The connection between mental and physical health : investigating the associations between psychosocial well-being, sleep and cardio-metabolic health in European children and adolescents

Abstract

Background The high prevalence of overweight and obesity and related cardio-metabolic disorders such as insulin resistance and hypertension in European children and adolescents is a matter of concern. Aspects of mental health have been suggested to be determinants of cardio-metabolic health and it has been hypothesised that lifestyle factors such as sleep may be part of the underlying mechanism. However, studies in young populations investigating the role of mental health for sleep or cardio-metabolic markers have mainly focussed on a psychopathological view of mental health. Further, studies on the association between sleep and specific cardio-metabolic markers are either limited or suffer from methodological limitations with respect to the measurement of sleep. Aims The present cumulative thesis consists of four original papers that aim to shed light on the associations between psychosocial well-being as one aspect of positive mental health and cardio-metabolic markers. A special focus was put on the role of sleep as a potential mediating factor. Methods Analyses were carried out based on data of children and adolescents from 8 European countries participating in the IDEFICS/I.Family study. The IDEFICS/I.Family study was set up to identify risk and protective factors for chronic non-communicable diseases and to develop and evaluate a community-based intervention for the prevention of childhood obesity. The data that were used for this thesis were collected during three examination waves with intervals of approximately 2 and 4 years in between them (Wave 1: 2007/2008, Wave 2: 2009/2010, Wave 3: 2013/2014). In 2015, these examination waves were complemented by an in depth examination of a subsample in which children with overweight were overrepresented. The samples on which the analyses for the different papers were based varied in size between 559 and 6,519 subjects depending on the available data for the respective research question. Psychosocial well-being comprised items on emotional well-being, self-esteem and social relationships. Sleep characteristics included questionnaire-based and objective measurements of sleep duration, sleep disturbances, sleep quality and sleep timing. Cardio-metabolic markers encompassed waist circumference, blood pressure, the homeostasis model assessment for insulin resistance (HOMA-IR), high-density lipoprotein cholesterol (HDL-C) and triglycerides. Associations were examined applying a variety of statistical methods including multilevel regression analysis, quantile regression and path analysis. Results Higher psychosocial well-being was found to be cross-sectionally associated with longer sleep duration and fewer sleep disturbances (N=6,336). However, well-being at the second examination wave did not predict sleep characteristics 4 years later (N=3,379). Using actigraphy- and sleep diary-derived sleep characteristics (sleep duration, sleep latency, sleep efficiency, bed- and wake time), the following distinct sleep subtypes were identified in a sample of 559 participants from whom detailed information on sleep was collected in 2015: (i) early birds, (ii) short sleep duration, (iii) optimal sleep and (iv) poor sleep quality. Neither sleep subtype nor the single sleep characteristics were found to be statistically significantly associated with body mass index. In contrast, an analysis conducted in 3,900 children and adolescents participating in the second and third examination wave revealed a cross-sectional inverse association between parent- or self-reported sleep duration and waist circumference. Longer sleep duration was also found to be indirectly associated with lower HOMA-IR through lower waist circumference. This indirect pathway was also observed longitudinally, i.e. longer sleep duration at the second examination wave was indirectly associated with lower HOMA-IR four years later following the pathway through waist circumference at the second and waist circumference at the third examination wave. After the associations (i) between psychosocial well-being and sleep and (ii) between sleep and cardio-metabolic markers were investigated in-depth, the associations between psychosocial well-being and cardio-metabolic markers considering sleep duration and other lifestyle factors as potential mediators were analysed in one cross-sectional (N=6,519) and one longitudinal path model (N=1,393). Cross-sectionally, higher psychosocial well-being was found to be indirectly associated with (i) lower waist circumference through a healthier lifestyle and with (ii) lower blood pressure, lower HOMA-IR, lower triglycerides and higher HDL-C through both a healthier lifestyle and lower waist circumference. These indirect effects were also shown in the longitudinal model where changes in psychosocial well-being over the 2- and 4-year-intervals, respectively, were investigated in relation to cardio-metabolic markers measured at the 6-year follow-up (third examination wave). Direct associations were observed between higher levels of psychosocial well-being and lower waist circumference, lower HOMA-IR and higher HDL-C independent of potential confounders and mediators. However, direct associations were less consistent across analyses, i.e. they were partially only observed in the cross-sectional or longitudinal analysis. Discussion and conclusions The results of the present thesis support the hypothesis that psychosocial well-being may be linked to cardio-metabolic health through sleep and other lifestyle factors in children and adolescents. One strategy to improve cardio-metabolic health of children and adolescents may therefore be to promote psychosocial well-being and a healthy sleep, e.g. through resilience training programs and mindfulness-based interventions. However, because of the scarcity of research more longitudinal studies designed for gaining further knowledge on the temporal relationships between positive mental health, lifestyle factors and cardio-metabolic health are needed