CSI TV.

Is sitting in front of the tube for hours really bad for your health?

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David Leventi / Gallery Stock

It's our guilty pleasure: Watching TV is the most common everyday activity, after work and sleep, in many parts of the world. Americans view a whopping five hours of TV each day, and while we know that spending so much time sitting passively can lead to obesity and other diseases, researchers have now quantified just how harmful being a couch potato can be.

In an analysis of data from eight large previously published studies, a Harvard-led group reported in the Journal of the American Medical Association that for every two hours per day spent channel surfing, the risk of developing Type 2 diabetes rose 20% over 8½ years, the risk of heart disease increased 15% over a decade, and the odds of dying prematurely climbed 13% during a seven-year follow-up. All of these outcomes are linked to a lack of physical exercise; that's not a revelation. But compared with other sedentary activities, like knitting, viewing TV may be especially effective at promoting unhealthy habits. For one, the sheer number of hours we pass watching TV dwarfs the time we spend on anything else. And other studies have found that watching ads for beer and pretzels may make you more likely to consume them.

Even so, the authors admit that they didn't compare different sedentary activities to determine whether TV watching was linked to a greater risk of diabetes, heart disease or early death compared with, say, reading. They also did not break down the health outcomes by people who watched the same amount of TV but had different levels of physical activity, like those who catch their favorite show while on a treadmill. For them, the health risks may be lower, but as the scientists note, for the most part those who log the most hours watching TV aren't the most physically active.

Sources: Journal of the American Medical Association; Associated Professional Sleep Societies meeting; Food and Drug Administration; Population Health Metrics

SLEEP

Cool Your Head to Fall Asleep

Can't sleep? You need to chill out. If drawing the shades and cocooning yourself in darkness doesn't help, consider trying a cooling cap.

Researchers report that cooling the brain may help some problem sleepers drift off faster and sleep longer. In a study involving 12 insomniacs and 12 healthy sleepers, when the troubled sleepers wore specially designed caps that circulated water at cool temperatures, they fell asleep about as quickly as the normal sleepers did. The chillier the water, the better those with insomnia slept.

The results support earlier findings that restless sleepers tend to show higher than normal brain activity in the frontal cortex--a region responsible for planning and reasoning--while they're trying to doze off. The heightened activity raises the brain's temperature just as the body starts to cool off at the end of the day to promote sleep. Cognitive behavioral therapy and drugs like melatonin can also help troubled sleepers get more rest, but cooling the brain may be one more way to get people to fall asleep and stay asleep--until morning.

SKIN CANCER

Clearer Labels for Sunscreens

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