Aims/hypothesis: Diabetes and hypertension are associated with poorer cognitive and brain health. Less is known about comorbid diabetes and hypertension and: cognitive and brain health in mid-life. We hypothesised that individuals with both diabetes and hypertension have worse cognitive and brain health.
Methods: Data from the UK Biobank, a population-based study which recruited 500,000 individuals, aged 40-69 years. Type-2 diabetes was assigned using self-report, HbA1c and clinical data, while hypertension was defined based on self-report. Our outcomes included a breadth of brain structural magnetic resonance imaging (MRI) parameters and cognitive function tests in a maximum of 38918 individuals. We tested associations between comorbid diabetes/hypertension (reference category, n=1283) and our outcomes by comparing this group with those with only diabetes (n=760), hypertension (n=9649) and neither disease (n=27226). Our analytical approach comprised linear regression models, with adjustment for a range of demographic and health factors.
Results: Those with diabetes had worse overall brain health, as indexed by multiple neuroimaging parameters, with the exception of gFA (white matter integrity) and the amygdala. The largest difference was observed in the pallidum (β=0.179, 95%CI=0.137;0.220). Individuals with diabetes had poorer performance on certain cognitive tests, with the largest difference observed in the symbol digit substitution test (β=0.132, 95%CI=0.079;0.187). Compared to individuals with comorbid diabetes and hypertension, those with only hypertension had better brain health overall, with the largest difference observed in the pallidum (β=0.189, 95%CI=0.241;0.137), while those with only diabetes differed in total grey volume (β=0.150, 95%CI=0.122;0.179). Compared with individuals who had comorbid diabetes and hypertension, those with only diabetes performed distinctly better on the verbal and numeric reasoning task (β=0.129, 95%CI=0.077;0.261), whereas those with only hypertension performed better on the symbol digit substitution task (β=0.117, 95%CI=0.048;0.186)
Conclusions/interpretation: Individuals with comorbid diabetes and hypertension have worse brain and cognitive health compared to those with only one of these diseases. These findings potentially suggest that prevention of both diabetes and hypertension may delay changes in brain structure, as well as cognitive decline and dementia diagnosis.