Here's how long you can work before your brain shuts down

I'm having a hard time starting this article.

According to research out of the University of Melbourne, that might be because I'm middle-aged and work too much. Economists determined that burning the midnight oil makes you, well, dumber.

"Our study highlights that too much work can have adverse effects on cognitive functioning," they conclude.

Tell us something we didn't know. Who hasn't, at the end of a seemingly endless workweek, found themselves staring blankly at their computer screen or into space unable to remember what they had for lunch, let alone form a coherent thought about the task at hand?

For some employees, of course -- the average resident physician or, these days, that "gig economy" worker who makes ends meet by banging away at multiple projects -- long hours are a fact of modern working life. And there's a cost. Medical researchers have shown that working too much can affect employees' physical and mental health.

So how much is too much? For people age 40 and older, working up to roughly 25 hours per week boosts memory, the ability to quickly process information and other aspects of cognitive function, according to the study, which drew on a longitudinal survey that tracks the well-being of 6,000 Australians.

One reason that's important: With baby boomers in the U.S. retiring in droves, the study suggests that a part-time job that requires working some 20-30 hours per week could be just what the doctor ordered for staying mentally sharp.

"Our results indicate that the part-time work is an effective way to maintain cognitive functioning relative to retirement or unemployment," the researchers write.

Beyond 25 hours a week, the middle-aged brain doesn't work as well, the study indicates, noting that the findings apply to both men and women.

Notably, employees in this age range who work especially long hours can do worse on cognitive tests, such as those involving memory or abstract reasoning, than people who don't work at all.

Whatever that means.

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    Alain Sherter covers business and economic affairs for CBSNews.com.