Sedentary Behaviors, Weight, and Health and Disease Risks

Prior to the 1980s, very little thought was given to sedentary behaviors and how they may impact health. In 1985, the first study to investigate the relationship between a sedentary behavior, television viewing, and weight status was published by Dietz and Gortmaker [1]. In this study, the relationship between television viewing and weight status in children and adolescents was examined cross-sectionally and longitudinally , using data from the National Health Examination Survey. Results indicated that television viewing was positively related to the prevalence of obesity, both cross-sectionally and longitudinally. This investigation led to a growing body of research examining the mechanisms by which television watching impacted weight status and if reducing television watching could improve weight status in children. Outcomes from this area of research informed the development of the recommendation that screen time should be limited to ≤2 hours per day in children [2]. Initially, the term " sedentary " was used to describe behaviors that were not considered to meet energy expenditure levels equivalent to moderate-intensity physical activity. Additionally , attention was focused on sedentary behaviors occurring during leisure time, thus television viewing and recreational computer use were the sedentary behaviors that were predominantly reported in early investigations of sedentary behaviors. Since the 1980s, sedentary behaviors have become more clearly defined and are now classified by energy expenditure level, similar to the way that physical activities are classified. Sedentary behaviors are characterized by minimal movement and a very low level of energy expenditure (<1.5 metabolic equivalent units (METs)) similar to that which is required to sit quietly [3, 4]. Thus, sedentary pursuits are primarily sitting behaviors that occur in a variety of domains (i.e., leisure, occupation, transportation, and recreation) and include working/playing on the computer, driving a car, and watching television. While sedentary behaviors have been associated with del-eterious health outcomes in children for almost thirty years, sedentary behaviors are now also associated with morbidity in adults. Recent observational epidemiological research indicates that the more time spent being sedentary, independent of time engaging in physical activity, the greater the risk of developing type 2 diabetes [5], cardiovascular disease [5, 6], metabolic syndrome [7], weight gain [8–10], and obesity [11, 12]. Furthermore, evidence suggests that sedentary behaviors are an independent risk factor for all-cause and car-diovascular-related mortality [5, 13–15]. There are many proposed mechanisms by which sedentary behaviors may negatively influence health. For television watching, it was initially proposed …