An ingredient in chocolate and red wine reputed to have anti-ageing properties may actually hinder the regeneration and repair of muscles in higher doses, researchers claim.
Resveratrol, widely sold in supplements, is said to have powerful antioxidant effects and an ability to combat many of the ills of ageing including heart disease, cancer and Alzheimer's.
But scientists found that its influence on muscle regeneration could be good or bad depending on the concentration used.
Laboratory tests showed that small doses supported cells in the repair process but higher doses had the opposite effect.
Lead researcher Dr Hans Degens, from Manchester Metropolitan University (MMU), said: " Stronger muscles and the ability of the muscle to repair damage are important for a healthy lifestyle, especially in older age where muscle decline can have a series of implications for a reduction in our quality of life.
"So we analysed if resveratrol was able to promote the repair of muscle and reduce oxidative stress where free radicals (destructive molecules) speed up the ageing process.
"Local muscle stem cells undergo a cycle when they repair and ultimately fuse with the damaged muscle fibre. At low doses, resveratrol did help the regeneration. However, if the dose is higher, it doesn't mitigate ageing from oxidative stress and even hampers the repair cycle.
"The results showed that the effects are dependent on the dose and it is unclear from the equivocal results if drinking wine or eating chocolate would have anti-ageing properties and repair muscle or the opposite."
The researchers, whose findings appear in the journal Scientific Reports, conducted experiments in the laboratory using muscle cells.
They tested the cycle of muscle regeneration which starts with the activation of muscle precursors called "satellite" cells.
A low 10 micromolar dose of resveratrol stimulated satellite cell activation and migration while higher concentrations of 40 to 60 micromolars stopped it, and even damaged the cells.