Body weight and quality of life among adolescents in krakow

A cross-sectional study was conducted among students from 17 junior high schools from different districts of Krakow between December 2013 and February 2015. Information about the study and its aims were given to the schoolchildren’s parents during periodical parent-teacher meetings. Only 70% of the parents have expressed their opinion and gave feedback about the child’s participation (either approval or refusal) in the study. Among those who responded, 14% refused their child’s participation in the study. The anonymous questionnaire, which took approximately 10-15 minutes to fill out, was administered in school classrooms and filled out individually by the adolescents in the presence of a research assistant. Data from 1465 adolescents were collected, which constituted 90.2% of those who agreed to participate. We excluded 174 questionnaires from this analysis because of missing data for the KIDSCREEN-27 questionnaire (n=69), weight or height (n=85) or age (n=8). Furthermore, we decided to exclude schoolchildren aged 12 (n=3) and 17 (n=9) because of small numbers and not being representative for this group of youth.

Finally, analysis was performed for 1291 adolescents, 632 (49.0%) girls and 659 (51.0%) boys. The sample comprised 391 adolescents from the 1st (30.3%), 462 from 2nd (35.8%) and 438 from 3rd years of junior high school (33.9%).

The study was reviewed and approved by the Jagiellonian University Bioethics Committee (approval number: KBET/143/B/2013). During the recruitment phase school principals of all the participating schools have given their approval for the study. Moreover, individual written informed consent was obtained from the parents of the participating students.

The quality of life was measured using the Polish version of the KIDSCREEN-27 questionnaire – child version [21]. The response range for each out of the 27 items is based on a 5-point Likert scale. The scale indicates the frequency of certain behaviors or feelings (1 = never to 5 = always) or the intensity of an attitude (1 = not at all to 5 = extremely). The time frame refers to the previous week [22, 23]. The final assessment covers 5 dimensions of QoL:

The Polish version of the KIDSCREEN-27 has shown both satisfactory validity and reliability to be used in the Polish population (Cronbach’s α for the subscale range from 0.791 to 0.878) [21].

Each participant’s QoL in each dimension (recoded to 0-100 scale) was categorized as low, average or high according to sex and age specific cut-point values for Polish adolescents, as described in the paper by Mazur et al. [21]. The detailed distribution of the quality of life in the studied population was described in detail elsewhere [24].

The data about weight and height were self-reported by the adolescents. The body mass index (BMI) was calculated as a ratio of weight in kilograms (kg) and the square of height in meters (m²). Based on BMI growth charts from the OLAF study [25] − national up-to-date BMI cut-off values were applied to define a participant’s body weight status – the cut-offs used are presented in Table I. Based on the recommendation of Centers of Disease Control and Prevention, underweight was defined as BMI below the 5^th percentile, normal weight as ranging from the 5^th percentile to less than the 85^th percentile, and excessive weight (overweight and obesity together) was at or above the 85^th percentile of BMI distribution specific for sex and age [26].

The other variables included in our analyses are: sex, age, regular physical activity and the presence of chronic conditions. “Regular physical activity” was assumed if the adolescent declared that he or she does sports regularly (at least once per week) and the “presence of chronic conditions” was based on the single question “Have you been diagnosed with any chronic disease/ condition?”.

Descriptive statistics were presented as frequencies and percentages. To assess the risk of having a low Qol related to the body weight status among adolescents the logistic regression model was applied. Firstly, crude models were estimated, which included only the weight status group, while later the relationship between the weight status and different QoL domains were adjusted for age, regular physical activity and the presence of chronic conditions. In all the comparisons across the weight status groups, the reference group was the one with normal weight. The models were developed for boys and girls separately. All the analyses were performed using IBM SPSS Statistics 24, with statistical significance set at p<0.05.

Excessive body weight was a predictor of a young person’s low QoL in two KIDSCREEN-27 dimensions: Physical Well-being and Social Support & Peers. Both girls and boys with excessive body weight had a higher risk of low Physical Well-being compared to their peers with normal body weight. Interestingly, among girls this was the only dimension affected by body weight (after adjustment for confounders). We did not confirm the relationship of abnormal body mass with other QoL subscales. Many studies indicate the existence of a relationship between excessive body weight and a worse QoL in the dimension that refers to physical well-being and overweight and /or obesity seems to be related to a lower quality of life [7, 18, 19, 27]. Lower QoL among adolescents with excessive weight could be related to the negative health consequences that may be experienced by adolescents with overweight and obesity. Young people with excessive body weight experience difficulties in taking up physical activities, due to the lack of energy, vigor and physical strength. They usually avoid any sport, because they get tired faster and have worse motor activity [19, 32].

