Objectively Measured Physical Activity and Fat Mass in a Large Cohort of Children

et al. (2007) Objectively measured physical activity and fat mass in a large cohort of children. PLoS Med 4(3): e97. doi:10.1371/journal.pmed. 0040097 Objectively Measured Physical Activity and Fat Mass in a Large Cohort of Children Andy R. Ness 0 1 2 3 4 5 6 Sam D. Leary 0 1 2 3 4 5 6 Calum Mattocks 0 1 2 3 4 5 6 Steven N. Blair 0 1 2 3 4 5 6 John J. Reilly 0 1 2 3 4 5 6 Jonathan Wells 0 1 2 3 4 5 6 Sue Ingle 0 1 2 3 4 5 6 Kate Tilling 0 1 2 3 4 5 6 George Davey Smith 0 1 2 3 4 5 6 Chris Riddoch 0 1 2 3 4 5 6 0 Glasgow, United Kingdom, 5 Medical Research Council Childhood Nutrition Research Centre, Institute of Child Health, University College London , London , United Kingdom 1 School of Public Health, University of South Carolina, Columbia, South Carolina, United States of America, 4 Division of Developmental Medicine, University of Glasgow 2 1 Department of Oral and Dental Science, University of Bristol, United Kingdom 2 Department of Social Medicine, University of Bristol , Bristol , United Kingdom , 3 Arnold 3 Current address: School for Health, University of Bath , Bath, United KIngdom 4 Academic Editor: Andrew Prentice, London School of Hygiene and Tropical Medicine , United Kingdom 5 Funding: This research was specifically funded by a grant from National Heart, Lung and Blood Institute (R01 HL071248-01A) and a grant from the Wellcome Trust GR068049MA. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript 6 6 London Sport Institute, Middlesex University , London , United Kingdom A B S T R A C T - Methods and Findings Previous studies have been unable to characterise the association between physical activity and obesity, possibly because most relied on inaccurate measures of physical activity and We carried out a cross sectional analysis on 5,500 12-year-old children enrolled in the Avon Longitudinal Study of Parents and Children. Total physical activity and minutes of moderate and vigorous physical activity (MVPA) were measured using the Actigraph accelerometer. Fat mass and obesity (defined as the top decile of fat mass) were measured using the Lunar Prodigy dual x-ray emission absorptiometry scanner. We found strong negative associations between MVPA and fat mass that were unaltered after adjustment for total physical activity. We found a strong negative dose-response association between MVPA and obesity. The odds ratio for obesity in adjusted models between top and the bottom quintiles of minutes of MVPA was 0.03 (95% confidence interval [CI] 0.010.13, p-value for trend ,0.0001) in boys and 0.36 (95% CI 0.170.74, p-value for trend 0.006) in girls. We demonstrated a strong graded inverse association between physical activity and obesity that was stronger in boys. Our data suggest that higher intensity physical activity may be more important than total activity. The Editors Summary of this article follows the references. Introduction The prevalence of childhood obesity is increasing in the United Kingdom [1], as it is across Europe [2], and in the United States [3]. This increase has important immediate and long-term health implications [4,5]. Obesity is fundamentally a result of chronic energy imbalance [6,7]. Diet survey data suggest that population levels of obesity have increased in the face of declining energy intake, implying that inactivity may be important in explaining the temporal trends in obesity [6,8]. While studies such as the National Heart Lung and Blood Institutes Growth and Health Study have reported associations between physical activity and obesity [9], the results of studies of the association between physical activity and obesity in children have been inconsistent [10]. This may reflect the fact that most studies have relied on inaccurate measures of physical activity or inaccurate measures of fat mass or both. Physical activity in children is sporadic [11,12], and children are less able than adults to recall or record their physical activity, consequently questionnaires provide a poor measure of physical activity in children. In contrast objective techniques such as heart rate monitors or accelerometers have been shown to provide an accurate measure of physical activity in children [13,14]. Body mass index (BMI) is a measure of weight for height and is widely used to assess population levels of childhood obesity because it is easy to measure and because population standards are available for comparison. It does not, however, distinguish well between fat and lean mass across the normal range [15] unlike methods such as dual energy x-ray absorptiometry (DXA), which produce an estimate of lean mass, fat mass, and regional distribution of body fat [16]. We examined the association between physical activity (measured objectively using accelerometers), and fat and lean mass (measured using total body DXA), and BMI in a large population of contemporary children. Study Population The Avon Longitudinal Study of Parents and Children (ALSPAC) is a prospective study that has been described in detail elsewhere [17] (http://www.alspac.bris.ac.uk). Briefly, 14,541 pregnant women living in one of three Bristol-based health districts in the former County of Avon with an expected delivery date between April 1991 and December 1992 were enrolled in the study. Detailed information has been collected using self-administered questionnaires, data extraction from medical notes, and linkage to routine information systems and at research clinics. Ethical approval for the study was obtained from the ALSPAC Law and Ethics Committee and Local Research Ethics Committees. Measurement of Physical Activity All children who attended the 11-year clinic were asked to wear an MTI Actigraph AM7164 2.2 accelerometer (Actigraph, http://www.theactigraph.com) for seven days. The Actigraph is an electronic motion sensor comprising a single plane (vertical) accelerometer. The Actigraph is small and light and is worn around the waist. Movement in a vertical plane is detected as a combined function of movement frequency and intensity and recorded as counts. The Actigraph has been validated in both children and adolescents against indirect calorimetry [18] observational techniques [19] and energy expenditure measured by doubly labelled water [20] and shown to be accurate. Actigraphs were initialised for each child using an Actigraph Reader Interface Unit (RIU-41A) with RIU software (version 2.26B, MTI Health Services, http://www.mtifwb.com). Children were asked to wear the Actigraph during waking hours and only to take it off for showering, bathing, or any water sports. Children were asked to record the times when they wore the Actigraph and time spent each day swimming or cycling, as the children did not wear the Actigraph when swimming, and the physical activity of cycling is not accurately recorded by the Actigraph. Actigraphs were returned by post and downloaded onto a PC using the Actigraph R (...truncated)