Regular Recreational Physical Activity and Risk of Hematologic Malignancies: Results From the Prospective Vitamins and Lifestyle (VITAL) Study
Authors: Walter Roland B. , Buckley Sarah A. , White Emily 
Published: October 2019

Abstract
Abstract 887

Background:
Recreational physical activity (PA) provides numerous health benefits, including a reduction in cardiovascular and metabolic diseases and promotion of mental health. Increasing evidence from epidemiological studies also links PA to a reduced risk of major human cancers, particularly those of the colon and breast. On the other hand, previous case-control and cohort studies examining the relationship of PA and incident hematologic malignancies yielded inconsistent results. Given these conflicting findings, we used a large prospective cohort study to examine this association.

Patients and Methods:
65,322 men and women aged 50–76 years were recruited from 2000–2002 to the VITamins And Lifestyle (VITAL) study. The PA questionnaire at baseline asked about walking by intensity and two broader categories of activities (mild and moderate/strenuous exercise) by type over the past 10 years. For each activity, a corresponding metabolic equivalent (MET) intensity was assigned. Incident hematologic malignancies (n=666) after study enrollment were identified through December 2009 by linkage to the SEER cancer registry. Hazards ratios (HRs) for total incident hematologic malignancies and cancer subcategories associated with PA averaged over the previous 10 years before baseline were estimated by Cox proportional hazards models. Models were adjusted for age, sex, race/ethnicity, education, smoking, self-rated health, daily fruit and vegetable consumption, body mass index, fatigue, self-reported anemia, and family history of leukemia/lymphoma.

Results:
After adjustment, there was a decreased risk of hematologic malignancies associated with any PA (HR=0.75 [95% CI: 0.61–0.94]) as well as any moderate/high-intensity activity (HR=0.72 [95% CI: 0.57–0.92]). The reduction in risk was greatest among the physically most active participants, both with regard to number of weekly episodes of activity (>4.8 episodes of all activities per week: HR=0.66 [95% CI: 0.51–0.86], P=0.005 for trend; >3.5 episodes of moderate/high-intensity activities per week: HR=0.60 [95% CI: 0.44–0.82], P=0.002 for trend) and metabolic activity (>13.625 MET of all activities per week: HR=0.71 [95% CI: 0.54–0.92], P=0.029 for trend; >11.2972 MET of moderate/high-intensity activities per week: HR=0.65 [95% CI: 0.48–0.89], P=0.005 for trend), respectively. To address the possibility of reverse causation, i.e. the possibility that study participants were physically less active as a result of a yet undiagnosed hematologic malignancy, we repeated these analyses after exclusion of the 146 incident cases that occurred within 2 years of baseline: the reduction in risk of incident hematologic malignancies among the physically most active participants in this study subset was relatively similar to that of the entire study cohort. When we stratified malignancies by WHO disease classification, we found that the association between PA and incident hematologic malignancy was strongest for myeloid neoplasms (HR=0.48 [95% CI: 0.29–0.79] for highest tertile of all PA, P=0.013 for trend; HR=0.40 [0.21-0.77] for highest tertile of moderate/high-intensity PA, P=0.016 for trend). There were also significant associations between episodes of moderate/high intensity PA and incident mature B-cell lymphomas other than chronic lymphocytic leukemia/small lymphocytic lymphoma (CLL/SLL) or plasma cell disorders (>3.5 episodes per week: HR=0.59 [95% CI: 0.36–0.97], P=0.035 for trend) and between episodes of all activities and incident CLL/SLL (>4.8 episodes per week: HR=0.52 [95% CI: 0.26–1.03], P=0.023 for trend). No associations were found with incident plasma cell disorders.

Conclusion:
Our study offers the strongest epidemiological evidence to date to suggest that regular recreational PA is associated with a dose-dependently reduced incidence of certain hematologic malignancies, with a greater than 50% reduction of risk for the development of neoplasms of myeloid origin for individuals within the top tertile of all or moderate/high-intensity activities. Our data also suggest a trend toward reduced risk for CLL/SLL and other mature B-cell NHLs except plasma cell disorders, although further studies in larger cohorts of participants will be required to assess these associations further. Together, our findings may thus suggest additional important health benefits attributable to regular PA.

Disclosures:
No relevant conflicts of interest to declare.