High systolic blood pressure, gait-balance deficiencies, and low self-reported health scores are linked to cognitive deficits in older adults with type 2 diabetes, a report shows.
The three health-related covariates were associated with deficits in neurocognitive speed, executive functioning, and episodic memory in diabetic vs. nondiabetic adults, based on cross-sectional data from the Victoria Longitudinal Study (VLS), an ongoing, multicohort study comprising initially healthy community-dwelling adult volunteers from Western Canada. The study participants undergo cognitive, neuropsychological, health, and physiologic assessment at 3-year intervals.
The current analysis included 499 participants, aged 53–90 years, drawn from the study's third independent sample. Excluded from the study were individuals who had been previously diagnosed with Alzheimer's disease or vascular dementia, those scoring less than 26 on the Mini-Mental Status Examination, and those with clusters of potential comorbid neurologic, cardiovascular, and psychiatric diseases (Neuropsychology 2010;24:547–62).
Type 2 diabetes was present in 41 participants who were compared with the remaining 458 participants without diabetes. The two groups were similar in age, education, and gender proportions, as well as marital and dwelling status, and no group differences were found for global cognition or visual or audio acuity, according to C. Peggy McFall of the University of Alberta, Edmonton, and colleagues.
The investigators identified from the literature 13 health-related potential covariates and identified relationships between the covariates and type 2 diabetes. Six potential covariates – systolic blood pressure, body mass index, gait-balance, depression, negative affect, and subjective health were found to be sensitive to type 2 diabetes associations with performance on seven cognitive measures. These measures were episodic memory, the Stroop Test, the Hayling Sentence Completion Test, the Color Trials Test 2, semantic speed, reaction time, and the Digit Symbol Substitution Test.
In the regression analyses, systolic blood pressure, gait-balance, and subjective health were found to mediate multiple cognitive outcomes. For example, systolic blood pressure attenuated the type 2 diabetes–cognition relationship by 30%–50% for episodic memory, neurocognitive speed, and executive function. As such, systolic blood pressure may be associated with type 2 diabetes-related vascular disturbance.
The gait-balance composite mediated type 2 diabetes cognition relationships for all seven cognitive measures, with attenuation effects ranging from 32% to 62%, the authors reported. The substantial influence of this composite might reflect the impact of diabetes on specific neural mechanisms associated with gait and balance or, more broadly, it might affect the “multiple overlapping areas [of the brain] associated with gait-balance and cognition.”
The subjective health composite accounted for 35%–50% of performance on five different cognitive tests. “Specifically, [type 2 diabetes] may exacerbate levels of psychosocial stress, depression, and (lower) health self efficacy – all of which may negatively affect motivation for performance on cognitive tests,” the authors wrote. Further, with diabetes, “processes of interoception may detect inner biological stimuli of discomfort or nutritional deficits that could be associated with lower subjective health ratings and, by extension, cognitive performance.”
The findings point to the need for “neuropsychological research on neural bases of [diabetes-related] cognitive decline, clinical research on intervention and treatment strategies, and larger-scale longitudinal epidemiological studies, all of which will help clarify the multilateral (and possibly dynamic) relationships and mechanisms of [type 2 diabetes], related comorbidities, and cognitive outcomes,” the authors concluded.