Table 1.

Characteristics of the included studies on the prevalence of xerostomia among e-cigarette or combustible tobacco users

Authors Year	Study design	Country	Sample size (Cases)	Prevalence of xerostomia	Age (years) Mean ± SD	Gender	The outcome(s) reported	Definition of smokers
Dyasanoor et al.25 2014	Case-control	India	Combustible tobacco: 60	37.00%	36.98 ± 11.52	NR	Modified Schirmer test and PROs	Daily smoking for six months
Ullah et al.26 2015	Cross-sectional	Pakistan	E-cigarettes/combustible tobacco: 250	10.40%	21.66 ± 2.07	100% male	PROs	NR
King et al.8 2019	Cross-sectional	USA	E-cigarettes: 1624	31.00%	18–24: 25.5% 25–44: 48.2% ≥45: 26.3%	56.1% male 43.9% female	PROs	Ever e-cigarette users
Kumar et al.27 2019	Cross-sectional	Pakistan	E-cigarettes/combustible tobacco: 377	15.12%	aged 28–64	90.45% male 9.55% female	PROs	NR
Lewek et al.28 2019	Cross-sectional	Poland	E-cigarettes: 1032	8.30%	25.9 ± 11.1	85.6% male 14.4% female	PROs	Ever smoked or currently smoking
Gallus et al.29 2020	Cross-sectional	Italy	E-cigarettes: 395	25.40%	51.3 ± 13.0	53.6% male 46.4% female	PROs	Current and ex-smokers
Habib et al.21 2020	Cross-sectional	Saudi Arabia	E-cigarettes: 49	24.49%	aged 18–23	NR	PROs	Ever smoked or currently smoking
Nazir et al.30 2020	Cross-sectional	Saudi Arabia	E-cigarettes/combustible tobacco: 199	31.20%	<16	NR	PROs	NR
King et al.9 2020	Cross-sectional	USA	E-cigarettes/combustible tobacco: 141	14.18%	16	60.2% male 39.8% female	PROs	Past 30-day smoking
Chaffee et al.20 2021	Cross-sectional	USA	E-cigarettes: 976	Occasionally: 54.2% Frequently: 5.4% Always: 0.4%	<18	36.6% male 60.9% female 2.6% other	PROs	Past 30-day smoking
Peng et al.31 2021	Case-control	China	E-cigarettes: 85 Combustible tobacco: 92	E-cigarettes: 35.29% Combustible tobacco: 8.69%	E-cigarettes: 21.87 ± 1.79 Combustible tobacco: 21.66 ± 2.36	E-cigarettes: 65.88% male 34.12% female Combustible tobacco: 58.7% male 41.3% female	PROs	History of smoking ≥1 year
Kabbash et al.32 2022	Cross-sectional	Egypt	E-cigarettes: 39	48%	NR	NR	PROs	NR
Tantawi et al.33 2022	Cross-sectional	Saudi Arabia	E-cigarettes/combustible tobacco: 657	18.60%	18–23	NR	PROs	NR
Alhajj et al.19 2022	Cross-sectional	11 countries: Croatia, Iraq, Jordan, Kuwait, Lebanon, Malaysia, Nigeria, Saudi Arabia, South Africa, Turkey, and Yemen	E-cigarettes: 255 Combustible tobacco: 596	E-cigarettes: 31.76% Combustible tobacco: 28.86%	E-cigarettes: ≤20 : 72 >20 : 183 Combustible tobacco: ≤20 : 178 >20 : 418	E-cigarettes: 65.88% male 30.98% female Combustible tobacco: 57.72% male 42.28% female	PROs	NR

NR: not reported. PROs: patient-reported outcomes.