Data from 388 people also indicated, however, that the potential blood sugar management potential of the grape compound may be limited to diabetics, with no benefits observed for non-diabetic persons.
Scientists from the Third Military Medical University in China report their findings in the American Journal of Clinical Nutrition.
Beyond blood sugar management
Resveratrol, a powerful polyphenol and anti-fungal chemical, is often touted as the bioactive compound in grapes and red wine, and has particularly been associated with the so-called 'French Paradox'. The phrase, coined in 1992 by Dr Serge Renaud from Bordeaux University, describes the low incidence of heart disease and obesity among the French, despite their relatively high-fat diet and levels of wine consumption.
Interest in the compound exploded in 2003 when research from David Sinclair and his team from Harvard reported that resveratrol was able to increase the lifespan of yeast cells. The research, published in Nature, was greeted with international media fanfare and ignited flames of hope for an anti-ageing pill.
According to Sinclair’s findings, resveratrol could activate a gene called sirtuin1 (Sirt1 – the yeast equivalent was Sir2), which is also activated during calorie restriction in various species, including monkeys.
Other studies with only resveratrol have reported anti-cancer effects, anti-inflammatory effects, cardiovascular benefits, anti-diabetes potential, energy endurance enhancement, and protection against Alzheimer’s.
The new meta-analysis, adds to the potential blood sugar management potential of resveratrol, but suggests that the benefits may not be applicable to non-diabetics.
Eleven randomized controlled trials were included in the new meta-analysis, with the data indicating that resveratrol significantly reduced levels of fasting glucose and insulin in diabetics. The data also supported resveratrol’s ability to reduce hemoglobin A1c (HbA1c), a marker of long-term presence of excess glucose in the blood, and insulin resistance in diabetics.
On the other hand, no significant effects were observed in non-diabetics.
Commenting on the potential mechanism of action for blood sugar control in diabetics, the researchers noted that the compound has been shown to activate Sirt1, which influences energy restriction and therefor blood sugar. The compound has also been reported to increase the expression of an insulin-dependent glucose transporter called GLUT4. A third option is that resveratrol may boost the uptake of glucose uptake in the absence of insulin.
In terms of resveratrol’s effect on insulin, the benefits may be linked to an ability to inhibit the secretion of insulin by pancreatic cells, or via anti-inflammatory mechanisms.
“In conclusion, resveratrol consumption significantly improved glucose control and insulin sensitivity in patients with [type-2 diabetics] but did not show a similar effect on non-diabetic participants,” wrote the researchers. “More high-quality RCTs with durations longer than 3 months are needed to further confirm the effects of resveratrol on glucose control and insulin sensitivity.
“In addition, these effects will be more convincing if studies can effectively rule out the potential confounding effect of medicine use.”
According to the World Health Organisation (WHO), diabetes affects over 220 million people globally and the consequences of high blood sugar kill 3.4 million every year. If such statistics weren’t scary enough, the WHO is predicting deaths to double between 2005 and 2030.
The total costs associated with the condition in the US alone are thought to be as much as $174 billion, with $116 billion being direct costs from medication, according to 2005-2007 American Diabetes Association figures.
Source: American Journal of Clinical Nutrition
Published online ahead of print, doi: 10.3945/ajcn.113.082024
“Effect of resveratrol on glucose control and insulin sensitivity: a meta-analysis of 11 randomized controlled trials”
Authors: K. Liu, R. Zhou, B. Wang, M-T. Mi