Lots of studies show that kids who watch TV are less healthy. Kids who watch TV probably spend less time playing outside and are able to get their parents to buy all sorts of sugary foods from commercials. But there have been no long-term studies of kids' TV-watching habits and their long-term health—until this one: a 26-year study of New Zealanders.

What the researchers wanted to know: How does watching television affect long-term health?

What they did: The study began in the early 1970s, when all kids born between April 1972 and March 1973 in Dunedin, on New Zealand's South Island, were invited to join. Over 1,000 children took part in the first follow-up at the age of 3. They were assessed again every two or three years, and 980 went in for the most recent assessment, at the age of 26. From the ages of 5 to 21, children or their parents answered questions on how much time they spent watching television. In the last assessment, the participants' height, weight, and blood pressure were measured, and they rode a stationary bicycle for exercise tests.

What they found: Watching more TV at ages 5–15 was correlated with a whole list of health evils at age 26: more excess weight, more likely to smoke, higher cholesterol, and lower aerobic power on the exercise bike. That was true even after adjusting for their socioeconomic status as children. And childhood TV viewing correlated with overweight even after adjusting for the kids' size at age 5 and their parents' size. The researchers didn't find any relationship between television and blood pressure.

What the study means to you: Come on, people! Turn off the television!

Caveats: OK, OK, this study doesn't prove that watching television caused the health problems. Maybe people who are genetically predisposed to obesity don't like physical activity—or maybe they're also genetically predisposed to spend all their time watching reruns. Also, the kids and parents had to remember how much television they watched; no one actually sat down and watched them watch TV.

Find out more: Even Nickelodeon wants you to turn off your TV (www.nick.com).

Read the article: Hancox, R.J., Milne, B.J., and R. Poulton. "Association Between Child and Adolescent Television Viewing and Adult Health: a Longitudinal Birth Cohort Study." Lancet. July 17, 2004, Vol. 364, pp. 257–262.

Abstract online: www.ncbi.nlm.nih.gov