The Consequences of Sedentary Behaviors: Keeping Interpretations Anchored in Evidence
In this issue of Exercise and Sport Sciences Reviews (ESSR), Professor Stuart Biddle and colleagues provide a brief review critically examining the evidence that sedentary behavior is causally related to adiposity in young people (4). They argue that despite some consistency of the evidence supporting the observation that increased sedentary behavior/screen/TV time is associated with undesirable adiposity measures in young people, the magnitude of the relations is usually small, based predominantly on associational research, and inconsistent between reported and direct measure methods and often fails to control or account for important factors (e.g., physical activity, diet, sleep) that could mediate or moderate the relations observed. The authors conclude that the current evidence does not support a causal association between sedentary behaviors and adiposity in young people, and they propose a conceptual model illustrating the complexity of this relation. Although the authors restrict their discussion to childhood obesity and adiposity, they remind us of the need to ensure that our research rhetoric does not supersede the underlying evidence.
Sedentary behavior research is in its infancy, or at best childhood, and although seems to be a plausible, prominent, and pervasive public health threat, there is some concern that related guidelines, recommendations, and messages may be ahead of the evidence supporting them. In addition to the caution conveyed by Biddle et al. (4), a recent American Heart Association Advisory (1) concluded that “further evidence is required to better inform public health interventions and future quantitative guidelines on sedentary behavior and cardiovascular health outcomes.” A comprehensive review by Prince et al. (5) “identifies the need for longitudinal studies, as well as further research on factors in the physical, social, and policy environments” and “recognizes the need to standardize methodology for collecting, defining, and reporting sedentary behavior and correlates.” Ekelund et al. (6) concluded that 60–75 min·d−1 of moderate-intensity physical activity may eliminate the increased risk of death associated with excessive sitting in adults but does not eliminate the elevated risk associated with high TV-viewing time specifically. The collective evidence is structurally weak if not equivocal.
Balancing the demand for public health guidance in relation to sedentary behaviors with the current state of the evidence is a challenge, and much more experimental research, with measures of the fidelity of interventions, is required. Nevertheless, as Biddle et al. (4) agree, the current approach of discouraging excessive sedentary behaviors, especially TV time, is sensible and the likelihood of benefit exceeds the risk of harm.