Exploring views of members of the public and policymakers on the acceptability of population level dietary and active-travel policies: a qualitative study

BACKGROUND

There is limited evidence on what shapes the acceptability of population level dietary and active-travel policies in England. This information would be useful in the decision-making process about which policies should be implemented and how to increase their effectiveness and sustainability. To fill this gap, we explored public and policymakers' views about factors that influence public acceptability of dietary and active-travel policies and how to increase public acceptability for these policies.

METHODS

We conducted online, semi-structured interviews with 20 members of the public and 20 policymakers in England. A purposive sampling frame was used to recruit members of the public via a recruitment agency, based on age, sex, socioeconomic status and ethnicity. Policymakers were recruited from existing contacts within our research collaborations and via snowball sampling. We explored different dietary and active-travel policies that varied in their scope and focus. Interviews were transcribed verbatim and analysed using thematic reflexive analysis with both inductive and deductive coding.

RESULTS

We identified four themes that informed public acceptability of dietary and active-travel policies: (1) perceived policy effectiveness, i.e., policies that included believable mechanisms of action, addressed valued co-benefits and barriers to engage in the behaviour; (2) perceived policy fairness, i.e., policies that provided everyone with an opportunity to benefit (mentioned only by the public), equally considered the needs of various population subgroups and rewarded 'healthy' behaviours rather than only penalising 'unhealthy' behaviours; (3) communication of policies, i.e., policies that were visible and had consistent and positive messages from the media (mentioned only by policymakers) and (4) how to improve policy support, with the main suggestion being an integrated strategy addressing multiple aspects of these behaviours, inclusive policies that consider everyone's needs and use of appropriate channels and messages in policy communication.

CONCLUSIONS

Our findings highlight that members' of the public and policymakers' support for dietary and active-travel policies can be shaped by the perceived effectiveness, fairness and communication of policies and provide suggestions on how to improve policy support. This information can inform the design of acceptable policies but can also be used to help communicate existing and future policies to maximise their adoption and sustainability.

Early-stage studies to larger-scale trials: investigators’ perspectives on scaling-up childhood obesity interventions

Background

Pilot/feasibility studies play an important role in the development and refinement of behavioral interventions by providing information about feasibility, acceptability, and potential efficacy. Despite their importance and wide-spread use, the approaches taken by behavioral scientists to scale-up early-stage studies to larger-scale trials has received little attention. The aim of our study was to understand the role that pilot studies play in the development and execution of larger-scale trials.

Methods

We conducted interviews with childhood obesity researchers who had published pilot behavioral interventions and larger-scale trials of the same or similar interventions. Questions were asked about the role of pilot studies in developing larger-scale trials and the challenges encountered when scaling-up an intervention based upon pilot findings. Data were coded and analyzed using an inductive analytic approach to identify themes.

Results

Twenty-four interventionists (54% women, 37–70 years old, mean 20 years since terminal degree) completed a total of 148 pilot studies across their careers (mean 6.4, range 1–20), of which 59% were scaled-up. Scaling was described as resource intensive and pilot work was considered essential to successfully competing for funding by 63% of the sample (n = 15). When asked to define a high-quality pilot study, interventionists described studies that allowed them to evaluate two independent factors: components of their intervention (e.g., acceptability, feasibility) and study parameters (e.g., sample size, measures). Interventionists expressed that more process implementation measures, different study designs, and additional iterations could improve decisions to scale-up. Most agreed that pilot studies were likely to produce inflated estimates of potential efficacy though only nine interventionists provided potential solutions for decreasing inflated measures of efficacy. Suggested major causes of inflated effects included high levels of oversight in pilot studies (e.g., researcher support), reliance on subjective measures, and utilizing convenience or highly motivated samples. Potential solutions included designing pilots for real-world implementation, only conducting randomized controlled pilot studies, and pre-registering pilot studies.

Conclusions

Pilot studies purposes are multifaceted and deemed essential to obtaining funding for larger-scale trials. Clarifying the form and function of preliminary, early-stage research may enhance the productive utilization of early-stage studies and reduced drops in efficacy when transitioning to larger scale studies.

