Physical activity and mortality among Norwegian women – the Norwegian Women and Cancer Study

BACKGROUND: Physical activity (PA) and its relationship with all-cause mortality suggest a strong and consistent inverse association. This study prospectively investigated the association between PA level and mortality among participants of the Norwegian Women and Cancer (NOWAC) Study. METHODS: A total of 66,136 NOWAC participants were followed-up until December 31st 2008. PA level and possible confounding factors were obtained through a self-administered questionnaire at enrolment. Cox proportional hazards regression was used to calculate adjusted relative risks (RRs) and 95% confidence intervals (CIs) for all-cause, cardiovascular disease (CVD) and cancer mortality and PA levels defined from 1 to 10 on a global scale. RESULTS: PA levels 1–4 were associated with a significantly increased risk of all-cause mortality (level 1 RR = 2.35; 95% CI: 1.94–2.84, level 2 RR = 1.71; 95% CI: 1.45–2.00, level 3 RR = 1.30; 95% CI: 1.14–1.49, level 4 RR = 1.07; 95% CI: 0.95–1.22), compared with PA level 5. CVD mortality risk increased in PA levels 1–3 (level 1 RR = 3.50; 95% CI: 2.41–5.10, level 2 RR = 1.50; 95% CI: 0.99–2.25, level 3 RR = 1.12; 95% CI: 0.79–1.60) as did cancer mortality risk (RR = 1.32; 95% CI: 0.96–1.81, RR = 1.48; 95% CI: 1.19–1.84, RR = 1.26; 95% CI: 1.06–1.50, respectively). The magnitude of the associations was consistent across strata of age, smoking, and body mass index. The population attributable fractions for PA levels 1–4 were: all-cause mortality, 11.5%; CVD mortality, 11.3%; cancer mortality, 7.8%. CONCLUSION: There is a significant trend of increased risk of all-cause, CVD and cancer mortality in relation to low PA levels among Norwegian women.