Unravelling the relation between physical activity, self-esteem and depressive symptoms among early and late adolescents: A mediation analysis

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Abstract

Purpose

Depression is a serious public health issue among adolescents; however, few studies have examined the role of protective factors, such as engagement in physical activity, on depressive symptoms. Preliminary evidence using community samples of mainly adolescent girls suggests that self-esteem may influence the benefits of physical activity on depressive symptoms. Thus, the objective of this study was to test the hypothesis that the inverse relation between physical activity and depressive symptoms would be mediated by self-esteem in both early and late adolescent boys and girls.

Methods

Secondary data analysis was conducted using self-reported measures of physical activity, self-esteem, depressive symptoms, and socio-demographic information completed by a sample of girls (n = 2109) and boys (n = 2095) during early (Mage = 14.7) and late (Mage = 16.2) adolescence selected from the National Longitudinal Study of Adolescent Health. Using the method suggested by Baron and Kenny (1986), mediation was tested separately for boys and girls during early and late adolescence.

Results

During early adolescence, self-esteem fully mediated the association between physical activity and depressive symptoms for adolescent boys only. Full mediation was obtained for both boys and girls during late adolescence.

Conclusions

In early and late adolescent boys, and only late adolescent girls, associations between physical activity and depressive symptoms were no longer significant once self-esteem was statistically controlled for. The study has important implications for depression prevention initiatives including the inclusion of physical activity components that are effectively structured to reliably enhance self-esteem, especially among early adolescents.

Highlights

► Examined a mediator of the physical activity-depression link among adolescents. ► Hypothesized that self-esteem would mediate the physical activity-depression link. ► Self-esteem fully mediated this association among early adolescent boys. ► Self-esteem fully mediated this association among late adolescent girls and boys. ► The study has implications for depression prevention initiatives.

Introduction

Depression is a significant public health issue facing adolescents and is reported to be the third most disabling condition in the world (World Health Organization, 2008). Depression often emerges during adolescence and persists into adulthood (Kessler, Avenevoli, & Merikangas, 2001) with lifetime prevalence estimates for adolescents ranging from 9.3% (Wittchen, Nelson, & Lachner, 1998) to 24.0% (Lewinsohn, Hops, Roberts, Seeley, & Andrews, 1993). The adolescent period is unique from adulthood in that it represents a time in which important developmental and gender differences emerge (e.g., varying rates of depressive symptoms; Galambos, Leadbeater, & Barker, 2004; Twenge & Nolen-Hoeksema, 2002). Thus, there is a critical need to broaden our understanding of the risk and protective factors for depression during this important developmental period. To date, much of the adolescent literature has historically placed more emphasis on risk factors for depression than critical protective factors that may buffer or lessen the experience of low mood. One burgeoning protective factor for depression is physical activity. Depressive symptoms among adolescents have been found to be inversely related to physical activity (Motl, Birnbaum, Kubik, & Dishman, 2004; Norris, Carroll, & Cochrane, 1992; Ussher, Own, Cook, & Whincup, 2007). However, it is unclear whether the beneficial effect of physical activity directly operates on depressive symptoms or whether intermediate mechanisms are responsible for the apparent relationship. Thus, understanding potential mediating mechanisms responsible for the association between physical activity and depressive symptoms during adolescence has significant public health importance. For instance, researchers could identify potential behaviours or cognitions to target in depression (e.g., strengthening self-esteem) prevention and intervention initiatives.