Supplementary Information

The online version contains supplementary material available at 10.1186/s40814-022-00991-8.

A longitudinal study investigating change in BMI z-score in primary school-aged children and the association of child BMI z-score with parent BMI

Background

This paper aims to explore change in BMI z-score through childhood and the association between parent BMI and child BMI z-score. This is important to understand for the development of effective obesity interventions.

Methods

Data from the longitudinal B-ProAct1v study (1837 participants) were analysed. A paired sample t-test examined changes in child BMI z-score between Year 1 and 4. Multivariable linear regression models examined the cross-sectional associations between child BMI z-score and parent BMI in Year 1 and 4. The influence of change in parental BMI between Year 1 and Year 4 on child BMI z-score in Year 4 was explored through regression analyses, adjusted for baseline BMI z-score.

Results

There was a strong association between child BMI z-score at Year 1 and 4. Child mean BMI z-score score increased from 0.198 to 0.330 (p = < 0.005) between these timepoints. For every unit increase in parent BMI, there was an increase in child BMI z-score of 0.047 in Year 1 (p = < 0.005) and of 0.059 in Year 4 (p = < 0.005). Parental BMI change was not significantly associated with Year 4 child BMI z-score.

Conclusion

The key indicator of higher child BMI at Year 4 is high BMI at Year 1. Further studies are needed to explore the impact of parental weight change on child BMI z-score and whether interventions targeted at overweight or obese parents, can improve their child’s BMI z-score.

NAP SACC UK: protocol for a feasibility cluster randomised controlled trial in nurseries and at home to increase physical activity and healthy eating in children aged 2-4 years

INTRODUCTION

Systematic reviews have identified the lack of intervention studies with young children to prevent obesity. This feasibility study examines the feasibility and acceptability of adapting the Nutrition and Physical Activity Self-Assessment for Child Care (NAP SACC) intervention in the UK to inform a full-scale trial.

METHODS AND ANALYSIS

A feasibility cluster randomised controlled trial in 12 nurseries in England, with 6 randomly assigned to the adapted NAP SACC UK intervention: nursery staff will receive training and support from an NAP SACC UK Partner to review the nursery environment (nutrition, physical activity, sedentary behaviours and oral health) and set goals for making changes. Parents will be invited to participate in a digital media-based home component to set goals for making changes in the home. As this is a feasibility study, the sample size was not based on a power calculation but will indicate the likely response rates and intracluster correlations. Measures will be assessed at baseline and 8-10 months later. We will estimate the recruitment rate of nurseries and children and adherence to the intervention and data. Nursery measurements will include the Environmental Policy Assessment and Observation score and the nursery staff's review of the nursery environment. Child measurements will include height and weight to calculate z-score body mass index (zBMI), accelerometer-determined minutes of moderate-to-vigorous physical activity per day and sedentary time, and diet using the Child and Diet Evaluation Tool. Questionnaires with nursery staff and parents will measure mediators. A process evaluation will assess fidelity of intervention delivery and views of participants.

ETHICS AND DISSEMINATION

Ethical approval for this study was given by Wales 3 NHS Research Ethics Committee. Findings will be made available through publication in peer-reviewed journals, at conferences and to participants via the University of Bristol website. Data will be available from the University of Bristol Research Data Repository.

TRIAL REGISTRATION NUMBER

ISRCTN16287377.

Managing the screen-viewing behaviours of children aged 5-6 years: a qualitative analysis of parental strategies

OBJECTIVES

The present study used qualitative methods to: (1) examine the strategies that were used by parents of children aged 5-6 years to manage screen viewing; (2) identify key factors that affect the implementation of the strategies and (3) develop suggestions for future intervention content.

DESIGN

Telephone interviews were conducted with parents of children aged 5-6 years participating in a larger study. Interviews were transcribed verbatim and analysed using an inductive and deductive content analysis. Coding and theme generation was iterative and refined throughout.

SETTING

Parents were recruited through 57 primary schools located in the greater Bristol area (UK).

PARTICIPANTS

53 parents of children aged 5-6 years.

