Depression has been associated with a host of physical (e.g., diabetes and obesity ) and psychosocial (e.g., academic performance, self-esteem, and suicidality [4,9]) health outcomes for adolescents. Concerning its lifetime prevalence among female adolescents, rates have ranged from 13% (16) to 15.9% (21); the rates for boys are lower (7.7%, ). Among adolescent boys and girls, 8.7% of those with a lifetime diagnosis of depression experience severe impairment (i.e., significant limitations in ability to perform basic life functions and severe to very severe levels of distress). Furthermore, more than 25% of adolescents experience elevated symptoms of depression, which causes difficulties in daily functioning (18). These studies and others (e.g., Ref. ) indicate that depression and depressive symptoms in adolescence are pervasive, vary by sex, and are associated with other negative health outcomes that may extend into adulthood. Thus, research examining depression in adolescents, in particular, factors that may exacerbate (e.g., overweight/obesity) or attenuate (e.g., physical fitness) symptoms, is warranted.
Several cross-sectional and longitudinal studies support a significant relationship between depression and obesity in adults and adolescents (2). For example, a meta-analysis of community studies with adult samples revealed a significant positive association (7), which was consistent with the 2005 National Health Interview Survey, which demonstrated a positive correlation between depression and body mass index (BMI, ). In a meta-analysis of longitudinal studies, however, not only did obesity increase the risk of depression but also depression predicted people becoming obese at later points in time (20). Among adolescents, the relation between depression and obesity was particularly high for girls (2), suggesting a need to consider sex when studying this age group.
Given the strong and protective health effects associated with physical activity and cardiorespiratory fitness (25), these factors have been examined in relation to decreased levels of depression among adolescents (16,22–24,30). For example, on the basis of data from retrospective reports of physical activity in childhood and current self-reported symptoms of depression, Jacka et al. (15) concluded that childhood physical activity could reduce the risk of experiencing depression in adulthood. In a study of obese adolescents (30), elevated symptoms of depression were associated with lower levels of cardiorespiratory fitness as measured by V˙O2max obtained through a cycle ergometer test; this relation was not moderated by the sex of the participant. Kelly et al. (18) examined the relations of physical activity, cardiorespiratory fitness, and psychosocial functioning (which included a measure of depression) in a sample of obese adolescents across a 6-month period. They found that vigorous physical activity was related to improvements in fitness (as measured by V˙O2max) and reductions in BMI and in body fat percentage from baseline to posttest. Furthermore, improvements in V˙O2max over the course of the study were associated with decreases in depression; these positive effects were unrelated to weight loss, changes in BMI, and reductions in body fat percentage. These findings suggest that it may be fitness, and not physical activity, that has the strongest palliative effects on depression and that the adolescents’ sex may not change the strength of the association.
Because depression is a condition that has debilitating effects on health outcomes and frequently begins during adolescence, especially among girls, research using an objective measure of physical fitness is needed to clarify the associations between weight status, health-related fitness standards, and depressive symptoms among adolescents (1). Consequently, we examined the relation of cardiorespiratory fitness and weight status (as represented by BMI) to depression in young adolescents and determine whether sex was associated with any differences in these relationships. Our hypothesis was that healthy levels of cardiorespiratory fitness would be related inversely to depressive symptoms, and unhealthy levels of BMI would be associated with more depressive symptomatology. Furthermore, we hypothesized that sex would affect the relation of weight status to depressive symptoms, such that girls would have greater odds than boys of being depressed. On the basis of past research (30), we hypothesized that sex would have no effect on the relation between cardiorespiratory fitness and depression.
The participants were 986 middle school students (54% female, 46% male), ranging in age from 11 to 15 yr (Mage = 12.5 yr), drawn from a public school district in the north Texas region; 38% were in the sixth, 33% in the seventh, and 29% in the eighth grade (Table 1). The participants’ race/ethnicity was predominantly white (60%), followed by Hispanic/Latino or Latina (29%), and African American (11%, n = 105). As for the social economic status (SES), the school district provided data showing that 37% received lunch support and 63% did not receive lunch support. Only students who had complete data on study variables were included in this report.
