Experts in Japan analysed the employment habits and cognitive test results for 3,000 men and 3,500 women above the age of 40 in Australia.
Results suggest that a generation of workers contemplating a future of toil beyond their 70th birthdays should be careful what they aim for. While giving up altogether seems to carry its own risks for the mind, too much work is just as bad.
The Times reports that calculations suggest that a part-time job is the best balance between keeping the brain stimulated and driving it into the ground with stress and exhaustion.
Participants were asked to read words aloud, to recite lists of numbers running backwards and to link letters and numbers in a particular pattern under time pressure.
They found that people who worked about 25 hours a week tended to get the best scores. Those who did not work at all scored about 18 per cent lower on the reading test, 20 per cent lower on the backwards numbers and 15 per cent lower on matching numbers and letters.
Working 40 hours a week was linked to a slightly smaller cognitive deficit, but working 55 hours or more seemed to be worse than being retired or unemployed.
Colin McKenzie, professor of economics at Keio University, said the evidence indicated that working too much or too little could cause a decline in cognitive performance. His team’s research, published in the Melbourne Institute’s working paper series, comes at a sensitive time as workers in Britain and several other developed countries steel themselves for significant jumps in their state pension ages.
“Many countries are going to raise their retirement ages by delaying the age at which people are eligible to start receiving pension benefits,” Professor McKenzie said. “This means that more people continue to work in the later stages of their life.
“The degree of intellectual stimulation may depend on working hours. Work can be a double-edged 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.
“We point out that differences in working hours are important for maintaining cognitive functioning in middle-aged and elderly adults. This means that, in middle and older age, working part-time could be effective in maintaining cognitive ability.”
The findings echo those of a celebrated study that has followed 10,000 middle-aged civil servants in Whitehall since 1985. One analysis of this data found that those who worked up to 55 hours a week did worse in a series of cognitive tests than those who generally kept to 40 hours at most.
The Australian survey, however, covered a much broader range of jobs as well as the retired and unemployed.
Marianna Virtanen, the Finnish occupational health expert who led the Whitehall study, said that the new research seemed to show “that middle-aged and older people should limit their working hours to keep their cognitive capacity fit”.
She had a few reservations: it was not entirely clear whether a long working week caused a drop in intelligence scores or vice versa, and different jobs could have very different effects on a worker’s cognitive sharpness.
“In certain jobs where a lot of intense focus and concentration is needed, working long hours may be more exhausting to cognition,” she said.