Rationale: Bipolar disorder (BD) is associated with deficits in executive functions and processing speed, yet little is known about risk factors that contribute to the development and sustainment of these deficits. Studies have demonstrated chronic inflammation, characterized by high levels of pro-inflammatory interleukin-6 (IL-6) and C-reactive protein (CRP), and reduced physical activity in BD. Both chronic inflammation and low physical activity are linked to cognitive deficits in other clinical populations, though less is known about these associations in BD. The current dissertation project proposed to a) explore associations between cognition, inflammation and physical activity in BD; and b) examine potential lagged influences between variable mood symptoms, a primary clinical feature of BD, and the amount of daily physical activity exhibited.
Design: Thirty-eight BD and 68 healthy comparison participants underwent psychiatric interview, neuropsychological assessment of executive functioning and processing speed, and a 15ml blood draw analyzed for blood serum concentration of IL-6 and CRP. For the following two weeks, participants submitted thrice-daily mood ratings on a smartphone device and wore an actigraphy watch designed to measure physical activity. Linear regression analyses determined associations between inflammation, cognition, and physical activity. Mixed effects linear regression determined the impact of mood on subsequent levels of physical activity.
Results: BD patients exhibited worse executive functioning and processing speed, less physical activity, and greater levels of IL-6 and CRP; higher BMI in the BD group appeared to explain group differences in inflammation and physical activity. There were no significant associations between inflammation, physical activity, and cognition in BD. Further, mood ratings did not predict subsequent levels of physical activity exhibited by BD individuals.
Conclusion: This study is among the first to examine relationships between inflammation, physical activity, and cognition in BD. Results suggest that inflammation and physical activity are not significant correlates of cognition in middle-aged BD individuals, and daily mood ratings do not predict next-day physical activity. Future studies are needed to better understand individual differences in cognitive performance in BD, as well as associations between inflammation and physical activity, in order to develop targeted treatment strategies aimed to reduce functional disability in this population.