In the U. S., about 5 million have Alzheimer's --1 in 9 people aged 65 and over.

People who delay retirement have less risk of developing Alzheimer's disease or other types of dementia, a study of nearly half a million people in France found.

It's by far the largest study to look at this, and researchers say the conclusion makes sense.

Working tends to keep people physically active, socially connected and mentally challenged -- all things known to help prevent mental decline.

Researchers used these records on more than 429000 workers, most of whom were shopkeepers or craftsmen such as baker and woodworkers.

"For each additional year of work, the risk of getting dementia is reduced by 3.2 percent." said Carole Dufouil, a scientist at INSERM, the French government's health research agency.

About 35 million people worldwide have dementia, and Alzheimer's is the most common type.

What causes the mind-robbing disease isn't known and there is no cure or any treatments that slow its progression.

They were 74 on average and had been retired for an average of 12 years.

Nearly 3 percent had developed dementia but the risk of this was lower for each year of age at retirement.

Someone who retired at 65 had about a 15 percent lower risk of developing dementia compared to someone retiring at 60, after other factors that affect those odds were taken into account, Dufouil said. Thank you.