Working shifts significantly damages people’s ability to think and remember, and doing so for at least a decade “ages” the brain by an extra six and a half years, new research has found.

The findings are the latest to link working outside normal hours to an increased risk of health problems.

Other studies have suggested links with cancers, heart attacks, strokes, ulcers and metabolic diseases such as diabetes.

Researchers from Université de Toulouse and Swansea University studied 3,000 people in south-west France who were either working, or had retired, in 1996, 2001 and 2006.

Those who worked abnormal hours or had done so were found to score lower for memory, speed of processing information and overall brainpower than participants who had never done so.

People who had worked rotating shifts (a mixture of mornings, afternoons or evenings) for 10 years or more also had poorer mental function than those who had not done so to the extent that they had suffered an extra 6.5 years of age-related cognitive decline, the scientists found.

That association was “highly significant”, they said.

While stopping working shifts did halt the decline in cognitive powers, it took five years for people to recover fully, according to the study, published in the journal Occupational and Environmental Medicine.

“Shift work chronically impairs cognition, with potentially important safety consequences not only for the individuals concerned, but also for society,” say the authors, led by Dr Jean-Claude Marquie, from the Université de Toulouse.