Chances are you've spent more than one night tossing and turning. Up to 70 million U.S. adults have a sleep disorder.

But if you're rapper Eminem and a tour means you're not in the same time zone for more than a night or two, getting a good night's sleep is an extra challenge.

His solution (odd, but the right impulse) is to put tinfoil on his hotel room windows to make sure not a ray of light gets through.

Studies confirm that darkness is linked to better sleep quality, and to a happier outlook. But in the United States and Europe, 99 percent of the public can't experience a natural dark night.

So, whether you have insomnia or not, you may want to adopt Eminem's strategy of light-blocking (but use something more permanent than tinfoil).

For a study published in the American Journal of Epidemiology, researchers measured the bedroom light of more than 800 older Japanese people.

Participants kept sleep diaries and were followed for two years. At the end of that time, people who were exposed to more than 5 lux of light (a 100-watt lightbulb gives off 60 lux) when trying to sleep at night were more likely to have symptoms of depression than those who slept in total darkness.

Why? Light at night might interfere with your body's internal clock and release of the sleep hormone melatonin, throwing off your brain chemistry.

Whether you're a homebody or a world traveler, invest in effective eyeshades and lobby your local government to adjust your town's illumination to reduce light pollution.