An association has been found between smoking and increased disease activity in rheumatoid arthritis (RA), according to a study recently published in The Journal of Rheumatology.
This study included 282 individuals diagnosed with RA who had 2 rheumatology-related visits to public hospitals within a 1-year period. Most participants were women (83%) with a mean age of 59.4±11.9 years. Each visit included data collected on disease activity and smoking status, with covariate data on obesity, age, use of medications, sex, and race or ethnicity.
Baseline was defined as the second visit to see a physician, and observations continued every 3 months for 27 months until completion, loss to follow-up, or the end of the study period. Causality between smoking and 27-month disease activity parameters was investigated using longitudinal targeted maximum likelihood estimation. This technique required identifying and accounting for any confounding influences.
The 2 primary measures of disease activity were the patient global score, in which smoking correlated with a 0.64-unit increase over nonsmoking (P =.01), and swollen joint counts, in which smoking correlated with 2.58 units more than nonsmoking (P <.001). Although a 2.11-point increase in clinical disease activity score was observed in smokers compared with nonsmokers, this did not achieve statistical significance (P =.22). Current smoking status also did not significantly correlate with levels of C-reactive protein (P =.61) or patient global score (P =.63). However, a significant inverse relationship was observed between current smoking status and 28 tender joint counts (-1.09; 95% CI, -2.16 to -0.02; P =.05).
Limitations to this study included a loss to followup, a lack of continuous obesity data, a lack of analysis stratified for anticyclic citrullinated peptide status and rheumatoid factor, and an inability to study the link between smoking and formation of nodules.
The study researchers conclude that “smoking is associated with higher levels of disease activity as measured by [patient’s global assessment] score and [swollen joint counts]. Methods used in our study may be useful for investigations of additional exposures on longitudinal outcome measures in rheumatologic disease.”
Gianfrancesco MA, Trupin L, Shiboski S, et al. Smoking is associated with higher disease activity in rheumatoid arthritis: a longitudinal study controlling for time-varying covariates [published online December 1, 2018]. J Rheumatol. doi: 10.3899/jrheum.180262