How does type 2 diabetes mellitus (DM) accelerate cognitive decline, and what is the relationship of coronavirus disease 2019 (COVID-19) to diabetes?

Updated: Sep 27, 2021
  • Author: Romesh Khardori, MD, PhD, FACP; Chief Editor: George T Griffing, MD  more...
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In a cross-sectional study of 350 patients aged 55 years and older with type 2 diabetes and 363 control participants aged 60 years and older without diabetes, diabetic individuals were more likely to have brain atrophy than cerebrovascular lesions, with patterns resembling those of preclinical Alzheimer disease. [31, 32] Type 2 diabetes was associated with hippocampal atrophy; temporal, frontal, and limbic gray-matter atrophy; and, to a lesser extent, frontal and temporal white-matter atrophy.

Type 2 diabetes was also linked with poorer performance on certain cognitive tests. The strength of these associations dropped by almost 50% when adjusted for hippocampal and total gray-matter volumes but was unchanged when adjusted for cerebrovascular lesions or white-matter volume. [31, 32] Patients with type 2 diabetes were more likely to have gray-matter atrophy in several bilateral regions of the cortices, especially in the left hemisphere, similar to the distribution of cortical atrophy described in early Alzheimer disease. [31]

In a 40-month study of 2977 middle-aged and older adults with long-standing type 2 diabetes, depression at baseline was associated with accelerated cognitive decline. [33, 34] The 531 subjects with scores of 10 or higher on the Patient Health Questionnaire Depression Scale at baseline had significantly lower scores on the Digit Symbol Substitution Test (DSST), the Rey Auditory Verbal Learning Test (RAVLT), and the modified Stroop test. Adjustment for other risk factors did not affect the association.


A study reported that out of 178 adult patients hospitalized with coronavirus disease 2019 (COVID-19), at least one underlying condition was found in 89.3%, the most common being hypertension (49.7%), obesity (48.3%), chronic lung disease (34.6%), diabetes mellitus (28.3%), and cardiovascular disease (27.8%). [35]

According to a report by Stokes et al, out of 287,320 US cases of COVID-19 in which the patient’s underlying health status was known, diabetes was the second most common underlying condition (30%), after cardiovascular disease (32%), which in this study included hypertension. [36, 37]

A report by Barrera et al looking at 65 observational studies (15,794 participants) found the overall prevalence of diabetes in patients with COVID-19 to be 12%, with the prevalence being 18% in severe COVID-19. [38, 39]

Results from a study by Guo et al suggested that in patients with COVID-19 infection, the increase in inflammatory and coagulation markers is greater in those with type 2 diabetes mellitus than in individuals without diabetes. This may help to indicate why the risk of more severe disease and death from COVID-19 infection is higher in patients with diabetes. [40, 41]

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