Is Teenage Obesity Associated with Depression and Low Self-Esteem?: A Pilot Study
Objectives: A pilot study to explore the impact of perceived and actual overweight on self-esteem and depression in Hong Kong teenagers. Methods: A cross-sectional questionnaire study on 152 Chinese adolescents aged 12-16 was conducted in a secondary school in Hong Kong. Overweight was defined as a body mass index (BMI) above 90 percentile of age-adjusted BMI reference. The short form Beck Depression Inventory (BDI-13) and the Chinese version of Piers-Harris 2 Self-Concept Scale were used to measure depression and self-esteem respectively. Results: Our results showed that perceived overweight but not actual overweight female subjects had statistically significantly lower Piers-Harris score and higher depression score. Kruskal-Wallis test showed that depression was significantly more common in female teenagers who perceived themselves as being overweight but who were not actually overweight compared to those with normal BMI and body image. On the contrary, male teenagers who perceived themselves as thin were more at risk for lower Piers-Harris subscale scores. Conclusions: Our findings suggest that perceived body image has more detrimental impact on depression and self-esteem than actual body mass index in both male and female Hong Kong teenagers. This may reflect a probable influence from the mass media, advertisement, or prevailing societal values in over-promoting a slim body-image which may result in self-depreciating tendencies if female teenagers perceived themselves as being overweight. Health care professionals need to pay attention to body image perception rather than focusing solely on the physical build of teenagers.
Keyword : Adolescent; Obesity; Self-esteem; Depression
Childhood and adolescent obesity has now become the most prevalent nutritional disorder in developed countries worldwide.1 In the United States, the prevalence of childhood overweight tripled between 1980 and 2000.2 Childhood obesity gives rise to long-term health problems and psychosocial problems. Severely obese children and adolescents in the United States have lower health-related quality of life (QOL) compared to children and adolescents who are healthy, with actual QOL approaching more similar to those being diagnosed as having cancer.3 Adverse outcomes in childhood obesity include metabolic syndrome, type 2 diabetes mellitus, inflammation, cardiovascular abnormalities and psychosocial abnormalities.4 Overweight children had higher scores on subscales of social problems, delinquent behaviour, aggressive behaviour and externalising problems compared to non-overweight children.5
In the Netherlands, both parents and teachers reported more behaviour problems in overweight children, particularly in those younger than 13 years of age. Lower body-esteem was found in older overweight girls, whereas higher levels of body-esteem were found in older overweight boys.6 Overweight female adolescents from the United States also seem to suffer from low self-esteem, though it may be mediated by negative body image.7
A descriptive analysis performed in 1991 found that nonwhite obese children from Pennsylvania scored particularly low on the Piers-Harris self-concept measures. Age, race, gender, and severity of obesity affected overall self-concept and individual subscale scores. Among the study subjects, younger girls (aged 8-11) and older males (aged 12-17) displayed the lowest level of self-concept. Self-concept theorists suggest that a negative self-image results from a lack of congruence or consonant fit between people's views of themselves and their perceptions about the way others see them.8
Another study on Dutch youths in 2006 reported that both body mass index (BMI) and body weight perception (BWP) were associated with internalising and externalising problem behaviour, social attention and thought problems. Multivariate analysis showed that BWP was more closely linked to problem behaviour than BMI. Adolescents who were either underweight or overweight but considered themselves in good shape had no more problems than the group with normal BMI and good BWP. The perception of being 'too thin' and particularly the perception of being 'too heavy' best predicted problem behaviour in both male and female adolescents. Overweight youngsters with an adequate perception of their weight had less somatic complaints compared to their normal-weight peers who perceived themselves as too heavy, but they showed higher social withdrawal, social problems, and anxiety/depression.9
The effect of obesity on psychological health in Hong Kong teenagers has not been fully explored. The aim of this pilot study is to shed light on this issue by comparing Piers-Harris self-concept scores and the short form Beck Depression scores among teenagers of different BMI. A further aim is to explore the discrepancy between perceived and actual overweight in Hong Kong teenagers.
This cross-sectional pilot study was carried out in a secondary school in Hong Kong. Self-administered anonymous questionnaires and informed consent forms were given to 210 Chinese first form students and their parents in April 2007. The study was approved by the principal of the secondary school and the Institutional Review Board of the University of Hong Kong and Hospital Authority Hong Kong West Cluster.
