Fitness, Sleep-Disordered Breathing, Symptoms of Depression, and Cognition in Inactive Overweight Children: Mediation Models

Abstract

Objectives: We used mediation models to examine the mechanisms underlying the relationships among physical fitness, sleep-disordered breathing (SDB), symptoms of depression, and cognitive functioning.

Methods: We conducted a cross-sectional secondary analysis of the cohorts involved in the 2003-2006 project PLAY (a trial of the effects of aerobic exercise on health and cognition) and the 2008-2011 SMART study (a trial of the effects of exercise on cognition). A total of 397 inactive overweight children aged 7-11 received a fitness test, standardized cognitive test (Cognitive Assessment System, yielding Planning, Attention, Simultaneous, Successive, and Full Scale scores), and depression questionnaire. Parents completed a Pediatric Sleep Questionnaire. We used bootstrapped mediation analyses to test whether SDB mediated the relationship between fitness and depression and whether SDB and depression mediated the relationship between fitness and cognition.

Results: Fitness was negatively associated with depression ( B = -0.041; 95% CI, -0.06 to -0.02) and SDB ( B = -0.005; 95% CI, -0.01 to -0.001). SDB was positively associated with depression ( B = 0.99; 95% CI, 0.32 to 1.67) after controlling for fitness. The relationship between fitness and depression was mediated by SDB (indirect effect = -0.005; 95% CI, -0.01 to -0.0004). The relationship between fitness and the attention component of cognition was independently mediated by SDB (indirect effect = 0.058; 95% CI, 0.004 to 0.13) and depression (indirect effect = -0.071; 95% CI, -0.01 to -0.17).

Conclusions: SDB mediates the relationship between fitness and depression, and SDB and depression separately mediate the relationship between fitness and the attention component of cognition.

Keywords: cognitive functioning; depression; pediatric obesity; physical fitness; sleep.

Figure 1.

Mediation model of the association between physical fitness and symptoms of depression mediated by sleep-disordered breathing (SDB) among overweight and obese inactive children aged 7-11 in public schools, based on study cohorts from project PLAY^,, (2003-2006) and the SMART study (2008-2011), Augusta, Georgia. Unstandardized regression coefficients, B, and 95% CIs in parentheses are reported for each path. Abbreviations: a, direct effect of physical fitness on SDB (P = .008); b, direct effect of SDB on symptoms of depression after controlling for fitness (P = .004); c, total effect of physical fitness on symptoms of depression (P = .002); c′, direct effect of physical fitness on symptoms of depression after controlling for SDB; ab, indirect effect of physical fitness on symptoms of depression mediated by SDB.

Figure 2.

Statistical (A) and conceptual (B) moderated mediation models, examining whether the association between fitness and symptoms of depression mediated by sleep-disordered breathing (SDB) was moderated by study cohort, W, among overweight and obese inactive children aged 7-11 in public schools, based on study cohorts from project PLAY^,, (2003-2006) and the SMART study (2008-2011), Augusta, Georgia. Formula for the conditional indirect effect of fitness on symptoms of depression mediated by SDB: ω = (a₁ + a₃ W)(b₁ + b₂ W), where W is the moderator (study cohort). We used moderated mediation model 59 in PROCESS, and we found no moderation by study cohort. Abbreviations: a₁, path from physical fitness to SDB; a₂, path from study cohort to SDB; a₃, path from fitness × study cohort to SDB; b₁, path from SDB to symptoms of depression; b₂, path from SDB × study cohort to symptoms of depression; c₁, path from physical fitness to symptoms of depression; c₂, path from study cohort to symptoms of depression; c₃, path from fitness × study cohort to symptoms of depression.

Figure 3.

Serial multiple mediation model examining the association between fitness and the attention component of cognition mediated by sleep-disordered breathing (SDB) and symptoms of depression among overweight and obese inactive children aged 7-11 in public schools, based on study cohorts from project PLAY^,, (2003-2006) and the SMART study (2008-2011), Augusta, Georgia. Cognition was measured with the Cognitive Assessment System Attention Scale, which requires the child to focus cognitive activity and inhibit responses to competing stimuli. Abbreviations: a₁₁, effect of physical fitness on SDB; a₁₂, effect of physical fitness on symptoms of depression; b₁, effect of SDB on attention; b₂, effect of symptoms of depression on attention; c, total effect of physical fitness on attention; c′, direct effect of physical fitness on attention, controlling for SDB and symptoms of depression; d, effect of SDB on symptoms of depression. Results: Physical fitness was significantly negatively associated with SDB (B = –0.005; 95% CI, –0.01 to –0.001; P = .016) and symptoms of depression (B = –0.03; 95% CI, –0.06 to –0.01; P = .004). The total effect of fitness on attention was not significant (B = 0.27; 95% CI, –0.03 to 0.57; P = .076), and the direct effect of physical fitness on attention, controlling for the mediators, was also not significant (B = 0.14; 95% CI, –0.16 to 0.43; P = .371). The serial indirect effect of fitness mediated by SDB and, in turn, by symptoms of depression was not significant (indirect effect = 0.006; 95% bootstrap CI, –0.001 to 0.02). However, the indirect effects of fitness on attention mediated only by SDB (indirect effect = 0.06; 95% bootstrap CI, 0.004 to 0.13) and only by symptoms of depression (indirect effect = 0.07; 95% bootstrap CI, 0.01 to 0.17) were both significant. The model including fitness, all mediators, and all covariates accounted for 8% of the variance in attention (R² = 0.079, P < .001).