Reduced Risk of Brain Cancer Mortality From Walking, Running
Of the 153,420 subjects with complete data and eligible for analyses, 18 were excluded for reporting a previous diagnosis of brain cancer on their baseline questionnaires. The remaining sample included 110 deaths that had brain cancer listed as the underlying cause during the 11.7 ± 3.1 yr follow-up (mean ± SD). Table 1 presents their sample characteristics. Social security number was provided by 79.8% of those who ran or walked <1.8 MET·h·d, 84.8% of those who ran or walked 1.8–3.5 MET·h·d, and 88.7% of those who ran or walked ≥3.6 MET·h·d.
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 walked or ran 1.8–3.6 MET·h·d (95% confidence interval [CI] = 2.6%–66.8% lower, P = 0.04) and 39.8% lower for those who walked or ran ≥3.6 MET·h·d (95% CI = 0.0%–64.0% lower, P = 0.05) when compared with <1.8 MET·h·d. These results provide little evidence for additional risk reduction higher than 1.8 MET·h·d, although there may be limited statistical power to detect any additional improvement. Table 2 shows that when pooled, the runners and walkers who expended ≥1.8 MET·h·d had a 42.5% lower risk of brain cancer mortality for the entire sample 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). The risk reduction was weakened slightly when race, education, type of activity, and cohort effects were disregarded (P = 0.07) and was somewhat stronger for subjects ≥50 yr of age versus younger subjects at baseline.
The risk for brain cancer mortality was also 4.13-fold greater for whites than nonwhites (95% CI = 1.02- to 16.80-fold, P = 0.05) and 1.91-fold greater for winter births (February vs August, 95% CI = 1.01- to 3.59-fold, P = 0.05) but was unrelated to height (HR = 0.36 per meter, 95% CI = 0.03–5.09, P = 0.45), BMI (HR = 1.00 per kilogram per square meter, 95% CI = 0.95–1.06, P = 0.87), medications for hypertension (HR = 1.04, 95% CI = 0.56–1.92, P = 0.11) or diabetes (HR = 0.51, 95% CI = 0.07–3.68, P = 0.80), or intakes of red meat (HR = 0.86 per serving per day, 95% CI = 0.49–1.50, P = 0.59), fruit (HR = 0.90 per piece per day, 95% CI = 0.76–1.07, P = 0.23), or alcohol (HR = 1.00 per gram per day, 95% CI = 0.99–1.00, P = 0.95). The adjustment for these additional variables did not eliminate the significantly lower risk for brain cancer mortality for ≥1.8 MET·h·d versus <1.8 MET·h·d run or walked, including adjustment for BMI (Table 2). The reduction in brain cancer mortality for ≥1.8 versus <1.8 MET·h·d also remained significant when the data were restricted to subjects who provided their social security numbers (41.4% risk reduction, 95% CI = 1.9%–65.0%, P = 0.04).
The results cited previously are entirely consistent with those from the less-restrictive logistic regression analyses that adjusted for follow-up duration, that is, the adjusted odds for brain cancer mortality were as follows: 1) 43.2% lower for those who walked or ran 1.8–3.5 MET·h·d (95% CI = 2.4%–66.9%, P = 0.04), 2) 40.3% lower for those who walked or ran ≥3.6 MET·h·d (95% CI = 0.0%–64.5%, P = 0.05), 3) 4.1-fold greater for whites than nonwhites (95% CI = 1.0- to 16.7-fold, P = 0.05), and 3) 1.9-fold greater for winter than summer births (February vs August, 95% CI = 1.0- to 3.6-fold, P = 0.05). Brain cancer mortality was unrelated to height (P = 0.44), BMI (P = 0.85), hypertension medication (P = 0.94), diabetes medications (P = 0.46), and intakes of red meat (P = 0.59), fruit (P = 0.24), or alcohol (P = 0.96).
Results
Of the 153,420 subjects with complete data and eligible for analyses, 18 were excluded for reporting a previous diagnosis of brain cancer on their baseline questionnaires. The remaining sample included 110 deaths that had brain cancer listed as the underlying cause during the 11.7 ± 3.1 yr follow-up (mean ± SD). Table 1 presents their sample characteristics. Social security number was provided by 79.8% of those who ran or walked <1.8 MET·h·d, 84.8% of those who ran or walked 1.8–3.5 MET·h·d, and 88.7% of those who ran or walked ≥3.6 MET·h·d.
Cox Proportional Hazard Analyses
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 walked or ran 1.8–3.6 MET·h·d (95% confidence interval [CI] = 2.6%–66.8% lower, P = 0.04) and 39.8% lower for those who walked or ran ≥3.6 MET·h·d (95% CI = 0.0%–64.0% lower, P = 0.05) when compared with <1.8 MET·h·d. These results provide little evidence for additional risk reduction higher than 1.8 MET·h·d, although there may be limited statistical power to detect any additional improvement. Table 2 shows that when pooled, the runners and walkers who expended ≥1.8 MET·h·d had a 42.5% lower risk of brain cancer mortality for the entire sample 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). The risk reduction was weakened slightly when race, education, type of activity, and cohort effects were disregarded (P = 0.07) and was somewhat stronger for subjects ≥50 yr of age versus younger subjects at baseline.
The risk for brain cancer mortality was also 4.13-fold greater for whites than nonwhites (95% CI = 1.02- to 16.80-fold, P = 0.05) and 1.91-fold greater for winter births (February vs August, 95% CI = 1.01- to 3.59-fold, P = 0.05) but was unrelated to height (HR = 0.36 per meter, 95% CI = 0.03–5.09, P = 0.45), BMI (HR = 1.00 per kilogram per square meter, 95% CI = 0.95–1.06, P = 0.87), medications for hypertension (HR = 1.04, 95% CI = 0.56–1.92, P = 0.11) or diabetes (HR = 0.51, 95% CI = 0.07–3.68, P = 0.80), or intakes of red meat (HR = 0.86 per serving per day, 95% CI = 0.49–1.50, P = 0.59), fruit (HR = 0.90 per piece per day, 95% CI = 0.76–1.07, P = 0.23), or alcohol (HR = 1.00 per gram per day, 95% CI = 0.99–1.00, P = 0.95). The adjustment for these additional variables did not eliminate the significantly lower risk for brain cancer mortality for ≥1.8 MET·h·d versus <1.8 MET·h·d run or walked, including adjustment for BMI (Table 2). The reduction in brain cancer mortality for ≥1.8 versus <1.8 MET·h·d also remained significant when the data were restricted to subjects who provided their social security numbers (41.4% risk reduction, 95% CI = 1.9%–65.0%, P = 0.04).
Verification Using Logistic Regression Analyses
The results cited previously are entirely consistent with those from the less-restrictive logistic regression analyses that adjusted for follow-up duration, that is, the adjusted odds for brain cancer mortality were as follows: 1) 43.2% lower for those who walked or ran 1.8–3.5 MET·h·d (95% CI = 2.4%–66.9%, P = 0.04), 2) 40.3% lower for those who walked or ran ≥3.6 MET·h·d (95% CI = 0.0%–64.5%, P = 0.05), 3) 4.1-fold greater for whites than nonwhites (95% CI = 1.0- to 16.7-fold, P = 0.05), and 3) 1.9-fold greater for winter than summer births (February vs August, 95% CI = 1.0- to 3.6-fold, P = 0.05). Brain cancer mortality was unrelated to height (P = 0.44), BMI (P = 0.85), hypertension medication (P = 0.94), diabetes medications (P = 0.46), and intakes of red meat (P = 0.59), fruit (P = 0.24), or alcohol (P = 0.96).