This is an excerpt from Sedentary Behavior and Health by Weimo Zhu & Neville Owen.
In addition to the relationships with overweight and obesity, there is mounting evidence that screen time is associated with other cardiometabolic risk factors such as hypertension, high cholesterol levels, insulin resistance and type 2 diabetes mellitus, and metabolic syndrome (Council on Communications and Media 2011). A study of 6- to 19-year-olds in the 2003-2004 and 2005-2006 NHANES found that the odds of having a higher cardiometabolic risk score (calculated from waist circumference, resting systolic blood pressure, non-high-density lipoprotein cholesterol, and C-reactive protein) were significantly higher for children who viewed 4 or more hours per day of television than for children who viewed less than 1 hour per day, adjusting for demographic characteristics, smoking, total calories from fat, total calories from saturated fat, dietary cholesterol intake, sodium intake, and physical activity (Carson and Janssen 2011). Similar results were found in a population-based sample of Portuguese 2- to 12-year-olds in the 2009 and 2010 Portuguese Prevalence Study of Obesity in Childhood, which found that higher television viewing time was significantly associated with an unfavorable cardiometabolic risk score (calculated from resting heart rate, resting diastolic blood pressure, resting systolic blood pressure, BMI, and skinfold thickness), adjusting for age, gender, parental education, parental BMI, perceptions of crime in the area, sleep duration, birth weight, duration of breastfeeding, a "bad diet" score, number of fruit portions eaten per week, and physical activity. This study also found significant positive associations between television viewing and resting systolic blood pressure and resting diastolic blood pressure (Stamatakis et al. 2013). In addition, a cross-sectional study of overweight and obese 14- to 18-year-olds found a significant positive association between television viewing and fasting insulin and HOMA-IR (indicators of insulin resistance), adjusting for demographic characteristics, waist-to-hip ratio, total caloric intake, percent of caloric intake from carbohydrate, and physical activity (Goldfield et al. 2013).
Although more limited than the television viewing research literature, studies provide some evidence for associations between computer use and video game playing with cardiometabolic risk factors. A cross-sectional study of overweight and obese 12- to 18-year-olds found a significant positive association between computer use and total cholesterol and low-density-lipoprotein cholesterol, adjusting for age, gender, pubertal stage, race/ethnicity, and physical activity (Altenburg et al. 2012). Another cross-sectional study of overweight and obese 14- to 18-year-olds found a significant positive association between video game playing and systolic blood pressure and ratio of total cholesterol to high-density lipoprotein, adjusting for demographic characteristics, BMI, sexual maturity, total caloric intake, percent of caloric intake from dietary fat, and physical activity (Goldfield et al. 2011).
Mechanisms Linking Screen Time and Obesity and Other Cardiometabolic Risks
Five mechanisms have been hypothesized to explain screen media viewing's contribution to obesity and other cardiometabolic risk factors (Council on Communications and Media 2011; Robinson 2001):
- Screen media viewing decreases metabolic rate.
- Screen media viewing displaces sleep or disturbs sleep patterns.
- Screen media viewing displaces physical activity, resulting in reduced energy expenditure.
- Dietary energy intake increases and dietary quality decreases during screen media viewing.
- Dietary energy intake increases and dietary practices worsen in response to advertising.
Although all of these mechanisms may be playing at least some role in the development of obesity and other cardiometabolic risk factors, limited evidence exists for the first three mechanisms. To date, the bulk of epidemiological and experimental studies are providing the greatest support for the fourth and fifth mechanisms.
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