Clinical and neuroimaging correlates of cardiorespiratory fitness in adolescents with bipolar disorder

Introduction Cardiovascular disease (CVD) is exceedingly prevalent, and occurs prematurely in individuals with bipolar disorder (BD). Cardiorespiratory fitness (CRF), arguably the most important modifiable CVD risk factor, is also associated with brain structure and function. There is a gap in knowledge regarding CRF in BD, particularly in relation to brain structure. Methods Adolescents with BD (n = 54) and healthy controls (HC; n = 53) completed semi-structured diagnostic interviews, self-report questionnaires, and 20 minutes of cardiorespiratory exercise at 60-80% of estimated maximum heart rate (HR) on a bicycle ergometer. Average power (watts/kg) within this HR range served as a previously validated proxy for CRF. Brain magnetic resonance imaging (MRI) structural analysis was done using FreeSurfer. Analyses controlled for age and sex. Results CRF was significantly lower in BD vs HC (0.91 +/- 0.32 vs 1.01 +/- 0.30,p = 0.03, F = 4.66, df=1, eta(2)=0.04). Within BD, greater depression symptoms were associated with lower CRF (P = .02), and greater physical activity (PA) was associated with greater CRF (P < .001). In multivariable analyses, there were significant main effects of diagnosis (HC>BD;P = .03) and sex (M > F;P < .001) on power. Significant predictors of power within BD included male sex (P = .02) and PA (P = .002) but not depression symptoms (P = .29). Significant diagnosis by CRF interaction effects was found in frontal, parietal, and occipital cortical regions. Conclusion CRF was reduced among adolescents with BD, particularly women, related in part to depression symptoms and inactivity and was differentially associated with regional brain structure. Studies seeking to improve CRF as a means of reducing psychiatric symptoms of BD are warranted.

Automated summary

The study found that adolescents with bipolar disorder had significantly lower cardiorespiratory fitness, particularly among women, which was related to depression symptoms and inactivity. Additionally, the research showed that CRF was differently associated with regional brain structure, and improving CRF may be a promising approach to reducing psychiatric symptoms of BD.