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We analyzed birth order differences in means and variances of height and body mass index (BMI) in monozygotic (MZ) and dizygotic (DZ) twins from infancy to old age. The data were derived from the international CODATwins database. The total number of height and BMI measures from 0.5 to 79.5 years of age was 397,466. As expected, first-born twins had greater birth weight than second-born twins. With respect to height, first-born twins were slightly taller than second-born twins in childhood. After adjusting the results for birth weight, the birth order differences decreased and were no longer statistically significant. First-born twins had greater BMI than the second-born twins over childhood and adolescence. After adjusting the results for birth weight, birth order was still associated with BMI until 12 years of age. No interaction effect between birth order and zygosity was found. Only limited evidence was found that birth order influenced variances of height or BMI. The results were similar among boys and girls and also in MZ and DZ twins. Overall, the differences in height and BMI between first- and second-born twins were modest even in early childhood, while adjustment for birth weight reduced the birth order differences but did not remove them for BMI.
A trend toward greater body size in dizygotic (DZ) than in monozygotic (MZ) twins has been suggested by some but not all studies, and this difference may also vary by age. We analyzed zygosity differences in mean values and variances of height and body mass index (BMI) among male and female twins from infancy to old age. Data were derived from an international database of 54 twin cohorts participating in the COllaborative project of Development of Anthropometrical measures in Twins (CODATwins), and included 842,951 height and BMI measurements from twins aged 1 to 102 years. The results showed that DZ twins were consistently taller than MZ twins, with differences of up to 2.0 cm in childhood and adolescence and up to 0.9 cm in adulthood. Similarly, a greater mean BMI of up to 0.3 kg/m2 in childhood and adolescence and up to 0.2 kg/m2 in adulthood was observed in DZ twins, although the pattern was less consistent. DZ twins presented up to 1.7% greater height and 1.9% greater BMI than MZ twins; these percentage differences were largest in middle and late childhood and decreased with age in both sexes. The variance of height was similar in MZ and DZ twins at most ages. In contrast, the variance of BMI was significantly higher in DZ than in MZ twins, particularly in childhood. In conclusion, DZ twins were generally taller and had greater BMI than MZ twins, but the differences decreased with age in both sexes.
Research suggests that repeatedly offering infants a variety of vegetables during weaning increases vegetable intake and liking. The effect may extend to novel foods. The present study aimed to investigate the impact of advising parents to introduce a variety of single vegetables as first foods on infants' subsequent acceptance of a novel vegetable. Mothers of 4- to 6-month-old infants in the UK, Greece and Portugal were randomised to either an intervention group (n 75), who received guidance on introducing five vegetables (one per d) as first foods repeated over 15 d, or a control group (n 71) who received country-specific ‘usual care’. Infant's consumption (g) and liking (maternal and researcher rated) of an unfamiliar vegetable were assessed 1 month post-intervention. Primary analyses were conducted for the full sample with secondary analyses conducted separately by country. No significant effect of the intervention was found for vegetable intake in the three countries combined. However, sub-group analyses showed that UK intervention infants consumed significantly more novel vegetable than control infants (32·8 (sd 23·6) v. 16·5 (sd 12·1) g; P =0·003). UK mothers and researchers rated infants' vegetable liking higher in the intervention than in control condition. In Portugal and Greece, there was no significant intervention effect on infants' vegetable intake or liking. The differing outcome between countries possibly reflects cultural variations in existing weaning practices. However, the UK results suggest in countries where vegetables are not common first foods, advice on introducing a variety of vegetables early in weaning may be beneficial for increasing vegetable acceptance.
For over 100 years, the genetics of human anthropometric traits has attracted scientific interest. In particular, height and body mass index (BMI, calculated as kg/m2) have been under intensive genetic research. However, it is still largely unknown whether and how heritability estimates vary between human populations. Opportunities to address this question have increased recently because of the establishment of many new twin cohorts and the increasing accumulation of data in established twin cohorts. We started a new research project to analyze systematically (1) the variation of heritability estimates of height, BMI and their trajectories over the life course between birth cohorts, ethnicities and countries, and (2) to study the effects of birth-related factors, education and smoking on these anthropometric traits and whether these effects vary between twin cohorts. We identified 67 twin projects, including both monozygotic (MZ) and dizygotic (DZ) twins, using various sources. We asked for individual level data on height and weight including repeated measurements, birth related traits, background variables, education and smoking. By the end of 2014, 48 projects participated. Together, we have 893,458 height and weight measures (52% females) from 434,723 twin individuals, including 201,192 complete twin pairs (40% monozygotic, 40% same-sex dizygotic and 20% opposite-sex dizygotic) representing 22 countries. This project demonstrates that large-scale international twin studies are feasible and can promote the use of existing data for novel research purposes.
