A new study in 2013 of nearly half a million people in France backs up the theory “use it or lose it” when it comes to brainpower and staying mentally sharp. People who delay retirement have less risk of developing Alzheimer’s or other types dementia.

It’s by far the largest study ever done on this subject, and researches say the conclusion makes sense. Working tends to keep people physically active, socially connected and mentally challenged—all the things known to help prevent mental decline.

“For each additional year of work, the risk of getting dementia is reduced by 3.2 percent,” said Carol Dufouil, a scientist who led the study.