Accumulating evidence suggests that, independent of physical activity levels, sedentary
behaviours are associated with increased risk of cardio-metabolic disease, all-cause
mortality, and a variety of physiological and psychological problems. Therefore, the
purpose of this systematic review is to determine the relationship between sedentary
behaviour and health indicators in school-aged children and youth aged 5-17 years.
Online databases (MEDLINE, EMBASE and PsycINFO), personal libraries and government
documents were searched for relevant studies examining time spent engaging in sedentary
behaviours and six specific health indicators (body composition, fitness, metabolic
syndrome and cardiovascular disease, self-esteem, pro-social behaviour and academic
achievement). 232 studies including 983,840 participants met inclusion criteria and
were included in the review. Television (TV) watching was the most common measure
of sedentary behaviour and body composition was the most common outcome measure. Qualitative
analysis of all studies revealed a dose-response relation between increased sedentary
behaviour and unfavourable health outcomes. Watching TV for more than 2 hours per
day was associated with unfavourable body composition, decreased fitness, lowered
scores for self-esteem and pro-social behaviour and decreased academic achievement.
Meta-analysis was completed for randomized controlled studies that aimed to reduce
sedentary time and reported change in body mass index (BMI) as their primary outcome.
In this regard, a meta-analysis revealed an overall significant effect of -0.81 (95%
CI of -1.44 to -0.17, p = 0.01) indicating an overall decrease in mean BMI associated
with the interventions. There is a large body of evidence from all study designs which
suggests that decreasing any type of sedentary time is associated with lower health
risk in youth aged 5-17 years. In particular, the evidence suggests that daily TV
viewing in excess of 2 hours is associated with reduced physical and psychosocial
health, and that lowering sedentary time leads to reductions in BMI.