The effect of weight status, lifestyle, andbody image perception on health-related quality of life in adolescents: A quantile approach

Objective: In recent years there has been an increase in the population of children and adolescents who are overweight and obese, mainly due to the spread of a pattern characterized by high calorie diets and over-sedentary lifestyles. This situation has significant public health implications because it establishes and promotes the onset of major chronic diseases. The main objective of this study is to evaluate the effect of excess weight, lifestyle factors and body image on HRQoL in a sample of 17 year olds selected from schools. Methods: Cross-sectional data of 2,507 seventeen-year-old adolescents was collected in 2008 as part of the So.N.I.A project, a nutritional surveillance study in the northern Italian region  of Emilia-Romagna, in order to assess the eating habits in the school population and the implications in terms of health and HRQoL. A two-stage sampling design was used in order to obtain a Health District representative sample of the regional population. HRQoL was assessed using the EQ-5D-Y questionnaire completed by the students at school. The association between weight categories, defined by means of the International Obesity Task Force cut points, physical exercise and body image perception and HRQoL as measured by the EQ-Visual Analogue Scale, was studied by means of a quantile regression analysis. The EQ-5D is a questionnaire for adults was developed in the late 80s by a group of European researchers (EuroQol Group) with the goal of obtaining a standardized tool for assessments of the quality of life in health care. It consists of two parts. The first part generates 243 possible health profiles starting from 5 domains: movement , self-care , daily activities, pain or discomfort and anxiety or concern. Each of these has three levels of severity (no problems, some problems, extreme problems). The second part consists of a Visual Analogue Scale (VAS) used to quantify HRQoL with a score ranging from 0 (worst imaginable health state) to 100 (best imaginable health state). An adapted version of the EQ-5D for pediatric subjects (8-18 years old), called EQ-5D –Y was validated in Italy in 2007. The impact of covariates on the distribution of VAS has been studied using a Quantile Regression, which has allowed us to assess the simultaneous effect of the variables considered at each percentile of the conditional distribution. The great advantage of the quantile regression is the ability to estimate all the distribution of the conditional quantiles of the response variable, so as to study the influence of the explanatory variables on the shape of the distribution of Y. In other words, the estimation of a value (conditioned mean) is replaced by the estimate of 99 values ​​(conditional quantiles). When estimating the 50th percentile conditional quantile, regression is also called median regression (LAD = Least Absolute Deviation). Results: Relying solely on OLS estimates would have resulted in useful information being lost, such as the differential effect of some covariates in the lower quantiles of the VAS distribution. Girls compared to boys reported lower HRQoL values, especially for the lower quantile of the VAS. Being overweight or obese was associated with a worse HRQoL, particularly for the lower quantile of the VAS. Lower weekly exercise was associated with a decreased perceived HRQoL. A negative self acceptance and an inadequate/incorrect body self perception are associated with a lower HRQoL for all percentiles. Conclusions: Quantile regression can help to highlight differences in the effects along all of the outcome distribution. The results obtained demonstrated that excess weight is not only crucial in terms of morbidity and mortality, as is well known in the literature, but also has strong repercussions on the perceived quality of life in adolescence. Excess weight, sedentary behavior and an unsatisfactory self-perception are associated with reduced HRQoL in this population-based sample.