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

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

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

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

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