Results of studies that examined the relationship between physical activity and non-Hodgkin lymphoid neoplasms (NHL) are inconsistent, and only one study to date examined time spent sitting in relation to NHL. We examined recreational physical activity and leisure-time sitting in relation to risk of NHL in the American Cancer Society Cancer Prevention Study II Nutrition Cohort. Between 1992 and 2007, 2,002 incident cases were identified among 146,850 participants who were cancer-free at enrollment. Cox proportional hazards regression was used to compute hazard ratios (HR) and 95% confidence intervals (CI) while adjusting for potential confounders. Women who sat for at least 6 hr/day were at 28% higher risk of NHL compared to women who sat for fewer than 3 hr/day. In analyses of specific subtypes, sitting time was associated with risk of multiple myeloma only (6+ vs. 3 hr/day sitting: HR = 2.40, 95% CI: 1.45-3.97). Women who engaged in any recreational physical activity had a nonsignificant 20%-30% lower risk of NHL (p-trend = 0.05) compared to women who reported no recreational physical activity. Neither leisure-time sitting nor recreational physical activity was associated with risk of NHL or major NHL subtype in men. There was no evidence of statistical interaction between physical activity and sitting time, or between body mass index and physical activity or sitting time. Further research is needed to confirm an association between sitting time and multiple myeloma and explore a possible association between physical activity and NHL.
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