Table 1.

Characteristics of included studies.

Study	Sample size	Design	Taking metformin		Not taking metformin
			n (%)	Age (years)	n (%)	Age (years)
Bramante et al., 2020	6256	Retrospective cohort	2333 (37.3%)	73 ± 10.3	3923 (62.7%)	75.6 ± 12.5
Chen et al., 2020	120	Retrospective cohort	43 (35.8%)	62.3 ± 9.6	77 (64.2%)	65.8 ± 11.4
Crouse et al., 2020	220	Retrospective cohort	76 (34.5%)	N/A	144 (65.5%)	N/A
Luo et al., 2020	283	Retrospective cohort	104 (36.7%)	62.3 ± 9.2	179 (63.3%)	64.5 ± 10
Wang et al., 2020	58	Retrospective cohort	9 (15.5%)	N/A	49 (84.5%)	N/A