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, η² =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.

Prevalence of white matter hyperintensities is not elevated in a large sample of adolescents and young adults with bipolar disorder

OBJECTIVE

The increased prevalence rate of white matter hyperintensities is one of the most consistently reported brain abnormalities in adults with bipolar disorder. However, findings in children and adolescents with bipolar disorder are less consistent. Prior studies have been constrained by small sample sizes and/or poor age- and sex-matching of healthy controls. We examined this topic in the largest sample of adolescents with bipolar disorder to date.

METHODS

T2-weighted 3-Tesla magnetic resonance imaging data were acquired for 83 adolescents with bipolar disorder diagnosed via the Kiddie Schedule for Affective Disorders and the Schizophrenia, Present and Lifetime version semi-structured interview and 64 age- and sex-matched healthy controls. All acquired scans were examined by neuroradiologists and the presence or absence of white matter hyperintensities was determined for each participant.

RESULTS

The prevalence of white matter hyperintensities did not differ between adolescents with bipolar disorder (13.3%) and controls (21.9%; χ2 = 1.90; p = 0.168).

CONCLUSION

In contrast to the study hypothesis, the prevalence of white matter hyperintensities was not higher in adolescents with bipolar disorder than controls. The large sample size and good matching for age and sex bolster the reliability of this negative finding. Future studies are warranted to evaluate the prevalence, incidence, and predictors of white matter hyperintensities in early-onset bipolar disorder prospectively.