I agree - there is a tremendously high risk of residual confounding in this study, even after adjusting for known/available risk factors. One of the findings,

I agree - there is a tremendously high risk of residual confounding in this study, even after adjusting for known/available risk factors. One of the findings, for example, is increased risk of death from cancer. Since this is an observational meta-analysis, I am inclined to wonder whether an equally true assessment is "as people near death from cancer, they tend to be more sedentary". I haven't yet logged in through the academic VPN required to gain access to this article and the articles from which its meta-analysis is derived, so I'll have to reserve judgment until I can do so. For now, it's a fascinating association but I'd be cautious about the interpretation of the direction of the arrow of causality.