The current literature in the field of physical activity and mental health has a shortage of mediation studies, which explains why little is known about the underlying mechanisms of influence and underscores the importance of employing statistical mediation methods (Biddle & Mutrie, 2008; Cerin, 2010). One variable that appears to be worthy of further investigation in the relationship between physical activity and depressive symptoms is self-esteem. Self-esteem represents a core component of psychological adjustment during adolescence (Rosenberg, 1985) and low self-esteem has been found to be predictive of depression (Goodman & Whitaker, 2002), particularly among adolescent girls (Park, 2003; Räty, Larsson, Söderfeldt, & Larsson, 2005). Several studies have reported a positive relationship between physical activity and self-esteem, wherein increased physical activity is associated with increased self-esteem among adolescents (Delaney & Lee, 1995; Schmalz, Deane, Birch, & Davison, 2007; Stein, Fisher, Berkey, & Colditz, 2007). Considering research has demonstrated that increased physical activity is associated with enhanced self-esteem (Delaney & Lee, 1995; Schmalz et al., 2007; Stein et al., 2007), it is possible that self-esteem might explain the previously reported association between physical activity and depressive symptoms in adolescent boys and girls.

Few studies have been conducted that specifically assess the association among physical activity, self-esteem, and depressive symptoms in adolescents. One notable exception is a study by Dishman and colleagues that examined whether physical self-concept and self-esteem mediated cross-sectional associations of physical activity and sport participation with depressive symptoms among a sample of late adolescent girls (Dishman et al., 2006). The authors found evidence suggesting that physical self-concept mediates the associations of physical activity and sport participation with self-esteem, which was inversely related to depressive symptoms among late adolescent girls. However, the study sample was limited to late adolescent girls and cannot be generalized to adolescent boys.

In contrast to the adolescent literature, there is relatively more literature using adult samples that examines the interplay among self-esteem, physical activity, and depression. For example, a cross-sectional study conducted by Van de Vliet and colleagues reported that reduced depressive symptomatology among adult psychiatric patients was proximally mediated by increased global self-esteem, arising from increased physical self-esteem that had been promoted by increased perceptions of physical strength and physical attractiveness (Van de Vliet et al., 2002). Moreover, Ryan (2008) conducted a study using a cross-sectional sample of non-clinical young adults. Ryan concluded that self-esteem and self-efficacy mechanisms may offer a sufficient explanation for the association between reported physical activity and depressive symptoms.

Furthermore, a longitudinal pilot study by White and colleagues investigated similar variables in a sample of adults with elevated symptoms of depression (White, Kendrick, & Yardley, 2009). The authors sought to examine whether depression and hypothesized mechanisms, such as self-esteem and self-efficacy, changed over time among individuals with elevated symptoms of depression who increased their physical activity. Interestingly, the authors found that changes in depressive symptoms occurred relatively rapidly when participants increased their physical activity, with initial reductions observed at the end of the first week. Changes in self-esteem appeared later than the other proposed mechanisms. The authors hypothesized that this finding might indicate that changes in self-esteem may not mediate initial improvement in depression, but mediate longer-term effects. Moreover, self-efficacy was found to mediate the relationship during early stages of the physical activity intervention (e.g., possibly as early at the first to third weeks). However, the authors were not able to determine whether any of the hypothesized mechanisms contributed to changes in depressive symptoms over time. Thus, the literature provides some initial evidence for the prospective mediating role of self-esteem in the association between physical activity and depressive symptoms, and further research is needed to explore the mediating role of self-esteem.

Within the adult literature on the physical activity-depression link, an important distinction is made between the relative importance of global self-esteem and physical self-esteem. The Exercise Self-Esteem Model (Sonstroem, Harlow, & Josephs, 1994) proposes that increases in physical activity leads to increases in physical self-esteem, which in turn, leads to increases in global self-esteem. Findings in the literature have been mixed wherein some studies have reported a direct effect of physical self-concept on depressive symptoms for females only (Ryan, 2008), while other studies have reported that physical self-esteem effects on depressive symptoms are fully mediated through global self-esteem for both males and females (Van de Vliet et al., 2002). Thus, the relative importance of global self-esteem compared to physical self-esteem in the physical activity-depression link is unclear.

