Table 1.
Data extracted from eligible observational studies in qualitative systematic review
| Study | Design | Subjects | Sex/age years | Outcome measures | Significant Results/Odds Ratios | Quality score |
|---|---|---|---|---|---|---|
| Sinclair et al. 1992 [18] | Cross-sectional | Total 90 (40 healthy, 25 T2DM with DR, 25 T2DM without DR) | Both/> 60 | Fundoscopy, measurements of TBA reactivity, GSH, AA, DHA, TGs, TChol, glucose, fructosamine |
-↓AA in DR vs. Others (P < 0.01) -↑DHA/AA in DR vs. Without DR (P < 0.001), or controls (P < 0.0001) -Negative correlation between AA and fructosamine in DR (r = −0.46, P < 0.05) |
2 |
| Gurler et al. 2000 [19] | Case-control |
Total 85 (26 healthy, 34 T2DM, 25 T2DM + DR) |
Both/42–69 | MDA-like metabolite, erythrocyte GPx, SOD, VC, HbA1C |
-↓VC in T2DM + DR -↑MDA-like metabolite in T2DM + DR -↑HbA1C in T2DM with/without DR |
3 |
| Gupta et al. 2005 [20] | Case-control |
Total 132 (50 healthy, 40 T2DM without DR, 42 T2DM+ DR) |
Both/38–54 | MDA, SOD, GPx, VC, BG, HbA1C |
-↓Serum level VC in T2DM with/without DR vs. healthy -↑Serum level MDA, SOD, GPx in T2DM with/without DR vs. Healthy -↓SOD, VC with DR progression -Positive correlation between MDA, HbA1C and duration of DR |
4 |
| Yildirm et al. 2007 [21] | Case-control |
Total 75 (25 non-T2DM, 25 T2DM+ DR proliferative, 25 T2DM + DR non-proliferative) |
Both/50–77 | HbA1C, serum Cu, Zn, NO, GSH, AOPP level, SOD |
-↑AOPP in T2DM Proliferative -↑NO, Cu in T2DM vs. Non-T2DM -↓GSH in T2DM vs. Non-T2DM -↑HbA1C in T2DM vs. Non-T2DM |
2 |
| Kumari et al. 2008 [10] | Case-control |
Total 118 (32 healthy, 36 T2DM, 50 T2DM + DR) |
Both/48–68 | MDA, VE, VC, lipid profile, FBS, 2hppBS |
-↑MDA in T2DM with/without DR -↓VE, VC in T2DM especially T2DM+ DR -Positive correlation betwen MDA/VE (r = 0.77) -Negative correlation between MDA/VC (r = −0.81) -Positive correlation between MDA/FBS (r = 0.81) -Positive correlation between MDA/lipid profile except HDL-C |
5 |
| Samuel et al. 2010 [22] | Case-control |
Total 90 (30 healthy, 30 T2DM, 30 T2DM+ DR) |
Both/35–65 | MDA, erythrocyte SOD, GSH, VC, FBS |
-↑MDA in T2DM+ DR -↓SOD, GSH, VC in all T2DM especially T2DM + DR -Negative correlation between FBS and antioxidant enzymes in T2DM + DR |
2 |
| Aldebasi et al. 2011 [23] | Case-control |
Total 160 (60 T2DM, 100 T2DM+ DR) |
Both/ 61 | FBS, HbA1C, MDA, 8-OhdG,Cu-Zn SOD |
-↑MDA, 8-OhdG in T2DM+ DR vs. Others -↓Cu-Zn SOD in T2DM+ DR vs. Others -Negative correlation between MDA or HbA1C and Cu-Zn SOD (r = −0.24, r = −0.23) |
4 |
| Lam et al. 2011 [24] | Case-control |
Total 420 T2DM (46 without DR, 161 background DR, 207 non-PDR, 6 PDR) |
Both/ <75 | FBS, lipid profile, HbA1C, DNA Damage, serum VC, SOD, TAS, GPx, VE lipid standardized, allantoin, urine level F2-isoprostanes |
-Positive correlation between DNA damage and HbA1C (r = 0.32), and FBS (r = 0.52) -Negative correlation between DNA damage and VC (r = −0.41) -Negative correlation between DNA damage and TAS (r = −0.21) -Positive correlation between VE lipid standardized and allantoin (r = 0.33) |
