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Table 1 Characteristics of the included studies

From: Antioxidant effects of vitamins in type 2 diabetes: a meta-analysis of randomized controlled trials

Author, years Country Treatments N (sample) Duration (weeks) Main outcome measures Age (years) Male (%) Jadad score
Aghamohammadi, 2011 [25] Iran Vitamin B9 5 mg/day
Placebo
70 8 MDA; TAC; vitamin concentration 58.7 ± 7.2
55.6 ± 9.3
100 3
Anderson, 2006 [26] Wales Vitamin C 1000 mg/day
Placebo
20 6 TBARS 52.7 ± 6.9
53.6 ± 7.9
40.0 2
Antoniades, 2004 [27] Greece Vitamin C 2000 mg/day
Placebo
17 4 Vitamin concentration; TNF 48.5 ± 6.6
52.6 ± 5.9
58.8 1
Ble-Castillo, 2005 [28] United States Vitamin E 800 IU/day
Placebo
33 6 Blood glucose; HbA1c; MDA; GPx 51.3 ± 14.0
55.3 ± 11.6
0 2
Chen, 2006 [29] United States Vitamin C 800 mg/day
Placebo
32 4 Blood glucose; vitamin concentration 50.0 ± 1.0 40.6 3
Dalan, 2016 [30] Singapore Vitamin D 4000 IU/day
Vitamin D 2000 IU/day
Placebo
64 16 HbA1c; vitamin concentration; GSH 52.2 ± 8.2
54.8 ± 10.8
51.6 5
Gariballa, 2013 [31] Arab Emirates Vitamin complex (B, C, E)
Placebo
100 12 MDA; TNF; vitamin concentration 52 (44–56)
51 (42–60)
41.0 2
Haghighat, 2014 [32] Iran Vitamin E enriched canola oil 15 ml/day Placebo oil 45 8 CRP; NO 55.9 ± 5.9
55.2 ± 5.6
26.7 2
Hejazi, 2015 [33] Iran Vitamin E 400 IU/day
Placebo
27 6 Blood glucose; MDA 48.0 ± 6.3
46.6 ± 7.6
26.0 3
Jamalan, 2015 [34] Iran Vitamin C 1000 mg/day
Vitamin E 300 mg/day
80 4 Blood glucose; CRP; TNF 52.0 ± 8.0 100 2
Jorde, 2009 [35] Norway Vitamin D 40,000 IU/week
Placebo
32 24 Blood glucose; HbA1c; vitamin concentration 57.7 ± 9.7
54.8 ± 5.9
56.2 2
Lai, 2008 [36] Japan Chromium 1000 µg
Vitamin E 800 IU + chromium
Placebo
30 24 Blood glucose; HbA1c; SOD; CAT; TBARS; TAS; GPx 53.2 ± 2.0
51.5 ± 1.7
50.5 ± 1.9
46.7 3
Lu, 2005 [37] Sweden Vitamin C 3000 mg/day
Placebo
20 2 Blood glucose; HbA1c; IL-6 60.0 2
Mahmoudabadi, 2014 [38] Iran Eicosapentaenoic acid 500 mg/day
Vitamin C 200 mg/day
Vitamin C + eicosapentaenoic acid
Placebo
81 8 Blood glucose; HbA1c; vitamin concentration; SOD; MDA; TAC; GPx 54.0 ± 5.0
53.0 ± 5.0
52.0 ± 6.0
50.0 ± 8.0
100 2
Manzella, 2001 [39] Italy Vitamin E 600 mg/day
Placebo
50 16 HbA1c; TBARS 64.3 ± 4.7
65.1 ± 3.9
3
Mason, 2016 [40] Australia Vitamin C 1,000 mg/day
Placebo
13 16 Insulin; GSH; IL-6 59.4 ± 3.5 92.3 3
Mazloom, 2011 [41] Iran Vitamin C 1,000 mg/day