The school district provided the following participant information: race/ethnicity, age, and SES (i.e., received or did not receive lunch support, which was based on the federal guidelines for determining which students were qualified for free or reduced lunch on the basis of family income ).
Physical fitness and BMI.
The FITNESSGRAM® test battery (6) provides measures of aerobic capacity (i.e., cardiorespiratory fitness), body composition, and muscular strength, endurance, and flexibility. Although all measures were administered in each middle school, as required by the State of Texas laws (SB 530, see Kelder et al. ), only the cardiorespiratory fitness estimate of maximal oxygen consumption using the Progressive Aerobic Cardiovascular Endurance Run (PACER) and BMI (i.e., measured as the participant’s weight relative to their height) results were used in this study. The PACER is an incremental running test that uses 20-m segments that require increasing speed for each segment. The total number of segments completed while maintaining the increasing speed is the score for the test. The PACER test result, sex, age, and BMI are used to provide an estimate of the maximal oxygen consumption. The FITNESSGRAM uses Healthy Fitness Zones™ to evaluate health-related fitness performance. Participants were classified into three zones, Healthy Fitness Zone, Need Improvement—Some Risk, and Need Improvement—High Risk, according to the FITNESSGRAM cut points for both cardiorespiratory fitness and BMI. We also created a dichotomous classification combining the Health Fitness Zone and Need Improvement—Some Risk, which was labeled Low Risk and contrasted with the Need Improvement—High Risk classification, which we labeled High Risk for both cardiorespiratory fitness and BMI. These FITNESSGRAM classifications are based on sex- and age-related criterion-referenced standards, which represent minimum levels of fitness that offer protection against diseases that result from sedentary living (6,34). The FITNESSGRAM/ACTIVITYGRAM® manual (6) provides full details about the tests and test protocols.
The 20-item Center for Epidemiological Studies—Depression Scale for Children (CES-DC ) measures behavioral and cognitive components of depression. The CES-DC is a revision of the CES-D, which was originally developed and validated for adults (27). Specifically, the language of the CES-D was revised to be more appropriate for children and adolescents. The participants respond to the items, such as “I felt sad,” using a four-point scale that ranges from 0 (not at all) to 3 (a lot). The total score, the sum of the items, is calculated and provides the user with an interpretive range from 0 (no symptoms) to 60 (high level of symptoms). Fendrich et al. (11) reported that the CES-DC was a reliable and valid measure in screening for elevated risk of depression in children and adolescents ranging from 12 to 18 yr and that a cut point of 16 was optimal for identifying major depressive disorder. In further support of the reliability and validity of the CES-DC, Motl et al. (24) demonstrated that its factor structure remains consistent across time in adolescent girls and boys enrolled in middle school grades.
This study was approved by the authors’ Institutional Review Board for Use of Humans in Research, the school district’s administrative offices, and the principals at each of the six middle schools surveyed. In accordance with the state-mandated FITNESSGRAM, testing was conducted at each of the six middle schools during the 2008–2009 academic year. Before participating in the study, written parental consent and participant assent were obtained. Correspondingly, adolescents for whom consent and assent had been obtained completed the CES-DC as part of a broader health-related questionnaire during their physical education classes (see the study of Greenleaf et al. ), which took approximately 30 min to complete. The participants’ code numbers were used to link their FITNESSGRAM performance scores (risk classification status) with their respective CES-DC scores. All the data for this study were collected during the normal operation of physical education classes and completed within approximately 1 wk. In an effort to ensure accurate questionnaire completion and FITNESSGRAM administration, teachers and research support staff supervised the entire data collection process.
