Delaying retirement may prevent dementia

It is by far the largest study to look at the issue, and researchers said the conclusion made sense. Working tends to keep people physically active, socially connected and mentally challenged – factors known to help prevent cognitive decline.

"For each additional year of work, the risk of getting dementia is reduced by 3.2%," said epidemiologist Dr Carole Dufouil of INSERM, the French government's health research agency, who led the study and presented the results yesterday at the Alzheimer's Association International Conference in Boston.

About 35 million people worldwide have dementia and Alzheimer's disease is the most common type. In the US, about five million people have Alzheimer's – one in nine people aged 65 and over. 

The researchers used the health records of more than 429,000 workers, most of whom were shopkeepers or craftsmen, such as bakers and woodworkers. They were aged 74 on average and had been retired for an average