in new findings that may explain the “excessive and premature mortality” related to heart disease in this patient population.
The investigators found that higher reactive hyperemia index (RHI) scores, a measure of endothelial function, were tied to mood severity in patients with higher mania, but not depression scores. These findings persisted even after accounting for medications, obesity, and other cardiovascular risk factors (CVRFs).
“From a clinical perspective, these findings highlight the potential value of integrating vascular health in the assessment and management of youth with BD, and from a scientific perspective, these findings call for additional research focused on shared biological mechanisms linking vascular health and mood symptoms of BD,” senior investigator Benjamin Goldstein, MD, PhD, full professor of psychiatry, pharmacology, and psychological clinical science, University of Toronto, said in an interview.
The study was published online in the Journal of Clinical Psychiatry.
‘Excessively present’
BD is associated with “excessive and premature cardiovascular mortality” and CVD is “excessively present” in BD, exceeding what can be explained by traditional cardiovascular risk factors, psychiatric medications, and substance use, the researchers noted.
“In adults, more severe mood symptoms increase the risk of future CVD. Our focus on endothelial function rose due to the fact that CVD is rare in youth, whereas endothelial dysfunction – considered a precursor of CVD – can be assessed in youth,” said Dr. Goldstein, who holds the RBC Investments Chair in children’s mental health and developmental psychopathology at the Centre for Addiction and Mental Health, Toronto, where he is director of the Centre for Youth Bipolar Disorder.
For this reason, he and his colleagues were “interested in researching whether endothelial dysfunction is associated with mood symptoms in youth with BD.” Ultimately, the motivation was to “inspire new therapeutic opportunities that may improve both cardiovascular and mental health simultaneously.”
To investigate the question, the researchers studied 209 youth aged 13-20 years (n = 114 with BD and 94 healthy controls [HCs]).
In the BD group, there were 34 BD-euthymia, 36 BD-depressed, and 44 BD-hypomanic/mixed; and within the groups who had depression or hypomania/mixed features, 72 were experiencing clinically significant depression.
Participants had to be free of chronic inflammatory illness, use of medications that might be addressing traditional CVRFs, recent infectious diseases, or neurologic conditions.
Participants’ bipolar symptoms, psychosocial functioning, and family history were assessed. In addition, they were asked about treatment, physical and/or sexual abuse, smoking status, and socioeconomic status. Height, weight, waist circumference, blood pressure, and blood tests to assess CVRFs, including C-reactive protein (CRP), were also assessed. RHI was measured via pulse amplitude tonometry, with lower values indicating poorer endothelial function.
Positive affect beneficial?
Compared with HCs, there were fewer White participants in the BD group (78% vs. 55%; P < .001). The BD group also had higher Tanner stage development scores (stage 5: 65% vs. 35%; P = .03; V = 0.21), higher body mass index (BMI, 24.4 ± 4.6 vs. 22.0 ± 4.2; P < .001; d = 0.53), and higher CRP (1.94 ± 3.99 vs. 0.76 ± 0.86; P = .009; d = –0.40).
After controlling for age, sex, and BMI (F3,202 = 4.47; P = .005; np2 = 0.06), the researchers found significant between-group differences in RHI.
Post hoc pairwise comparisons showed RHI to be significantly lower in the BD-depressed versus the HC group (P = .04; d = 0.4). Moreover, the BD-hypomanic/mixed group had significantly higher RHI, compared with the other BD groups and the HC group.
RHI was associated with higher mania scores (beta, 0.26; P = .006), but there was no similar significant association with depression mood scores (beta, 0.01; P = .90).
The mood state differences in RHI and the RHI-mania association remained significant in sensitivity analyses examining the effect of current medication use as well as CVRFs, including lipids, CRP, and blood pressure on RHI.
“We found that youth with BD experiencing a depressive episode had lower endothelial function, whereas youth with BD experiencing a hypomanic/mixed episode had higher endothelial function, as compared to healthy youth,” Dr. Goldstein said.
There are several mechanisms potentially underlying the association between endothelial function and hypomania, the investigators noted. For example, positive affect is associated with increased endothelial function in normative samples, so hypomanic symptoms, including elation, may have similar beneficial associations, although those benefits likely do not extend to mania, which has been associated with cardiovascular risk.
They also point to several limitations in the study. The cross-sectional design “precludes making inferences regarding the temporal relationship between RHI and mood.” Moreover, the study focused only on hypomania, so “we cannot draw conclusions about mania.” In addition, the HC group had a “significantly higher proportion” of White participants, and a lower Tanner stage, so it “may not be a representative control sample.”
Nevertheless, the researchers concluded that the study “adds to the existing evidence for the potential value of integrating cardiovascular-related therapeutic approaches in BD,” noting that further research is needed to elucidate the mechanisms of the association.