The impact of smoking on disease measures in rheumatoid arthritis: the need for appropriate adjustment of time-varying confounding

Abstract

In a recent publication, Quintana-Dunque et al. studied patients with early onset rheumatoid arthritis (RA) and showed that baseline smoking status was inversely associated with disease activity and disability at 36 months. The authors conclude that smoking may not be as deleterious as previously considered in RA disease course. However, the authors fail to highlight several limitations of study design and analysis, including time-varying confounding, which may have a direct impact on results and corresponding conclusions.

Dusty trades and associated rheumatoid arthritis in a population-based study in the coal mining counties of Appalachia

“…The epidemiological relationship between cigarette smoking, past or current, and RA is complex. Based on observational data it even has been argued the active smoking may be protective against severity, a conclusion that may not sufficiently consider time varying confounding 17. Analysing the relationship between occupation and smoking is similarly fraught with time varying confounding in the context of ‘the healthy worker survivor effect.’18 Thus, when taking into account the potential the concomitant effects of smoking, RA, and occupation, caution is certainly warranted.…”