α-Tocopherol influences glycaemic control and miR-9-3 DNA methylation in overweight and obese women under an energy-restricted diet: a randomized, double-blind, exploratory, controlled clinical trial

BACKGROUND: Excess weight is a strong risk factor for the development of dysglycaemia. It has been suggested that changes in the metabolism microRNAs, small non-coding RNAs that regulate gene expression, could precede late glycaemic changes. Vitamin E in turn may exert important functions in methylation and gene expression processes. This study aimed to determine the effect of α-tocopherol on glycaemic variables and miR-9-1 and miR-9-3 promoter DNA methylation in overweight women. METHODS: A randomized, double-blind, exploratory, placebo-controlled study was conducted in overweight and obese adult women (n = 44) who ingested synthetic vitamin E (all-rac-α-tocopherol), natural source vitamin E (RRR-rac-α-tocopherol) or placebo capsules and were followed up for a period of 8 weeks. Supplemented groups also received dietary guidance for an energy-restricted diet. An additional group that received no supplementation and did not follow an energy-restricted diet was also followed up. The intervention effect was evaluated by DNA methylation levels (quantitative real-time PCR assay) and anthropometric and biochemical variables (fasting plasma glucose, haemoglobin A1C, insulin, and vitamin E). RESULTS: Increased methylation levels of the miR-9-3 promoter region (P < 0.001) and reduced haemoglobin A1C (P < 0.05) were observed in the natural source vitamin E group after intervention. Increased fasting plasma glucose was observed in the synthetic vitamin E group, despite the significant reduction of anthropometric variables compared to the other groups. CONCLUSIONS: α-Tocopherol from natural sources increased methylation levels of the miR-9-3 promoter region and reduced haemoglobin A1C in overweight women following an energy-restricted diet. These results provide novel information about the influence of vitamin E on DNA methylation. TRIAL REGISTRATION: ClinicalTrials.gov, NCT02922491. Registered 4 October, 2016. ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (10.1186/s12986-018-0286-7) contains supplementary material, which is available to authorized users.