The available data from the West indicated that the mean and standard deviation of Piers-Harris score (total) in a non-white sample was 49.4 and 13.3 respectively in obese group and 59.9 and 10.0 respectively in control group.8 As we take 90 percentile cut-off of age-adjusted BMI, the projected ratio of the two sample sizes of overweight and normal weight subjects was thus estimated to be equal to 9. We take the usual significance level of 0.05 and a power of 0.80. The sample size needed for comparing the means of two normally distributed samples of unequal size was estimated to be 134.10
One hundred and fifty-two students and their parents consented to participate in the study and the completed questionnaires were returned within one week, giving a response rate of 72.38%. The students with BMI above 90% of the age adjusted BMI would be defined as overweight.11 Perceived body image was classified as 5 categories in the questionnaire. Those who regarded themselves as 'very thin', 'thin' and 'normal' were interpreted as 'perceived not overweight' whereas those who regarded themselves as 'overweight' and 'very overweight' were interpreted as 'perceived overweight'.
Depression was measured by the short form Beck Depression Inventory (BDI-13) which has been validated for use in Chinese populations.12-15 This is a rapid screening tool consisting of 13 questions with a scoring scheme: no depression (0-4); mild depression (5-7); moderate depression (8-15); and severe depression (16 or above).
Self-esteem was measured by the validated Chinese version of Piers-Harris 2 Self-Concept Scale.16,17 The scale consists of 60 yes-or-no answers. A total score (TOT) and scores of 6 sub-groups including behavioural adjustment (BEH), intellectual and school status (INT), physical appearance and attributes (PHY), freedom from anxiety (FRE), popularity (POP) and happiness and satisfaction (HAP) can be calculated.
The data were expressed as mean (sd), range and number (percentage) as appropriate. Further analysis of data was performed by chi-square test and analysis of variance followed by post-test Tukey and Kruskal-Wallis test.
There were 82 boys and 70 girls who participated in this study, and most were between 12 to 13 years of age (Table 1). 16.7% of boys and 10% of girls were above 90 percentile of the age-adjusted BMI reference (Table 2). Chi-square test showed perceived overweight to be highly associated with actual overweight in both boys and girls (Table 3). For the discrepancy between perceived and actual overweight, 31 out of 142 (21.8%) subjects perceived themselves to be overweight while in fact they were not. Only two boys and none of the girls perceived themselves to be not overweight while being actually overweight.
Comparing Depression and Piers-Harris Scores by Analysis of Variance
The body build status of the subjects were categorised into 3 groups: (A) not overweight and perceived not overweight, (B) not overweight but perceived as overweight and (C) overweight and perceived as overweight. Analysis of variance showed statistically significantly lower Piers-Harris scores including total, behavioural adjustment, intellectual and school status, freedom from anxiety, and happiness and satisfaction in female subjects who were not overweight but who perceived themselves as being overweight (Table 4). No statistical differences in the total and subscores were found in the 3 groups of male teenagers.
The significant differences in the Piers-Harris total and subscores in the 3 groups of all study participants could be attributed to the findings in the female teenagers. Depression score by BDI-13 was significantly higher in girls who were not overweight but who perceived themselves as being overweight compared to girls with normal body weight and body image.
Comparing Depression Status by Kruskal-Wallis Test
The distribution of BDI-13 scores is summarised in Tables 5 and 6. Analysis by the Kruskal-Wallis test showed significant differences in the depression status between the three groups of female participants (Table 7). The mean rank was significantly higher in the female students who were not overweight but who perceived themselves as being overweight. There was no significant difference among the groups in male subjects.
Independent Sample T-test for Perceived Thinness
We further explored whether boys who perceived themselves to be thin were vulnerable to depressed mood or lower self esteem. We categorised teenagers who regarded themselves as 'very thin' and 'thin' as 'perceived thin', whereas the 'normal', 'overweight' and 'very overweight' as 'perceived not thin' and the data were analysed with an independent sample t-test (Table 8). Significantly lower behavioural adjustment and lower happiness and satisfaction scores were noted in male subjects who perceived themselves as 'thin' compared to those who perceived themselves as being not thin.
