Researchers have backed the popular belief that working less could be better for your brain.

New research from the University of Melbourne has found working part-time for about 25 to 30 hours a week had a positive impact on the cognitive function for Australians aged over 40.

But for those working more than three days a week, research found stress and fatigue could erase those positive impacts.

Sorry, this video has expired Why you shouldn't work more than 25 hours a week.

The study analysed the work habits and brain-testing results of 3,000 men and 3,500 women over the age of 40 in Australia.

Specifically, the participants' results in three different cognitive skill areas were tested, which included a memory score test, a reading test and a perceptive ability test.

"In all three cases [tests] it was found around 25-30 hours of work per week will maximise your cognitive skill," said Professor Colin McKenzie at Keio University who took part in the study.

"And going for less hours or more hours reduces your cognitive skills."

Professor McKenzie said one of the key findings showed working both zero hours and at the other end of the spectrum, 50-60 hours, led to the same levels of cognitive skill.

"Too much work leads to stress and fatigue and that's probably the key cause of this decline in cognitive skills after 25-30 hours a week," he said.

Optimal working week unclear

Interestingly, no key differences between men and women in terms of the optimal hours of work were found.

The researchers said their findings are particularly important at a time when many countries are raising their retirement age.

Professor McKenzie said future studies should look at how other dimensions of health were impacted by work.

He said it would also be interesting to determine what the optimal number of hours per week were in different countries.

"If the number of hours doesn't peak at the same place, there may be systemic reasons for that difference, for example Australia has four weeks of annual leave which tends to be longer than Japan," Professor McKenzie said.

"So these chances to refresh your body and brain may be important in determining the optimum peak."