Table 1 Characteristics of the 9 randomized controlled trials included in the analysis

Brasnyo et al.

Randomized placebo-controlled double-blinded parallel clinical trial

N = 19 patients with T2DM

4 weeks

N = 10;10 mg/d

N = 9; Placebo

Fasting plasma glucose, fasting insulin, HbA1c, HOMA-IR

Bhatt et al.

Open-label, randomized, controlled trial

N = 57 patients

with T2DM

3 months

N = 28;250 mg/d

N = 29; Empty-control

Fasting plasma glucose, HbA1c

Movahed et al.

Randomized placebo-controlled double-blinded parallel clinical trial

N = 64 patients

with T2DM

45 days

N = 33;1 g/d

N = 31; Placebo

Fasting plasma glucose, fasting insulin, HbA1c, HOMA-IR

Goh et al.

Randomized double-blind

N = 10 patients

with T2DM

12 weeks

N = 5;3 g/d

N = 5; Placebo

Fasting plasma glucose, fasting insulin, HbA1c, HOMA-IR

Tome-Carneiro et al.

Randomized placebo-controlled triple -blinded parallel clinical trial

N = 35 patients with T2DM

12 months

N = 13;

RSV-enriched grape extract (8 mg/d)

N = 22; Placebo

Fasting plasma glucose, HbA1c

Bashmakov et al.

Randomized placebo-controlled examiner -blinded parallel clinical trial

N = 24 patients with diabetic foot syndrome

60 days

N = 14; 50 mg/day

N = 10; Placebo

Fasting plasma glucose, fasting insulin

Thazhath et al.

Randomized, double-blind, crossover design

N = 14 patients with T2DM

5 weeks

N = 14;1 g/d

N = 14; Placebo

Fasting plasma glucose, HbA1c

Timmers et al.

Randomized double-blind crossover study

N = 17 patients with T2DM

30 days

N = 17;150 mg/d

N = 17; Placebo

Fasting plasma glucose, fasting insulin, HbA1c, HOMA-IR

Javid et al.

Randomized placebo-controlled double-blinded parallel clinical trial

N = 43 patients with T2DM

4 weeks

N = 21;480 mg/d

N = 22; Placebo

Fasting plasma glucose, fasting insulin, HOMA-IR