Table 4.

Outcomes by subgroups of patients.

ID	Author	Intervention	Subgroup	Outcome	Intervention	Comparison	P Value
1	Fowdar [28]	NAC	Dose	Exacerbation			NR
			(i) 600 mg/day		0.90 (0.82–1.00)
			(ii) <600 mg/day		0.83 (0.69–0.99)
			Use time				NR
			(i) >6 months		0.85 (0.74–0.98)
			(ii) <6 months		0.81 (0.54–1.21)
4	Tse [33]	NAC	High risk of exacerbation:	Time to exacerbation	258.2 (20.8)	203.6 (20.4)	0.02
			(i) Categories C-D
			Low risk of exacerbation:		272.1 (39.0)	337 (21.3)	0.34
			(i) Categories A-B
			High risk of exacerbation:	Amount of hospital admissions
			(i) Categories C-D
			(ii) 4 months		0.31 (0.1)	0.29 (0.09)	0.91
			(iii) 8 months		0.49 (0.14)	0.56 (0.13)	0.69
			(iv) 12 months		0.51 (0.14)	0.93 (0.18)	0.079
			Low risk of exacerbation:
			(i) Categories A-B
			(ii) 4 months		0.08 (0.08)	0.07 (0.07)	0.9
			(iii) 8 months		0.23 (0.12)	0.13 (0.13)	0.6
			(iv) 12 months		0.31 (0.17)	0.13 (0.13)	0.43
			FEV1:	Exacerbation frequency	1.21 (0.25)	2.3 (0.36)	0.16
			(i) <50%
10	Martineau [39]	Vitamin D	Levels	Time to moderate or severe exacerbation
			(i) <50 nmol/L		0.57		0.021
			(ii) 50 nmol/L		1.45		0.21
			(iii) or more
14	Jolliffe [40]	Vitamin D	Levels	Incidence of moderate or severe exacerbation
			(i) <25 nmol/L			0.55 (CI 95%: 0.36; 0.84)∗∗	0.006
			(ii) ≥25 nmol/L			1.04 (CI 95%: 0.85; 1.27)∗∗	0.71
			Levels	Incidence of moderate or severe exacerbation
			(i) 25.0–49.9 nmol/L			1.00 (CI 95%: 0.77; 1.31)∗∗	0.97
			(ii) 50.0–74.9 nmol/L			1.06 (CI 95%: 0.70; 1.61)∗∗	0.78
			(iii) ≥75 nmol/L			1.17 (CI 95%: 0.73; 1.87)∗∗	0.52

NAC : N-Acetylcysteine; ^∗ relative risk (95% CI); ^∗∗ aIRR: adjusted incidence rate ratio.