Excessive TV watching linked to increased risk for type 2 diabetes, cardiovascular disease

Grøntved A. JAMA. 2011;doi:10.1001/jama.2011.812.

Those who watch at least 2 to 3 hours of TV each day are at an increased risk for type 2 diabetes, cardiovascular disease and all-cause mortality. This finding is significant because Americans spend an average of 5 hours a day watching TV, according to recent reports.

Watching TV is the most common daily activity in many parts of the world, apart from work and sleep, but results of a new study from Harvard School of Public Health (HSPH) indicate that this behavior must change to improve the overall health of the US population.

“The message is simple. Cutting back on television watching can significantly reduce risk of type 2 diabetes, heart disease and premature mortality,” Frank B. Hu, MD, PhD, professor of nutrition and epidemiology at HSPH in Boston, said in a press release. “We should not only promote increasing physical activity levels but also reduce sedentary behaviors, especially prolonged television watching.”

More TV, higher risk

The US numbers for TV viewing are higher than those in other parts of the world. Europeans spend an average of 40% of their daily free time in front of the TV vs. Australians, who spend 50% of their free time watching TV, which equates to approximately 3 to 4 hours. The negative health effects of TV viewing and other sedentary activities such as video gaming have been documented in prior studies, including associations with reduced physical activity levels and unhealthy diets.

Hu and Anders Grøntved, MPH, MSc, a doctoral student and visiting researcher in the HSPH department of nutrition, conducted a meta-analysis that included eight large prospective cohort studies from the US, Europe and Australia from 1970 to 2011.

Results of the meta-analysis indicate that more than 2 hours of TV daily is related to an increased risk for type 2 diabetes and cardiovascular disease. More than 3 hours of daily viewing is linked to an increased risk of premature death. For each additional 2 hours of TV viewing per day, the risk for type 2 diabetes, cardiovascular disease and premature death increased by 20%, 15% and 13%, respectively.

For type 2 diabetes (four studies), the total number of people was 175,938, with 6,428 incident cases during an average follow-up of 8.5 years. For fatal or nonfatal cardiovascular disease (four studies), the total number was 34,253, with 1,052 incident cases during an average follow-up of 10.4 years. For all-cause mortality (three studies), the total number was 26,509, with 1,879 deaths during an average follow-up duration of 6.8 years.

Based on disease incidence in the United States, according to the study researchers, it is estimated that among 100,000 people per year, each 2-hour increment in TV viewing per day was associated with 176 new cases of type 2 diabetes, 38 new cases of fatal cardiovascular disease and 104 new cases of all-cause mortality.

The study had a few limitations, including the relatively small number of studies and that the assessment of TV viewing was self-reported by participants. In addition, most of the studies did not assess the role of diet and physical activity in explaining the adverse effects of TV watching on chronic disease risk.

“Sedentary lifestyle, especially prolonged television watching, is clearly an important and modifiable risk factor for type 2 diabetes and cardiovascular disease,” Grøntved said in the press release. “Future research should also look into the effects of extensive use of new media devices on energy balance and chronic disease risk.”

Previous studies

The researchers mentioned in their study two previous randomized controlled trials in children that showed the benefits of reducing TV viewing time. A school-based study of 192 children aged 9 years found that a reduction in TV viewing and video game playing slowed increases in BMI and decreased the number of meals eaten in front of the television. However, this reduction in sedentary activity did not result in an increase in self-reported physical activity.

Another study of 70 children with a BMI above the 75th percentile showed that a reduction in TV viewing and computer time by 50% during a 2-year period resulted in a significant reduction of BMI and energy intake. Again, this change in behavior did not result in an increase of objectively measured physical activity.

Grøntved and Hu said these earlier short-term experimental studies suggest that reducing TV viewing time may lead to improvement in diet, physical activity or BMI.

Regarding their own findings, they concluded that “further study is needed to determine whether reducing prolonged television viewing can prevent chronic disease morbidity and mortality.”

Gerald Whitman

In an article by Grontved and Hu analyzing the effect of television viewing on the risk of type 2 diabetes, cardiovascular disease and mortality (JAMA, June, 2011), the statistical meta-analysis was very clear. In adults, increased television viewing was shown to be associated with an increase in all 3 health areas analyzed. The paper did not discuss whether the same risks would be seen in children, though some areas of probable similarities were pointed out (such as poorer eating habits). The American Academy of Pediatrics has issued a policy statement (Pediatrics Vol. 107 No. 2 February, 2001) in which they discuss the maximum amount of television time a child should be exposed to at various ages. Included in their recommendations was the concern of increased weight with increased television watching (a known contributor to all the issues raised in the article by Grontved and Hu). In addition, the AAP guidelines also talk about the increased time playing video games and the concern that this is additive to the time spent watching television.

I think it makes sense for pediatricians to utilize this data in adults as part of a cautionary tale for parents and children regarding the significant concerns of children watching too much television. Added to the pediatrician’s concern with excessive television viewing are also issues involving behavioral, interpersonal and academic performance that are frequently raised in the pediatric literature, but are not address in this paper.

—Gerald Whitman, MD
Infectious Diseases in Children Editorial Board member

Disclosure: Dr. Whitman reports no relevant financial disclosures.

This analysis of disease risk in adults has strong relevance for pediatricians and their patients. This clearly shows an increase in the chronic disease, type 2 diabetes, and cardiovascular disease, both of which are childhood onset disorders. Children and adolescents are at risk for a shorter life, given the death rate from all causes linked to TV watching if they are TV addicts as adults, an addiction that starts in childhood. TV viewing patterns, eating habits and reduced physical activity have been shown to be linked to the growing childhood obesity epidemic in this country. This report shows the continuity of these factors into the adult years and the serious health consequences for youth as they enter adulthood. The risks for diabetes and for cardiovascular disease are in a linear relationship with the amount of TV one watches, and this relationship stays even when weight issues are controlled for in the analysis.

Weight adds to the risks, of course, but TV brings its own, separate drag on wellness, according to this report. From a policy perspective, the AAP should look again at the standard advice of limiting screen time in teens and children to 2 hours per day. Perhaps this should be adjusted downward, given this analysis of adults' risk for these serious diseases. This whole report reminds me of the glacial pace with which the US acknowledged the link between smoking and cancer. The evidence was there, it was all in one direction and yet it was hard to accept. In the case of TV, the toxic substance isn't so obvious, but the links to poor health outcome with excessive TV viewing are all there. The study adds to this pile of evidence and means that as child health care providers we have to work harder at getting the TV time down, get the TV out of the bedroom and get kids off the couch and out the door.

—Suzanne Dixon, MD
Infectious Diseases in Children Editorial Board member

Disclosure: Dr. Dixon reports no relevant financial disclosures.

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