronic myeloid leukemia. Risk reductions associated with high levels of vigorous activity were more pronounced with higher body mass index (BMI): BMI < 25 (OR 0.93; 95% CI = 0.61-1.40); BMI > 25 to <30 (OR 0.75; 95% CI = 0.40-1.21); BMI > or = 30 (OR = 0.50; 95% CI = 0.28-0.95). CONCLUSION: Our study suggests that higher categories of vigorous physical activity may decrease the risk of adult leukemia.