Placebo
27 6 Plasma lipid parameters; MDA 47.0 ± 8.9 46.6 ± 7.6 42.1 2
Mullan, 2002 [42] United Kingdom Vitamin C 500 mg/day
Placebo
30 4 Plasma lipid parameters; LDL-ox 61.0 ± 6.5
57.9 ± 6.6
73.4 3
Nikooyeh, 2011/2014 [43, 44] Iran Yogurt (150 mg calcium/250 mL)
Vitamin D fortified (150 mg calcium + 500 IU/250 mL)
Vitamin D fortified (250 mg of calcium + 500 IU/250 mL)
*Two bottles/day = 500 mL/day
90 12 Blood glucose; HbA1c; vitamin concentration; SOD; MDA 50.8 ± 6.6
51.4 ± 5.4
49.9 ± 6.2
38.9 2
Paolisso, 2000 [45] Italy Vitamin E 600 mg/day
Placebo
40 8 TBARS; vitamin concentration 58.3 ± 6.4
56.7 ± 5.3
52.5 3
Park, 2002 [46] Korea Vitamin E 200 mg/day
Placebo
98 8 Blood glucose; HbA1c; SOD; CAT 49.4 ± 9.3
49.5 ± 10.1
59.2 2
Reaven, 1995 [47] United States Vitamin E 1600 lU/day
Placebo
21 10 Blood glucose; HbA1c; LDL-ox 60.8 ± 6.1
61.8 ± 8.4
100 2
Shab-Bidar, 2015 [48] Iran Vitamin D fortified Yogurt 500 UI, 500 ml/day Yogurt 100 12 Blood glucose; HbA1c; SOD; MDA; TAC; GSH 52.6 ± 6.3
52.4 ± 8.4
43.0 3
Sugden 2007 [49] United Kingdom Vitamin D 100,000 UI/day Placebo 34 8 HbA1c; vitamin concentration; NO 64.9 ± 10.3
63.5 ± 9.5
52.9 5
Tessier, 2009 [50] Canada Vitamin C 500 mg/day
Vitamin C 1000 mg/day
Placebo
36 12 Plasma lipid parameters; GSH 72.0 ± 5.0
72.0 ± 4.0
71.0 ± 4.0
22.2 3
Vafa, 2015 [51] Iran Vitamin E enriched canola oil 15 ml/day Canola oil 45 8 Blood glucose; MDA; TAC 55.9 ± 5.9
55.2 ± 5.6
73.3 4
Winterbone, 2007 [52] United Kingdom Vitamin E 1200 IU α-tocopherol/day Placebo 19 4 Blood glucose; insulin; vitamin concentration 62.7 ± 1.8
61.9 ± 1.9
100 2
Witham, 2010 [53] United Kingdom Vitamin D3 100,000 IU/day
Vitamin D3 200,000 IU/day
Placebo
41 16 HbA1c; vitamin concentration; GSH 65.3 ± 11.1
63.3 ± 9.6
66.7 ± 9.7
67.2 3
Wu, 2007 [54] Australia Vitamin E α-tocopherol 500 mg/day
Vitamin E mixed tocopherols 500 mg/day
Placebo
55 6 SOD; GPx 64.0 ± 7.0
58.0 ± 4.0
62.0 ± 7.0
74.5 2
Yiu, 2013 [55] China Vitamin D 500 IU/day
Placebo
100 12 Blood glucose; HbA1c; SOD 65.8 ± 7.3
64.9 ± 8.9
50.0 4
  1. CAT catalase; CRP C-reactive protein; GPx glutathione peroxidase; GSH glutathione; HbA1c glycated hemoglobin; IL-6 interleukin; LDL-ox oxidized low-density lipoprotein; MDA malondialdehyde; NO nitric oxide; SOD superoxide dismutase; TAC total antioxidant capacity; TBARS thiobarbituric acid reactive substances; TNF tumor necrosis factor