A longitudinal study that tracked the cognitive functioning of individuals diagnosed with type 1 diabetes (T1D) over 32 years indicated that individuals who maintained better control over their glycemia and hypertension experienced less cognitive decline than those with less control. The results of this study were published recently in The Lancet Diabetes and Endocrinology.
Researchers recruited 1441 individuals aged between 13 and 39 years (median age, 27 years) who were participating in the Diabetes Control and Complications Trial (DCCT) and the Epidemiology of Diabetes Interventions and Complications (EDIC) study between 1983 and 1989. Investigators administered cognitive tests that were most sensitive to glycemia 5 times, once to obtain a baseline, and then 2, 5, 18, and 32 years later. Investigators then analyzed this data to track the trajectory of cognitive changes and identify specific risk factors associated with cognitive decline.
The battery of tests assessed 3 cognitive domains: immediate memory recall, delayed recall, and psychomotor and mental efficiency. Immediate memory tests entailed recall of two stories from the Logical Memory subtest of the Wechsler Memory Scale and recall of 9 symbols following completion of the Wechsler Adult Intelligence Scale (WAIS) Digit Symbol Substitution Test.
Delayed recall involved 2 stories from the Logical Memory Subtest after a 10- to 15-minute delay.
The psychomotor and mental efficiency tests calculated the time to complete the Grooved Pegboard using the dominant and then nondominant hand, the WAIS Digit Symbol Substitution Test (total number correct in 90 seconds), the time to complete Trail Making Part B, and verbal fluency. Psychomotor and mental efficiency tests measured executive functioning, requiring the participants to demonstrate focused attention, follow a set of rules, plan a series of actions, execute those actions quickly, evaluate their accuracy, correct errors appropriately, and store information effectively in working memory. These skills are required to effectively manage T1D and perform complex activities of daily living.
The Montreal Cognitive Assessment was administered only at year 32. Prior to cognitive test administration, investigators monitored the participants’ capillary blood glucose levels to ensure lack of hypoglycemia during testing. Blood glucose levels above 90 mg/dL were required for testing to continue.
Data analysis demonstrated small improvements in cognitive functioning at years 2 and 5. At year 18, investigators noted a statistically significant, moderate decrease since baseline in psychomotor and mental efficiency (z-score, -0.24; P <.0001). Psychomotor and mental efficiency further declined more than 5 times as much between years 18 and 32 (z-score, –1.36; P <.0001). Researchers noted smaller changes on the immediate and delayed memory recall tests.
The most significant predictors of decline across all cognitive domains were older age and fewer years of education. Impaired kidney function negatively impacted immediate memory, while a history of cardiovascular autonomic neuropathy was associated with a decline in delayed memory.
Declines in psychomotor and mental efficiency positively correlated with higher hemoglobin A1c (HbA1c) levels, higher systolic blood pressure, elevated body mass index (BMI) and pulse rate, higher triglyceride levels, lower high-density lipoprotein (HDL) cholesterol levels, severe hypoglycemic events, and other diabetes complications such as nephropathy, neuropathy, retinopathy, and cardiovascular disease.
The primary strengths of this study were its longitudinal aspect as well as the high rate of participation, with 92% of participants completing the 32-year follow-up.
Limitations included the absence of an age-matched control group without diabetes, lack of diversity in the participant sample, and lack of generalizability to individuals with other types of diabetes. Two other limitations included the selective use of cognitive tests sensitive only to glycemia such that other cognitive domains were not effectively examined, and the inability to rule out whether the outcomes were affected by cognitive decline impacting self-management of diabetes rather than poor self-management of diabetes causing cognitive decline.
Enhanced clinical control and patient self-management of glycemia and hypertension are needed to alter the course of cognitive decline and improve the quality of life in patients with T1D.
According to the researchers, “This study reveals the cognitive path expected for individuals with long-standing type 1 diabetes as they age and brings into clear view the value of better management of glycaemia and hypertension to change this course.”
Disclosure: Some study authors declared affiliations with biotech, pharmaceutical, and/or device companies. Please see the original reference for a full list of authors’ disclosures.
Jacobson AM, Ryan CM, Braffett BH, et al; DCCT/EDIC Research Group. Cognitive performance declines in older adults with type 1 diabetes: results from 32 years of follow-up in the DCCT and EDIC Study. Lancet Diabetes Endocrinol. Published online May 27, 2021. doi:10.1016/ S2213-8587(21)00086-3