Part D. Chapter 3: Individual Diet and Physical Activity Behavior Change
Sedentary Behavior, Including Screen Time
The Physical Activity Guidelines for Americans recommend that adults engage in at least 150 minutes (2.5 hours) of moderate- to vigorous-intensity physical activity each week and two days a week of strength training.48 Youth ages 6 to 17 years should engage in 60 minutes or more of daily physical activity.48 Unfortunately, the vast majority of Americans do not get the physical activity they need; only 20 percent of adults meet both the aerobic and strength training recommendations and less than 20 percent of adolescents meet the youth guideline. 49, 50 In addition, one-third of adults engage in no leisure-time physical activity.51 Regular physical activity is associated with myriad health benefits, including reduced risk of chronic disease, and physical, mental, and cognitive benefits, irrespective of body weight.48 Physical inactivity is associated with increased risk of overweight and obesity, CVD, type 2 diabetes, breast and colon cancer, and overall all-cause mortality.52
Sedentary behavior, which refers to any waking activity predominantly done while in a sitting or reclining posture, is gaining considerable public health interest as a chronic disease risk factor and therefore a potential area for interventions to target, with reducing screen time often a focus. The American Academy of Pediatrics (AAP) recommends no more than 2 hours a day of screen time (including television and other types of media) for children ages 2 years and older and none for children younger than age 2 years.53 However, children ages 8 to 18 years spend an average of 7 hours on screen time each day.54 The U.S. Report Card on Physical Activity for Youth gave the sedentary behavior indicator a grade of “D” for youth meeting the AAPs screen time recommendation.55 Rates of screen time are similar among males and females, yet disproportionately higher for African American youth compared to Caucasian youth (63.3 percent not meeting AAP recommendation vs. 44.6 percent).56 For this topic, two questions were addressed by the DGAC, the first with a NEL systematic review focused on the transition from childhood to adulthood and sedentary behavior in adults. The second question used the 2014 Community Preventive Services Task Force Obesity Prevention and Control (Community Guide) systematic review to examine the effectiveness of interventions among youth to reduce sedentary screen time and increase physical activity.
Question 4: What is the relationship between sedentary behavior and dietary intake and body weight in adults?
Source of evidence: NEL systematic review
Moderate and consistent evidence from prospective studies that followed cohorts of youth into adulthood supports that adults have a higher body weight and incidence of overweight and obesity when the amount of TV viewing is higher in childhood and adolescence. DGAC Grade: Moderate
Moderate evidence from prospective studies suggests no association between sedentary behavior in adulthood and change in body weight, body composition, or incidence of overweight or obesity in adulthood. DGAC Grade: Moderate
Insufficient evidence exists to address the association between sedentary behavior and dietary intake in adults. DGAC Grade: Grade Not Assignable
Sedentary behavior, including TV watching and screen time, should be limited during childhood to lower the likelihood of excess body weight or overweight and obesity in adulthood. Federal, state, and local policies and programs to support school and community-based programs to identify and reduce sedentary behavior among children and adolescents are needed to help them achieve and maintain healthy weight status as they transition into adulthood. Although an apparent lack of association exists between sedentary behavior and change in body weight status in adulthood, adults are encouraged to adopt and sustain levels of physical activity consistent with the Physical Activity Guidelines for Americans to promote health and to achieve and sustain a healthy weight status.
Review of the Evidence
This evidence review included 23 studies from 18 prospective cohorts that examined the relationship between sedentary behavior and body weight status in adults.57-79 Study locations included six studies from Australia,59, 60, 65, 74, 75, 77 six studies from the United Kingdom,61, 69, 70, 73, 76, 78 seven studies from the United States,57, 58, 62, 66, 67, 71, 79 two studies from New Zealand,63, 64 and one study each from Canada72 and Spain.68 The mean age of participants ranged from 23 years to 60 years. Longitudinal studies followed participants from childhood (5 to 16 years) to adulthood (21 to 45 years). Three studies (two cohorts)57, 59, 75 had an all-female sample and the remainder of the studies included both males and females.
