Despite this finding, supplementation with this natural phenol, did not result in a higher insulin sensitivity nor an improvement to fasting plasma glucose values.
“Resveratrol 150 milligrams per day (mg/d) for six months had no beneficial effect on insulin sensitivity, nor on outcome parameters related to liver fat accumulation, body composition, dyslipidaemia, energy metabolism, physical performance, and quality of life and sleep, compared with placebo,” the team says led by Dr Patrick Schrauwen from Maastricht University Medical Center in the Netherlands.
“Resveratrol supplementation did give lower HbA1c concentrations compared with the placebo arm. Supplying resveratrol with a higher dose may be needed to achieve more profound health effects.”
“A dose of 150 mg/d was chosen because we have previously and consistently shown that this dose can improve muscle mitochondrial function.”
Resveratrol, a natural polyphenol present in various food items, was identified as a promising activator of the protein sirtuin 1 (SIRT1).
SIRT1 plays a central role in mediating effects in metabolic stress situations such as high-fat diet-induced obesity as shown in mice.
Therefore, compounds that activate SIRT1 directly or indirectly might offer protection against the onset of metabolic dysregulation and promote healthy aging.
Studies in overweight individuals and patients with Type 2 Diabetes (T2D) show improvements in muscle mitochondrial oxidative capacity after several weeks of low-dose resveratrol supplementation.
Dr Schrauwen and his team enrolled forty-one overweight men and women into a parallel-group, double-blind clinical trial.
During the initial two-week run-in period they were asked to stop consuming resveratrol-rich food items such as grapes, red wine, and peanuts.
Subjects were then randomised to receive either 150 mg/d of resveratrol (sample size = 20) or placebo (sample size = 21) for six months.
Resveratrol and placebo supplements were identical in appearance and were supplied by DSM Nutritional Products.
Participants were instructed to consume two supplements of 75 mg resveratrol/placebo per day—one during lunch and one during dinner.
Body weight and blood pressure were measured, and a blood sample was obtained for the analysis of plasma resveratrol.
The primary outcome of the study was insulin sensitivity with secondary outcome measures included intrahepatic lipid (IHL) content, body composition, resting energy metabolism, blood pressure, plasma markers, physical performance, quality of life, and quality of sleep.
Results revealed no differences observed between the two treatment groups with insulin sensitivity unaffected after 6 months of resveratrol treatment.
However, the research team found a significant difference in postintervention glycated haemoglobin (HbA1c) between the groups with the treatment group lower after resveratrol intervention (35.8 millimoles per mol (mmol/mol) compared with placebo (37.6 mmol/mol).
No differences were found in intrahepatic lipid (IHL), body composition, blood pressure, energy metabolism, physical performance, or quality of life and sleep between treatment arms.
Alteration in haemoglobin glycation?
“HbA1c is a marker of long-term glycaemic control, and it reflects average plasma glucose values of the preceding three months,” the study explains.
“Observing an effect on HbA1c and not on plasma glucose concentrations could imply an alteration in the glycation of haemoglobin or erythrocyte life span rather than a decrease in average plasma glucose concentrations.”
The team also found resveratrol treatment did not affect total cholesterol, HDL and LDL cholesterol, free fatty acids, and triglycerides, commenting that these results and previous studies suggests that resveratrol appears unsuitable for treating dyslipidaemia.
“We also measured plasma markers related to safety: bilirubin, creatinine, urea, aspartate aminotransferase (AST), and alanine aminotransferase (ALT),” the study says.
“None of the plasma markers changed during the six months, neither within nor between the groups, which implies that supplying 150mg of resveratrol per day for six months can be regarded as safe, as also previously established.”
Source: The American Journal of Clinical Nutrition
Published online ahead of print: doi.org/10.1093/ajcn/nqaa125
“No effect of resveratrol supplementation after 6 months on insulin sensitivity in overweight adults: a randomized trial.”
Authors: Marlies de Ligt et al.