Table 1. Basic characteristics of the included studies.

Study (year)	Country	Type of study	Experimental group			Control group
			Sample size	Age, years		Sample size	Age, years
Kurku, 2019	Turkey	Case-control	101	13.2±1.6		18	13.1±2.3
Malecki, 2020	Poland	Case-control	16	11.0±2.2		14	10.6±4.5
Kwon, 2020	Korea	Case-control	53	10.8±1.3		73	10.8±1.4
Thompson, 2017	USA	Case-control	20	13.2±3.1		10	13.8±2.1
Battal, 2018	Turkey	Case-control	32	13.3±2.8		24	12.8±3.3
Elkabany, 2020	Egypt	Case-control	31	9.98±3.39		49	8.3±2.73
Gupta, 2020	India	Case-control	62	10.52±2.2		38	9.32±2.4
Hattar, 2011	USA	Case-control	20	12.2±2		17	12.4±2.1
Hu W, 2017	China	Case-control	29	10.23±1.35		16	9.72±1.61
Liu F, 2022	China	Case-control	48	11.24±0.59		54	10.16±0.48
Antunes, 2013	Brazil	Clinical trial	34	13.6±1.1		34	13.6±1.0
Grønbæk H, 2012	Denmark	Clinical trial	117	12.3±1.3		117	12.1±1.3
Grønbæk H, 2012	Denmark	Clinical trial	71	13.4±1.3		117	12.1±1.3
Koot BG, 2011	The Netherlands	Clinical trial	144	14.1±2.3		144	14.1±2.3
Verduci, 2013	Italy	Clinical trial	46	6–14		46	6–14
Nier, 2018	Austria	Clinical trial	16	7.8±0.3		36	7.3±0.2

Data are shown as number, range, or mean ± standard deviation.