PHILADELPHIA (CBS) – It is no real secret that employees working long hours is a common theme worldwide, but does working too much eventually start to diminish cognitive skills?

A study from the American Journal of Epidemiology examined the association between long working hours and cognitive function in middle aged employees.

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Researchers collected data from a study of 2,214 British civil servants, who were full time employees in 1997-1999 and then performed a follow up study in 2002-2004.

The study performed a series of cognitive tests, including short-term memory, semantic fluency and phonemic fluency.

The research revealed that those working 55 hours per week or more had lower scores in the vocabulary at both the baseline and the follow up, compared to those who worked 40 hours per week at the most.

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Those who worked long hours also saw a decline in their performance on reasoning tests.

The connection between working hours and cognitive function is adjustable due to several potential factors such as, age, gender, marital status, education, career, income, health risk.

Not surprisingly, the study also found that working long hours was associated with short sleep duration and psychologic distress, but not with sleep disturbances.

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