Dietary antioxidative supplements and diabetic retinopathy; a systematic review
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There is controversial data regarding the effects of dietary antioxidative supplements on diabetic retinopathy (DR). We conducted a systematic review of both observational and randomized controlled clinical trials (RCTs) to clarify whether they are effective or not.
All observational and RCTs conducted by antioxidative supplements on DR published up to 1 January 2018 in PubMed, Web of Sciences, Scopus and Cochrane Library databases were included. Exclusion criteria were animal studies, and studies conducted in Type 1 diabetes mellitus (T1DM), children or pregnant women. Main outcome measures were reporting the incidence or progression of DR in T2DM by assessment of visual fields, and measurements of oxidative and antioxidative biomarkers. The quality of reporting of included articles and risk of bias were assessed.
Finally, we reached 14 observational studies and 7 RCTs that conducted on 256,259 subjects. Due to severe methodological heterogeneity, only qualitative synthesis was carried. All studies were reported a significantly lower level of antioxidants and higher level of oxidative stress biomarkers in DR compared with others. There was an inverse significant correlation between vitamin C and malondialdehyde (MDA) (r = −0.81) or DNA damage (r = −0.41). These figures were statistically significant between vitamin E and MDA (r = 0.77) or superoxide dismutase (r = 0.44). Coefficient of correlation between MDA and zinc (−0.82), coenzyme Q10 (0.56), and magnesium (−0.73) was significant. Multi-oxidants trials were shown non-significant beneficial effects on DR.
Although our study supports the positive effects of antioxidative supplements on DR, more high quality studies are needed to confirm.
KeywordsType 2 diabetes mellitus Diabetic retinopathy Oxidative stress Antioxidants
Non-proliferative diabetic retinopathy
Proliferative diabetic retinopathy
International Diabetes Federation
Protein kinase C
Advanced glycation end products
Reactive oxygen species
Alpha lipoic acid
Type 2 diabetes mellitus
Randomized controlled trials
Preferred Reporting Items for Systematic reviews and Meta-Analyses
Total antioxidant status
Strengthening the reporting of observational studies in epidemiology
American Diabetes Association
Best-corrected visual acuity
Retinal nerve fiber layer thickness
Free oxygen radical test
Central macular thickness
Nuclear translocation factor- κB
Vascular endothelial growth factor
Biological antioxidant potential
This paper is the outcome of an in-house study without any financial support.
Both OTM and NN helped to collect data, data interpretation, and drafting article. OTM and EAL equally designed, conceived of the study, data analysis and interpretation. SN and RBJ helped to written drafting article, and critical revision of the article. BL conceived of the study, helped to data interpretation, and drafting article. All authors read and approved the final draft of the article.
Compliance with ethical standards
Ethics approval and consent to participate
Consent for publication
The authors certify that there is no conflict of interest with any financial organization regarding the material discussed in the manuscript.
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