RESULTS

Parents reported that for many children, screen viewing was a highly desirable behaviour that was difficult to manage, and that parents used the provision of screen viewing as a tool for reward and/or punishment. Parents managed screen viewing by setting limits in relation to daily events such as meals, before and after school, and bedtime. Screen-viewing rules were often altered depending on parental preferences and tasks. Inconsistent messaging within and between parents represented a source of conflict at times. Potential strategies to facilitate reducing screen viewing were identified, including setting screen-viewing limits in relation to specific events, collaborative rule setting, monitoring that involves mothers, fathers and the child, developing a family-specific set of alternative activities to screen viewing and developing a child's ability to self-monitor their own screen viewing.

CONCLUSIONS

Managing screen viewing is a challenge for many parents and can often cause tension in the home. The data presented in this paper provide key suggestions of new approaches that could be incorporated into behaviour change programmes to reduce child screen viewing.

Lessons learned from the AFLY5 RCT process evaluation: implications for the design of physical activity and nutrition interventions in schools

Background

Systematic reviews have highlighted that school-based diet and physical activity (PA) interventions have had limited effects. This study used qualitative methods to examine how the effectiveness of future primary (elementary) school diet and PA interventions could be improved.

Methods

Data are from the Active For Life Year 5 (AFLY5) study, which was a cluster randomised trial conducted in 60 UK primary schools. Year 5 (8–9 years of age) pupils in the 30 intervention schools received a 12-month intervention. At the end of the intervention period, interviews were conducted with: 28 Year 5 teachers (including 8 teachers from control schools); 10 Headteachers (6 control); 31 parents (15 control). Focus groups were conducted with 70 year 5 pupils (34 control). Topics included how the AFLY5 intervention could have been improved and how school-based diet and PA interventions should optimally be delivered. All interviews and focus groups were transcribed and thematically analysed across participant groups.

Results

Analysis yielded four themes.

Child engagement: Data suggested that programme success is likely to be enhanced if children feel that they have a sense of autonomy over their own behaviour and if the activities are practical.

School: Finding a project champion within the school would enhance intervention effectiveness. Embedding diet and physical activity content across the curriculum and encouraging teachers to role model good diet and physical activity behaviours were seen as important.

Parents and community: Encouraging parents and community members into the school was deemed likely to enhance the connection between schools, families and communities, and “create a buzz” that was likely to enhance behaviour change.

Government/Policy: Data suggested that there was a need to adequately resource health promotion activity in schools and to increase the infrastructure to facilitate diet and physical activity knowledge and practice.

Discussion and Conclusions

Future primary school diet and PA programmes should find ways to increase child engagement in the programme content, identify programme champions, encourage teachers to work as role models, engage parents and embed diet and PA behaviour change across the curriculum. However, this will require adequate funding and cost-effectiveness will need to be established.

Trial registration

ISRCTN50133740

The influence of friends and siblings on the physical activity and screen viewing behaviours of children aged 5-6 years: a qualitative analysis of parent interviews

OBJECTIVES

The present study uses qualitative data to explore parental perceptions of how their young child's screen viewing and physical activity behaviours are influenced by their child's friends and siblings.

DESIGN

Telephone interviews were conducted with parents of year 1 children (age 5-6 years). Interviews considered parental views on a variety of issues related to their child's screen viewing and physical activity behaviours, including the influence that their child's friends and siblings have over such behaviours. Interviews were transcribed verbatim and analysed using deductive content analysis. Data were organised using a categorisation matrix developed by the research team. Coding and theme generation was iterative and refined throughout. Data were entered into and coded within N-Vivo.

SETTING

Parents were recruited through 57 primary schools located in Bristol and the surrounding area that took part in the B-ProAct1v study.

PARTICIPANTS

Fifty-three parents of children aged 5-6 years.

RESULTS

Parents believe that their child's screen viewing and physical activity behaviours are influenced by their child's siblings and friends. Friends are considered to have a greater influence over the structured physical activities a child asks to participate in, whereas the influence of siblings is more strongly perceived over informal and spontaneous physical activities. In terms of screen viewing, parents suggest that their child's friends can heavily influence the content their child wishes to consume, however, siblings have a more direct and tangible influence over what a child watches.

