Working too much overtime causes burnout, and it might also cause cognitive decline. A long-term study of middle aged British civil servants shows that people who worked more than 55 hours per week had lower scores on two cognitive tests than their peers who put in 40 or fewer hours per week. It’s possible that long working hours could be associated with increased risk of dementia, though more research is needed.

The study (Virtanen et al., 2009) had knowledge workers, also called white-collar workers, complete a series of tests once between1997 and 1999 and again five years later, between 2002 and 2004. More than 2,000 people participated.

After the five years had passed, people who worked more than 55 hours per week had lower scores on average on two of the tests than people who worked around 40 hours per week. One of the test presents a list of 20 short words at two-second intervals, and then the subjects must write down as many words as they can remember in any order in two minutes. The other test is a set of 32 verbal and 33 mathematical reasoning questions with increasing difficulty. This second test measures fluid intelligence, which the authors explain “is seen to be intrinsically associated with information processing and involves short-term memory, abstract thinking, creativity, ability to solve novel problems, and reaction time.”

Even when controlling for factors such as education, occupational position, physical diseases (cardiovascular dysfunction), psychosocial stress factors, and sleep problems, the outcomes were the same. When controlling for sex, the researchers found “a significant negative association between working hours and vocabulary score at baseline and at follow-up among men but not among women.”

The analysis comes from the Whitehall II Study, a multiyear research and data collection project that involved several thousand British civil servants. The study is unique because a lot of research asking what happens when people work overtime uses shift workers. Shift workers are people who don’t work 9-to-5. They typically either long shifts, such as long-haul airline pilots, or overnight shifts, such as emergency room personnel. It’s rare for studies of working hours to look at more traditional office work schedules.

Resources

Virtanen, M., Singh-Manoux, A., Ferrie, J. E., et al. (2009). Long Working Hours and Cognitive Function The Whitehall II Study, American Journal of Epidemiology, 169(5):596-605.

Image by AMISOM Public Information, CC.