Baby boomers, take note: For every year you put off retirement, your chances of developing Alzheimer’s disease or other types of dementia are cut by 3 percent.

The findings are the result of a massive French study, which looked at the records of 429,000 workers. The scientists presented their results Monday at the Alzheimer’s Association International Conference in Boston.

“For each additional year of work, the risk of getting dementia is reduced by 3.2 percent,” Carole Dufouil, a scientist at INSERM, the French government’s health-research agency, told The Associated Press.

The findings underpin the often-repeated advice to prevent mental decline: “Use it or lose it.” Doctors have said that keeping the brain mentally challenged is one way to prevent dementia and related diseases.

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The French workers who were part of the study were age 74, on average, and had been retired for an average of 12 years.

The study found that nearly 3 percent had developed dementia, but that the risk of developing the disease was lower for each year of age at retirement.

For example, someone who retired at 65 had a 15 percent lower risk than someone who retired at 60, Dufouil said.

Economists have noted that the recession, which wiped out millions of Americans’ retirement funds, has led to people putting off retirement.

Since the mid-1990s, American workers have been working longer, but that trend accelerated sharply during the most recent economic calamity.

About 35 million people worldwide have dementia, and Alzheimer’s is the most common type. In the U.S., about 5 million have Alzheimer’s — 1 in 9 people aged 65
or over. What causes the mind-robbing disease isn’t known, and there is no cure or any treatments that slow its progression.

Health officials predict an estimated 450,000 people will die in 2013 from the disease.

The new study is by far the largest to look at this, and researchers say the conclusion makes sense. Working tends to keep people physically active, socially connected and mentally challenged — all factors known to help prevent mental decline.

France has had some of the best Alzheimer’s research in the world, partly because its former president, Nicolas Sarkozy, made it a priority. The country also has detailed health records on self-employed people who pay into a Medicare-like health system.

Most of the workers who were studied were shopkeepers or craftsmen such as bakers and woodworkers.

To rule out the possibility that mental decline may have led people to retire earlier, researchers did analyses that eliminated people who developed dementia within 5 years of retirement, and within 10 years of it.

“The trend is exactly the same,” suggesting that work was having an effect on cognition, not the other way around, Dufouil said.

France mandates retirement in various jobs — civil servants must retire by 65, she said.

The new study suggests “people should work as long as they want” because it may have health benefits, she said.

June Springer, who just turned 90, thinks it does. She was hired as a full-time receptionist at Caffi Plumbing & Heating in Alexandria, Va., eight years ago.

“I’d like to give credit to the company for hiring me at that age,” she said. “It’s a joy to work, being with people and keeping up with current events. I love doing what I do. As long as God grants me the brain to use, I’ll take it every day.”

Heather Snyder, director of medical and scientific operations for the Alzheimer’s Association, said the study results don’t mean everyone needs to delay retirement.

“It’s more staying cognitively active, staying socially active, continue to be engaged in whatever it is that’s enjoyable to you” that’s important, she said.

“My parents are retired but they’re busier than ever. They’re taking classes at their local university, they’re continuing to attend lectures and they’re continuing to stay cognitively engaged and socially engaged in their lives.”