CONCLUSIONS

Friends and siblings influence young children's physical activity and screen viewing behaviours. Child-focused physical activity and screen viewing interventions should consider the important influence that siblings and friends have over these behaviours.

Dietary changes and associations with metabolic improvements in adults with type 2 diabetes during a patient-centred dietary intervention: an exploratory analysis

OBJECTIVES

Describe dietary intake of participants enrolled in a non-prescriptive dietary intervention and dietary changes at 6 months and explore whether these changes had a role in observed improvements in glycated haemoglobin (HbA1c), weight, lipids and blood pressure.

DESIGN

Secondary analysis of data from the Early ACTivity in Diabetes randomised controlled trial.

PARTICIPANTS

262 patients with newly diagnosed type 2 diabetes randomised to the dietary intervention.

OUTCOMES AND ANALYSIS

Changes in energy intake, macronutrients, fibre and alcohol and in weight, waist circumference, lipids, HbA1c and blood pressure at baseline and 6 months. Multivariate models were used to examine associations between dietary changes and metabolic variables.

RESULTS

Men reported reducing mean energy intake from 1903±462 kcal to 1685 kcal±439 kcal (p<0.001), increasing carbohydrate intake from 42.4±6.6% to 43.8±6.6% (p=0.002) and reducing median alcohol intake from 13 (0-27) g to 5 (0-18) g (p<0.001). Women reported reducing mean energy intake from 1582±379 kcal to 1459±326 kcal (p<0.001) with no change to macronutrient distribution and alcohol. Fibre intake was maintained. In men (n=148), weak and clinically insignificant associations were found between increased carbohydrates and reduction in HbA1c (β=-0.003 (-0.006, -0.001); p=0.009), increased fibre and reduction in total cholesterol (β=-0.023 (-0.044, -0.002); p=0.033), decreased total fat and reduction in low-density lipoprotein (LDL)-cholesterol (β=0.024 (0.006, 0.001); p=0.011), and decreased alcohol and reduction in diastolic blood pressure (β=0.276 (0.055, 0.497); p=0.015). In women (n=75), associations were found between a decrease in transfats and reductions in waist circumference (β=-0.029 (0.006, 0.052); p=0.015), total cholesterol (β=0.399 (0.028, 0.770); p=0.036) and LDL cholesterol (β=0.365 (0.042, 0.668); p=0.028).

CONCLUSIONS

Clinically important metabolic improvements observed in a patient-centred dietary intervention were not explained by changes in macronutrients. However, a non-prescriptive approach may promote a reduction in total energy intake while maintaining fibre consumption.

TRIAL REGISTRATION NUMBER

The Early ACTID trial number ISRCTN92162869.

Prevalence of obesity among 10-11-year-old Maltese children using four established standards

OBJECTIVE

The objective of this study was to establish, through measured height and weight, the prevalence of overweight and obesity in a representative sample of Maltese children aged 10-11 years.

METHODS

Height and weight were measured in a sample, stratified by sex, region and type of school, of 874 year 6 children and their body mass index classified as normal weight, overweight, and obese using International Obesity Task Force (IOTF), World Health Organization (WHO), US Centre for Disease Control and U.K. Department of Health standards.

RESULTS

IOTF standards indicated 20.4% overweight and 14.2% obese, while WHO standards indicated 23.1% overweight and 20.9% obese. All four standards reported significant sex differences, classifying more boys in the overweight and obesity categories.

CONCLUSIONS

The prevalence of overweight and obesity among 10-11-year-old Maltese children are higher than previously estimated through self-reported height and weight and all other countries in the world except Greece. These high rates confirm the urgent need to identify causes and tackle childhood obesity in Malta.

Longitudinal associations between BMI, waist circumference, and cardiometabolic risk in US youth: monitoring implications

OBJECTIVE

This study examined whether change in body mass index (BMI) or waist circumference (WC) is associated with change in cardiometabolic risk factors and differences between cardiovascular disease specific and diabetes specific risk factors among adolescents. We also sought to examine any differences by gender or baseline body mass status.

DESIGN

The article is a longitudinal analysis of pre- and post-data collected in the HEALTHY trial. Participants were 4,603 ethnically diverse adolescents who provided complete data at 6th and 8th grade assessments.

