Understanding the interrelationships of type-2 diabetes and hypertension with brain and cognitive health: a UK Biobank study
Authors: Newby Danielle , Garfield Victoria 
Published: November 2021

ABSTRACTAims/hypothesisDiabetes 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.MethodsWe used the UK Biobank cohort, 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 in a cross sectional design firstly between those with diabetes (n = 2043) versus those without (reference category, n = 36875) then 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.ResultsThose 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/interpretationIndividuals 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.Research in contextWhat is already known about this subject?Diabetes and hypertension are both independently associated with poorer brain health, cognition and increase in dementia risk50% of adults with diabetes also have hypertensionComorbid diabetes and hypertension are associated with excess dementia riskWhat is the key question?Do individuals with both diabetes and hypertension have worse cognitive and brain health?What are the new findings?Individuals with diabetes have poorer brain health and cognitive performance using a breadth of neuroimaging measures and cognitive testsThose with both diabetes and hypertension have worse brain health and cognitive performance (particularly processing speed) compared to those with only hypertensionHow might this impact on clinical practice in the foreseeable future?Prevention of both diabetes and hypertension may help delay changes in brain structure and cognitive decline as well as reduce future dementia risk.