Approximately two-thirds of American adults over age 20 are overweight and close to one-third are obese . Whereas overweight and obesity weren’t even acknowledged as a national health threat until the 1950s, they have since been rapidly on the rise and have now surpassed smoking as a risk factor for death in the US. Researchers have been looking into the reasons behind this trend for the last four decades.

Most obviously, doctors attribute overweight and obesity to high calorie diets combined with a lack of physical activity. Many modern advances have unfortunately allowed sedentary lifestyles to become the norm. Perhaps the hallmark of these advances was the introduction of the household TV in the 1950s, triggering a shift in American home life that persists today. Substituting television for more energetic activities can certainly contribute to weight gain, which may be further exacerbated by program content and advertising that encourages poor nutritional choices.

Some previous research has identified an association between television watching and childhood health problems, including obesity, high cholesterol , poor physical fitness, and even smoking. To take this research one step further, a New Zealand study published in the July 17, 2004 issue of The Lancet examined the long-term health consequences of television viewing behavior among children. Their conclusion: watching more than two hours of TV as a child increases the risk of overweight, poor fitness, and related problems well into adulthood.

About the Study

Researchers collected data on the television watching habits of approximately 1,000 people (predominantly Caucasian) born in Dunedin, New Zealand between 1972 and 1973. They tracked daily viewing habits from age five until age 15, then compared this data with final health assessments performed at age 26. The children’s parents reported weekday TV hours for children ages 5–11, while children ages 13–15 reported their own weekday and weekend TV hours. Health status at age 26 was measured by body-mass index (BMI, a common measure of weight in research), blood pressure , cholesterol levels , cardiovascular fitness level , and smoking status.

The researchers also collected information on the children’s socioeconomic status at ages 5–15, BMI at the study’s onset (age 5), physical activity level at age 15, and television watching at age 21. They also recorded parents’ BMI’s and smoking status.

The Findings

As the number of child and adolescent television viewing hours increased, so did the degree of overweight, poor fitness, high cholesterol, and smoking in adulthood. No significant correlation, however, was found between television viewing and high blood pressure . Overall, the study estimates that 17% of overweight, 15% of raised blood cholesterol, 17% of smoking, and 15% of poor fitness in adults can be attributed to watching television for more than two hours a day during childhood and adolescence.

While these findings are significant, more comprehensive analysis is warranted. Though researchers did consider a number of factors other than television that might affect health, such as socioeconomic status, there are many others factors they were unable to take into account. And while the study did not find that childhood exercise levels altered the ill effects of television watching, it was only measured once―at age 15.

How Does This Affect You?

This study provides evidence for what could already be safely assumed: a lifestyle habit that increases risk for poor health as a child might also increase risk for poor health further down the line. Consequences of bad habits adopted during childhood may not manifest right away; rather, they may turn up a decade later.

More studies are needed to pinpoint what aspects of TV watching contribute to poor health outcomes. It may be that its sedentary nature may only be a partial explanation. For example, is there a variation in health outcome according to different types of programming viewed? If advertisements for junk food were limited or banned, would health outcomes be altered? It may not be legitimate to denounce television in its entirety. But in the name of prevention, research suggests that parents should try to limit children’s television watching to under two hours a day, also bearing in mind that watching any television at all has yet to be associated with any health benefit.