METHODS

The main outcome measures were percent change in the following cardiometabolic risk factors: fasting triglycerides, systolic and diastolic blood pressure, high density lipoprotein cholesterol, and glucose as well as a clustered metabolic risk score. Main exposures were change in BMI or WC z-score. Models were run stratified by gender; secondary models were additionally stratified by baseline BMI group (normal, overweight, or obese).

RESULTS

Analysis showed that when cardiometabolic risk factors were treated as continuous variables, there was strong evidence (P < 0.001) that change in BMI z-score was associated with change in the majority of the cardiovascular risk factors, except fasting glucose and the combined risk factor score for both boys and girls. There was some evidence that change in WC z-score was associated with some cardiovascular risk factors, but change in WC z-score was consistently associated with changes in fasting glucose.

CONCLUSIONS

In conclusion, routine monitoring of BMI should be continued by health professionals, but additional information on disease risk may be provided by assessing WC.

Fat distribution, physical activity and cardiovascular risk among adolescent girls

BACKGROUND AND AIMS

It is not clear whether changes in waist circumference (WC), sums of skinfold thickness (SSF), or levels of physical activity (PA) during adolescence are associated with cardiovascular risk factors, or if associations are independent or interactive.

METHODS AND RESULTS

In a US cohort of adolescent girls (n = 617-904) girls, examined at ages 12 and 14, WC, SSF, PA, systolic and diastolic blood pressure (SBP & DBP) were assessed. Fasting blood samples were used to determine concentrations of triglycerides (TG), cholesterol (TC), high and low density lipoproteins (HDL-C and LDL-C), and apolipoprotein A1 and B (Apo-A1 and Apo-B). After adjustment for change in SSF and PA, increases in WC were associated with change in TG (z = 1.73, 95% CI = 0.77, 2.69), TC (z = 0.45, 95% CI = 0.01, 0.90), HDL-C (z = -0.18, 95% CI = -0.37, -0.01), LDL-C (z = 0.41, 95% CI = 0.03, 0.80), Apo-A1 (z = -0.52, 95% CI = -1.02, -0.02), Apo-B (z = 0.60, 95% CI = 0.24, 0.97) and SBP levels (z = 0.31, 95% CI = 0.15, 0.47). Associations between changes in SSF and PA with cardiovascular risk were eliminated after adjustment for WC, and all interactions between WC, SSF and PA were non-significant at conventional levels.

CONCLUSIONS

Changes in WC were independently associated with the development of cardiovascular risk factors, whereas changes in SSF and PA were not. Clinicians should consider the routine screening of WC to monitor cardiovascular health in adolescent girls.

Combined influence of healthy diet and active lifestyle on cardiovascular disease risk factors in adolescents

To investigate the combined influence of diet quality and physical activity on cardiovascular disease (CVD) risk factors in adolescents, adolescents (n = 1513; 12.5-17.5 years) participating in the Healthy Lifestyle in Europe by Nutrition in Adolescence study were studied. Dietary intake was registered using a 24-h recall and a diet quality index was calculated. Physical activity was assessed by accelerometry. Lifestyle groups were computed as: healthy diet and active, unhealthy diet but active, healthy diet but inactive, and unhealthy diet and inactive. CVD risk factor measurements included cardiorespiratory fitness, adiposity indicators, blood lipid profile, blood pressure, and insulin resistance. A CVD risk score was computed. The healthy diet and active group had a healthier cardiorespiratory profile, fat mass index (FMI), triglycerides, and high-density lipoprotein cholesterol (HDL-C) levels and total cholesterol (TC)/HDL-C ratio (all P ≤ 0.05). Overall, active adolescents showed higher cardiorespiratory fitness, lower FMI, TC/HDL-C ratio, and homeostasis model assessment index and healthier blood pressure than their inactive peers with either healthy or unhealthy diet (all P ≤ 0.05). Healthy diet and active group had healthier CVD risk score compared with the inactive groups (all P ≤ 0.02). Thus, a combination of healthy diet and active lifestyle is associated with decreased CVD risk in adolescents. Moreover, an active lifestyle may reduce the adverse consequences of an unhealthy diet.

