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Table 4 Multivariate analyses showing lifetime cigarette consumption variables associated with IL-6 serum levels (N = 527)

From: Predictors of circulating INTERLEUKIN-6 levels in head and neck cancer patients

Factors Categories N (%) Median IL–6 (ng/L) (IQR) Adjusted β* (SE) P-value
Duration of cigarette smoking (years) Never smokers 30 (5.7) 2.2 (1.0–3.3) Reference  
Ever smokers     
<  32 120 (22.8) 2.6 (1.5–3.7) 0.36 (0.13) 0.008
≥ 32 < 40 116 (22.0) 3.0 (2.2–4.6) 0.48 (0.13) 0.0004
≥ 40 < 47 131 (24.9) 3.3 (2.5–4.3) 0.50 (0.13) 0.0001
≥ 47 130 (24.7) 3.7 (2.7–5.4) 0.57 (0.13) <  0.0001
   P-trend < 0.0001
   P-trend 0.03 (excluding never smokers)
Average number of cigarettes per day Never smokers 30 (5.7) 2.2 (1.0–3.3) Reference  
Ever smokers     
<  20 119 (22.6) 2.9 (2.2–4.3) 0.40 (0.13) 0.003
≥ 20 < 25 70 (13.3) 3.0 (2.1–4.3) 0.52 (0.14) 0.0003
≥ 25 < 30 167 (31.7) 3.3 (2.4–4.6) 0.54 (0.13) <  0.0001
≥ 30 141 (26.8) 3.2 (2.3–4.9) 0.49 (0.13) 0.0002
   P-trend 0.003
   P-trend 0.25 (excluding never smokers)
Pack-years of cigarettes Never smokers 30 (5.7) 2.2 (1.0–3.3) Reference  
Ever smokers     
<  32 123 (23.3) 2.7 (2.0–4.0) 0.35 (0.13) 0.008
≥ 32 < 47 125 (23.7) 3.0 (2.3–4.3) 0.52 (0.13) <  0.0001
≥ 47 < 67 123 (23.3) 3.3 (2.4–4.7) 0.55 (0.13) <  0.0001
≥ 67 126 (23.9) 3.5 (2.5–5.2) 0.52 (0.13) <  0.0001
   P-trend 0.0002
   P-trend 0.03 (excluding never smokers)
Years since cigarette smoking cessation ≥ 10 107 (20.3) 2.8 (2.0–4.3) Reference  
≥ 1 <  10 60 (11.4) 3.2 (2.4–4.9) 0.21 (0.08) 0.010
<  1 201 (38.1) 3.0 (2.3–4.4) 0.20 (0.11) 0.060
   P-trend 0.02
  1. β is the parameter estimate associated with the increment of one unit of ln IL-6; IQR Interquartile range, SE Standard error. * β ajusted for all factors in Table 3, except for tobacco consumption