When researchers ask people the most miserable part of their day, the same activity comes up again and again -- commuting. Spending long stretches getting to work, particularly in traffic, increases stress, harms the environment, and -- you probably don't need a scientific study to tell you this -- reduces the amount of time spent with loved ones, one of the biggest predictors of happiness.

All those factors are probably enough to make you loathe the time you spend getting to work, but energetic scientists aren't content to rest there. They've recently dug up yet another reason to hate your commute -- it's apparently also making you dumber.

Bad for your heart, bad for your brain

To come to this disturbing conclusion researchers out of the UK's University of Leicester and an area hospital teamed up to analyze a massive trove of data on the lifestyles of more than 500,000 Brits aged 37 to 73. At the beginning of the study and occasionally over a five year period the participants' intelligence and memory was assessed.

The researchers found a startling correlation when they crunched the numbers -- the more you drove, the dumber you got.

Study subjects who reported driving more than two hours a day, not only had less brain power when the researchers first assessed them, but they also saw more rapid declines in intelligence over the course of the research.

What's the problem with all that time spent driving? The researchers suggest the issue isn't something car specific like exhaust fumes or the ergonomics of the driver's seat. Instead, it's a combination of sitting and being bored to tears that seems to dent your intelligence.

"We know that regularly driving for more than two to three hours a day is bad for your heart. This research suggests it is bad for your brain, too, perhaps because your mind is less active in those hours," commented Kishan Bakrania, an epidemiologist who worked on the research.

In fact, a large body of existing research shows that a sedentary lifestyle is terrible for your brain, as well as your body. And the researchers themselves claimed not to be terribly surprised by the results.

What's the takeaway for those currently enduring awful commutes? Sadly, probably nothing you don't already know. If there's any way to switch to a job nearer to home, to swap a bike or public transport for part of your trip, or to talk your boss into letting you work from home occasionally, these changes won't just make you happier, they'll also probably make you smarter too.