How does physical activity and fitness influence glycaemic control in young people with Type 1 diabetes?

AIMS

To assess physical activity and fitness levels of young people with Type 1 diabetes compared with siblings without diabetes, and to investigate the association between physical activity, physical fitness and glycaemic control (HbA(1c)) in those young people with diabetes.

METHODS

The study consisted of 97 young people aged 8 to 16 years (62% male) from a Paediatric Diabetes Service in South West England. Sixty participants (67% male) had Type 1 diabetes and 37 participants (54% male) were siblings without diabetes (control group). We measured weight, height and waist circumference, calculated BMI and waist-height ratio and recorded pubertal status, blood pressure and current insulin regimen information. We assessed physical activity by accelerometry, from which we calculated light and moderate-to-vigorous intensity activity. We measured physical fitness by multistage sub-maximal bicycle ergometer test. We obtained HbA(1c) by venipuncture.

RESULTS

There were no differences between the young people with diabetes and siblings without diabetes in body composition, blood pressure, physical activity and fitness. Moderate-to-vigorous physical activity was associated with better glycaemic control, accounting for 30-37% (R(2) = 0.295-0.374) of the variance for HbA(1c). Physical fitness was not associated with HbA(1c).

CONCLUSIONS

Moderate-to-vigorous physical activity was associated with better glycaemic control while fitness was not. Findings suggest that developing strategies to increased moderate-to-vigorous physical activity may prove an effective method of improving glycaemic control in young people with diabetes.

Cardiovascular risk factors in multi-ethnic middle school students: the HEALTHY primary prevention trial

OBJECTIVE

The objective of this study was to examine the effects of an integrated, multi-component, school-based intervention programme on cardiovascular disease (CVD) risk factors among a multi-ethnic cohort of middle school students.

METHODS

HEALTHY was a cluster randomized, controlled, primary prevention trial. Middle school was the unit of randomization and intervention. Half of the schools were assigned to an intervention programme consisting of changes in the total school food environment and physical education classes, enhanced by educational outreach and behaviour change activities and promoted by a social marketing campaign consisting of reinforcing messages and images. Outcome data reported (anthropometrics, blood pressure and fasting lipid levels) were collected on a cohort of students enrolled at the start of 6th grade (∼11-12 years old) and followed to end of 8th grade (∼13-14 years old).

RESULTS

Forty-two middle schools were enrolled at seven field centres; 4363 students provided both informed consent and CVD data at baseline and end of study. The sample was 52.7% female, 54.5% Hispanic, 17.6% non-Hispanic Black, 19.4% non-Hispanic White and 8.5% other racial/ethnic combinations, and 49.6% were categorized as overweight or obese (body mass index ≥ 85th percentile) at baseline. A significant intervention effect was detected in the prevalence of hypertension in non-Hispanic Black and White males. The intervention produced no significant changes in lipid levels.

CONCLUSIONS

The prevalence of some CVD risk factors is high in minority middle school youth, particularly males. A multi-component, school-based programme achieved only modest reductions in these risk factors; however, promising findings occurred in non-Hispanic Black and White males with hypertension.

Physically active families - de-bunking the myth? A qualitative study of family participation in physical activity

BACKGROUND

The benefits of physical activity for reducing obesity and related chronic diseases are well known. The need for more family-based interventions to increase physical activity is frequently cited in the literature; however, little is known about if and how families are physically active together, and what factors might influence family-based participation in regular physical activity. This study examined the types of activities (physical and sedentary) engaged in as a family and explored parents' perceptions of the importance, frequency, nature and barriers to family physical activity.

METHODS

Semi-structured telephone interviews were conducted with 30 parents (26 female, four male) of 10- to 11-year-old schoolchildren who attended either low, middle or high socio-economic status schools in Bristol, UK. Interviews were transcribed verbatim, anonymized and analysed using conventional content analysis.

RESULTS

The majority of parents rated family engagement in physical activity as important, and identified benefits such as increased parent-child communication, spending time together, enjoyment, enhanced mental health, weight control and physical fitness. Despite these benefits most parents reported their families did little or no physical activity together as a family unit during the week, and any activities performed together were usually sedentary in nature. They reported increased family physical activity on the weekends but rarely including the full family unit simultaneously. Parents in two-parent households commonly paired off with one or more children because of complexities of schedules. Commonly reported barriers were busy lifestyles, diverse ages and interests of children and adults, bad weather, and lack of access to facilities, transportation and money to support activities.

