It can be hard to strike a balance between feeling overworked and underutilized, especially for middle-aged and older adults. While holding a job can help keep the brains of adults stimulated, working too much can cause fatigue and mental exhaustion. So, what’s the perfect amount of work for people over 40? According to a recent study published in the Melbourne Institute’s Working Paper Series [PDF], a three-day work week may be ideal for remaining productive without burning out.

The Telegraph reports that researchers from Japan and Australia analyzed the impact of working hours on the cognitive abilities of 3000 men and 3500 women over 40 in Australia. Volunteers from a range of professions were asked to perform a series of cognitive tasks, including reading words aloud, reciting sequences of numbers, and connecting letters and numbers in specific patterns. Researchers found that working approximately 25 hours a week had a positive impact on cognitive functioning, while not working at all, or working more than 25 hours a week, had a negative impact. No statistically significant differences were found between the effects of working hours on men and women.

Their findings imply that, in order for employees over 40 to function at the highest possible capacity, a three-day (or 25 hour) work week may be best. However, researchers note that full time work—approximately 40 hours—seems to be less damaging than not working at all. Working more than 55 hours a week, meanwhile, may be the most damaging, taking a greater toll on cognitive functioning than total unemployment.

Researchers note that, in many countries, the age of retirement has started to increase in recent years. Understanding the healthiest employment habits for middle-aged and older adults could help them continue to work into their later years without too much strain. “In middle and older age, working part-time could be effective in maintaining cognitive ability,” the study explains. “Work can be a double-edge sword, in that it can stimulate brain activity, but at the same time long working hours can cause fatigue and stress, which potentially damage cognitive functions.”

[h/t The Telegraph]