Is it smoking or related lifestyle variables that increase metabolic syndrome risk?

Metabolic syndrome is considered as mainly caused by a deleterious lifestyle (sedentarity and diet). That smoking contributes to metabolic syndrome had been suggested by several small studies and a meta-analysis. The interesting study by Slagter et al. published in BMC Medicine is the first very large study confirming this association in both genders, in all classes of body mass index, and in a dose-related manner. Surprisingly, smoking is even associated with increased abdominal fat. Rather than a direct causal effect of smoking, the reason for these associations is most probably the frequent presence of other lifestyle components in smokers. For example, physical inactivity and alcohol drinking are known to be more often present in smokers and could completely explain the observations of the Slagter et al. study. Unfortunately, these factors, already not properly checked in the first studies, were not assessed at all in the present one. However, as it is still on-going, we hope that other lifestyle factors will be included in future publications.