CONCLUSIONS

Family-based interventions might be more effective if they are designed to accommodate the complex demands and needs of two-parent and single-parent families and provide affordable, diverse activities appealing to a wide range of interests.

BMI from 3–6 y of age is predicted by TV viewing and physical activity, not diet

OBJECTIVE

To investigate whether, diet, physical activity, sedentary behavior or television (TV) viewing predicted body mass index (BMI) among 3-7-y-old children.

DESIGN

A triethnic cohort of 3-4-y-old children was followed for 3 y from 1986 to 1989.

MEASUREMENTS

BMI was assessed at the beginning and end of each measurement year. Heart rate monitoring and observation were used to assess physical activity. Diet (calories, % calories from fat and carbohydrate), sedentary behavior and TV viewing were assessed by direct observation in each year. A repeated measures regression analysis with year as a factor and BMI at the end of each year as dependent variables was run. Nonsignificant variables were removed in a stepwise backward deletion process and significant interactions graphed.

RESULTS

The interactions between minutes of TV viewing per hour and study year and minutes of physical activity per hour and study year were significant (P<0.05). There were also significant main effects for TV viewing, physical activity and BMI from the beginning of the study. The model accounted for 65% of the variance in BMI across the three study years. Plotting the significant interactions demonstrated that physical activity was positively associated with BMI in year 1, and negatively associated in years 2 and 3 with a stronger negative relationship in year 3 than 2. TV viewing became positively associated with BMI during the third study year.

CONCLUSION

Physical activity and TV viewing were the only significant predictors (other than baseline BMI) of BMI among a triethnic cohort of 3-4-y-old children followed for 3 y with both physical activity (negatively associated) and TV viewing (positively associated) becoming stronger predictors as the children aged. It appears that 6 or 7 y is a critical age when TV viewing and physical activity may affect BMI. Therefore, focusing on reducing time spent watching television and increasing time spent in physical activity may be successful means of preventing obesity among this age group.

Ethics and paediatric exercise science: issues and making a submission to a local ethics and research committee

Research with children presents issues beyond those normally encountered in adult exercise science research. This paper explores the specific ethical issues that are encountered when conducting paediatric research in the exercise sciences. We identify the historical, moral and philosophical underpinnings of ethical conduct. The issue of consent and children's ability to provide informed consent is discussed, as is the nature of therapeutic and non-therapeutic research. Finally, we examine the information that is required by a local ethics and research committee and provide guidance material to help in the formulation of an application to such a committee.

Electron microscopy of carotid body hyperplasia

Hyperplastic carotid bodies from an 80-year-old woman with sustained systemic hypertension were examined ultrastructurally and compared with those from six normal subjects. Hyperplasia involved both elongated sustentacular and Schwann's cells, both of which were more numerous than normal. They formed concentric whorls around a diminished core of chief cells. The Schwann's cells adopted a peripheral position in each cell cluster, whereas the sustentacular cells were located closer to the central core. The characteristics of both types of cell were similar so that they could not be distinguished from each other in every instance. They were associated with numerous nerve axons with which they usually displayed a simple mesaxonal relationship. The myelin sheaths formed by Schwann's cells were well developed but those encountered in sustentacular cells were usually rudimentary. A few fibroblasts were also present, but generally the process of hyperplasia was not one of fibrosis; neither did it involve pericytes.

Glomic cells and blood vessels in the hyperplastic carotid bodies of spontaneously hypertensive rats

Carotid bodies from 21 normotensive Wistar albino rats were compared with those from 20 spontaneously hypertensive rats of the Okamoto strain. From serial histological sections the volume of the carotid bodies was estimated by Simpson's rule. Differential and absolute cell counts were also performed on the chief and elongated cells which surround them. The glomic vasculature was examined by light and electron microscopy. Although the carotid bodies of Okamoto rats were nearly three times as large as those of Wistar rats of comparable body weight, there was no difference in the proportion of the two types of cell. The organisation of glomic cells was also similar in the two strains. The main carotid body artery consists of a muscular tube with a valve-like cushion at its orifice. In the Okamoto rats branches of this artery were occluded by intimal proliferations of myofibroblasts embedded within a copious, loose matrix of acid mucopolysaccharide ground substance. These proliferations appeared to originate from intimal pads situated at the origins of many glomic arteries and arterioles. These findings are in sharp contrast to those in the hyperplastic human carotid body.

