Associations of cigarette smoking with rheumatoid arthritis in African Americans.
OBJECTIVE
To examine the associations of cigarette smoking with rheumatoid arthritis (RA) in African Americans, and to determine whether this association is impacted by the HLA-DRB1 shared epitope (SE).


METHODS
Smoking status, cumulative smoking exposure, and SE status were determined in African American patients with RA and African American healthy controls. Associations of smoking with RA were examined using age- and sex-adjusted logistic regression analyses. Additive and multiplicative SE-smoking interactions were examined.


RESULTS
After adjustment for age and sex, ever smoking (odds ratio [OR] 1.45, 95% confidence interval [95% CI] 1.07, 1.97) and current smoking (OR 1.56, 95% CI 1.07, 2.26), relative to never smoking, were more common in African American patients with RA (n = 605) than in controls (n = 255). The association of smoking with RA was limited to those with a cumulative exposure exceeding 10 pack-years, associations that were evident both in autoantibody-positive and in autoantibody-negative disease. There was evidence of a significant additive interaction between SE status and heavy smoking (≥10 pack-years) in relation to RA risk (attributable proportion [AP] due to interaction 0.58, P = 0.007), with similar results for the additive interaction between SE status and ever smoking (AP 0.47, P = 0.006). There was no evidence of multiplicative interactions.


CONCLUSIONS
Among African Americans, cigarette smoking is associated not only with the risk of autoantibody-positive RA but also with the risk of autoantibody-negative disease. The risk of RA attributable to smoking is limited to African Americans with more than 10 pack-years of exposure and is more pronounced among individuals positive for the HLA-DRB1 SE.
Mikuls
Ted R
TR
University of Nebraska Medical Center and Omaha Veterans Affairs Medical Center, Omaha, USA. tmikuls@unmc.edu
Sayles
Harlan
H
Yu
Fang
F
Levan
Tricia
T
Gould
Karen A
KA
Thiele
Geoffrey M
GM
Conn
Doyt L
DL
Jonas
Beth L
BL
Callahan
Leigh F
LF
Smith
Edwin
E
Brasington
Richard
R
Moreland
Larry W
LW
Reynolds
Richard J
RJ
Bridges
S Louis
SL
D000328:Adult; D001741:Black or African American / Q000235:genetics; D000368:Aged; D000483:Alleles; D001172:Arthritis, Rheumatoid / Q000453:epidemiology* / Q000235:genetics / Q000276:immunology*; D001323:Autoantibodies / Q000097:blood; D016022:Case-Control Studies; D000939:Epitopes / Q000235:genetics; D005260:Female; D006684:HLA-DR Antigens / Q000097:blood / Q000235:genetics; D059811:HLA-DRB1 Chains; D006801:Humans; D016015:Logistic Models; D008297:Male; D008875:Middle Aged; D012307:Risk Factors; D012907:Smoking / Q000009:adverse effects*; D013997:Time Factors
D001323:Autoantibodies; D000939:Epitopes; D006684:HLA-DR Antigens; D059811:HLA-DRB1 Chains