Purpose: This study aimed to test prospectively whether exercise is associated with lower brain cancer mortality in 111,266 runners and 42,136 walkers from the National Runners’ and Walkers’ Health Studies.
Methods: Hazard ratios and 95% confidence intervals (95% CI) from Cox proportional hazards analyses of mortality versus metabolic equivalent hours per day of exercise (MET-hours per day, where 1 MET = 3.5 mL O2·kg−1·min−1, or approximately 1-km run).
Results: The National Death Index identified 110 brain cancer deaths during an 11.7-yr average follow-up. Runners and walkers were combined because the brain cancer risk reduction did not differ significantly between MET-hours per day run and MET-hours per day walked (P = 0.66). When adjusted for sex, age, race, education, and cohort effects, the risk for brain cancer mortality was 43.2% lower for those who exercised 1.8 to 3.5 MET·h·d−1 (95% CI = 2.6%–66.8% lower, P = 0.04) and 39.8% lower for those who exercised ≥3.6 MET·h·d−1 (95% CI = 0.0%–64.0% lower, P = 0.05) compared with <1.8 MET·h·d−1 at baseline. Pooling the runners and walkers who expended ≥1.8 MET·h·d−1 showed a 42.5% lower risk of brain cancer mortality for the entire sample (95% CI: 8.0 to 64.1, P = 0.02) and 40.0% lower risk when three deaths that occurred within 1 yr of the baseline survey were excluded (95% CI = 1.3%–62.4%, P = 0.04).
Conclusions: The risk for fatal brain cancer decreased in association with running and walking energy expenditure. Our ability to detect an exercise–brain cancer relationship may relate to the use of cohorts specifically designed to detect exercise–health associations, and the calculation of exercise energy expenditure from kilometers per day walked and run rather than time spent exercising.
Ernest Orlando Lawrence Berkeley National Laboratory, Berkeley, CA
Address for correspondence: Paul T. Williams, Ph.D., Donner Laboratory, Life Sciences Division, Ernest Orlando Lawrence Berkeley National Laboratory, Berkeley, CA 94720; E-mail: firstname.lastname@example.org.
Submitted for publication June 2013.
Accepted for publication September 2013.