Long working hours among middle-aged people increase the risk of dementia, including decline in cognitive function, a study suggests. The paper carried in the March issue of the American Journal of Epidemiology by the Finnish Institute of Occupational Health said 2,214 middle-aged British civil servants participated in the study which was a part of the Whitehall II study.

"When compared with employees with normal working hours (35-40 per week), employees working very long hours (over 55 hours per week) and those with an average length of working week (40 hours) performed worse in a vocabulary test already at the baseline study," it said.

Test subjects in different groups who work different weekly working hours took five different cognitive tests, including short-term cognitive function, a vocabulary test, and a cognitive reasoning test.

The longer the working hours, the lower the vocabulary and cognitive reasoning abilities, the results show. The team said it was not yet known why long working hours have adverse effect on cognitive function, but several factors may contribute to the process, for example increased sleeping problems, depression, unhealthy lifestyle and cardiovascular diseases. "All these factors together may have an effect to the brain function which eventually is shown as a decline in cognitive function," it adds.