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 |