People who delay their retirement are less likely to develop Alzheimer's disease and other forms of dementia than those who leave their jobs at age 60, a French study released this week shows.

In the study, which followed more than 429,000 former workers in France, the likelihood of getting dementia seemed to decline for each additional year they worked.

The study is "adding to the research that staying cognitively active — so things that promote mental stimulation — is beneficial in reducing individual’s risk of developing Alzheimer’s disease," said Heather Snyder, director of medical and scientific relations, with the U.S.-based Alzheimer's Association.

"It may not actually be working to an older age, but it’s staying active. My parents are in their 60s, they’re retired, but they’re busier than ever," she told the Lang & O'Leary Exchange.

The study seems to indicate that the old adage "use it or lose it" applies to mental power in the later years.

"Things that promote mental stimulation, lifelong learning – whether that’s taking a class, reading a book or reading a newspaper every day — whatever that may mean to you to keep your brain active," Snyder said. "Staying physically active – there is strong literature around the benefits of physical activity in reducing risk."

15% reduction

The research, presented at the Alzheimer's Association International Conference in Boston, was funded by at INSERM, the French government’s health research agency. It examined the health records of workers, many of them shopkeepers and craftsmen, who had been retired an average of five years.

Nearly three per cent of those studied had some form of  dementia, but workers who retired at 65 had about a 15 per cent lower risk of developing dementia compared with workers who retired at 60, the study found.

Snyder says much more research is needed into what happens biologically to aging brains and why lifestyle changes can help delay Alzheimer's.

"The underlying biology associated with Alzheimer’s disease is actually present a decade or more before someone has changes with their memory.  It’s the idea that we could potentially detect early biological changes," she said.

Dean Hartley, director of science initiatives at the Alzheimer's Association, said the research is an important starting point in determining why a later retirement might be good for long-term mental health.

"What you understand from this observational research is that there's a correlation, but whether it's actually causative is unknown," he said.    

"More research will need to be done to physically identify what's actually changing in the brain as a result of delaying retirement," Hartley told Reuters.

British research into dementia released today found the incidence of the disease is dropping as people become better educated and healthier, primarily by controlling high blood pressure and cholesterol.

Researchers at the Cambridge Institute of Public Health said the number of dementia cases had fallen 25 per cent since 1994.