Reduced Risk of Brain Cancer Mortality From Walking, Running
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·min, 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 (95% CI = 2.6%–66.8% lower, P = 0.04) and 39.8% lower for those who exercised ≥3.6 MET·h·d (95% CI = 0.0%–64.0% lower, P = 0.05) compared with <1.8 MET·h·d at baseline. Pooling the runners and walkers who expended ≥1.8 MET·h·d 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.
An estimated 24,560 malignant tumors of the brain and central nervous system are projected to occur in 2013. Seventy percent of all adult malignant primary brain tumors are gliomas, that is, tumors arising from glial cells. The risk for glioma increases with age is approximately 40% greater for males than females and is greater in whites than blacks. Taller individuals may be at greater risk than those who are short. The only established modifiable risk factor for glioma is exposure to ionizing radiation, which accounts for only a small proportion of cases. Prognosis depends on age, tumor grade, histology, prior progressions, and performance status.
Studies to date reported only a weak, mostly nonsignificant effect of physical activity on glioma, including the Million Woman Study cohort and the European Prospective Investigation into Cancer and Nutrition study. The National Institutes of Health–American Association of Retired Persons study of slightly more than 300,000 subjects found 35% lower glioma risk for subjects who recalled being physically active when they were between 15 and 18 yr old, but no significant risk reduction for activity later in life. Prognosis may be improved with exercise, that is, Ruden et al. reported that median survival time was 68% greater in patients with recurrent malignant glioma who exercised ≥1.3 MET·h·d versus less active patients. Performance status has also been associated with prognosis, and although physical activity is a strong determinant of performance status, their effects on prognosis are apparently independent.
This report tests whether exercise deceases the risk of brain cancer mortality prospectively in the National Walkers' and Runners' Health Study cohorts. These cohorts were specifically designed to maximize the statistical power to detect exercise–health associations. In addition to their large sample size, the broad range of energy expenditures, and the use of subjects knowledgeable of their exercise routines, their exercise energy expenditures were calculated from kilometers walked and run, which has been shown to be a superior metric to traditional time-based calculations. This is important because nondifferential errors in recall of physical activity are likely to bias results toward the null in most existing studies.
For these reasons, significant associations between exercise and brain cancer might be detected in the specialized cohorts of the current report, but not in general-purpose cohorts of primarily sedentary individuals reported by others.
Abstract and Introduction
Abstract
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·min, 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 (95% CI = 2.6%–66.8% lower, P = 0.04) and 39.8% lower for those who exercised ≥3.6 MET·h·d (95% CI = 0.0%–64.0% lower, P = 0.05) compared with <1.8 MET·h·d at baseline. Pooling the runners and walkers who expended ≥1.8 MET·h·d 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.
Introduction
An estimated 24,560 malignant tumors of the brain and central nervous system are projected to occur in 2013. Seventy percent of all adult malignant primary brain tumors are gliomas, that is, tumors arising from glial cells. The risk for glioma increases with age is approximately 40% greater for males than females and is greater in whites than blacks. Taller individuals may be at greater risk than those who are short. The only established modifiable risk factor for glioma is exposure to ionizing radiation, which accounts for only a small proportion of cases. Prognosis depends on age, tumor grade, histology, prior progressions, and performance status.
Studies to date reported only a weak, mostly nonsignificant effect of physical activity on glioma, including the Million Woman Study cohort and the European Prospective Investigation into Cancer and Nutrition study. The National Institutes of Health–American Association of Retired Persons study of slightly more than 300,000 subjects found 35% lower glioma risk for subjects who recalled being physically active when they were between 15 and 18 yr old, but no significant risk reduction for activity later in life. Prognosis may be improved with exercise, that is, Ruden et al. reported that median survival time was 68% greater in patients with recurrent malignant glioma who exercised ≥1.3 MET·h·d versus less active patients. Performance status has also been associated with prognosis, and although physical activity is a strong determinant of performance status, their effects on prognosis are apparently independent.
This report tests whether exercise deceases the risk of brain cancer mortality prospectively in the National Walkers' and Runners' Health Study cohorts. These cohorts were specifically designed to maximize the statistical power to detect exercise–health associations. In addition to their large sample size, the broad range of energy expenditures, and the use of subjects knowledgeable of their exercise routines, their exercise energy expenditures were calculated from kilometers walked and run, which has been shown to be a superior metric to traditional time-based calculations. This is important because nondifferential errors in recall of physical activity are likely to bias results toward the null in most existing studies.
For these reasons, significant associations between exercise and brain cancer might be detected in the specialized cohorts of the current report, but not in general-purpose cohorts of primarily sedentary individuals reported by others.
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