TABLE 1

Association of asthma and smoking status on pre- and post-bronchodilator spirometry at 10, 18 and 26 years

	10 years				18 years				26 years
	Nonsmokers without asthma	Nonsmokers with asthma	Difference	p-value	Nonsmokers without asthma	Nonsmokers with asthma	Difference	p-value	Nonsmokers without asthma	Nonsmokers with asthma	Difference	p-value
*Nonsmokers with asthma versus* nonsmokers without asthma**
Subjects n	422	80			417	74			313	62
FEV₁ L	2.04	2.00	−0.05 (−0.16–0.04)	0.273	4.05	3.77	−0.27 (−0.37–−0.17)	<0.001	4.02	3.75	−0.28 (−0.41–−0.14)	<0.001
Post-bronchodilator FEV₁ L					4.18	4.02	−0.16 (−0.30–−0.02)	0.023	4.16	4.02	−0.13 (−0.28–0.02)	0.078
FVC L	2.30	2.31	0.00 (−0.12–0.12)	0.984	4.60	4.46	−0.14 (−0.26–0.02)	0.024	4.96	4.90	−0.06 (−0.22–0.11)	0.497
Post-bronchodilator FVC L					4.63	4.56	−0.08 (−0.24–0.08)	0.322	4.92	4.87	−0.06 (−0.22–0.11)	0.510
FEV₁/FVC	0.89	0.87	−0.03 (−0.04–−0.01)	<0.001	0.88	0.85	−0.03 (−0.05–−0.02)	<0.001	0.81	0.77	−0.04 (−0.06–−0.03)	<0.001
Post-bronchodilator FEV₁/FVC					0.91	0.89	−0.02 (−0.03–−0.01)	0.021	0.85	0.83	−0.02 (−0.03–0.00)	0.052
FEF_25–75% L	2.49	2.25	−0.25 (−0.440–−0.059)	0.010	4.56	4.00	−0.56 (−0.75–−0.36)	<0.001	4.05	3.31	−0.75 (−1.01–−0.49)	<0.001
Post-bronchodilator FEF_25–75% L					4.98	4.56	−0.42 (−0.67–−0.17)	0.001	4.64	4.24	−0.40 (−0.67–−0.13)	0.004
*Smokers without asthma versus* nonsmokers without asthma**
Subjects n	422	203			417	176			313	142
FEV₁ L	2.04	2.03	−0.02 (−0.09–0.05)	0.526	4.05	4.00	−0.05 (−0.12–0.02)	0.149	4.02	3.93	−0.10 (−0.19–0.00)	0.052
Post-bronchodilator FEV₁ L					4.18	4.18	0.00 (−0.10–0.10)	0.975	4.16	4.08	−0.08 (−0.18–0.02)	0.131
FVC L	2.30	2.28	−0.03 (−0.11–0.05)	0.506	4.60	4.59	−0.02 (−0.10–0.06)	0.617	4.96	4.97	0.01 (−0.10–0.12)	0.863
Post-bronchodilator FVC L					4.63	4.66	0.03 (−0.09–0.14)	0.643	4.92	4.93	0.00 (−0.11–0.12)	0.970
FEV₁/FVC	0.89	0.89	0.00 (−0.01–0.01)	0.645	0.88	0.87	−0.01 (−0.02–0.00)	0.075	0.81	0.80	−0.02 (−0.03–−0.01)	0.002
Post-bronchodilator FEV₁/FVC					0.91	0.90	−0.01 (−0.02–0.01)	0.359	0.85	0.83	−0.02 (−0.03–−0.01)	0.005
FEF_25–75% L	2.49	2.44	−0.05 (−0.18–0.08)	0.465	4.56	4.47	−0.10 (−0.23–0.04)	0.157	4.05	3.76	−0.31 (−0.49–−0.13)	0.001
Post-bronchodilator FEF_25–75% L					4.98	4.90	−0.09 (−0.27–0.08)	0.299	4.64	4.38	−0.27 (−0.46–−0.09)	0.004
*Smokers with asthma versus* nonsmokers without asthma**
Subjects n	422	40			417	32			313	30
FEV₁ L	2.04	2.01	−0.04 (−0.18–0.08)	0.469	4.05	3.73	−0.33 (−0.48–−0.19)	<0.001	4.02	3.74	−0.30 (−0.49–−0.12)	0.001
Post-bronchodilator FEV₁ L					4.18	4.03	−0.17 (−0.36–0.02)	0.080	4.16	3.95	−0.23 (−0.42–−0.03)	0.021
FVC L	2.30	2.32	0.01 (−0.14–0.17)	0.858	4.60	4.60	−0.01 (−0.18–0.16)	0.894	4.96	4.96	0.00 (−0.22–0.22)	0.99
Post-bronchodilator FVC L					4.63	4.72	0.08 (−0.14–0.30)	0.483	4.92	5.03	0.11 (−0.12–0.33)	0.351
FEV₁/FVC	0.89	0.86	−0.03 (−0.05–−0.01)	0.002	0.88	0.82	−0.06 (−0.09–−0.04)	<0.001	0.81	0.76	−0.06 (−0.08–−0.04)	<0.001
Post-bronchodilator FEV₁/FVC					0.91	0.86	−0.05 (−0.07–−0.03)	<0.001	0.85	0.79	−0.06 (−0.08–−0.04)	<0.001