Data Analysis Strategy
Preliminary means and SD for each of the participants’ age, BMI, PACER, and CES-DC scores were calculated and further subdivided by CES-DC risk status and sex (Tables 1 and 2). Independent t-tests (alpha restricted to <0.01) and effect sizes (ES) were used to contrast the differences between the CES-DC risk status classifications (15 or less/16 or more) for the measured variables. Logistic regression analysis was used to estimate the relation between Low Risk versus High Risk cardiorespiratory fitness and Low Risk versus High Risk BMI with CES-DC classification while controlling for the participants’ age, SES, sex, and ethnicity. The adjusted odds ratios (OR) and 95% confidence intervals were calculated for three regression models: (a) model 1 was performed using CES-DC dichotomy (15 or less/16 or more) as the dependent variable with Low Risk versus High Risk cardiorespiratory fitness or Low Risk versus High Risk BMI as the independent variable; (b) model 2 used the CES-DC dichotomy as the dependent variable with Low Risk versus High Risk cardiorespiratory fitness or Low Risk versus High Risk BMI as the independent variable but was controlled for age (years), SES, ethnicity, and sex, serving as the independent variables; and (c) model 3 was the same as model 2 but the other fitness measure (cardiorespiratory fitness or BMI) was controlled.
Descriptive statistics for SES, race/ethnicity, age, cardiorespiratory fitness (estimated V˙O2max), BMI, and CES-DC total scores are presented in Table 1 for girls and boys on the basis of their risk classification. Similarly, descriptive statistics for age, cardiorespiratory fitness (estimated V˙O2max), BMI, and CES-DC total scores are presented in Table 2 on the basis of their elevated risk classification for the CES-DC. For the combined group of boys and girls, the adolescents with elevated risk classification of 16 or more were found to be significantly older (P < 0.01, ES = 0.23), higher on BMI (ES = 0.22), and lower on cardiorespiratory fitness (ES = 0.36) than the participants in the lower risk classification of the CES-DC (15 or less).
For the combined sample of boys and girls, the prevalence percentage of elevated depression was 13% higher for the children in the High Risk classification for cardiorespiratory fitness and 6% higher for those in the High Risk for BMI. The logistic regression analyses indicated significantly elevated odds of higher depression classification for all three models for children with High Risk status on cardiorespiratory fitness, which ranged from 66% to 78% higher than those children in Low Risk classification for cardiorespiratory fitness. However, all three models indicated nonsignificant relations between BMI and CES-DC risk status. When examining the covariates in model 3 for elevated risk of depression, the participants who received school lunch support (OR = 1.42, CI = 1.01–2.01), the girls (OR = 2.17, CI = 1.62–2.91), and the older students (OR = 1.28, CI = 1.11–1.48) were related significantly to an elevated risk of depression; no significant effects emerged for ethnicity (Table 3).
In Table 4, we conducted the previous logistic regression analyses by sex. The findings for BMI for both boys and girls were similar to the combined sample. For cardiorespiratory fitness, the results differed from the combined sample. For boys, significantly elevated OR was found for all three models. There was an increase of 109% to 145% in the OR for High Risk classification. For girls, the OR was elevated by 38% to 63% across the three models for the High Risk classification but was not statistically significant. In splitting the sample by sex, the sample sizes were reduced, which decreased the statistical power.
State-mandated fitness testing in middle schools provides an excellent opportunity for researchers to examine and analyze cross-sectional associations between fitness levels, BMI levels, and depression among adolescents. Given the dearth of adolescent research in this area (1), we examined the relations between meeting versus not meeting health-related standards for cardiorespiratory fitness and BMI and depressive symptoms. Expanding upon the study of Greenleaf et al. (13) that examined middle school-age adolescents’ BMI, cardiorespiratory fitness, body satisfaction, and self-esteem, the present study demonstrated that the boys and girls who were not in the healthy fitness zone (HFZ) for cardiorespiratory fitness demonstrated a higher risk for depression; no such risk existed between BMI and depression (despite a 6% higher prevalence rate for those in the BMI—High Risk classification). The boys and girls who were not in the HFZ—High Risk for cardiorespiratory fitness endorsed more depressive symptoms than those in the Low Risk (i.e., those in the Healthy Fitness Zone or in the Need Improvement Low Risk group) classification. Unexpectedly for BMI, but not cardiorespiratory fitness, the participants’ sex did not moderate the relations among the variables.
