Table 3.

Effect of body mass index on COPD development stratified by smoking status in model 4.

Smoking status	BMI (kg/m2)	n	COPD	Duration (PY)	IR (per 1000 PY)	Adjusted hazard ratio (95% confidence interval)
Non	< 18.5	373,492	733	3,097,951.84	0.2366	1.238 (1.143, 1.342)
	18.5–22.9	1,898,831	3,328	15,783,062.79	0.2109	1 (Ref.)
	23.0–24.9	560,928	1,062	4,672,641.79	0.2273	1.002 (0.934, 1.075)
	25.0–29.9	545,375	1,218	4,538,107.85	0.2684	1.117 (1.042, 1.196)
	≥ 30.0	106,463	286	871,630.26	0.3281	1.300 (1.147, 1.473)
Former	< 18.5	19,826	75	164,084.37	0.4571	1.739 (1.366, 2.214)
	18.5–22.9	228,044	566	1,926,575.18	0.2938	1 (Ref.)
	23.0–24.9	158,092	372	1,349,430.21	0.2757	0.873 (0.765, 0.995)
	25.0–29.9	195,218	434	1,660,678.75	0.2613	0.779 (0.687, 0.884)
	≥ 30.0	31,180	88	259,978.92	0.3385	0.971 (0.773, 1.218)
Current	< 18.5	86,147	368	712,860.63	0.5162	1.708 (1.529, 1.908)
	18.5–22.9	823,800	2,205	6,904,363.16	0.3194	1 (Ref.)
	23.0–24.9	489,875	1,138	4,128,554.96	0.2756	0.808 (0.752, 0.868)
	25.0–29.9	657,152	1,524	5,527,492.37	0.2757	0.766 (0.716, 0.819)
	≥ 30.0	130,346	387	1,077,722.96	0.3591	0.975 (0.870, 1.093)

Model 4: adjusted for age, sex, smoking, alcohol consumption, regular exercise, asthma, pneumonia, and metabolic syndrome.

BMI: body mass index; COPD: chronic obstructive pulmonary disease; PY: person-year; IR: incidence rate; Ref.: reference.