Background
Adolescent obesity is a major health concern across most Western societies, including Australia, with one in four Australian adolescents overweight or obese [
1]. The World Health Organization (WHO) defines overweight and obesity in children and adolescents (aged 5-19) as having a standardized body mass index (BMI-z) greater than one or two standard deviations (SD) above the mean, respectively [
2]. The physical health implications of adolescent obesity are numerous and widely understood, including increased risk of asthma, cardiovascular risk factors and chronic inflammation [
3]. However, there is emerging evidence to suggest that physical health conditions like obesity and cardiovascular disease also share a direct relationship with mental health and wellbeing [
4,
5]. These conditions are complex, and interventions need to be aimed at the individual and the environment in which children live. The home environment is important as including parenting in interventions for adolescents with a range of mental health and psychosocial issues has generally been found to increase the efficacy of interventions, as well as promoting whole of family health and mental health [
6]. Therefore, the impact of obesity on psychosocial problems in adolescents is one area of research being explored [
7].
Health-Related Quality of Life (HRQoL) is a construct commonly used to conceptualize both physical and psycho-social functioning and wellbeing [
8]. Including measures of social, physical and emotional functioning [
9], HRQoL is often captured in adolescents with generic tools like the Pediatric Quality of Life Inventory (PedsQL) [
10]. A systematic review of 22 studies, which pooled a total sample of 104,093 participants, investigated the effect of weight status on adolescents’ and children’s HRQoL [
8]. Twelve studies revealed a significant inverse relationship between weight status and global HRQoL in both community and clinical samples. Pooled analyses of studies utilizing the PedsQL (n = 12,835, k = 13) indicated that weight status was linearly related to both poorer self-reported and parent reported HRQoL. This relationship was verified for global HRQoL and its psychosocial and physical sub domains.
Given the established link between adolescent obesity and poorer HRQoL outcomes, one avenue for further exploration is the role of intervening mechanisms or conditional factors. Findings from a study investigating the inverse relationship between obesity and depression has suggested that the relationship is much more complex than a direct causal chain whereby increases in weight lead to increases in depressive symptoms [
11]. The authors proposed that moderation analysis, within a well powered sample, is the next step to fully understanding how the relationship functioned between obesity and depression. Testing moderation effects may uncover the factors which exacerbate or reduce the negative impact of obesity on HRQoL in adolescents.
Previous research investigating the effect of family factors on the inverse relationship between weight status and HRQoL has primarily focused on adolescent perceived social support. Zeller and Modi [
12] found that perceived social support from classmates was a strong predictor of quality of life; however, the greatest level of support came from parents and friends. The authors concluded that overall provision of support is an important target for obesity intervention and is related to improved HRQoL outcomes [
12]. Whilst an inverse relationship was not supported between weight and quality of life, social support was also found to be an important factor in the wellbeing of a clinically overweight sample of adolescents [
13]. Expanding on this research, Herzer, Zellar, Rausch and Modi [
14] investigated social support providers and obesity-specific HRQoL in 74 obese adolescent and caregiver dyads, and found that parents and close friends should be included in obesity prevention and treatment interventions, as they were the most valued providers of emotional appraisal and instrumental support for obese youth. Interestingly, only classmates were found to significantly influence HRQoL [
14]. Taken together these studies highlight the importance of supportive networks for overweight or obese adolescents in any consideration of their overall functioning.
These studies highlight some common limiting characteristics of the HRQoL and social support literature and suggest areas to be addressed by future research. Firstly, studies utilized small samples, only including adolescents with overweight or obesity [
12‐
14], thus it remains unclear whether social support influences the HRQoL differently in this group than in adolescents with normal weight. A number of studies found that a lack of social support was associated with reductions in the HRQoL of adolescents with obesity [
12‐
14]; however, it remains unclear whether a lack of social support augments the impact of increasing weight on HRQoL, or is an independent risk factor. Another general limitation was that these studies addressed clinical samples seeking treatment for their weight. Treatment-seeking adolescents may suffer greater functional impairment and possess greater motivation for change than adolescents in the community, and therefore may not be representative of overweight adolescents in the population [
8]. Also, seeking treatment may already be indicative of being part of a supportive social network, as the family is motivated to take part in a weight loss intervention [
12]. Herzer et al. [
14] also concluded that receiving general support may not be the best predictor of obesity-specific HRQoL. The authors proposed that support of obesity-specific behaviors such as parental encouragement to engage in healthy eating and physical activity may be an important direction for future research [
14].
This study aims to determine whether the relationship between HRQoL and obesity is moderated by parental encouragement of a healthy lifestyle among adolescents. It was predicted that greater encouragement of healthy lifestyle behaviors from parents would be associated with higher HRQoL scores, and that parental encouragement of healthy lifestyle behaviors would moderate an inverse relationship between weight status and HRQoL.
Discussion and conclusions
Our hypotheses that greater encouragement of healthy lifestyle behaviors from parents would be associated with higher HRQoL scores, and that parental encouragement of healthy lifestyle behaviors would moderate the relationship between weight status and HRQoL, were partly supported by the results of this study. Parental encouragement of healthy behaviors was found to significantly moderate the relationship between weight status and physical functioning and wellbeing in the adjusted model. Two explanations may account for this finding. As was illustrated in Figure
1, receiving a medium or high amount of parental encouragement (compared to low) seemed to be protective of physical functioning and wellbeing among normal weight adolescents. However adolescents in the overweight or obese group had similar physical functioning and wellbeing at low and medium parental encouragement. This may indicate that high levels of parental encouragement are needed to protect the physical functioning and wellbeing in adolescents with overweight or obesity. Since only the physical functioning scale shows this result, it may be indicative of the adolescent’s perceived physical limitations that come with increased body size, however more research is required to elucidate the obesity-related factors that may impact on functional difficulties [
8]. However, previous research has found familial social support to be important in improving adolescent HRQoL [
12‐
14], therefore the direction of the interaction is contrary to what would be expected. Further consideration is required to determine whether the interaction was a chance finding in this sample, or has meaningful implications for the development of future interventions.
