Department of Infectious Diseases, Tropical Medicine and AIDS, Academic Medical Center, Meibergdreef 9, 1100 DD Amsterdam, The Netherlands
The paper by Kujala et al. (1) on modifiable risk factors for all-cause mortality presents convincing evidence on the role of genetics with respect to risk factors such as participation in vigorous activity, doing sedentary work, and heavy alcohol use. I was intrigued by the low mortality risks associated with sedentary work and with vigorous physical activity. In the Discussion, it was suggested that the low risk associated with sedentary work could be explained in part by socioeconomic status. The authors noted that the odds ratio was further reduced after adjustment for smoking, heavy alcohol use, and vigorous physical activity. The latter adjustment might not be the best way of dealing with the issue, since it seems more likely that sedentary work promotes vigorous physical activity than the other way around.
Since the beneficial effect of vigorous physical activity may be greatest among persons who do sedentary work, I was wondering whether the authors assessed interaction between these two variables. If such interaction exists, this may need to be taken into account in the analysis of familial aggregation.
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