Background: There is substantial evidence that higher levels of activity reduce the risk of mortality, but several research questions remain about the protective effect of physical activity. We aimed to quantify the effect of physical activity on overall mortality in younger women and to assess the effect of past versus current activity.
Methods: During 1991-1992, we enrolled 99,099 women, age 30-49 years, from the entire country of Norway and one Swedish region, in a population-based cohort study. The women provided information on physical activity level at age 14 and 30 years and at enrollment, as well as information on other personal characteristics at enrollment. We achieved complete follow-up into 2003 using record linkages to nationwide registers. We used Cox proportional hazard models to calculate multivariate relative risks (RRs) of dying from any cause.
Results: During an average 11.4 years of follow-up, 1,313 women died. Risk of death decreased with increasing physical activity at enrollment (5 categories; P for trend<0.0001) and was reduced by half in the highest compared with the lowest category (RR=0.46; 95% confidence intervals=0.33-0.65). This protective effect was consistent across strata of age at entry, smoking, country, and education. After adjustment for physical activity at enrollment, activity at age 14 and 30 was not associated with mortality.
Conclusions: Current physical activity substantially reduces mortality among women. This association is observed even with low levels of physical activity and is accentuated with increased physical activity.