Increasing levels of TV viewing during childhood and adolescence predicted higher BMI64, 65, 69, 76 and increased incidence of overweight and obesity in adulthood.58, 64, 65, 76 The lack of association between adult sedentary behavior (TV viewing, commute time or composite measures of sedentary behavior) and body weight change or body weight status are mostly consistent, despite methodological differences in measurement of sedentary behavior. Among two studies that assessed the relationship between sedentary behavior in adulthood and dietary intake, one study found an association between TV viewing and lower compliance with recommended dietary guidance.66 The other study found that more TV viewing was associated with greater intake of calories from fat, but not total calories or calories from sweets.71
Methodological approaches differed with regard to population and cohort size, types of sedentary behavior considered, and timeframes studied. Only one study directly measured sedentary behavior61 and few studies adjusted analysis for energy intake and other potential mediators, such as dietary intake. The majority of studies were conducted in Caucasian populations; therefore diverse ethnic and racial groups were underrepresented.
For additional details on this body of evidence, visit: http://NEL.gov/topic.cfm?cat=3343
Question 5: How effective are behavioral interventions in youth that focus on reducing recreational sedentary screen time and improving physical activity and/or diet?
Source of evidence: Community Preventive Services Task Force Obesity Prevention and Control: Behavioral Interventions that Aim to Reduce Recreational Sedentary Screen Time (Community Guide)80 Available at: http://www.thecommunityguide.org/obesity/RRbehavioral.html
The DGAC concurs with the Community Guide,80 which found strong evidence that behavioral interventions are effective in reducing recreational sedentary screen time among children ages 13 years and younger. Limited evidence was available to assess the effectiveness of these interventions among adults and no evidence was available for adolescents ages 14 years and older. DGAC Grade: Strong
The Community Guide identified effective behavioral interventions to reduce recreational screen time and recommended that they be implemented in a variety of settings. The DGAC concurs with this recommendation because of the potential for these interventions to have beneficial effects on childrens diet and weight status. Multifaceted interventions to reduce recreational sedentary screen time may include home, school, neighborhood, and pediatric primary care settings, and emphasize parental, family, and peer-based social support, coaching or counseling sessions, and electronic tracking and monitoring of the use of screen-based technologies.
Review of the Evidence
The Community Guide review classified behavioral screen time interventions as: 1) screen-time-only interventions that focus only on reducing recreational sedentary screen time, and 2) screen-time-plus interventions, which focus on reducing recreational sedentary screen time and increasing physical activity and/or improving diet. These interventions are used to teach behavioral self-management skills through one or more of the following components: classroom-based education, tracking and monitoring, coaching or counseling sessions, and family-based or peer social support. The Community Guide review focused on both high- and low-intensity interventions to reduce sedentary behavior in youth. High-intensity interventions included the use of an electronic monitoring device to limit screen time or at least three personal or computer-tailored interactions. Low-intensity interventions included two or fewer personal or computer-tailored interactions. This review included 49 studies with 61 arms. Studies were included that had an intervention component with one or more outcomes of interest. Study duration was 1.5 months to 2 years.
The study populations were mostly children younger than age 13 years and collectively were racially and ethnically diverse. All studies were conducted in the United States within a variety of settings, including schools (20 studies), homes (8 studies), communities (6 studies), primary care clinics (4 studies), research institutes (5 studies), and in multiple settings (4 studies). Settings were a mix of urban and suburban areas.
Evidence indicated that behavioral screen time interventions are effective in reducing recreational sedentary screen time (47 study arms), improving physical activity (42 study arms), improving diet (37 study arms), and improving or maintaining weight status (38 study arms). Studies were found to be effective among children ages 13 years and younger. The evidence showed that both screen-time-only and screen-time-plus interventions are both effective at reducing recreational sedentary screen time. However, screen-time-only interventions showed greater reductions in TV viewing and composite screen time compared to screen-time-plus interventions. All studies demonstrated effectiveness among both males and females. Forty-five studies that reported racial distribution showed intervention effectiveness in all groups: white (20 studies), black (14 studies), Hispanic (11 studies), Asian/Pacific Islander (10 studies), American Indian or Alaska Native (3 studies), and other (7 studies).
For additional details on this body of evidence, visit: http://www.thecommunityguide.org/obesity/RRbehavioral.html