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Diabetes and Cognitive Decline

Cognitive decline in older adults with T2 may start to develop years before diagnosis, even in the prediabetes stages

People with diabetes mellitus may be at increased risk for cognitive decline. Correlating these findings with activities of daily living and with degree of DM control is needed, but this study provides further evidence that treating DM may decrease the burden of cognitive decline in older adults.

To analyze the incidence of cognitive decline in those with and without pre-existing or incident diabetes mellitus, researchers tracked 7,740 participants aged ≥65 years from the Chicago Health and Aging Project. Diabetes mellitus (DM) was determined based on the use of hypoglycemic medications, Medicare claims with the diagnosis, or both. Participants completed tests of executive function, episodic memory, and the Mini Mental State Examination every 3 years for up to 12 years. The researchers compared a composite cognitive score between those with and those without incident or pre-existing DM after adjustment for age, sex, education, body-mass index, hypertension, stroke, and antihypertensive and statin medication use. Differences between participants of black and European descent were also determined.

Those with incident DM had similar baseline cognitive scores compared with those without DM. On the other hand, among black participants, those with pre-existing DM had significantly lower baseline cognitive scores than those with no DM. Both the black and European groups with incident DM had faster rates of cognitive decline than those without DM.

Type 2 diabetes is known to be associated with decrements in memory and executive functions and information-processing speed. It is less clear, however, at which stage of diabetes these cognitive decrements develop and how they progress over time. In this study, they investigated cognitive functioning of patients with recent screen-detected type 2 diabetes, thus providing insight into the nature and severity of cognitive decrements in the early stage of the disease.

Included in this study were 183 diabetic patients from a previously established study cohort and 69 control subjects. A full neuropsychological assessment, addressing six cognitive domains, was made for each participant. Raw test scores were standardized into z scores per domain and compared between the groups. Possible risk factors for cognitive decrements were examined with multivariate linear regression.

This study shows that modest cognitive decrements are already present at the early stage of type 2 diabetes. A history of macrovascular disease and smoking are significant risk factors for some early decrements.

Type 2 diabetes is associated with accelerated cognitive decline and an increased risk of dementia, particularly in older individuals. Previous studies have shown decrements in memory function, executive function, and information-processing speed. These decrements in cognitive functioning are associated with modest brain atrophy and vascular lesions on brain magnetic resonance imaging. Diabetes-related factors, such as insulin resistance, chronic hyperglycemia, hypertension, and lipid disorders probably are relevant determinants.

It is unclear in which stage of diabetes the cognitive decrements become manifest and how they progress over time. Most studies have focused on patients with a known history of diabetes of several years. However, type 2 diabetes typically develops insidiously and may often be undiagnosed in the early stages. Therefore, cognitive decrements may start to develop years before the actual diagnosis, even in the prediabetes stages. Detailed neuropsychological data on the early stage of type 2 diabetes are not yet available. Moreover, possible risk factors for early cognitive decrements are not completely known.

In this study they assessed cognition in the early stage of diabetes by means of a detailed neuropsychological assessment (NPA) in a substantial population of patients with recent screen-detected diabetes. Possible risk factors were also addressed.

This study shows that patients with recent screen-detected type 2 diabetes performed significantly worse on memory functions, in particular, the immediate and the incidental memory, compared with control subjects. A history of macrovascular diseases and current smoking were the strongest determinants of a lower information-processing speed in the diabetic group.

The effect sizes for the difference in cognition between the diabetic and control groups found in this study are small compared with those in other studies, possibly reflecting the relatively short duration of diabetes in this population.

In summary, cognitive decrements can be found in the early stages of type 2 diabetes. This finding may have implications for diabetes education and self-management behavior in diabetic patients. Diabetes educators should at least take into account the immediate memory and learning rate and the incidental memory of patients with a recent diagnosis of diabetes. If one wishes to prevent diabetes-associated cognitive decrements, interventions may need to be initiated at a very early stage. Offering a smoking cessation consultation would be the best option in those patients who are smokers. Whether other therapies might be beneficial to decrease the risk of cognitive impairment remains uncertain.

Practice Pearls:

  • Cognitive decline can be found in the early stages of type 2 diabetes.
  • Cognitive decrements may start to develop years before the actual diagnosis, even in the prediabetes stages.
  • Treating type 2 diabetes can help to prevent or delay the progression of cognitive decline

Diabetes Care 2015 Jul; 32(7): 1261-1265. http://dx.doi.org/10.2337/dc08-2143

Stewart R.:Type 2 diabetes mellitus, cognitive impairment and dementia. Diabet Med 1999; 16: 93112