Physical activity and health benefits

Abstract

Physical activity (PA), due to its role in health promotion and disease prevention, is of particular interest to be investigated. The aims of this thesis were: to assess the associations between PA and different health outcomes (lower urinary tract symptoms, cancer incidence, and mortality) in the Cohort of Swedish Men (COSM); to perform a dose-response meta- analysis of published associations between walking and incidence of coronary heart disease (CHD); and to provide user-friendly software packages for dose-response meta-analysis and for sensitivity analysis of biases in observational studies. The COSM is a population-based prospective cohort of 45,906 men between 45 to 79 years of age in central Sweden who were cancer-free and completed a questionnaire about current and historical PA, diet, and other life- style factors at enrollment in 1997.

At baseline 6905 men reported moderate to severe lower urinary tract symptoms (LUTS). A significant inverse relationship was seen between total PA and moderate and severe LUTS (highest vs lowest quartile odds ratio=0.72; 95% confidence interval (CI)=0.66-0.79). Men who were physically active at work as well as during leisure-time showed 50% reduction in risk of moderate to severe LUTS (95% CI=0.40-0.60) compared to those who were sedentary. Conversely, men with long-term sedentary lifestyles (5 hours/day watching TV both at age 30 years and current) reported a 2-fold increase (95% CI=1.41-2.59) risk to these symptoms when compared to men more active at both time periods.

After 7 years of study enrollment 3714 men of the COSM were diagnosed with cancer and 1153 of them died due to the disease. We observed a strong inverse linear association between total daily PA and death from any form of cancer. For each increment of 4 metabolic equivalent (MET)-hours/day of total PA (approximately 1 hour daily of moderate effort) cancer incidence tended to be decreased by 2% and cancer mortality decreased significantly by 12% (95% CI = 6-18%).

During 9.7 years of follow-up, we identified a total of 4086 deaths from all causes. Compared to men who were lean and active (BMI < 25 kg/m2; top tertile total PA) the adjusted rate ratios of death from all causes were 1.44 (95% CI=1.11-1.86) for obese-active men (BMI 30 kg/m2), 1.54 (95% CI=1.34-1.77) for lean but inactive men (bottom tertile total PA), and 1.81 (95% CI=1.48-2.23) for obese-inactive men. After excluding the first 3 years of follow-up, current and former smokers, those who had lost weight from age 20 years to baseline, and heavy manual workers, the adjusted rate ratios of death from all causes were 1.65 (95% CI=1.20-2.27) for overweight-to-obese and active men, 2.15 (95% CI=1.59-2.91) for lean-inactive men, and 2.04 (95% CI=1.52-2.74) for overweight-to-obese and inactive men compared to lean-active men.

During 10 years of follow-up a total of 2735 men were diagnosed with prostate cancer, of which 190 were fatal. We observed an inverse linear association between lifetime (average of age 30, 50 and baseline) walking/bicycling duration and incidence of total prostate cancer risk. The multivariable-adjusted rate ratio decreased by 8% (95% CI=2-13%) for every 30 min/day increment of lifetime walking/bicycling in the range of 30 to 120 min/day. The fatal prostate cancer rate among those men who hardly ever walked or biked was two-fold that of men in the highest average lifetime walking/bicycling of 120 min/day, although this increased rate was not significant. In the dose-response meta-analysis of eight epidemiological studies we found that every increment of 8 MET-hours/week of walking (moderate-intensity about 30 min/day on 5 days of the week) was associated with 19% decrease (95% CI=14-23%) of CHD risk.

In conclusion, we observed that increased PA levels may lower the risk of LUTS, all-cause and cancer mortality, prostate cancer, and CHD. Furthermore, the two statistical components developed for Stata® software can greatly facilitate dose-response meta-analyses (glst) and support sensitivity analysis (episens) of epidemiological findings.