Adolescents experience many competing influences during this important developmental period including peers and school [
30]. Weight status, parental encouragement and the covariates examined by this study explained only a small proportion of the total variance in global HRQoL, including psychosocial and physical functioning and wellbeing. Therefore moderation may not have been supported in this study because the relationship is influenced by other factors. For example, it may be that peer support, rather than parental, is more influential on weight and HRQoL as there is the tendency for a greater conformity to peer groups as children reach adolescence [
30]. Low parental encouragement may also be an independent risk factor for HRQoL outcomes in adolescents, regardless of weight status. Compared to low, high parental encouragement to engage in healthy behaviors was related to improvements in global, psychosocial and physical functioning HRQoL scores by almost four points.
The significant main effects of the current study expand upon findings from past research, and taken together can be used to help ensure that future obesity interventions also target quality of life. Zeller and Modi [
12] and Herzer et al.[
14] both found perceived classmate support to be a significant predictor of HRQoL in a small, treatment-seeking sample of obese adolescents. The current research builds upon this finding by examining perceived parental encouragement in a large, community-based sample. Collectively, it is likely that parent and classmate encouragement play a unique role in fostering positive HRQoL outcomes in adolescents regardless of weight status. The significant positive association between parental encouragement of healthy behaviors and HRQoL is also in line with past research that has investigated the effect of behavior-specific encouragement, from parents and families, on other psychosocial outcomes [
31,
32].
A major strength of the study is being the first of its kind to examine the moderating role of parental encouragement of health behaviors on the inverse relationship between weight status and HRQoL. Also the use of a large community-based sample and objective measurement of anthropometric outcomes were advantageous. However, obtaining data from a large community-based study has its restraints; the ability to gather in-depth and specific information on all study variables is relinquished and complex constructs are often represented by only a few items. For example, the measure of parental encouragement used in this study can act only as an indicator as it was formed using four survey questions. The extent to which parents were encouraging of healthy behaviours was self-reported by adolescents, which may be subject to recall issues and participants responding according to social desirability. Furthermore, asking adolescents about the level of encouragement they receive from their parents lacks objectivity. Concordance of child and parent perceptions of familial support is approximately 70%, according to a recent study [
33]; however, considering that conformity to parental control decreases as children reach adolescence [
30], agreement may not be so high between adolescents and their parents. Therefore, collecting data from multiple sources may be needed to verify the findings of this study. Due to the cross-sectional design of the current study relationships among variables should not be interpreted as causal. A major limitation was the response rate of around 50%. Although quite low, this response rate is similar to other similar community-based interventions [
34,
35]. Lastly, generalizability was limited as the sample was predominately European Australian and the geographic locations from which they were drawn were quite homogenous.
These findings suggest that irrespective of weight status, physical activity level or diet quality, age, sex and school attended, it may be important for parents to be encouraging of healthy eating and physical activity practices. In doing so, parents can help increase global, psychosocial and physical functioning of their adolescent offspring. Furthermore, variation found between HRQoL subscales indicates that some areas of functioning may be more heavily influenced by parental encouragement and weight than others. Specifically, only high levels of parental encouragement were associated with increments in psychosocial functioning, whereas both medium and high levels of encouragement are sufficient to significantly increase the physical and global functioning of adolescents. The results may also have significant implications for developing interventions. Parental encouragement of healthy behaviors has been identified as a factor particularly impacting on physical functioning. Therefore parental encouragement can form an additional target for obesity interventions, especially those involving physical exercise. Rather than focusing on the difficult task of weight reduction [
8], targeting parents to increase their levels of encouragement of healthy behaviors, as a mechanism to increase HRQoL, may be an effective strategy for reducing adolescent obesity.
This study represents an initial exploratory step towards establishing whether the inverse relationship between weight and HRQoL differs as a result of parental encouragement of healthy behaviors in adolescents. Future studies should investigate the longitudinal relationship between increasing weight and HRQoL, and the role of moderating factors. This will shed light on the temporal ordering of variables, thus where and when to intervene to prevent or reverse the negative effect of obesity on HRQoL outcomes. Prospective moderation analyses should focus on additional sources of encouragement, including parents, grandparents, classmates, friends and teachers using multi-informant and comprehensive measures.
Acknowledgements
The authors would like to thank the many people involved in the Pacific OPIC Project including co-investigators, other staff and postgraduate students, partner organizations, and especially the schools, students, parents and communities. The funding for the project was from the Victorian Department of Health, the National Health and Medical Research Council (in conjunction with the Health Research Council [New Zealand] and the Wellcome Trust [UK] as part of their innovative International Collaborative Research Grant Scheme), and AusAID. The current paper was supported by additional funding from the Swedish Council for Working Life and Social Research (Sweden).
The corresponding author affirms that she has listed everyone who contributed significantly to the work in the Acknowledgements.
Competing interests
The authors declare that they have no competing interests.
Authors’ contributions
LN drafted the manuscript, participated in the design of the study and performed the statistical analysis. AL and LM conceived the study, participated in its design and coordination and helped draft the manuscript. LM also performed statistical analysis. MM, BS and SP were involved in revising the manuscript critically for important intellectual content. All authors have read and given final approval of the version published and agree to be accountable for all aspects of the work.