Noel Cameron

Relationships between media use, body fatness and physical activity in children and youth: a meta-analysis

OBJECTIVE: To review the empirical evidence of associations between television (TV) viewing, video/computer game use and (a) body fatness, and (b) physical activity.DESIGN: Meta-analysis.METHOD: Published English-language studies were located from computerized literature searches, bibliographies of primary studies and narrative reviews, and manual searches of personal archives. Included studies presented at least one empirical association between TV viewing, video/computer game use and body fatness or physical activity among samples of children and youth aged 3–18 y.MAIN OUTCOME MEASURE: The mean sample-weighted corrected effect size (Pearson r).RESULTS: Based on data from 52 independent samples, the mean sample-weighted effect size between TV viewing and body fatness was 0.066 (95% CI=0.056–0.078; total N=44 707). The sample-weighted fully corrected effect size was 0.084. Based on data from six independent samples, the mean sample-weighted effect size between video/computer game use and body fatness was 0.070 (95% CI=−0.048 to 0.188; total N=1722). The sample-weighted fully corrected effect size was 0.128. Based on data from 39 independent samples, the mean sample-weighted effect size between TV viewing and physical activity was −0.096 (95% CI=−0.080 to −0.112; total N=141 505). The sample-weighted fully corrected effect size was −0.129. Based on data from 10 independent samples, the mean sample-weighted effect size between video/computer game use and physical activity was −0.104 (95% CI=−0.080 to −0.128; total N=119 942). The sample-weighted fully corrected effect size was −0.141.CONCLUSION: A statistically significant relationship exists between TV viewing and body fatness among children and youth although it is likely to be too small to be of substantial clinical relevance. The relationship between TV viewing and physical activity is small but negative. The strength of these relationships remains virtually unchanged even after correcting for common sources of bias known to impact study outcomes. While the total amount of time per day engaged in sedentary behavior is inevitably prohibitive of physical activity, media-based inactivity may be unfairly implicated in recent epidemiologic trends of overweight and obesity among children and youth. Relationships between sedentary behavior and health are unlikely to be explained using single markers of inactivity, such as TV viewing or video/computer game use.

Physical activity and sedentary behaviours in youth: issues and controversies

There is growing concern over the effects of sedentary lifestyles on the health of young people. Recent rapid increases in juvenile obesity have received a great deal of attention in the scientific and popular press and have been attributed partly to television viewing, computer games and other sedentary behaviours. These are thought to compete with physical activity. There is a ‘moral panic’ concerning the ‘couch kids’ culture in modern western society. Project STIL (Sedentary Teenagers and Inactive Lifestyles) at Loughborough University is investigating ‘what young people do’ and focuses on active and inactive pursuits chosen in their leisure time. The following issues are addressed in this paper with specific reference to young people: how do we define ‘sedentary behaviour’ and do key sedentary behaviours displace physical activity? Are key sedentary behaviours obesogenic? What are the secular trends for children and youth for TV viewing? Our results for young people suggest that:1. TV viewing and video-game playing are largely uncorrelated with physical activity, suggesting that there is time for both2. meta-analytic findings show that body fatness is not related in any clinically meaningful way with key sedentary behaviours3. although more children and youth have greater access to TVs than in previous generations, the amount of TV watched per head has not changed for 40 years. Preliminary findings from Project STIL suggest that inactivity is more complex than we sometimes think. Indeed, measures of ‘couch potato-ism’, such as TV viewing, may be inappropriate markers of inactivity.

Body mass index cut offs to define thinness in children and adolescents

A new chart will be most useful in countries in social, economic, and nutritional transition where both undernutrition and overnutrition are prevalent

Homo naledi, a new species of the genus Homo from the Dinaledi Chamber, South Africa

Homo naledi is a previously-unknown species of extinct hominin discovered within the Dinaledi Chamber of the Rising Star cave system, Cradle of Humankind, South Africa. This species is characterized by body mass and stature similar to small-bodied human populations but a small endocranial volume similar to australopiths. Cranial morphology of H. naledi is unique, but most similar to early Homo species including Homo erectus, Homo habilis or Homo rudolfensis. While primitive, the dentition is generally small and simple in occlusal morphology. H. naledi has humanlike manipulatory adaptations of the hand and wrist. It also exhibits a humanlike foot and lower limb. These humanlike aspects are contrasted in the postcrania with a more primitive or australopith-like trunk, shoulder, pelvis and proximal femur. Representing at least 15 individuals with most skeletal elements repeated multiple times, this is the largest assemblage of a single species of hominins yet discovered in Africa. DOI: http://dx.doi.org/10.7554/eLife.09560.001

