Smoking is associated with higher levels of disease activity in rheumatoid arthritis (RA), according to a recent study. Researchers included 282 individuals with an RA diagnosis using electronic health record data collected at a public hospital between 2013 and 2017. Current smoking status and disease activity were assessed at each visit; covariates included sex, race/ethnicity, age, obesity, and medication use. They used longitudinal targeted maximum likelihood estimation to estimate the causal effect of smoking on disease activity measures at 27 months, and compared results to conventional longitudinal methods. Findings included:

• Smoking was associated with an increase of 0.64 units in the patient global score compared to nonsmoking, and with 2.58 more swollen joints.
• While smoking was associated with a higher clinical disease activity score (2.11), the difference was not statistically significant.
• We found no association between smoking and physician global score, or C-reactive protein levels, and an inverse association between smoking and tender joint count.
• Analyses using conventional methods showed a null relationship for all outcomes.