To assess attributions for overweight and the level of support for policy initiatives in Great Britain.
Cross-sectional. Respondents indicated their agreement (5-point scales: strongly disagree to strongly agree) to three potential causes of overweight (environment, genes, willpower) and five policies (free weight-loss treatment, taxing unhealthy foods, healthy lifestyle campaigns, food labelling, advertising restrictions).
Data were collected as part of a computer-assisted, face-to-face Omnibus survey of adults (aged >15 years) from across Great Britain in April 2012 carried out by a market research company.
A population-representative sample of British adults (n 1986).
More people attributed overweight to the food environment (61 %) and lack of willpower (57 %) than to genes (45 %). Policy support was highest for healthy lifestyle campaigns (71 %) and food labelling (66 %), and lowest for taxing unhealthy foods (32 %). Food environment attributions were associated with higher support for all policies (P < 0·001). Genetic attributions were associated with higher support for free weight-loss treatments and healthy lifestyle campaigns (P < 0·001), but not other policies. Attributions to lack of willpower were not associated differentially with support for any policies (P > 0·01).
Belief that overweight is caused by the food environment or genes – both seen as outside individual control – was associated with greater support for government policies to prevent and treat obesity. Improving awareness of the multiple causes of obesity could facilitate acceptance of policy action to reduce obesity prevalence.
Misperception of social norms may result in normalising unhealthy behaviours. The present study tested the hypothesis that parents overestimate both the frequency of unhealthy snacking in pre-school children other than their own (descriptive norms) and its acceptability to other parents (injunctive norms).
A cross-sectional, self-report community survey. Questions assessed the frequency with which respondents’ own child ate unhealthy snacks and their beliefs about the appropriate frequency for children to snack. Perceived descriptive norms were assessed by asking parents to estimate how often other 2–4 year-old children in their area ate snacks. Perceived injunctive norms were assessed by asking them about other parents’ beliefs regarding the appropriate frequency for snacks. Misperceptions were assessed from (i) the difference between the prevalence of daily snacking and parents’ perceived prevalence and (ii) the difference between acceptability of daily snacking and parents’ beliefs about its acceptability to others.
Pre-schools and children's centres in one borough of London, UK.
Parents (n 432) of children age 2–4 years.
On average, parents believed that more than half of ‘other’ children had snacks at least daily, while prevalence data indicated this occurred in only 10 % of families. The same discrepancy was observed for perceived injunctive norms: parents overestimated other parents’ acceptance of frequent snacking, with two-thirds of parents having a self v. others discrepancy.
Misperceptions were identified for descriptive and injunctive norms for children's snacking. Accurate information could create less permissive norms and motivate parents to limit their child's intake of unhealthy snacks.
Gemini is a cohort study of young twins in the United Kingdom designed to assess genetic and environmental influences on early childhood weight trajectories with a focus on infant appetite and the family environment. A total of 2402 families with twins born in England and Wales between March and December 2007 agreed to participate and returned completed baseline questionnaires. The sample includes 1586 same-sex and 816 opposite-sex twins. The study is currently funded for 5 years of follow-up, but is planned to continue into early adolescence and beyond, pending funding. With current funding of the study, families will be followed up when twins are: 8 months old (baseline), and then at 15, 20, 24, 36 and 48 months of age. Gemini is in its early stages, with baseline and first follow-up data collection completed. This is the first twin cohort to focus on childhood weight gain with detailed and repeated measures of children's appetite, food preferences, activity behavior and parental feeding styles, alongside detailed and repeated collection of anthropometrics. This article reviews the rationale for the Gemini study, its representativeness and the main measures.