Association between poor glucose tolerance and rapid post natal weight gain in seven-year-old children

Summary A number of studies have shown that glucose tolerance falls with decreasing birth weight and that people with low birth weight and high body mass index (BMI) as adults are those at greatest risk of developing Type II (non-insulin-dependent) diabetes mellitus. No such studies have been carried out in African populations. Therefore we investigated the relation between glucose tolerance and birth weight in a group of 7-year-old black South Africans for whom longitudinal anthropometric data were available. Oral glucose tolerance tests (OGTTs) were carried out on 152 subjects and inverse correlations were found between birth weight and the total amount of insulin secreted during the first 30 min (r = –0.19, p = 0.04) and last 90 min (r = –0.19, p = 0.04) of the oral glucose tolerance test and also between birth weight and the 30 min glucose concentrations (r = –0.20, p = 0.02). Children born with low birth weights but who had high weights at 7 years had higher insulin concentrations and indices of obesity compared with those with low birth weights and low weights at 7 years. There were also positive correlations between weight velocity and BMI (r = 0.24, p = 0.02) and weight velocity and insulin resistance (r = 0.18, p = 0.04) as measured using homeostasis model assessment (HOMA). Thus, low birth weight in conjunction with rapid childhood gains in weight especially as subcutaneous fat, produces poor glucose tolerance in 7-year-old children and can make them susceptible to the development of Type II diabetes later in life. [Diabetologia (1998) 41: 1163–1167]

Cohort Profile: The Born in Bradford multi-ethnic family cohort study

Bradford Institute for Health Research, Bradford Teaching Hospitals Foundation Trust, Bradford, UK, School of Health Studies, University of Bradford, Bradford, UK, Edinburgh Ethnicity and Health Research Group, Centre for Population Health Sciences, College of Medicine and Veterinary Medicine, University of Edinburgh, Edinburgh, UK, School of Sport, Exercise and Health Sciences, Loughborough University, Leicestershire, UK, Medical Research Council Centre for Causal Analyses in Translational Epidemiology, School of Social and Community Medicine, University of Bristol, Bristol, UK, Paediatric Epidemiology Group, Centre for Epidemiology and Biostatistics, Leeds Institute of Genetics, Health and Therapeutics, Faculty of Medicine and Health, University of Leeds, Leeds, UK and Department of Health Sciences, University of York, York, UK

Growth reference charts for use in the United Kingdom

Since the introduction of new growth charts in the mid 1990s, there has been confusion about which charts should be used, with many districts using more than one version. Because of this uncertainty, an expert working party, the Growth Reference Review Group, was convened by the Royal College of Paediatrics and Child Health to provide guidance on the validity and comparability of the different charts currently in use. This paper describes the technical background to the construction and evaluation of growth charts and outlines the groups findings on the validity of each growth reference in relation to contemporary British children. The group concluded that for most clinical purposes the UK90 reference is superior and for many measures is the only usable reference that can be recommended, while the original Tanner–Whitehouse and the Gairdner–Pearson charts are no longer reliable for use at any age. After the age of 2 the revised Buckler–Tanner references are still suitable for assessing height. There are presently no reliable head circumference reference charts for use beyond infancy. The group propose that apart from refinements of chart design and layout, the new UK90 reference should now be “frozen”, with any future revisions only undertaken after careful planning and widespread consultation

The prevalence of leisure time sedentary behaviour and physical activity in adolescent boys: An ecological momentary assessment approach

