Objectively measured physical activity and sedentary behaviour in UK children of primary school age: a longitudinal cohort study

Abstract

BackgroundThere is growing evidence of the health benefits of physical activity for young people, including reduced risk of obesity and improved psychological wellbeing. Conversely, sedentary behaviour is now recognised to increase the risk of later poor health. Patterns of physical activity and sedentary behaviour are established in early childhood. In July, 2011, the UK Chief Medical Officers released new guidelines for all young people, recommending engagement in moderate to vigorous intensity physical activity for at least 60 min every day, incorporation of vigorous intensity activities on at least 3 days each week, and minimising time spent being sedentary for extended periods. Information about the extent to which UK children of primary school age are meeting these recommendations is sparse. We measured time spent in different intensities of physical activity, and assessed adherence to guidelines, in a UK-wide representative sample of children of primary school age taking part in a longitudinal cohort study. We used accelerometer-based activity monitors because this approach allowed the frequency, intensity, and duration of free-living activity to be objectively measured. MethodsNearly 13 000 7-year-old children taking part in the UK Millennium Cohort Study consented to wear an Actigraph activity monitor during all waking hours for 7 days, apart from during bathing or other aquatic activities (eg, swimming). Valid accelerometer data (≥2 days, ≥6 h wear each day) were obtained from nearly 7000 singletons. For each child several variables were produced: mean daily min of sedentary (defined as <100 counts per min [cpm]), moderate (2240–3840 cpm) and vigorous (>3841 cpm) activity. Time spent in moderate and vigorous activity was combined to establish adherence to activity guidelines. We fitted logistic regression models to compare adherence to guidelines according to individual (sex, ethnicity) and family (maternal social class, numbers of children in household, lone parenthood) factors, and country or region of residence. FindingsOn average, children accumulated 27 and 11 min per day of moderate and vigorous activity, respectively, and were sedentary for 5 h per day. Only 15% of all children achieved 60 min or more of daily moderate to vigorous intensity physical activity. Activity varied by ethnic group, with those of Indian and Bangladeshi origin the least active and black children the most active. Within adjusted analyses, significant differences were reported in adherence to activity guidelines between girls and boys (p<0·001), children whose mothers were small employers or own account workers compared with those whose mothers had routine occupations (p=0·04), and between children living in Northern Ireland compared with those in England (p=0·02). InterpretationOnly a small proportion of children of primary school age in the UK meet guidelines and are sufficiently active. A substantial part of their day is spent in sedentary behaviour and striking differences in activity are evident between boys and girls, different ethnic or social groups, and UK countries. Although we recognise the importance of some sedentary pursuits, such as reading and homework, measures to increase children's engagement in physical activity are needed for social and health benefits. FundingThe Wellcome Trust (grant 084686/Z/08/A).