4 |
| Ates et al., 2013 [11] | Case-control |
Total 100 (50 healthy, 50 T2DM + DR proliferative) |
Both/50–70 | Ubiquinone-10, total coenzyme Q10, ubiquinol-10/ubiquinone-10, MDA |
-Positive correlation between MDA and coenzyme Q10 (r = 0.557) -↑MDA in T2DM+ DR -↑Ubiquinone-10 in T2DM+ DR -↓Ubiquinol-10/ubiquinone-10 in T2DM+ DR |
4 |
| Roopa et al. 2013 [25] | Case-control |
Total 150 (50 healthy, 50 T2DM, 50 T2DM + DR) |
Both/ NA | MDA, VC, VE, hs-CRP |
-↑MDA and hs-CRP in T2DM with/without DR especially in DR -↓VC, VE in T2DM with/without DR especially in DR |
3 |
| Said et al. 2013 [26] | Case-control |
Total 120 (30 healthy, 30 T2DM, 30 T2DM+ PDR, 30 T2DM+ non-PDR) |
Both/40–70 | FBS, lipid profile, SOD, GPx, VE |
-↑Lipid profile (except HDL-C) in T2DM+ DR -↓SOD, GPx, VE in T2DM + DR especially proliferative -Positive correlation between GPx and VE (r = 0.34) -Positive correlation between SOD and VE (r = 0.44) |
3 |
| Kumari et al. 2014 [12] | Case-control |
Total 112 (40 healthy, 30 T2DM, 42 T2DM + DR) |
Both/50–70 | FBS, Mg, Zn, VC, VE, MDA |
-↓Mg, Zn in T2DM especially with DR -↑MDA in T2DM with/without DR -↓VC,VE in T2DM with/without DR -Negative correlation between MDA and Mg (r = −0.73), and Zn (r = −0.82) |
3 |
| Kundu et al. 2014 [27] | Case-control |
Total 150 (50 healthy, 50 T2DM, 50 T2DM + DR) |
Both/40–70 | FBS, HbA1C, MDA, erythrocyte GSH, VC |
-↑FBS, HbA1C, MDA, SBP in T2DM with/without DR -↓VC, erythrocyte GSH in T2DM with/without DR -Negative correlation between FBS and VC (r = −0.58) -Positive correlation between FBS and MDA (r = 0.47) |
4 |
| Longo-Mbenza et al. 2014 [28] | Case-control |
Total 192 (45 healthy, 84 T2DM, 66 T2DM+ DR) |
Both/37–70 | 8-isoprostane, 8-oHdG, serum GGT, antibody against OxLDL, TBARS, GSH, SOD, GPx, FBS, HOMA, TAS, Zn, Se, Mg, VC, VD, VE, ApoB, eye examination, visual acuity, Lipid profile |
-↑Lipid profile in T2DM vs. healthy -Highest oxidant markers and lowest antioxidants in T2DM+ DR vs. others -↑HOMA in T2DM vs. healthy |
5 |
T2DM Type 2 diabetes mellitus, DR Diabetic retinopathy, MDA Malondialdehyde, SOD Superoxide dismutase, GPx Glutathione peroxidase, VC, Vitamin C; BG Blood glucose, HbA1C Glycosylated hemoglobin, vs. versus, GSH Reduced glutathione, FBS Fasting blood sugar, VE Vitamin E, 2hppBS 2 h post prandial blood sugar, HDL-C High density lipoprotein cholesterol, 8-oHdG 8-hydroxydexoxyguanosine, GGT Gamma-glutamyltransferase, OxLDL Oxidized low density lipoprotein, TAS Total antioxidant status, Mg Magnesium, VD Vitamin D, ApoB Apolipoprotein B, TBARS Thiobarbituric acid reacting substances, HOMA Hemostasis model-based insulin resistance, NO Nitric oxide, AOPP Advanced oxidation protein products, Zn Zinc, Cu Copper, Se Selenium, SBP Systolic blood pressure, NA Non access, Hs-CRP High sensitivity c-reactive protein, AA Ascorbic acid, DHA Dehydroascorbic acid, TChol Total cholesterol, PDR Proliferative diabetic retinopathy