The same issue of The Journal of the American Medical Association that had last week's column topic had another article about the influence of watching TV on type 2 diabetes, heart disease and all-cause mortality. (1) I have a problem with this TV-causes-obesity thing because the purported mechanism of how TV does this involve unhealthy eating, taking time away from physical activity and exposure to advertisements for bad food. But those things studied individually don't have any effect on obesity. How could TV indirectly do it. Another clue that there is something wrong with this idea is that there are so many studies of TV in this regard. If the evidence is strong why do we need more studies of the issue.
Anyway here's another report. These authors do a meta-analysis of 8 studies of the effect of hours of TV watched on incidence of type 2 diabetes, heart disease and overall mortality. Most studies of TV are done on kids but this one examines the fewer ones done on adults.
They did detect an increase of 20% in the incidence of type 2 diabetes, 15% increase in heart disease and 13% increase in all cause mortality for each 2 hours of watching TV. These effects were decreased, but not wiped out, when corrected for how fat the subjects were to begin with. There seems like a pernicious effect of watching TV.
But this is small and could be do to reverse causality; that is, obese people or people who are going to have bad hearts... are more inclined to watch TV. Or maybe they are poor.
These authors cite 3 studies of taking TV away to see if it improves things. One study of 192 9-year-old children found that reducing time of TV viewing and video game playing slowed the increase in BMI and decreased the number of meals eaten in front of the TV but was not associated with change in physical activity.(2) Another study of 70 children with BMIs above the 75 percentile showed that reducing TV viewing and computer time by 50% over 2 years resulted in significant reduction of BMI and calorie intake but did not increase objectively measured physical activity.(3) The third study was conducted in 36 overweight or obese adults and it did not find a significantly greater change in calorie intake or BMI after restricting TV viewing time by 50% over a 3 week period; however, a significant increase in objectively measured exercise was observed.(4)
So I guess we just need to spend more time and money to study this issue. Not.
1. Grontved A, Hu f. Television viewing and risk of type 2 diabetes, cardiovasular disease, and all-cause mortality. A met-analysis. JAMA. 2011;305(23):2448-2455.
2. Robinson TN. Reducing children's television viewing to prevent obesity:a randomized controlled trial. JAMA. 1999;282(16):1561-7.
3. Epstein LH, et al. A randomized trial of the effects of reducing television viewing and computer use on body mass index in young children. Arch Pediatr Adolesc Med. 2008;162(22):239-45.
4. Otten JJ, et al. Effects of television viewing reduction on energy intake and expenditure in overweight and obese adults: a randomized controlled trial. Arch Intern Med. 2009;169(22):2109-2115.