Given the considerable lack of research on the mediating role of self-esteem in the association between physical activity and depressive symptoms in adolescents, the current study adds to the extant literature in several ways. First, the study by Dishman and colleagues only examined the mediating role of self-esteem in a sample of late adolescent girls (Dishman et al., 2006). It is not known how this relationship functions among adolescent boys. Considering adolescent boys tend to have higher levels of physical activity (Prasad, St-Hilaire, Wong, Peterson, & Loftin, 2009) and self-esteem (Quatman & Watson, 2001), and lower levels of depressive symptoms (Galambos et al., 2004) compared to adolescent girls, further research is required in order to determine whether self-esteem functions as a mediator between physical activity and depressive symptoms in adolescent boys. Furthermore, the sample used by Dishman and colleagues was limited to late adolescence (Dishman et al., 2006). It would be beneficial to extend the findings beyond late adolescence, investigating this prospective relationship during two developmental periods, early and late adolescence. Lastly, the extant literature has been limited to adults and young adults experiencing elevated depressive symptoms (Ryan, 2008; White et al., 2009), clinical samples (Van de Vliet et al., 2002), and community samples (Dishman et al., 2006); therefore, it would be advantageous to broaden the findings to a large, nationally representative sample of adolescents.

With the previous considerations in mind, the goal of the current study was to test the proposed model that the inverse relation of physical activity with depressive symptoms would be completely or partially mediated by self-esteem in both early and late adolescence in a large, population-based sample of adolescent boys and girls. Additionally, it was explored whether this mediational model is distinct for adolescent girls and boys. There are several reasons for this approach. First, rates of depression are higher among adolescent girls compared to adolescent boys (Galambos et al., 2004). Second, adolescent girls tend to have lower levels of physical activity compared to adolescent boys (Prasad et al., 2009). Finally, several studies have demonstrated that adolescent girls tend to have lower levels of self-esteem than adolescent boys (Quatman & Watson, 2001). As a result, it is possible that if the proposed mediation model is accurate, then mediation may be stronger for girls. Furthermore, age differences between adolescent boys and girls were also considered. Gender differences in depressive symptoms typically begin to emerge during early adolescence with girls' rates rising precipitously (Galambos et al., 2004; Twenge & Nolen-Hoeksema, 2002). The largest gender difference in depressive symptoms is generally observed during mid-late adolescence (ages 15–18), wherein adolescents face the greatest risk for depression onset (Hankin et al., 1998). Accordingly, the mediation model was examined at two developmental stages, early and late adolescence.

On the basis of available evidence from both the adolescent and adult literature, it was hypothesized that self-esteem would be found to fully or partially mediate the association between physical activity and depressive symptoms in early and late adolescent girls. Similarly, it was also expected that self-esteem would fully or partially mediate the relationship between physical activity and depressive symptoms in early and late adolescent boys. Keeping in mind the gender and developmental differences in regards to depressive symptoms, self-esteem, and physical activity reported in the literature, it was hypothesized that the mediation would be strongest for late adolescent girls.

Section snippets

Data

The current study used a population-based sample from the public database of The National Longitudinal Study of Adolescent Health (Add Health; Carolina Population Center, 1996). All high schools in the United States that had an 11th grade and at least 30 enrollees in the school were eligible to be selected to participate in the study. A random sample of 80 high schools and 52 middle schools were selected relative to enrolment size and stratified by region of country, urbanicity, school size,

Results

Descriptive statistics are provided in Table 1. In general, girls tended to report higher depressive symptoms, lower self-esteem, and engaged less frequently in physical activity compared to boys at both time-points (see Table 1). The effect sizes indicate that the gender differences in these variables were small, as most effect sizes were .06 or smaller as indicated by partial eta squared.

Results from the regression analyses separated by gender are presented in Table 2. When separate analyses

Discussion

The current study tested the hypothesis that self-esteem mediates the inverse relationship between physical activity and depressive symptoms in a population-based sample of adolescent boys and girls while controlling for age, race/ethnicity, parent education, and BMI. The findings were consistent with this hypothesis. In both early and late adolescent boys, and only late adolescent girls, associations between physical activity and depressive symptoms were no longer significant once self-esteem

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