Recent research has demonstrated an association between mid-life obesity and increased risk of later-life dementia. This concerning relationship has prompted the investigation and identification of a link between obesity and cognitive dysfunction in mid-life. Many questions remain regarding the domains of cognition affected; the contribution of obesity to cognitive function independent of obesity-related co-morbidities; and the subjective experience of such impairment in individuals with obesity.
A series of three studies addressed these identified limitations of the literature. A systematic review assessed the evidence of domain-specific cognitive dysfunction, and the independent contribution of obesity to cognitive function in mid-life adults with obesity. The review examined seventeen articles containing evidence of obesity-related deficits in the domains of intellectual functioning, psychomotor performance and speed, visual construction, concept formation and set-shifting, and decision making. However, given few studies employed consistent methodologies (including appropriate control groups, exclusion criteria), there was insufficient evidence to conclude an independent association between obesity and cognitive function.
The remaining two empirical studies examined a sample of 69 treatment-seeking individuals with obesity and 65 healthy-weight individuals (matched for age and gender). Participants each completed a range of clinical health, psychological, and neuropsychological measures. Individuals with obesity demonstrated poorer cognitive performance than healthy-weight controls, independent of education, in the domains of psychomotor performance and speed, verbal learning and memory, complex attention, semantic verbal fluency, working memory, and concept formation and set-shifting, but not visual construction, visual memory, phonemic verbal fluency or inhibition. The significant between group differences in each of these domains (except verbal memory) remained following control for obesity-related co-morbidities (e.g., mood, sleep, and cardiovascular disease risk factors). The second empirical paper employed a self-report questionnaire to investigate the subjective experience of cognitive impairment. Levels of subjective cognitive impairment did not differ between adults of obese and healthy weight, with the majority of individuals in both groups reporting low levels of cognitive impairment. Self-reported cognitive dysfunction was not associated with objective cognitive performance in individuals of obese or healthy weight, with depression and anxiety symptoms the only significant correlates in both groups.
Overall, this series of studies adds to the growing evidence of mid-life obesity-related cognitive dysfunction, and of obesity independently contributing to cognitive performance across a range of cognitive domains. These early subtle cognitive deficits however do not appear to be of significant concern to individuals with obesity. Further research is needed to clarify the brain regions and mechanisms underlying obesity-related cognitive impairment, and clarify the impact of this obesity-related cognitive dysfunction in mid-life. The long-term aim of this research area should be to determine the potential for mid-life weight-loss to improve mid-life obesity-related cognitive dysfunction and attenuate late-life dementia risk. This research will be of particular significance given the growing levels of obesity and the ageing population in Australia.