Understanding the relationship between cardiovascular disease risk factors and cognition in bipolar disorder.
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2024-04
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Melbourne Authors
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Psychiatry
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PhD thesis
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Open Access
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© 2024 Elysha Jayne Ringin
Abstract
More than 50% of those with bipolar disorder (BD) experience cognitive impairment that persists during euthymic phases and is known to adversely impact psychosocial functioning and general quality of life. Physical health is an important consideration in relation to cognitive symptoms in BD, given that people with BD are disproportionately affected by cardiovascular diseases and experience higher rates of conventional risk factors for these diseases in comparison to the general population. These cardiovascular disease risk factors have been associated with cognitive impairment in the general population, yet there is a sparsity of research exploring the presence and nature of these associations in BD. This Thesis aimed to address this by empirically exploring associations of type 2 diabetes (T2D), physical activity, and sedentary behaviour with cognition, as well as looking at both physiological and behavioural cardiometabolic disease risk more broadly.
The first empirical study of this Thesis explored the association of T2D with cognition in people with BD and healthy controls. T2D was associated with poorer visuospatial memory performance in the BD group only. Worse processing speed and prospective memory performance was also found in those with T2D compared to those without. These associations were moderated by age, such that in BD participants with comorbid T2D, processing speed remained stable, and visuospatial memory performance was better as a function of age. In those with BD without comorbid T2D, performance on both these domains was worse as a function of older age but remained relatively equivalent to controls. That worse processing speed and visuospatial memory in those with BD and T2D was evident at the beginning of the age ranged indexed in the study, suggests earlier cognitive ageing in this group than what would normally be expected.
The second empirical study of this Thesis explored whether individual variation in physical activity and sedentary behaviour (both mentally-active and mentally-passive) was directly associated with cognition in BD and healthy controls, and/or whether this variation moderated the extent of decrements in cognitive function occurring as a function of age. Cognition was inversely associated with physical activity and passive sedentary behaviour and positively associated with mentally-active sedentary behaviour in both groups, although the latter association was stronger in those with BD. Mentally-active sedentary behaviour also moderated the association of age and cognition in both BD patients and controls, such that age-related decrements in cognition were more apparent in those who engaged in less mentally-active sedentary behaviour compared to those who engaged in more.
A third empirical study investigated whether cognition measured at an initial timepoint was associated with objective physical activity and sedentary time measured years later. Findings suggested a small but significant prospective association of better cognitive function with greater moderate-to-vigorous physical activity and sedentary time, and less light physical activity, in BD and controls. These associations were not moderated by age.
The final empirical investigation explored the extent to which cardiometabolic disease health-risk behaviours, in comparison to physiological cardiometabolic disease risk factors, were more, less, or equally relevant to cognition in BD, and whether this varied as a function of age. Lower mentally-active and higher passive sedentary behaviour, higher levels of physical activity, inadequate sleep duration, higher systolic and lower diastolic blood pressure, and lower handgrip strength were associated with worse cognitive function in BD, with several associations restricted to either mid (<60 years of age) or later-life (>/=60 years of age).
The findings of this Thesis collectively provide evidence that cardiovascular disease risk is an important contributor to cognitive functioning in BD as well as in healthy individuals. Health-risk behaviours appear to be particularly relevant to BD, although several physiological risk factors – namely T2D, blood pressure, and handgrip strength also appear to be associated with cognition in this group. These risk factors may be associated with age-related variation in cognitive function, as the interactive effect of T2D and BD putatively conferred premature age-related cognitive decline, but mentally-active sedentary behaviour appeared to attenuate age-related cognitive decline. These findings suggest that cardiovascular disease risk factors represent treatment targets for cognitive symptoms in BD and may also be useful in the identification of cognitive impairment and thus prognostic prediction.
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Bipolar disorder, Mood disorders, Cognition, Cardiovascular disease risk factors, Type 2 diabetes, Physical activity, Sedentary behaviour