Children's diets contain too few fruits and vegetables and too many foods high in saturated fat. Food intake is affected by multiple individual and family factors, which may differ for core foods (that are important to a healthy diet) and non-core foods (that are eaten more for pleasure than health). Data came from a sample of twins aged 11 years (n 342) and their parents from the Twins Early Development Study. Foods were categorised into two types: core (e.g. cereals, vegetables and dairy) and non-core (e.g. fats, crisps and biscuits). Parents' and children's intake was assessed by an FFQ. Mothers' and children's preference ratings and home availability were assessed for each food type. Parental feeding practices were assessed with the child feeding questionnaire and child television (TV) watching was maternally reported. Physical activity was measured using accelerometers. Correlates of the child's consumption of each food type were examined using a complex samples general linear model adjusted for potential confounders. Children's non-core food intake was associated with more TV watching, higher availability and greater maternal intake of non-core foods. Children's core food intake was associated with higher preferences for core foods and greater maternal intake of core foods. These results suggest that maternal intake influences both food types, while preferences affect intake of core foods but not of non-core foods, and availability and TV exposure were only important for non-core food intake. Cross-sectional studies cannot determine causality, but the present results suggest that different approaches may be needed to change the balance of core and non-core foods in children's diets.
Childhood obesity has multiple causes, most of them capable of explaining only
one part of the problem. The population-wide impact of sedentary lifestyles and
availability of energy-dense food is undeniable, but substantial individual
differences in body weight persist, suggesting that individuals respond
differently to the ‘obesogenic’ environment. One plausible
mechanism for this variation is the early expression of appetitive traits,
including low responsiveness to internal satiety signals, high responsiveness to
external food cues, high subjective reward experienced when eating liked foods
and preferences for energy-dense foods. Case–control studies support
the existence of abnormalities in these traits among obese children compared
with normal-weight children, and correlations between psychometric measures of
child appetite and child weight suggest that appetitive trait profiles may not
only promote obesity but also protect against it. The origins of appetitive
traits are as yet uncharted, but will include both genetic and environmental
influences. Parental feeding style may affect the development of appetite but
the exact nature of the relevant behaviours is unclear and many studies are
cross-sectional or begin late in childhood, obscuring causal relationships.
Future research should explore determinants and biological mechanisms by using
prospective designs beginning early in life, measuring relevant biomarkers such
as gut hormones and incorporating neuroimaging and genotyping technologies.
Potential clinical applications include the identification of ‘at
risk’ children early in life and interventions to modify appetitive
traits or ameliorate their impact on intake and weight.
Omnivores have the advantage of a variety of food options but face a challenge in identifying foods that are safe to eat. Not surprisingly, therefore, children show a relative aversion to new foods (neophobia) and a relative preference for familiar, bland, sweet foods. While this may in the past have promoted survival, in the modern food environment it could have an adverse effect on dietary quality. This review examines the evidence for genetic and environmental factors underlying individual differences in children's food preferences and neophobia. Twin studies indicate that neophobia is a strongly heritable characteristic, while specific food preferences show some genetic influence and are also influenced by the family environment. The advantage of the malleability of human food preferences is that dislike of a food can be reduced or even reversed by a combination of modelling and taste exposure. The need for effective guidance for parents who may be seeking to improve the range or nutritional value of foods accepted by their children is highlighted.
Childhood obesity poses one of the greatest challenges to paediatric health in the 21st century. Developing effective strategies for treatment and prevention is therefore a priority for clinical medicine and public health. This process is taking place at a time of unprecedented change in the understanding of the role of genetic factors in human health and disease, and genetic research into obesity has challenged assumptions about causal processes. In the spirit of the conference theme, the present paper will discuss the implications of the understanding of genetic and environmental influences on obesity for the development of effective behavioural treatments.
Depression and specific health problems
Lucy Cooke, Health Behaviour Unit Department of Epidemiology and Public Health, University College London, London, UK,
Jane Wardle, Health Behaviour Unit, Department of Epidemiology and Public Health, University College London, London, UK
The most common research strategy in the literature is to examine simple associations between obesity and depression. Friedman and Brownell published a seminal review examining the psychological correlates of obesity. This chapter summarizes the findings of earlier reviews and presents a more detailed examination of recent research into associations between obesity and depression in both community-based and clinical samples. It also includes tables covering the principal studies in the field since the publication of Friedman and Brownell's review. The chapter focuses on studies of individuals seeking treatment for obesity, although a parallel literature has investigated weight status in clinically depressed individuals. More recent studies of obese patients have generally confirmed the older literature in finding large excesses of lifetime prevalence of depression and current depression as measured by the Beck Depression Inventory (BDI) or the Brief Symptom Inventory (BSI).
