Table 1.

Demographic characteristics of the studies included

Study/year	Location	Treatment arm (n)	Sex (male/female)	Duration of follow-up (months)	Age (years)	Duration of diabetes (years)	BMI (kg/m2)	HbA1c (%)	MMSE score (0[worst]-30[best])
Isik,2017 [36]	Turkey	sita: 43 met: 69 insu: 22	sita: 47/57 met + insu: 35/66	6	77.05 ± 8.50 77.12 ± 7.87 77.61 ± 9.40	13.38 ± 8.5 12.95 ± 4.99 15.66 ± 6.97	28.86 ± 4.21 29.78 ± 4.71 28.33 ± 5.24	7.29 ± 1.49 6.90 ± 1.29 7.50 ± 1.19	22.73 ± 5.64 23.55 ± 5.38 23.50 ± 4.03
Borzi,2019 [37]	Italy	vild + met: 30 met: 30	vild + met: 14/16 met:13/17	6	77.67 ± 8.23 75.46 ± 7.89	16.72 ± 5.81 15.49 ± 6.83	29.55 ± 5.92 28.48 ± 6.69	8.02 ± 1.27 7.09 ± 1.21	21.00 ± 1.41 20.77 ± 1.22
Biessels,2019 [38]	Netherland	lina: 800 pla: 745	lina: 503/297 pla: 501/244	30	67.8 ± 8.3 67.7 ± 8.0	14.8 ± 9.2 15.4 ± 9.4	32.5 ± 5.1 32.8 ± 5.3	7.8 ± 0.9 7.8 ± 0.9	28.3 ± 1.7 28.2 ± 1.8
Xue, 2020 [39]	China	dpp4i: 30 sulfo: 30	dpp4i: 17/13 sulfo: 14/16	6	68.5 ± 7.1 67.4 ± 5.9	8.17 ± 3.05 8.97 ± 2.65	25.71 ± 3.76 25.59 ± 4.28	8.56 ± 1.25 8.86 ± 3.17	25.42 ± 1.22 25.37 ± 1.16
Bulut,2020 [40]	Turkey	vild: 43 pla: 35 con: 52	vild: 18/25 pla + con: 20/32	6	74.4 ± 7.9 79.7 ± 4.8 74.2 ± 7.8	18.4 ± 9.9 11.3 ± 7.6 16.4 ± 10.6	29.3 ± 5.1 28.5 ± 4.2 29.1 ± 4.5	7.63 ± 1.37 6.01 ± 0.49 7.12 ± 1.57	21.81 ± 6.16 24.94 ± 4.31 26.04 ± 5.04
Biessels,2021 [41]	Netherland	lina: 1618 glim: 1545	lina: 1002/616 glim: 958/587	40	64.4 ± 9.1 64.4 ± 9.3	7.7 ± 6.2 7.4 ± 5.9	30.8 ± 5.0 30.7 ± 4.9	7.1 ± 0.5 7.1 ± 0.6	28.5 ± 1.7 28.5 ± 1.7

Values are expressed as the mean ± SD. Abbreviations: n: number of participants per group; HbA1c: glycated haemoglobin; sita: sitagliptin; vild: vildagliptin; pla: placebo; con: conventional treatment; met: metformin; insu: insulin; sulfo: sulfonylurea; lina: linagliptin; gli: glimepiride; MMSE: Mini-Mental State Examination