The results showed that female teenagers displayed lower self-esteem, in various scales including overall self-concept, behavioural adjustment, intellectual and school status, freedom from anxiety, and happiness and satisfaction, if they perceived themselves to be overweight regardless of whether or not they were actually overweight. Although the scores for physical appearance and popularity seemed to be lower in the perceived overweight group, this association was not significant. This may be due to the small sample size of selected subgroup of subjects included in the study.
Depressed mood was prevalent among the teenagers in our study. However, Coyne et al cited a number of studies in which the majority of subjects having elevated scores on BDI did not actually suffer from clinical depression when followed up with a full clinical assessment and interview.18 Self-report measures like the BDI-13 in the normal population may assess general nonspecific distress or negative affectivity rather than specific depressive states. Although some depressive symptoms such as sadness or dysphoria are relatively common, rates of diagnosable depression are comparatively rare.19,20 The Adolescent Depression Rating Scale (ADRS) may discriminate better between adolescents with and without depression.21 However, a validated Chinese version of ADRS is not yet available. In Akron Children Hospital, Ohio, USA, a screening study for adolescent depression using the BDI-2nd edition was performed on 351 patients aged 13-19 who presented to the Emergency Department reported a similar prevalence. Participants reported minimal (n=192, 55%), mild (n=52, 15%), moderate (n=41, 11%), or severe depressive symptoms (n=66, 19%). A substantial proportion of patients with nonpsychiatric chief complaints reported moderate or severe depressive symptoms.22
Our data indicated that compared to girls with normal weight and perceived normal weight a significantly higher depression score was obtained by female subjects who were not overweight but who perceived themselves as being so. Further testing (Kruskal-Wallis test) also showed that complaints of depressive symptoms were significantly more common in female students who were not overweight but who perceived themselves as being overweight.
Our data also indicated that self-esteem and self-concept were more likely to be affected by their perception of body build in females than in males. This pattern has also been reported in overseas studies. However, we did not see the effect of actual obesity on self-esteem, which is different from the result of the study from Pennsylvania in 1991.8 Our study showed that perceived body image was more important than actual overweight. This may reflect the impact of the mass media, advertisement, or societal values in over-promoting the desirabililty of a slim body-image, which may result in self-depreciating feelings if female teenagers perceived themselves to be overweight even though physically they may not be so.
It had also been shown that the perception of being 'too thin' was associated with internalising and externalising problem behaviour in both male and female adolescents.9 In our sample we have found that overweight was more common in males (16.7%) than in females (10%). Yet, males who perceived themselves to be overweight did not show higher depression and lower self-concept scores.
Interestingly, we found significantly lower behavioural adjustment and lower happiness and satisfaction scores in male subjects who perceived themselves as 'thin'. We also noted a trend (although not significant) pointing to lower Piers-Harris scores and higher BDI-13 score in male teenagers who perceived themselves as thin. Further study with a bigger sample size and power is needed to confirm this issue.
There are a number of limitations in the present study. Concerns might be raised that first form students from a secondary school may not be representative of all Hong Kong teenagers as sampling was convenient and not random. Self-reported weight and height may also be a source of error.23 The weighing scales used may vary in different families. Calculation of age-adjusted BMI was based on reported age. One could not control for the accuracy of the answers in self-reported questionnaires with 78 questions such as that used in this study. The short form Beck Depression Inventory (BDI-13) is not a gold standard to estimate adolescent depression. Although the Chinese version of Piers-Harris 2 Self-Concept Scale is an excellent tool to measure self-concept of Chinese, a comprehensive picture of psychological health cannot be achieved by one questionnaire alone. Confounding factors such as ethnicity, socioeconomic status, academic or sports performance, peer and family influence were not measured in the study. We hope that future studies can overcome the above limitations.
Our results not only showed lower self-esteem score but also increased complaints of depressive symptoms in female teenagers who perceived themselves as overweight but who were actually not overweight. Health care professionals need to pay attention to the psychological aspect rather than focusing solely on the physical obesity for Hong Kong teenagers. Further studies, which may include other potential confounding factors such as ethnicity, socioeconomic status, academic performance, peer and family influence in a larger cohort of teenagers with a wide range of age will be needed to explore the issue further.
We deeply appreciate Miss Lo Man Wa for her enormous help with school arrangement and technical problems we faced during data collection procedure. We would like to thank the staff of the school, the students and the parents for consenting to participate in this study.
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