TV and Inactivity Are Separate Contributors to Metabolic Risk Factors in Children

Abstract

In 1993 the journal Pediatrics published an editorial entitled “TV or not TV: Fat is the question” [1]. It critiqued a study that used both cross-sectional and longitudinal analyses to ask whether after-school TV viewing was associated with adiposity and physical inactivity in adolescent American girls [2]. Surprisingly, this study found virtually no association. This counter-intuitive result emphasises the complexity of the inter-relationships between diet, physical activity, and a host of possible confounding factors in the causation of obesity and its related metabolic disturbances. It remains possible that the obesity pandemic has unexpected causes related to infections or environmental contaminants [3], or even to the cumulative effects of assortative mating (obese people choosing obese partners, hence concentrating the genetic propensity). Nevertheless, most observers are happy to apply Occam's razor (i.e., the principle that the simplest explanation is the preferred one) and accept that obesity is the natural biological response to a massive self-imposed change in mankind's external environment, involving the ready availability of energy-dense foods and a rapid adoption of very sedentary lifestyles. However, this most basic of explanations conceals a myriad of complexities that need to be understood in order to better devise preventive and therapeutic interventions. For eons humans and their hominid forebears have been physically active, but in the past 50 years we have discovered how to substitute fossil-fuel energy for human muscular work—from occupational work to modes of transport, and from domestic tasks to leisure pursuits. As if this were not enough, we have also invented a whole new genre of entertainment in the form of television, electronic games, and the Internet that seduces us to spend hours each day sitting almost totally inactive. Viewed from this evolutionary perspective, it becomes easy to accept that excessive TV viewing In the past 50 years we have discovered how to substitute fossil-fuel energy for human muscular work.. and physical inactivity might be implicated as important contributory factors to the kinds of metabolic disturbances that are increasingly being reported among children in affluent societies [4]. But are they on a single causal pathway, or might they have discrete effects? In a paper in PloS Medicine, Ekelund et al. [5] suggest that the latter is the case.