The results from the present study are consistent with previous studies that have shown relations between physical fitness and physical activity and depression among adolescents (e.g., [1,18,30]). For example, within a sample of obese female adolescents, Kelly et al. (18) found that improvements in V˙O2max for a 6-month intervention were associated with decreases in self-reported depressive symptoms and increases in emotional well-being. Interestingly, these positive changes in emotional well-being and functioning were unrelated to weight loss, BMI changes, or decreases in body fat among the participants. Our results corroborate suggestions based on past research findings (e.g., Ref. [1,18]) that regardless of body composition, adolescents may clinically benefit from meeting the HFZ for cardiorespiratory fitness. Further research in this regard is warranted. In particular, although there is some evidence for both physical and psychological factors that may explain how cardiorespiratory fitness could serve as a protective function against depressive symptoms (12,13), which is consistent with a biopsychosocial model of depression (see Ref. , for a review), research clarifying the associations between such variables (e.g., body image, self-esteem, hippocampal plasticity, hypothalamic-pituitary-adrenal axis dysregulation, sleep activity, and social activity) is needed. Because our study and past findings (e.g., Ref. ) demonstrate a significant inverse association between physical fitness and depression, an important question is apparent: “What are the plausible biological or psychological mechanisms mediating or underlying these associations?” Examination of the empirical literature indicates that very limited evidence exists about biological mechanisms that explain the influences of physical activity or exercise on mental health (8,26). However, experimental animal studies demonstrate changes in brain neural circuits with both forced and voluntary exercise that would be associated with mental health (14,28,33). These adaptations appear in neurotransmitters, neuromodulators and their receptors, neuropeptides that influence neurotransmission, and neuronal growth factors. The Physical Activity Guidelines Advisory Committee Report (26) indicates that a variety of psychological and social variables positively affected by physical activity and fitness, including improvements in body satisfaction, increases in self-esteem and self-concept, and decreased social isolation, would logically be related to a lower risk of mental health problems, including depression.
The present study has several strengths that are unique and expand upon the current literature. First, we draw upon nationally recognized fitness standards to differentiate adolescents who are within HFZ and those who are not. These standards represent objective measures of fitness that are linked to underlying V˙O2max, which is an improvement over studies that have relied on self-reported physical activity or fitness measurements (e.g., Ref. ). Second, we used an empirically validated measure of depression in adolescence that allowed us to classify the adolescents according to their level. Third, the focus of our study is on a population that has been identified as deserving greater attention, which could facilitate a greater understanding of timely intervention strategies while addressing current health concerns.
The primary limitation of the present study is that it is based on cross-sectional data, which inhibits our ability to make any cause–effect inferences. Thus, we are unable to clarify the direction of the positive relationship between body mass and depression (20). However, our methodology was appropriate given the state of research in this area among adolescents (31). As data accumulate concerning the relations among BMI, physical activity, cardiorespiratory fitness, and depression, longitudinal and experimental research is recommended to clarify our theoretical understanding that increases in physical activity would lead to improvements in physical fitness, which, in time, would assist in lowering depression (1), beyond any potential effect of body mass. Second, researchers can begin to test potential mediators (a) such as self-esteem, body satisfaction, or general self-concept, in the relationship between physical activity and/or physical fitness and depression, and (b) such as emotional eating, self-esteem, and low social support, in the depression–overweight association. Taking this approach would provide some clarity on the potential mechanisms that underlie these relations. Finally, consistent with Ahn and Fedewa’s (1) recommendations and our findings, we suggest that future research should examine potential moderators of the relations between physical fitness, obesity, and depression. The extant literature remains unclear as to the effect of SES, sex, ethnicity, social support, and other psychosocial factors on the relation between physical fitness, depression, and obesity.
Appreciation is extended to the schools that were involved as well as to the teachers and students for their assistance.
This research was funded in part by a grant to SBM, CG, and TP from the National Association for Sport and Physical Education.
The authors have no conflicts of interest to declare.
The results of the present study do not constitute endorsement by the American College of Sports Medicine.
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