A1c Time in Range and Risk for Dementia in Older Adults
by IDS Director of Intensive Diabetes Management, Tavia Vital
A study by Underwood PC, et al, published August 2nd, 2024, in the Journal of the American Medical Association showed a strong correlation between keeping a high Time in Range of the individualized A1C results for older adults correlated with a lower risk of Alzheimer disease and related dementias (ADRD) over a 10-year period.
While we typically focus on Time in Range (TIR) related data with Continuous Glucose Monitoring (CGM) to evaluate how well someone’s glucose management is going, in some cases there is no CGM data available. A study published in May 2023 by Goldberg, et al, described a linear correlation between TIR and A1c values. The study, titled “Correlation Between Time in Range and HbA1c in People with Type 2 Diabetes on Basal Insulin: Post Hoc Analysis of the SWITCH PRO Study” stated:
A 5% increase in TIR corresponded to estimated decreases in HbA1c of -0.4% (-4.4 mmol/mol),-0.7% (-7.7 mmol/mol), and -0.1% (-1.1 mmol/mol) in the full cohort, baseline HbA1c7.5% (58.5 mmol/mol) subgroup, and baseline HbA1c <7.5% (<58.5 mmol/mol) subgroup, respectively.
This linear correlation allowed the researchers to extrapolate an option they titled, “the HbA1c Time in Range.” A1c TIR is especially useful when CGM may not be a part of a patient´s usual diabetes self-management care plan. The HbA1c TIR is the percentage of time a person keeps their A1c within a goal range of A1c levels over a three-year period.
The research team hypothesized that keeping an A1c at target and relatively stable over a range over of the time would reduce the risk for ADRD. Summarized in the study titled, “Glycated Hemoglobin A1c Time in Range and Dementia in Older Adults with Diabetes,” the researchers reviewed data for 374,?021 US Veterans who met the inclusion criteria.
The baseline characteristics of the study include an average entry age of 73 years and identifying as:
- Male: 99%
- Female: 1%
- White: 87%
- Black: 11%
- Hispanic: 1%
- Asian: 0.4%
- Other: 1%
Importantly, they found with an unadjusted analysis, an A1c TIR of 80% had the lowest risk for ADRDs. They found the highest risk for ADRD occurred in people who spent between 0 and 20% of A1c TIR.
After adjusting for covariates such as age, sex, hypoglycemia, Diabetes Complication Severity Index score, and other covariates (see additional details found in Table 3 here) the study showed:
- People who spent more than 60% of A1c Time Below Range (TBR) had the highest incidence of ADRDs compared to an A1c TIR of 60% or more
- The lowest incidence of ADRD occurred in people who spent greater than or equal to 60% A1c TIR
- There was a minimal increased risk for ADRD in people who had an A1c Time Above Range of greater than 60%
- Establish an older person´s individualized A1c goal based on age, life expectancy, and co-morbidities.
- Ensure the person with diabetes keeps their A1c relatively stable and in the individualized range over time.
- Ensure the person does not have significant amounts of time below their individualized A1c target range.
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