Want to stay mentally sharp? Work part time

Researchers say they’ve found the secret for maintaining brain sharpness in middle and older age: a 25-hour workweek.

Part-time work represents the sweet spot, researchers affiliated with Japanese and Australian universities found in a recent study. It offers mental stimulation without the fatigue and stress of full-time work, which can potentially damage cognitive functions. “Maybe they’re onto something,” said Gary Small, geriatric psychiatrist and director of the UCLA Longevity Center and co-author of the book, “The Alzheimer’s Prevention Program.” Both chronic stress and early retirement have been identified as risk factors for Alzheimer’s disease.

Researchers looked at how the number of hours worked affected the brainpower of people age 40 and over living in Australia. They controlled for individual characteristics that might affect cognitive functioning, such as natural smarts, in order to isolate the impact of hours worked. Subjects were given three cognitive tests, including one involving memorizing a string of numbers and reciting them backwards.

In designing their experiment, researchers set out to test the boundaries of “use it or lose it,” they wrote. Mental functioning can decline if the brain isn’t stimulated, and indeed researchers found that working hours up to around 25 hours a week boosted cognitive functioning as subjects used their minds.

But too much work may be harmful, researchers found. Working more than 25 hours a week was associated with a negative impact on brain functioning.

The paper didn’t go into detail about the jobs that the subjects held. A separate recent research brief from the Center for Retirement Research at Boston College looked at how white-collar workers aren’t immune from the effects of aging on the job.

Blue-collar workers tend to retire earlier than white-collar workers, due to physical strain. But desk jockeys may see their performance suffer due to cognitive decline, researchers found.

White-collar workers in professions that rely heavily on acquired knowledge tend to stay on the job longer than workers in jobs that require complex problem solving. “Engineers have a tougher time than teachers,” said Geoffrey T. Sanzenbacher, research economist at the Center for Retirement Research.

Regardless of their profession, few workers have the luxury of scaling back to part-time work. Only 69% of workers reported they and/or their spouse had saved money for retirement, and a quarter of workers have less than $1,000 in any kind of savings, according to the 26th annual Retirement Confidence Survey released last month by the Employee Benefit Research Institute. A spokesman said the institute doesn’t track the number of workers who work part-time by choice.