The present study was conducted to examine the developmental patterning of food preferences in a large sample of British schoolchildren and to investigate possible gender differences. Using a cross-sectional survey design, the study was carried out in three primary and three secondary schools in West London, UK. A total of 1291 children aged from 4 to 16 years completed a 115-item food preference questionnaire in class time, supervised by class teachers and assistants. Children indicated whether they had ever tried each item and, if so, how much they liked it. We observed age-related increases in the number of foods tried (P<0·001), liked (P<0·005) and disliked (P<0·05). Controlling for the number of foods tried rendered the increase in dislikes non-significant and reversed the age effect on the number liked. Girls liked fruit (P<0·05) and vegetables (P<0·001) more than boys did; boys liked fatty and sugary foods (P<0·005), meat (P<0·001), processed meat products (P<0·001) and eggs (P<0·05) more than girls did. Some age differences were apparent in liking for categories of food, although the effects were not linear. Across ages and genders, children rated fatty and sugary foods most highly, although ratings for fruit were also high. Children's food preferences overall are not consistent with a healthy diet. Interventions should focus on increasing the familiarity, availability and accessibility of healthy foods and should be mindful of the need to target messages appropriately for boys who have less healthful food preferences than girls at all ages.
Individual differences in several aspects of eating style have been implicated in the development of weight problems in children and adults, but there are presently no reliable and valid scales that assess a range of dimensions of eating style. This paper describes the development and preliminary validation of a parent-rated instrument to assess eight dimensions of eating style in children; the Children's Eating Behaviour Questionnaire (CEBQ). Constructs for inclusion were derived both from the existing literature on eating behaviour in children and adults, and from interviews with parents. They included reponsiveness to food, enjoyment of food, satiety responsiveness, slowness in eating, fussiness, emotional overeating, emotional undereating, and desire for drinks. A large pool of items covering each of these constructs was developed. The number of items was then successively culled through analysis of responses from three samples of families of young children (N = 131; N = 187; N = 218), to produce a 35-item instrument with eight scales which were internally valid and had good test-retest reliability. Investigation of variations by gender and age revealed only minimal gender differences in any aspect of eating style. Satiety responsiveness and slowness in eating diminished from age 3 to 8. Enjoyment of food and food responsiveness increased over this age range. The CEBQ should provide a useful measure of eating style for research into the early precursors of obesity or eating disorders. This is especially important in relation to the growing evidence for the heritability of obesity, where good measurement of the associated behavioural phenotype will be crucial in investigating the contribution of inherited variations in eating behaviour to the process of weight gain.
The Food Choice Questionnaire (FCQ), which measures the reported importance to a given individual of nine factors underlying food choice, and a food frequency questionnaire, were administered to 241 participants, who were also required to classify their diet as either 'standard', 'low in red meat' or 'vegetarian'. Respondents describing their diet as low in red meat attributed greater importance to health, natural content, weight control and ethical concern in their food choice than did those who described their diets as standard, whereas vegetarians differed significantly from those with a standard diet only on the score for ethical concern. Differences between men and women and between students and non-students in the frequency of consumption of a number of foods were shown to be mediated by differences in the importance attached to FCQ factors. Thus the generally healthier diets of women compared to men appeared to be accounted for by the greater importance attributed by women to weight control, natural content and ethical concerns.
Patients' beliefs about the causes of anxiety problems have received comparatively little attention. In the present study, agoraphobic patients rated the contribution of eight factors in causing their condition. They also selected the major cause of their agoraphobia and evaluated that in relation to the elements of attributional style. The most commonly selected major cause was stress, which also attracted the highest average ratings. This was followed in frequency by disposition (being a naturally nervous person), circumstances (staying home too much) and childhood experiences. Depression was associated with stronger beliefs in the contribution of several of the causal factors and with rating the major cause as more stable and global. Anxiety was associated with a stronger belief in medical illness as a cause, and with a lower sense of controllability of the major causes. These results suggest that agoraphobic patients' views of the causes of their condition vary, and could usefully be evaluated in relation to the provision of treatment in order to modify the way treatment options are presented to the patients.
Pain mechanisms: a new theory. R. Melzack and P. D. Wall. Science, 150, 971-9,1965.
Effects of coping behavior on gastric lesions in rats as a function of the complexity of coping tasks. A. Tsuda, M. Tanaka, T. Nishikawa and H. Hirai. Physiology and Behavior, 30, 805-8, 1983.