Among boys excessive body weight was also related with a higher risk of rating low in the Social Support & Peers dimension. Excessive weight among boys is a very frequent reason for teasing, mocking and rejection by peers. Adolescents with excess body weight often experience social exclusion and even bullying by peers [33, 34, 35]. Similar results, but in both sexes, were found in the studies conducted among American and Iranian adolescents, where young people with excessive body weight rated their social functioning as worse than their normal-weight peers [7, 16, 19]. On the other hand, observations in other populations do not confirm this relationship [17, 18]. It is worth mentioning that a higher risk of low QoL in the Social Support & Peers dimension among girls with excessive weight was observed only in the crude model, which took into consideration BMI exclusively. Many studies indicate that girls want to be perceived by others as desirable, attractive and to be accepted in their peer group [36]. However, we do not observe the relationship after the adjustment for age, regular physical activity and the presence of chronic diseases, thus this relation may have been due to the above factors, especially age.

We did not observe a significant relationship between excessive body weight and the other dimensions of QoL that were assessed, either among boys or girls. In our study we observed no significant relationship between excessive body weight and the young person’s mental health, which is in line with the studies of Cui et al. and Helseth et al [17, 32]. Researchers of the KIDSCREEN project also indicated that there was no significant relationship between excessive body weight and psychological wellbeing, which can be explained by the fact that this dimension mainly measures positive aspects, such as a sense of satisfaction and happiness [37]. However, some other authors indicated that obese adolescents suffer from depression, experience embarrassment and social degradation [7, 33]. The differences between studies can result from a different age distribution of the population analyzed by these studies. Swallen et al. showed that in the dimension of emotional functioning, overweight and obesity influenced the occurrence of depression and low self-assessment among younger obese adolescents, but not among older ones [16]. Moreover, we did not observe a relationship between excessive body weight and the QoL in the Autonomy & Parents dimension. This may be related to the fact that the parents of obese children are often obese themselves, so due to their own experience of being obese, this factor does not impair their relationships with their children. Moreover, it leads to their losing perception of excessive weight [38].

In our study, the relation between too low a body weight and low QoL was found only among boys. Underweight was a predictor of a low QoL score in the Physical Well-being, Autonomy & Parents and Social Support & Peers dimensions, to a greater extent than excessive weight. It is worth mentioning that there is little information on the relationship between body weight deficiency and the adolescent’s QoL in the literature available. In our study boys with underweight had an over threefold higher risk of low Physical Well-being than boys with normal body weight. This might be related to the fact that boys with underweight do not have well-built muscles, so they can have problems with taking up physical activities. The study of Swallen et al. showed that underweight adolescents were significantly more likely to have functional limitations [16]. When considering the Autonomy & Parents dimension among boys and its relation with underweight, one can suggest that a body weight deficiency may be associated with perceiving the adolescents’ health as worse by their parents, especially when compared with the ideal muscular stature of men subsequently having greater control over their bodies. It is also possible that underweight is related to the poor financial condition of the family, which means that the adolescents receive less money for their own expenses (the dimension Autonomy & Parents includes two questions referring to the financial resources of the respondents). However, a large study conducted on a nationally representative sample of Polish school-age children and adolescents does not confirm a significant relationship between family income and the risk of underweight [39]. The third dimension for which the relation between underweight and low QoL was observed among boys was Social Support & Peers. These results are in line with the study conducted among Chinese children [20]. This may be related to the fact that a boy with underweight may be easier to bully by his peers because of his body than a muscular boy, with an athletic body shape who can cause fear among peers [40]. The lack of this relation among girls can be partly explained by the observation of Olweus [34] who pointed out that physical bullying is more frequent among boys, and the victims are likely to be physically weaker than their peers or may simply perceive themselves as physically or mentally weaker than the perpetrator [34].

The presented study has raised questions why underweight is a more pronounced factor affecting QoL in Polish boys than girls, and why, unlike the results of many other studies, in Polish girls excess weight was significantly related only with physical limitations.

Perhaps this observation is an effect of mass-media created ideals: among boys, to be physically strong is synonymous of a high status among peers, while being skinny is an indication of weakness; among girls, there is no advantage in being physically superior, on the contrary there is great pressure on young girls to be slim. On the other hand, however, in girls with excess weight we have not observed a deterioration of QoL except in the area of the physical dimension. Maybe this is a consequence of the rising prevalence of excessive weight in the whole population, and thus greater acceptability of this phenomenon by young people.

Some limitations of our study should be mentioned. Firstly, taking into account the fact that our research was of a cross-sectional nature, it did not enable the demonstration of the causality between improper body mass and QoL. Moreover, we did not measure the body weight and height of the young people studied, as the data concerning the body weight and height of the participants were obtained from the questionnaires filled in by the teenagers themselves.

The research also has some unique advantages. We tested the association between the body weight status and QoL on a large sample of adolescents from the general population. QoL was assessed by means of the KIDSCREEN-27 questionnaire, which was validated and used across many countries. In addition, both the classification of the body weight status and the QoL among the participants was made based on the Polish cut-off points specific for sex and age. It should be emphasized that our study observed a significant relationship between underweight and quality of life in boys, which is not a frequent finding. Most of the previous studies had paid attention mainly to the relationships between excessive body weight and different aspects of the youth’s QoL.