If you’re over 40, working more than 25 hours of work a week could be impairing your intelligence, according to a study released by researchers at the Melbourne Institute of Applied Economic and Social Research in Australia.
The team conducted reading, pattern and memory tests in more than 6,000 workers aged over 40, to see how the number of hours worked each week affects a person’s cognitive ability.
Working 25 hours a week (part-time or three days a week) was the optimum amount of time spent working a week for cognitive functioning, while working less than that was detrimental to the agility of the brain for both men and women, the study found.
“Work can stimulate brain activity and can help maintain cognitive functions for elderly workers, the ‘lose it or use it hypothesis’,” said lead researcher Colin McKenzie, a professor of economics at Keio University in Tokyo.
“But at the same time, excessively long working hours can cause fatigue and physical and/or psychological stress, which potentially damage cognitive functioning.”
But why is age 40 the turning point for the mind?
According to McKenzie, our “fluid intelligence”, which is how well we process information, starts declining around the age of 20 and “crystallised intelligence”, or the ability to use skills, knowledge and experience starts decreasing after 30 years of age. McKenzie said that by age 40, most people perform less well at memory tests, pattern recognition and mental agility exercises.
As many countries have already increased their retirement ages, delaying when people are eligible to start receiving pension payments, McKenzie’s latest findings on cognitive fatigue are important.
“Work can be a double-edged sword, in that it can stimulate brain activity, but at the same time, long working hours and certain types of tasks can cause fatigue and stress which potentially damage cognition,” he said.
McKenzie’s findings suggest that although economics may now be forcing us to work much longer than in previous generations, biologically and emotionally our minds may not be designed for the stress and repetition of working nine-to-five, five days a week when we are over 40.
Previous studies have shown that workers of various ages doing overtime can suffer chronic stress, cognitive impairment and also mental illness. One 1996 study from the Boston University School of Public Health indicated that overtime work had adverse effects on the mental health of employees in the automobile industry, such as on the assembly line in a factory.