HbA1c levels above 9% may be associated with higher dementia risk

A cohort study found higher dementia risk among type 2 diabetes patients ages 50 years and older whose HbA1c levels were usually in the 9% to 10% or 10% and above range compared to those with tighter glycemic control.

Dementia risk was highest among adults with average HbA1c levels of 9% or more, a study found.

Researchers conducted a cohort study in a northern California integrated health care system, including 253,211 patients with type 2 diabetes who were ages 50 years or older during the study period of January 1996 to September 2015. HbA1c level measurements were categorized as less than 6%, 6% to less than 7%, 7% to less than 8%, 8% to less than 9%, 9% to less than 10%, and 10% or more. Dementia diagnosis was based on ICD-9 codes. Results were published April 17 by JAMA Neurology.

Patients with more than half of their recorded HbA1c levels at 9% to less than 10% or 10% or above had significantly greater risk of dementia compared with those who did not reach these levels as often (adjusted hazard ratios [aHRs], 1.31 [95% CI, 1.15 to 1.51] and 1.74 [95% CI, 1.62 to 1.86], respectively). Having more than half of one's HbA1c levels in the ranges of less than 6%, 6% to less than 7%, and 7% to less than 8% was associated with reduced risk of dementia compared to having higher levels (respective aHRs, 0.92 [95% CI, 0.88 to 0.97], 0.79 [95% CI, 0.77 to 0.81], and 0.93 [95% CI, 0.89 to 0.97]).

The authors noted that it's important that the study did not find a significant increase in dementia risk at moderately higher HbA1c levels, as more relaxed glycemic control has been recommended by groups including the American Geriatrics Society, the Department of Veterans Affairs, and ACP for older patients with multiple comorbidities, poor health, or limited life expectancy.

The study lacked information on the age of diabetes onset, duration of diabetes before patients enrolled in the health care system, or HbA1c measurements earlier in life, “which would result in an underestimate of the association of cumulative exposure to HbA1c thresholds with dementia hazard if we assume earlier glycemic control was associated with dementia risk,” the authors said.

They noted that more studies are needed before these findings can be fully implemented in clinical practice. “Mean glycemic control and variation in glycemic control are different constructs, and it is unclear whether they are complementary or if one should be given priority over the other at the individual patient level,” the authors wrote, adding that “weighing the risks of attempting to lower the mean HbA1c concentration if it contributes to greater glycemic variability remains in the realm of an informed conversation between clinician and patient.”