Table 1.

Characteristics of included studies.

Study	Country	Study design	Vitamin D supplementation group			Non-vitamin D supplementation group
			No.	Age	Sex, male	No.	Age	Sex, male
Alcala-Diaz et al., 2021	Spain	Retrospective, multicenter cohort study	79	69 ± 15	42 (53.2%)	458	67 ± 16	275 (60.0%)
Annweiler et al., 2020	France	Quasi-experimental study	16	58.4 ± 7	11 (68.8%)	32	64.1 ± 7.9	19 (59.4%)
Castillo et al., 2020	Spain	Parallel pilot randomized open label, double-masked clinical study	50	56.8 ± 14.2	27 (54.0%)	26	55.8 ± 15	18 (69.2%)
Cereda et al., 2021	Italy	Cohort observational study	38	68.8 ± 10.6	16 (42.1%)	286	70.5 ± 13.1	141 (49.3%)
Hernández et al., 2020	Spain	Retrospective case–control study	19	63.5 ± 4.6	7 (36.8%)	197	59.9 ± 3.8	123 (62.4%)
Murai et al., 2021	Brazil	Multicenter, double-blind, randomized, placebo-controlled study	120	53.1 ± 10.8	70 (58.3%)	120	52.8 ± 9.4	65 (54.2%)
Nogues et al., 2021	Spain	Observational cohort study	447	61.8 ± 15.5	264 (59.1%)	391	62.4 ± 17.2	231 (59.1%)
Tan et al., 2020	Singapore	Cohort observational study	17	85.8 ± 1.5	11 (64.7%)	26	88 ± 2.3	15 (57.7%)