Author + information
- Olivier Luc Charansonney, MD, MSc∗ ( and )
- Alain Cohen-Solal, MD, PhD
- ↵∗Centre hospitalier Sud Francilien Cardiology, 116 boulevard Jean Jaurès, Corbeil-Essonnes 91106, France
We read with great interest both the paper by Schnohr et al. (1) on the dose of jogging and mortality in the CCHS (Copenhagen City Heart Study) cohort and the editorial comment by Lee et al. (2). There is one major confounder in the original paper we would like to emphasize: sedentary nonjoggers were more often women (57%) and strenuous joggers were mostly men (80%). This unbalance is of uttermost importance for mortality studies because the men–women life expectancy difference at 44 years (mean baseline age in the CCHS) was –3.9 years in Denmark in 2001 (Eurostat). In a previous paper, the same Danish team reported that jogging could increase survival by 6.2 years in men and 5.6 years in women (3). Therefore, the effect of sex on the outcome (mortality) is of the same order of magnitude as the effect of the variable of interest (jogging). The only reasonable approach in that case is to analyze men and women in 2 separate studies. There is no need to use statistics to test the hypothesis of an effect of sex on mortality, because this effect is not a hypothesis but a fact. Pooling men and women together and adjusting by sex can only decrease the power of the analyses and fails to show a potential difference between sedentary nonjoggers and strenuous joggers. A simple rule of thumb calculation with the previously described estimates of both sex and jogging effects shows that, compared with a putative all-men sedentary nonjogger group of the same age, the sedentary nonjogger and strenuous jogger groups of the CCHS would have an increased life expectancy of 4.2 and 3 years, respectively, which could mistakenly be interpreted as an increased risk for the strenuous joggers. Therefore, we strongly recommend men and women being considered separately when conducting mortality studies.
Please note: Both authors have reported that they have no relationships relevant to the contents of this paper to disclose.
- 2015 American College of Cardiology Foundation
- Schnohr P.,
- O’Keefe J.H.,
- Marott J.L.,
- Lange P.,
- Jensen G.B.
- Lee D.C.,
- Lavie C.J.,
- Vedanthan R.