Nutritional intervention and impact of polyphenol on glycohemoglobin (HbA1c) in non-diabetic and type 2 diabetic subjects: Systematic review and meta-analysis

ABSTRACT

Polyphenols have been extensively studied for their antioxidant and anti-inflammatory properties. Recently, their antiglycative actions by oxidative stress modulation have been linked to the prevention of diabetes and associated complications. This article assesses the evidence for polyphenol interventions on glycohemoglobin (HbA1c) in non-diabetic, pre-diabetic, and type 2 diabetes mellitus (T2DM) subjects. A systematic review of polyphenols' clinical trials on HbA1c in humans was performed according to the Preferred Reporting Items for Systematic Review and Meta-Analysis. Thirty-six controlled randomized trials with HbA1c values were included. Polyphenols (extracts, supplements, and foods) were supplemented (28 mg to 1.5 g) for 0.7 to 12 months. Combining all subjects (n = 1954, mean baseline HbA1c = 7.03%, 53 mmol/mol), polyphenol supplementation significantly (P < 0.001) lowered HbA1c% by –0.53 ± 0.12 units (–5.79 ± 0.13 mmol/mol). This reduction was significant (P < 0.001) in T2DM subjects, specifically (n = 1426, mean baseline HbA1c = 7.44%, 58 mmol/mol), with HbA1c% lowered by –0.21 ± 0.04 units (–2.29 ± 0.4 mmol/mol). Polyphenol supplementation had no significant effect (P > 0.21) in the non-diabetic (n = 258, mean baseline HbA1c = 5.47%, 36 mmol/mol) and the pre-diabetic subjects (n = 270, mean baseline HbA1c = 6.06%, 43 mmol/mol) strata: –0.39 ± 0.27 HbA1c% units (–4.3 ± 0.3 mmol/mol), and –0.38 ± 0.31 units (–4.2 ± 0.31 mmol/mol), respectively. In conclusion, polyphenols can successfully reduce HbA1c in T2DM without any intervention at glycemia, and could contribute to the prevention of diabetes complications.

Keywords:

• Glycation
• polyphenols
• nutrition
• supplementation
• meta-analysis
• antioxidant

Acknowledgment

Susana A. Palma-Duran wrote the manuscript, conducted research, and analyzed the data. Antonis Vlassopoulos conducted research, contributed to discussion, and reviewed the manuscript. Mike Lean reviewed/edited the manuscript and contributed to discussion. Lindsay Govan reviewed the manuscript and contributed to the statistical analysis. Emilie Combet designed the research, supervised the project, reviewed/edited the manuscript, and contributed to discussion. All authors read and approved the final manuscript.

Susana A. Palma-Duran is the guarantor of this work, and as such had full access to all the data in the study and takes responsibility for the integrity of the data and the accuracy of the data analysis. The authors declare no conflict of interest.

Funding

Susana A. Palma-Duran is in receipt of a CONACyT PhD scholarship; and Antonis Vlassopoulos is in receipt of a Yorkhill Children Foundation scholarship.