According to research, full time work may be bad for your brain

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Don't do an IQ test after a full week's work if you are 40 years or older. You could be disappointed. If you're over 40, working more than 25 hours of work a week could be impairing your intelligence, according to a study released in February by researchers for 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.

The science behind it: 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. McKenzie's research differs in that his team has found that such health and cognitive issues can occur at a much lower threshold than previously thought — that is, in people over 40 working a regular week, rather than doing overtime.

'Sandwich years' are when many adults have at least one person to look after, a child or an elderly parent, on top of working full-time.The negative effects of stress on the mind are well-documented in neurological research. Stress affects cognitive functioning primarily through hormones, in particular, steroid hormones and the stress hormone, cortisol, in the brain which in turn can affect short-term memory, concentration, inhibition and rational thought. But there may be other factors at play as to why 40 seems to be a critical turning point. McKenzie's team is now looking into the driving factors behind their research such as the "sandwich years" when many adults have at least one person to look after, a child or an elderly parent, on top of working full-time.

McKenzie's research differs in that his team has found that such health and cognitive issues can occur at a much lower threshold than previously thought — that is, in people over 40 working a regular week, rather than doing overtime. The negative effects of stress on the mind are well-documented in neurological research. Stress affects cognitive functioning primarily through hormones, in particular, steroid hormones and the stress hormone, cortisol, in the brain which in turn can affect short-term memory, concentration, inhibition and rational thought.

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But there may be other factors at play as to why 40 seems to be a critical turning point.

McKenzie's team is now looking into the driving factors behind their research such as the "sandwich years" when many adults have at least one person to look after, a child or an elderly parent, on top of working full-time.