Dark cell proliferation in carotid body hyperplasia

The histopathology of the enlarged carotid bodies, in both qualitative and quantitative terms, is described in two cases. One was in a woman of 80 years with systemic hypertension and the other in a man of 72 years with pan-acinar emphysema complicated by chronic hypoxaemia. In both instances there was generalized hyperplasia of sustentacular cells, perhaps with involvement of Schwann cells and fibrocytes, with superimposed focal proliferation of dark or 'pyknotic' variants of chief cells. The functional significance of both froms of tissue response in the carotid bodies is speculated upon.

The vasculature of the carotid body

A histological and electron microscopical study was carried out on the vasculature of the carotid bodies in seven subjects coming to necropsy. None of these had suffered from chronic hypoxaemia or systemic hypertension during life and none had hypertrophy of the right or left ventricle. The vasculature of the carotid bodies showed three distinct components. There was a proximal portion, comprising elastic interlobular arteries, which had a wall in which elastic tissue predominated and in which many nerve fibrils could be demonstrated. This is considered to be baroreceptor in nature. There was an intermediate portion comprising muscular intralobular arterioles which are believed to be capable of controlling the level of blood supply to the parenchyma of the carotid bodies. Finally there are glomic capillaries surrounded by elongated pericytes and sustentacular cells. One or other of these elongated cells is thought to be responsible for the carotid body hyperplasia which is associated with systemic hypertension and states of chronic hypoxaemia.

Structure of the glomic arteries

The structure of the arteries which supply blood tp the carotid bodies was examined in five cases in which the weights of the cardiac ventricles were normal and in which hypoxaemia due to emphysema or systemic hypertension were absent. The right glomic arteries were studied by light microscopy, and the left by electron microscopy. A sixth case, also free from myocardial hypertrophy, was used solely for an examination of the common carotid artery, the carotid sinus and the internal carotid artery by light and electron microscopy. The glomic arteries resembled the carotid sinus in being highly elastic with a rich supply of non-myelinated nerve fibres and thus had a structure consistent with having a baroreceptor function.

Hyperplasia of the carotid body

The histopathology of hyperplasia of the carotid bodies was studied in 6 cases of hypoxaemia and right ventricular hypertrophy secondary to pan-acinar emphysema, and in five cases of systemic hypertension with left ventricular hypertrophy. The features of the hyperplasia were the same in the two groups. There was proliferation of sustentacular (type II) cells and compression of central cores of chief (type I) cells. It is speculated that the hyperplasia of sustentacular cells is associated in some way with the prevention of retention of sodium ions and water which characterises hypoxic cor pulmonale in "blue bloaters", systemic hypertension, and ascent to high altitude with the complications of acute mountain sickness, and pulmonary and cerebral oedema.

Anatomical variation and quantitative histology of the normal and enlarged carotid body

The carotid bodies from 150 consecutive cases coming to necropsy were examined to determine the degree of anatomical variation of the organ. Single, double and bilobed variants were found. The origin of the carotid body was variable, the angle of the carotid bifurcation being the most typical, but a minority were encountered on the internal or external carotid arteries, the common carotid artery and the ascending pharyngeal artery. Carotid bodies which were enlarged had no preferred site or origin, but some showed early or pronounced nodularity. Both carotid bodies from 100 of these cases were subjected to detailed qualitative and quantitative histological study. From these measurements we were able to define hyperplasia of the organ as a differential sustentacular cell count in excess of 47 per cent., a lobular diameter over 565 micrometers, and a combined carotid body weight over 30 mg. Carotid body hyperplasia occurred in cases of myocardial hypertrophy secondary to both hypoxaemia and systemic hypertension.