Healthy jogger effect might explain differences in mortality

EDITOR—In their cohort study of mortality in Danish men, Schnohr et al compared the mortality in 96 men who reported that they were joggers at two examinations in 1976–8 and 1981–3 with that in 4562 men who were non-joggers at both examinations.1 The authors followed up the cohort from 1976–8 to 1998 and found that the joggers' relative risk of death was 0.39 (95% confidence interval 0.19 to 0.73).

The participants rather than the authors defined jogging. The paper does not include information on how or how much the men exercised at the time of the examinations or in between and after the examinations. It is not clear whether the men agreed on a common definition of jogging.

At the time of the two examinations, in 1976–8 and 1981-3, 217 (4.7%) and 202 (4.3%) respectively of the 4658 men, aged 20-79, reported that they were joggers. These numbers are surprisingly low. According to a study carried out in 1994 by the Danish National Institute for Public Health, 59.5% of men aged ≥16 exercised or considered themselves to be physically active. Even among men aged ≥67, 55.4% exercised or considered themselves …