Diabetes Speeds Cognitive Decline

The findings suggest that preventing diabetes may help maintain cognitive function in older patients, the researchers said.

To assess whether diabetes increases the risk of cognitive decline, and whether poor glucose control is associated with worse cognitive performance among elderly adults, Yaffe and colleagues conducted the prospective Health, Aging, and Body Composition (Health ABC) Study at two community clinics, totaling 3,069 patients whose mean age was 74.2 at baseline.

Patients completed the Modified Mini-Mental State Examination (3MS) and the Digit Symbol Substitution Test (DSST) at baseline and at certain intervals over the following 10 years. They also had their HbA1c levels measured at baseline, and 4, 6, and 10 years later.

At baseline, 23.4% of patients had diabetes, and 159 people, or 5.2%, developed diabetes over the course of the study.

The researchers found that at baseline, those with diabetes had significantly lower scores on both tests of cognitive function than those without the condition (P=0.001 for both), and adjusting for age, race, sex, and education didn't change the results.

After 9 years, Yaffe and colleagues saw greater cognitive decline among those who had diabetes at baseline than those who didn't have diabetes (P=0.008 for 3MS, P=0.001 for DSST), and the results remained the same in multivariate models.

Patients who developed diabetes over the course of the study tended to score between the other two groups, but they weren't statistically different from the group without diabetes, the researchers said.

They also found that among patients who were diabetic at baseline, higher HbA1c levels were associated with lower mean cognitive scores. Over about 3.5 years, patients with a mid-range (7% to 8%) or high (8% or up) HbA1c level had significantly lower mean cognitive scores than those with a low level (7% or less) (P=0.003 for 3MS, P=0.04 for DSST).

After adjustment, the findings remained significant for 3Ms scores, but not for DSST scores, they reported.

Yaffe and colleagues said the findings are consistent with prior studies, and suggest that the severity of diabetes may contribute to accelerated cognitive aging.

Some of the mechanisms linking diabetes with cognitive decline include greater inflammation and microvascular disease, as well as the fact that patients with diabetes are at risk of renal disease, depression, stroke, hypertension, hyperlipidemia, and cardiovascular disease -- all of which can impair cognitive performance.

Thus, delaying or preventing the onset of diabetes may be beneficial for maintaining cognitive function in older adults, the researchers wrote.

The study was limited by the small number of patients who developed diabetes over the course of the study, and by a lack of information on duration or severity of diabetes for patients with the condition at baseline.

Other limitations included only two measures of cognitive function, small differences on the cognitive function tests between groups, and inability to evaluate HbA1c well over time due to use of different assays during different years.

Still, the researchers said further studies are needed to determine whether early diagnosis and treatment of diabetes diminishes the risk of developing cognitive impairment.

• A prospective study over 9 years found an association between having diabetes at baseline and cognitive decline among older adults without dementia.
• Explain that those with higher HbA1c as the study progressed also had more significant cognitive decline.
• Note that, while the study found an association between diabetes and mental decline, it did not show a cause-and-effect relationship.

Yaffe K, et al "Diabetes, glucose control, and 9-year cognitive decline among older adults without dementia" Arch Neurol 2012; DOI: 10.1001/archneurol.2012.1117.