The over-40s are at their best if they work fewer than 25 hours a week, according to new research.

The study, published by the University of Melbourne, looked at the cognitive ability of Australians aged over 40. For up to 25 hours a week, cognitive function was improved by working more. However, after that increasing working hours begins to have a negative impact on cognition.

“In the middle and older age, working part-time could be effective in maintaining cognitive ability,” conclude the authors. “Our study highlights that too much work can have adverse effects on cognitive functioning.”

The researchers used the Household, Income and Labour Dynamics in Australia (HILDA) Survey and three measures of cognitive ability. Their results are outlined in the chart below.

Image: Shinya Kajitani, Colin McKenzie and Kei Sakata

The charts highlight the peak in cognitive skills at around the 25-hour mark – for both men and women. This initially declines gradually, until a steep drop as working hours become much longer.

However, the study did only assess over-40s, so whether they are any different from the rest of the population is not clear. Equally, the gradual decline indicates that longer working hours up to a point are possible, without significant impact on performance.

Geraint Johnes, professor of economics at Lancaster University is quoted by the BBC as saying: “The research looks only at over-40s, and so cannot make the claim that over-40s are different from any other workers.”

An ageing population

The results are potentially significant as the global population ages and people work later in life. The authors highlight that for those over the age of 40, working part-time – for example three days a week – could have cognitive benefits, both for workers and business.