In type 2 diabetes (T2D), a greater degree of hyperlipidemia and hypertension, although not hyperglycemia, was associated with measurable cognitive impairment even among patients with only a 4-year mean disease duration, according to a substudy of the GRADE trial.
The association of these cardiovascular (CV) risk factors with impairments in cognition has been reported before, but the findings are notable because the mean duration of T2D was short in a relatively healthy study population, reported a multicenter team of investigators.
The relative impairments in cognitive function “may not be clinically significant given the very small size of the differences,” conceded the authors of this study, led by José A. Luchsinger, MD, but they are consistent with previous reports of the same association in older patients with a longer duration of diabetes. In other words, the data suggest the risk of cognitive loss from CV risk factors in T2D patients begins early.
“A potential explanation for the small differences, compared with those previously reported, is that the GRADE cohort is relatively young with a healthier cardiovascular profile and shorter diabetes duration compared with other studies,” reported the investigators, whose results were published online July 20, 2021, in Diabetes Care.
99% complete cognitive assessments
In the GRADE (Glycemia Reduction Approaches in Diabetes: Comparative Effectiveness) trial, 5,018 (99.4%) of the 5,047 enrolled patients completed a battery of cognitive assessments at baseline. Patients were excluded from this study if they had any major CV event in the previous year, if they had T2D for more than 10 years, if they had significant renal impairment, and if they had any history of stage 3 or greater heart failure. Their mean age was 56.7 years.
By cross-sectional analysis, cognitive evaluations, including the Digit Symbol Substitution Test (DSST) and the Spanish English Verbal Learning Test, were evaluated in relation to baseline LDL cholesterol levels, systolic and diastolic blood pressure, hemoglobin A1c, and statin use.
Unlike previous studies in T2D patients, no relationship was observed between cognitive function and A1c level at baseline. However, LDL cholesterol greater than 100 mg/dL was associated with cognitive impairment as measured with the DSST after adjustment for age, sex, education, and general health. The mean difference relative to LDL cholesterol below 70 mg/dL was only 1.8 points, but this was highly significant (P < .001).
Similarly, significant but modest cognitive impairment on DSST score after adjustment for variables were seen for those with a systolic BP between 120 mg and <140 mg relative to either <120 mm Hg or at least 140 mm Hg (P = .014). The same was seen for diastolic BPs of 80 to <90 when compared with either <80 mm Hg or to 90 mm Hg or higher (P = .01).
For those taking statins versus no statins at baseline, there was a 1.4-point mean advantage in DSST score after adjusting for variables (P < .001).
Modest cognitive impairments recorded
Again, the absolute mean differences in the DSST cognitive scores, despite their statistical significance, were modest, according to the authors. In general, the mean difference was rarely greater than 2.0 points and often 1.0 point or less. The authors acknowledged that these changes are of an uncertain clinical significance, but they considered the findings consistent with the association of CV risk factors with cognitive deficits in older T2DM patients or T2DM patients with longer duration of disease.
One difference between this GRADE substudy and previous studies was the lack of an association between cognitive impairment and hyperglycemia. In the ACCORD trial for example, increased levels of blood glycemia were associated with lower performance on numerous tests of cognitive function.
In the Diabetes Control and Complications Trial (DCCT), poorer glycemic control was related to poorer performance on tests of executive function.
Both of those studies also linked hypertension and hyperlipidemia with cognitive deficits, but given that patients in ACCORD had T2DM of substantially longer duration and those in DCCT were older, “it seems reasonable to speculate that, in patients with diabetes duration of less than 10 years, the association between hyperglycemia and cognitive performance may not yet be evident,” the GRADE authors reported.
GRADE trial compares drugs in four classes
The GRADE trial was conducted to compare four classes of T2D therapies for long-term glycemic control as expressed by A1c control over time. The results of the trial, presented recently at the 2021 annual scientific sessions of the American Diabetes Association, found that insulin glargine and the glucagonlike peptide–1 receptor agonist liraglutide performed best on the primary endpoint of maintaining A1c below 7.0%. Both performed significantly better than the sulfonylurea glimepiride and the dipeptidyl peptidase–4 inhibitor sitagliptin.
This substudy of baseline cognitive function in the relatively large GRADE trial provided a unique opportunity to evaluate the impact of CV risk factors in patients with T2D of relatively short duration.
Dr. David R. Matthews
While the data support the adverse impact of inadequately controlled modifiable risk factors on cognitive function in T2D patients, David R. Matthews, DPhil, BM, BCh, emeritus professor of diabetes medicine at the University of Oxford (England), noted that the association was weak and advised a cautious interpretation.
“The effect size is very small indeed. The data are found as a subset of multiple testing,” he said in an interview. He suggested the associations might be the result of “data farming,” and he emphasized that the relationships between these risk factors and cognitive deficits are associations that do not imply causation.
Nevertheless, and despite their unclear clinical implications, Dr. Matthews said that these data might still have a message.
“It is another reminder that for many reasons we all need to be alert to the need for lowering hyperlipidemia and hypertension to normal levels – the benefits may not just be limited to cardiovascular outcome,” Dr. Matthews stated.
The lead author of the study, Dr. Luchsinger, also cautioned against overinterpreting the data.
While the data show that “lipid and blood pressure control within recommended guidelines are associated with marginally better cognitive function in patients with type 2 diabetes of less than 5 years duration on average,” he added that “the study is limited by its cross-sectional nature.”
He indicated that further analysis will be helpful in assessing the implications.
“Longitudinal analyses of the same group of individuals will be conducted next year,” noted Dr. Luchsinger, associate professor of medicine and epidemiology, Columbia University Medical Center, New York.
Dr. Luchsinger reported financial relationships with vTv therapeutics. Dr. Matthews reported no potential conflicts of interest.