STUDY OBJECTIVE To use ecological momentary assessment to describe how adolescent boys in the United Kingdom spend their leisure time. Design. Cross-sectional, stratified, random sample from secondary schools in 15 regions within the United Kingdom. The data are from a larger study of adolescent lifestyles (Project STIL). PARTICIPANTS A total of 561 boys with a mean age of 14.6 years (range 12.7-16.7 years). The majority were white-European (86.5%). MAIN RESULTS Television viewing occupied the most leisure time on both weekdays (131 minutes) and weekend (202.5 minutes) days. On weekdays the five most time consuming sedentary activities (television viewing, homework, motorised travel, playing computer/video games and shopping/hanging out) occupied on average 272.2 minutes. On weekend days, the five most time consuming sedentary activities (television viewing, shopping/hanging out, motorised travel, sitting and talking and playing computer/video games) occupied 405.5 minutes. In total, 54 minutes were occupied by active transport or sports and exercise per weekday and 81 minutes per weekend day. Only a minority watched more than 4 hours of TV per day (8.9% on weekdays and 33.8% on weekend days). Differences were noted in the means and prevalence between weekend and weekdays, reflecting the greater discretionary time available at the weekend. CONCLUSIONS Adolescent boys engage in a variety of sedentary and active free time behaviours. It appears prudent to encourage adolescents to adopt overall healthy lifestyles by considering the combination of both active and sedentary pursuits an individual engages in and by moving beyond a focus on any one single behaviour.

Relation between weight gain and beta-cell secretory activity and non-esterified fatty acid production in 7-year-old African children: results from the Birth to Ten study.

Aims/hypothesis. This study aimed to assess the effects of fetal and childhood growth on beta-cell activity and insulin sensitivity in 7-year-old children. Methods. Insulin, des-31,32 proinsulin, proinsulin, non-esterified fatty acids and glucose concentrations were measured in oral glucose tolerance tests in 152 South African children for whom longitudinal weight data was available. Results. Children with low weights at birth and 7 years (low–low) had relatively low beta-cell activity whereas children with low birth weight and high weight at 7 years (low–high) had relatively high beta-cell activity. The low–low group had higher 30-min glucose concentrations than children with high birth weights. When each insulin-related peptide was expressed as a percentage of all these peptides the low–low children had the highest percentage of insulin but the lowest of the prohormones. The low–high children had the lowest percentage of insulin but the highest of the prohormones. Non-esterified fatty acid concentrations were lowest and their suppression post-glucose load highest in the low–high group. Conclusion/interpretation. Poor fetal and neonatal growth give rise to low beta-cell numbers compensated for by increased efficiency of proinsulin processing to insulin. Poor fetal followed by higher postnatal growth results in low beta-cell numbers and reduced whole-body glucose uptake which leads to reduced efficiency in the processing of proinsulin. Growth in utero and postnatally therefore have profound effects on beta-cell activity and insulin sensitivity with poor fetal coupled with high postnatal growth being detrimental to these processes but not detrimental to the suppression of lipolysis. [Diabetologia (2000) 43: 978–985]

Differences in bone size and bone mass between black and white 10-year-old South African children

IntroductionBlack and white South Africans hail from vastly disparate cultural and socio-economic backgrounds the result of which exposes black children to numerous factors known to impact negatively on bone mass. Thus, we studied ethnic differences in bone size and bone mass between 476 10-year-old black and white South African girls and boys (black boys n=182, white boys n=72, black girls n=158, white girls n=64) who formed part of a longitudinal cohort of children born in Johannesburg, South Africa, during 1990.MethodsBone area (BA) and bone mineral content (BMC) were measured at the whole body, total hip, femoral neck, lumbar spine (L1–L4) and mid- and distal radii by dual energy X-ray absorptiometry (DXA). Vertebral heights and metacarpal indices were measured. Anthropometry, skeletal maturity and pubertal development were also assessed.ResultsAfter correction for height, weight, gender and puberty, black children had greater BMC at the femoral neck (P<0.0001), total hip (P<0.05) and mid-radius (P<0.001) than white children.. At the whole body, lumbar spine, and distal one-third of the radius, there were no differences in BMC between black and white children after correction for differences in body size. After correction for height and puberty, vertebral heights were less in black children than white children, and cortical areas at the second metacarpal were greater in black children.ConclusionThese findings suggest that, at the femoral neck, total hip and mid-radius, these differences are not a result of differences in anthropometry, bone age or pubertal stage, or environmental factors but are most likely to result from genetic differences.