Television is known as the most widely-viewed screen around the world, and just as much, as a major contributor to the obesity epidemic. Easy access to smartphones, tablets, and laptops — not just television — account for a child’s total screen time, which reflects a steady increase in sedentary behavior and a decrease in physical activity. For every added hour of television kids watch over time, they are likely to gain half a pound, according to a recent study.

The American Academy of Pediatrics recommends that children and teens engage in entertainment media for no more than one or two hours per day — granted that it is high-quality content — which also includes texting, using computers, and playing video games. Engaging in more than the recommended amount of screen time amounts in “sit time” and typically leads to gaining excess weight. TV encourages kids to have poor diets because it gives them the opportunity to snack on unhealthy foods while their hands are free — add to that the promotion of high-calorie foods during commercial breaks.

Researchers wanted to independently assess the relationship between TV, video/computer games, and DVD/videos, and total screen time with change in adolescent body mass index (BMI). Data was collected from the Growing Up Today Study II survey responses, which surveyed children and adolescents in three waves. The researchers focused on baseline and two-year change in reported screen time when compared to change in BMI among over 4,200 girls and over 3,500 boys whose average age was 14. The participants were surveyed biannually about their weight and screentime.

The results showed that 24 percent of the boys were either overweight or obese, compared to 14 percent of the girls. The researchers found that an increase in total screen time was associated with a 0.07-point increase in BMI for girls and a 0.05-point increase for boys. The changes in television and total screen time were correlated with BMI gains among overweight girls. Female participants also saw the most weight gain, which correlated with an increase in using electronic games and videos, most likely due to the influences of product placements and advergames.

From one survey to the next, the researchers found each one-hour increase in adolescents’ TV watching was tied to an increase of about 0.1 points on the BMI scale — or about a half-pound. The increases in screen time throughout the years were linked to similar but relatively smaller changes in BMI.

"The weight of the evidence is pretty strong that television viewing is related to unhealthy changes in weight among youth," Jennifer Falbe, lead author of the study, told Reuters. "It's important for parents to be aware of all the potentially obesogenic screens that they should really be limiting in their children's lives."

Watching TV is on of the biggest offenders when it comes to weight gain in kids. The environmental setting of the sedentary activity encourages the viewer to be in a hibernating-like state resulting in little to no physical activity when compared to playing even a computer game.

While the study remains consistent with previous findings related to the subject matter, it does pose some limitations. The researchers noted the there weren’t many non-white or poor children suggesting that the findings may not apply to all U.S. youth.

The researchers also delved into BMI changes among youth that could have been influenced by food advertising. TV was still found to be the "steadiest medium for delivering food advertising," and was consistently associated with changes in BMI among subgroups, the researchers wrote, according to Medscape. Older youth were just as susceptible to being influenced by food marketing.

Food-related TV ads for adolescents typically consist of high-calorie, low-nutrient foods and drinks. Food marketing directed at kids through websites, advergames, social networking, and product placements should be monitored to evaluate how the specific techniques advertisers use affect BMI, and how they can reduce unhealthy exposure, the researchers said.

The Centers for Disease Control and Prevention says that more than one-third of children and adolescents are either overweight or obese. Excess weight gain is associated with an increased risk of heart disease, type 2 diabetes, stroke, several types of cancers, and osteoarthritis in obese kids, who are likely to become obese as adults. Healthy lifestyle habits, such as healthy eating and an increase in physical activity can lower the risk of obesity and other diseases related to the epidemic.

Source: Falbe J, Field AE, Hu F, et al. Adiposity and Different Types of Screen Time. Pediatrics. 2013.