Social stress and atherosclerosis in normocholesterolemic monkeys. J. R. Kaplan, S. B. Manuck, T. B. Clarkson, F. M. Lusso, D. M. Taub and E. W. Miller. Science, 220, 733-5, 1983.
Mental stress and the induction of silent myocardial ischemia in patients with coronary artery disease. A. Rozanski, C. N. Bairey, D. S. Krantz, J. Friedman, K. J. Resser, M. Morell, S. Hilton-Chalfen, L. Hestrin, J. Bietendorf and D. S. Berman. New England Journal of Medicine, 318,1005-12, 1988.
Depressed lymphocyte function after bereavement. R. W. Bartrop, E. Luckhurst, L. Lazarus, L. G. Kiloh and R. Penny. Lancet, i, 834-6, 1977.
Psychological stress and susceptibility to the common cold. S. Cohen, D. A. J. Tyrrell and A. P. Smith. New England Journal of Medicine, 325, 606-12, 1991.
Section 1 documented some of the empirically verified links between life stress, support and health. The question that arises is what are the processes through which factors in the psychosocial environment influence disease aetiology? Unless descriptive studies of clinical phenomena are coupled with a knowledge of mechanism, the study of psychosocial factors will remain outside the mainstream of biobehavioural research and understanding. The readings in Section 2 describe the psychophysiological processes linking behavioural stressors and emotional distress with disease aetiology. The papers highlight the importance of psychophysiological processes in several clinical conditions, including pain, gastrointestinal lesions, cardiovascular pathology and resistance to infection. These readings have been selected to illustrate the diverse research strategies that have proved valuable, and include the analysis of clinical phenomena (Melzack and Wall), acute and chronic stress studies with animals (Tsuda et al.; Kaplan et al.), short-term experiments with humans (Rozanski et al.) and the experience of life stress (Bartrop et al.; Cohen et al.).
The psychophysiological processes relevant to the aetiology and course of disease are complex. It is well established that noxious stimuli and challenging conditions may elicit a broad range of autonomic, neuroendocrine and immunological adjustments.
Randomised controlled trial of nicotine chewing-gum. M. J. Jarvis, M. Raw, M. A. H. Russell and C. Feyerabend. British Medical Journal, 285, 537-40, 1982.
Conditioned side effects induced by cancer chemotherapy: prevention through behavioral treatment. T. G. Burish, M. P. Carey, M. G. Krozely and F. A. Greco. Journal of Consulting and Clinical Psychology, 55, 42-8, 1987.
Improvement of medication compliance in uncontrolled hypertension. R. B. Haynes, D. L. Sackett, E. S. Gibson, D. W. Taylor, B. C. Hackett, R. S. Roberts and A. L. Johnson. Lancet, i, 1265-8, 1976.
Effect of psychosocial treatment on survival of patients with metastatic breast cancer. D. Spiegel, J. R. Bloom, H. C. Kraemer and E. Gottheil. Lancet, ii, 888-91, 1989.
Alteration of type A behavior and its effect on cardiac recurrences in post myocardial infarction patients: summary results of the recurrent coronary prevention project. M. Friedman, C. E. Thoresen, J. J. Gill, D. Ulmer, L. H. Powell, V. A. Price, B. Brown, L. Thompson, D. D. Rabin, W. S. Breall, E. Bourg, R. Levy and T. Dixon. American Heart Journal, 112, 653-65, 1986.
Can lifestyle changes reverse coronary heart disease? The Lifestyle Heart Trial. D. Ornish, S. E. Brown, L. W. Scherwitz, J. H. Billings, W. T. Armstrong, T. A. Ports, S. M. McLanahan, R. L. Kirkeeide, R. J. Brand and K. L. Gould. Lancet, 336, 129-33, 1990.
The recognition that behavioural scientists have a contribution to make to treatment outside the psychiatric arena was first widely acknowledged at a conference on behavioural medicine held in Yale, USA, in 1977 (Schwartz and Weiss, 1977). Since that time, the range of treatments which have been used, and target conditions to which psychological treatments have been applied, has expanded enormously. A growing number of specialist journals and handbooks are now available and illustrate the expansion in research in the area. The involvement of health psychologists in clinical settings has also increased, allowing research developments to be put into practice (Pearce and Wardle, 1989). The readings in this section have been selected to illustrate the range of psychological interventions which have proved effective in clinical settings.