Wednesday, April 08, 2015
Exercise doesn't help much
Medical researchers tend to get very excited even when they detect a very small effect of something. Below is such a case. When everything was controlled for in their analyses, they found a pathetic .66 hazard ratio ("the adjusted hazard ratios for all-cause mortality were 0.66"). Statisticians don't usually conclude that something real is going on until the ratio exceeds 2.0. So the lifespan benefits of taking regular exercise are somewhere between tiny and negligible. Pity that.
Effect of Moderate to Vigorous Physical Activity on All-Cause Mortality in Middle-aged and Older Australians
By Klaus Gebel et al.
Importance: Few studies have examined how different proportions of moderate and vigorous physical activity affect health outcomes.
Objective: To examine whether the proportion of total moderate to vigorous activity (MVPA) that is achieved through vigorous activity is associated with all-cause mortality independently of the total amount of MVPA.
Design, Setting, and Participants: We performed a prospective cohort study with activity data linked to all-cause mortality data from February 1, 2006, through June 15, 2014, in 204 542 adults aged 45 through 75 years from the 45 and Up population-based cohort study from New South Wales, Australia (mean [SD] follow-up, 6.52 [1.23] years). Associations between different contributions of vigorous activity to total MVPA and mortality were examined using Cox proportional hazards models, adjusted for total MVPA and sociodemographic and health covariates.
Exposures: Different proportions of total MVPA as vigorous activity. Physical activity was measured with the Active Australia Survey.
Main Outcomes and Measures: All-cause mortality during the follow-up period.
Results: During 1 444 927 person-years of follow-up, 7435 deaths were registered. Compared with those who reported no MVPA (crude death rate, 8.34%), the adjusted hazard ratios for all-cause mortality were 0.66 (95% CI, 0.61-0.71; crude death rate, 4.81%), 0.53 (95% CI, 0.48-0.57; crude death rate, 3.17%), and 0.46 (95% CI, 0.43-0.49; crude death rate, 2.64%) for reporting 10 through 149, 150 through 299, and 300 min/wk or more of activity, respectively. Among those who reported any MVPA, the proportion of vigorous activity revealed an inverse dose-response relationship with all-cause mortality: compared with those reporting no vigorous activity (crude death rate, 3.84%) the fully adjusted hazard ratio was 0.91 (95% CI, 0.84-0.98; crude death rate, 2.35%) in those who reported some vigorous activity (but <30% of total activity) and 0.87 (95% CI, 0.81-0.93; crude death rate, 2.08%) among those who reported 30% or more of activity as vigorous. These associations were consistent in men and women, across categories of body mass index and volume of MVPA, and in those with and without existing cardiovascular disease or diabetes mellitus.
Conclusions and Relevance: Among people reporting any activity, there was an inverse dose-response relationship between proportion of vigorous activity and mortality. Our findings suggest that vigorous activities should be endorsed in clinical and public health activity guidelines to maximize the population benefits of physical activity.
JAMA Intern Med.
Posted by John J. Ray (M.A.; Ph.D.).