Cut down on the multitasking, and focus on tasks for 90 minutes at a time.

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RODALE NEWS, EMMAUS, PA—We all get tired and cranky at the end of a long work week—and now it seems we get dumber, too. A new study published in the American Journal of Epidemiology has found that people who work more than 55 hours a week score lower on vocabulary and reasoning tests than people who work normal 40-hour weeks.

THE DETAILS: Researchers analyzed data from 2,214 participants of a long-term study of British civil servants. Their sample, made up primarily of men, included people who were employed and who had taken five cognitive tests on memory, reasoning skills, vocabulary, and language during both of the last two phases of the study, which were five years apart. After adjusting for complicating factors, such as education levels, possible health problems, and occupational position, the researchers found that people who worked more than 55 hours per week scored lower on vocabulary tests during both phases of the study, and they didn’t perform as well on the reasoning tests at the second follow-up five years later. In fact, working late was so tough on mental abilities that, the authors write, “the difference in aspects of cognitive functioning between employees working long hours and those working normal hours is similar in magnitude to that of smoking, a risk factor for dementia which has been found to affect cognition,” they write.

WHAT IT MEANS: You aren’t doing yourself any favors by burning the midnight oil at the office. In today’s economic climate, where downsizing has left a lot of employees doing the work of two or three, we all feel the need to pull our weight or end up next on the chopping block. However, if you’re working late because you don’t feel like you’re getting enough done during the day, a few adjustments to your work habits may save you some time.