Table 2. Subgroup analyses of the association between smoking and DN.

Subgroup	n	Summary hazard ratio		Heterogeneity		Subgroup differences
		HR (95%CI)	P-value	I2 (%)	P-value	Q	P-value
Total	18	1.07 (1.01–1.133)	0.01	68.8	<0.01	—	—
Sex
Predominance of males	7	1.10 (0.53–2.27)	0.08	80.5	<0.001	1.38	0.24
Balanced	11	1.20 (0.96–1.50)	0.11	46	0.05
Follow-up
≤5 years	7	1.2(0.85–1.70)	0.29	74.4	<0.001	0.61	0.43
>5 years	11	1.05 (1.00–1.10)	0.03	66.6	<0.001
Loss to follow-up
≤30%	16	1.07(1.01–1.13)	0.02	71.1	<0.001	0.05	0.83
>30%	2	1.17(0.52–2.63)	0.71	54.6	0.14
Criteria
Proteinuria	17	1.07 (1.01–1.13)	0.01	70.7	<0.001	0.01	0.94
GFR	1	1.05 (0.63–1.75)	0.85	—	—
Smoking
Current	3	1.69 (0.79–3.64)	0.17	90.8	<0.001	3.12	0.21
Former	3	1.04(1.03–1.05)	<0.001	0	0.59
Total	12	1.17 (0.97–1.41)	0.1	56.5	0.01
NOS
9 score	12	1.05 (1.00–1.09)	0.04	65.9	<0.001	0.85	0.36
8 score	6	1.30 (0.81–1.81)	0.26	68.6	0.01
Adjusted
Yes	11	1.05(0.00–1.11)	0.04	73.7	<0.001	0.28	0.6
No	7	1.14 (0.85–1.53)	0.38	56.8	0.03
Effect size
HR	8	1.03(1.00–1.07)	0.03	57.1	0.02	0.75	0.69
OR	4	1.23(0.76–1.99)	0.4	85.7	<0.001
RR	6	1.13 (0.81–1.81)	0.46	63.9	0.02
Sample size
≤500	4	1.54 (0.92–2.60)	0.1	72.4	0.01	2.25	0.13
>500	14	1.03(1.00–1.08)	0.06	55.8	0.006
Geographic location
Americas	3	1.42(0.62–3.27)	0.41	84.2	0.002	3.58	0.17
Asia and Oceania	2	1.51(1.00–2.27)	0.05	5.1	0.3
Europe	13	1.04 (1.00–1.09)	0.05	60.6	0.002
Type
T1DM	11	1.05(1.00–1.11)	0.05	75.3	<0.001	0.49	0.48
T2DM	7	1.15(0.90–1.47)	0.25	50.2	0.06