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Dubbed the 'elixir of youth', it's the red wine ingredient which has prompted debate for years.

Now it seems resveratrol really does make you live longer, but only in small doses - and too much could actually speed up the ageing process rather than slowing it down, the Daily Mail reports.

Scientists looked at how the chemical interacted with 'satellite cells', which play a role in repairing damaged muscle as part of the body's natural regeneration.

The team discovered the chemical, which is found in red wine, chocolate and health supplements, had a different effect depending on the concentration they used.

Laboratory tests showed that small doses supported cells in the repair process but higher doses had the opposite effect.

The findings, led by Dr Hans Degens of Manchester Metropolitan University, could strike a blow to those who tout resveratrol as fighting heart disease, cancer and Alzheimer's.

Dr Degens 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.

Resveratrol protects red grapes, cacao beans and Japanese knotweed against infections and drought, and has divided experts for a decade over reports it could make humans live longer.

A study in the journal Nature in December confirmed its positive role, saying it imitated another protective enzyme which had not been studied in detail before.

In tests on mice they found that when resveratrol and the enzyme TyrRS were combined - as can happen naturally in the body - the pair imitating a cell-healing amino acid called tyrosine.