Arthritis Research & Therapy
Vol 5 No 3
Krishnan et al.
Research article
Eswar Krishnan1, Tuulikki Sokka2,3, Pekka Hannonen2
1Department 2Jyvskyl
Open Access
Smoking–gender interaction and risk for rheumatoid arthritis
of Medicine, Stanford University, Palo Alto, California, USA Central Hospital, Jyvskyl, Finland 3Vanderbilt University, Nashville, Tennessee, USA Corresponding author: Eswar Krishnan (e-mail: eswar_krishnan@hotmail.com) Received: 27 Nov 2002 Revisions requested: 10 Jan 2003 Revisions received: 20 Jan 2003 Accepted: 21 Feb 2003 Published: 24 Mar 2003 Arthritis Res Ther 2003, 5:R158-R162 (DOI 10.1186/ar750) 2003 Krishnan et al., licensee BioMed Central Ltd (Print ISSN 1478-6354; Online ISSN 1478-6362). This is an Open Access article: verbatim copying and redistribution of this article are permitted in all media for any purpose, provided this notice is preserved along with the article's original URL.
Abstract
The present case–control study was conducted to investigate the relationship between smoking and rheumatoid arthritis, and to investigate formally the interaction between sex, smoking, and risk for developing rheumatoid arthritis. The study was performed in the Central District of Finland. Cases were patients with rheumatoid arthritis and the control group was a random sample of the general population. Logistic regression models were used to evaluate the effect of smoking on risk for rheumatoid arthritis, after adjusting for the effects of age, education, body mass index, and indices of general health and pain. Overall, 1095 patients with rheumatoid arthritis and 1530 control individuals were included. Patients were older, less well educated, more disabled, and had poorer levels of general
Keywords: etiology, interaction, risk, rheumatoid arthritis, sex, smoking
health as compared with control individuals (all P < 0.01). Preliminary analyses revealed the presence of substantial statistical interaction between smoking and sex (P < 0.001). In separate multivariable analyses, past history of smoking was associated with increased risk for rheumatoid arthritis overall in men (odds ratio 2.0, 95% confidence interval 1.2–3.2) but not in women. Among men, this effect was seen only for rheumatoid factor-positive rheumatoid arthritis. There were significant interactions between smoking and age among women but not among men. We conclude that sex is a biologic effect modifier in the association between smoking and rheumatoid arthritis. The role of menopause in the etiology of rheumatoid arthritis merits further research.

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