FEF_25–75% L	2.49	2.22	−0.28 (−0.54–−0.03)	0.027	4.56	3.66	−0.93 (−1.21–−0.65)	<0.001	4.05	3.15	−0.93 (−1.28–−0.59)	<0.001
Post-bronchodilator FEF_25–75% L					4.98	4.30	−0.74 (−1.09–−0.38)	<0.001	4.64	3.67	−1.00 (−1.36–−0.65)	<0.001
*Smokers with asthma versus* nonsmokers with asthma**
Subjects n	80	40			74	32			62	30
FEV₁ L	2.00	2.01	0.01 (−0.15–0.17)	0.930	3.77	3.73	−0.06 (−0.23–0.11)	0.483	3.75	3.74	−0.03 (−0.24–0.19)	0.813
Post-bronchodilator FEV₁ L					4.02	4.03	−0.01 (−0.23–0.21)	0.925	4.02	3.95	−0.09 (−0.32–0.13)	0.414
FVC L	2.31	2.32	0.02 (−0.17–0.20)	0.869	4.46	4.60	0.13 (−0.07–0.32)	0.215	4.90	4.96	0.06 (−0.20–0.31)	0.676
Post-bronchodilator FVC L					4.56	4.72	0.16 (−0.10–0.42)	0.225	4.87	5.03	0.16 (−0.10–0.43)	0.227
FEV₁/FVC	0.87	0.86	−0.01 (−0.03–0.02)	0.690	0.85	0.82	−0.03 (−0.06–0.00)	0.022	0.77	0.76	−0.02 (−0.04–0.01)	0.312
Post-bronchodilator FEV₁/FVC					0.89	0.86	−0.03 (−0.06–−0.01)	0.013	0.83	0.79	−0.04 (−0.07–−0.02)	0.001
FEF_25–75% L	2.25	2.22	−0.04 (−0.33–0.26)	0.817	4.00	3.66	−0.36 (−0.70–−0.05)	0.022	3.31	3.15	−0.17 (−0.590–0.225)	0.379
Post-bronchodilator FEF_25–75% L					4.56	4.30	−0.30 (−0.73–0.09)	0.130	4.24	3.67	−0.59 (−1.03–−0.19)	0.005
*Smokers with asthma versus* smokers without asthma**
Subjects n	203	40			176	32			142	30
FEV₁ L	2.03	2.01	−0.03 (−0.17–0.11)	0.704	4.00	3.73	−0.28 (−0.43–−0.13)	<0.001	3.93	3.74	−0.21 (−0.40–−0.01)	0.036
Post-bronchodilator FEV₁ L					4.18	4.03	−0.17 (−0.37–0.03)	0.098	4.08	3.95	−0.15 (−0.35–0.06)	0.153
FVC L	2.28	2.32	0.04 (−0.12–0.20)	0.618	4,59	4,60	0.01 (−0.17–0.19)	0.916	4.97	4.96	−0.01 (−0.24–0.22)	0.922
Post-bronchodilator FVC L					4.66	4.71	0.05 (−0.18–0.29)	0.658	4.93	5.03	0.10 (−0.13–0.34)	0.386
FEV₁/FVC	0.89	0.86	−0.03 (−0.05–−0.009)	0.006	0.87	0.82	−0.05 (−0.08–−0.03)	<0.001	0.80	0.76	−0.04 (−0.064–−0.013)	0.003
Post-bronchodilator FEV₁/FVC					0.90	0.86	−0.05 (−0.07–−0.02)	<0.001	0.83	0.79	−0.04 (−0.07–−0.02)	<0.001
FEF_25–75% L	2.44	2.22	−0.24 (0.50–0.03)	0.081	4.47	3.66	−0.84 (−1.13–−0.54)	<0.001	3.76	3.15	−0.62 (−0.99–−0.26)	0.001
Post-bronchodilator FEF_25–75% L					4.90	4.30	−0.64 (−1.01–−0.27)	0.001	4.38	3.67	−0.73 (−1.10–−0.36)	<0.001

Data are the mean spirometry parameters pre- and post-salbutamol with mean difference (95% CI) and associated p-value from longitudinal modelling. Results are divided according to asthma and smoking status at 26 years: nonsmokers without asthma, nonsmokers with asthma, smokers without asthma and smokers with asthma. Results for 10 and 18 years from generalised estimating equations longitudinal model for 10–18 years adjusted for sex; results for 26 years from a similar model for 18–26 years data. Differences may not add up due to rounding. Post-bronchodilator parameters only available at 18 and 26 years. Data from 10 to 18 years represents results available for 699 participants with data at each point; for the 18–26 years analysis, results available for 454 participants; post-bronchodilator results available for 428 participants. FEV₁: forced expiratory volume in 1 s; FVC: forced vital capacity; FEF_25–75%: forced expiratory flow at 25–75% of FVC.