Williams PT.
Med Sci Sports Exerc. 2013 Oct 1. [Epub ahead of print]

Abstract
PURPOSE: 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 (HR) and 95% confidence intervals (95%CI) from Cox proportional hazards analyses of mortality vs. metabolic equivalent hours per day of exercise (MET-hours/d, where one MET=3.5 ml O2/kg/min, or approximately 1 km run).

RESULT: The National Death Index identified 110 brain cancer deaths during 11.7-year average follow-up. Runners and walkers were combined because the brain cancer risk reduction did not differ significantly between MET-hours/d run and MET-hours/d 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 MET-hours/d (95%CI: 2.6% to 66.8% lower, P=0.04), and 39.8% lower for those who exercised ≥3.6 MET-hours/d (95%CI: 0.0% to 64.0% lower, P=0.05), compared to

CONCLUSION: 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 detect exercise-health associations, and the calculation of exercise energy expenditure from km/day walked and run rather than time spent exercising.

PubMed Reference:  http://www.ncbi.nlm.nih.gov/m/pubmed/24091993/