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Table 2 Relative risk of rheumatoid arthritis by smoking status, intensity, duration and pack-years of cigarette smoking among (ever smokers) in the Swedish Mammography Cohort, 2003 to 2010

From: Cigarette smoking and smoking cessation in relation to risk of rheumatoid arthritis in women

  Person-years1 Cases, number1 Age-adjusted relative risk 95% CI Multivariable relative risk3 95% CI
Smoking status
Never 137,162 79 1.00 (ref)   1.00 (ref)  
Former 59,466 60 1.65 1.17, 2.32 1.68 1.19, 2.38
Current 58,368 80 2.24 1.63, 3.07 2.20 1.58, 3.04
Intensity, cigarettes/day 2
Never 137,162 79 1.00 (ref)   1.00 (ref)  
1 to 7 34,032 47 2.23 1.54, 3.21 2.31 1.59, 3.36
8 to 14 32,010 45 2.23 1.54, 3.24 2.19 1.50, 3.21
> 14 (median 18) 35,586 33 1.45 0.96, 2.20 1.46 0.96, 2.23
Duration, years
Never 137,162 79 1.00 (ref)   1.00 (ref)  
1 to 25 39,634 39 1.55 1.05, 2.30 1.60 1.07, 2.38
25 to 40 53,219 68 2.01 1.43, 2.83 1.99 1.40, 2.82
> 40 (median 45) 23,528 32 2.36 1.55, 3.58 2.33 1.52, 3.57
Pack-years
Never 137,162 79 1.00 (ref)   1.00 (ref)  
1 to 5 27,534 28 1.67 1.08, 2.58 1.72 1.11, 2.67
6 to 13 30,613 40 2.13 1.45, 3.13 2.19 1.48, 3.25
14 to 22 36,990 35 2.10 1.40, 3.14 2.04 1.35, 3.09
> 22 (median 28) 27,628 31 1.81 1.19, 2.76 1.82 1.19, 2.79
  1. 1Numbers do not add up to the totals because of missing values; 2lifetime average among ever smokers; 3Adjusted for age (continuous), menopause status (pre- or postmenopausal), parity (0, 1, 2, or ≥ 3 children), alcohol use (none, former, or current), educational level (lower than high school, high school, or university), and body mass index (quartiles). Intensity, duration and pack-years were not mutually adjusted [35]. Ref, reference group.