Believe it or not (and I know this will seem incredible), kids who watch a lot of TV tend to get fat. According to a new study from New Zealand in the International Journal of Obesity, which followed kids from birth through age 15, "BMI and prevalence of overweight at all ages were significantly associated with mean hours of television viewing reported in the assessments up to that age. These associations were stronger in girls than boys. The associations remained significant after adjusting for parental body mass indices and socio-economic status." The investigators say the effect size is small, but actually larger than those commonly reported for nutritional intake and physical activity.
Meanwhile, there has been controversy about whether TV also makes kids stupid, or more accurately, educational underachievers. The difficulty is in deciding whether kids who just aren't interested in school work to begin with watch more TV, or whether TV watching in fact makes them do poorly in school. And maybe "educational TV" is good for your brain, who knows?
What appears to have been the same cohort was also assessed up to 26 years of age for dropping out of high school and getting a college degree. According to a report in the Archives of Pediatric and Adolescent Medicine (subscription only, sorry):
The mean time spent watching television during childhood and adolescence was significantly associated with leaving school without qualifications and negatively associated with attaining a university degree. Risk ratios for each hour of television viewing per weeknight, adjusted for IQ and sex, were 1.43 (95% confidence interval [CI], 1.24–1.65) and 0.75 (95% CI, 0.67–0.85), respectively (both, P<.001). The findings were similar in men and women and persisted after further adjustment for socioeconomic status and early childhood behavioral problems. Television viewing during childhood (ages 5–11 years) and adolescence (ages 13 and 15 years) had adverse associations with later educational achievement. However, adolescent viewing was a stronger predictor of leaving school without qualifications, whereas childhood viewing was a stronger predictor of nonattainment of a university degree.
These are very strong effects -- and note that they control for IQ. Here's a picture:
Note that about 40% of the kids who watched less than an hour of TV per weeknight graduated from college, while 10% of kids who watched 3 hours or more did so.
So now you know how to make your kids fat and stupid. Glad I could help.
Apologies: I forgot to give the reference to the article. Hancox et al. Association of Television Viewing During Childhood With Poor Educational Achievement
Arch Pediatr Adolesc Med.2005; 159: 614-618.