Rates of long-term cognitive decline are steeper in those who have diabetes compared with people with normal blood sugar control, according to a new study published in the journal Diabetologia.
A person performs a glucose screening. Image credit: Sgt. Jessica A. DuVernay, U.S. Army.
The study, led by Imperial College London researchers, is one of the largest to establish the direct relationship between HbA1c (levels of glycated hemoglobin, a measure of overall blood sugar control) and subsequent risk of cognitive decline.
“Our study provides evidence to support the association of diabetes with subsequent cognitive decline. Moreover, our findings show a linear correlation between circulating HbA1c levels and cognitive decline, regardless of diabetic status,” the scientists said.
They used data from wave 2 (2004-2005) to wave 7 (2014-2015) of the English Longitudinal Study of Ageing (ELSA) for the analysis.
Cognitive function was assessed at baseline (wave 2) and reassessed every 2 years at waves 3-7. Computer modeling was then used to establish any possible associations.
The study comprised 5,189 participants (55.1% women, mean age 65.6 years) with baseline HbA1c levels ranging from 15.9 to 126.3 mmol/mol (3.6–13.7%). Current cut-offs for defining diabetes using HbA1c are 6.5% and above. The mean follow-up duration was 8.1 years and the mean number of cognitive assessments was 4.9.
The analysis revealed that a 1 mmol/mol increase in HbA1c was significantly associated with an increased rate of decline in global cognitive z scores, memory z scores and executive function z scores, all signs of cognitive function decline.
While cognitive function declined with age (as expected) in all of the participants, whether diabetic or not, compared with participants with normal blood sugar control, the global cognitive decline associated with prediabetes and diabetes was significantly increased.
Similarly, memory, executive function and orientation z scores showed an increased rate of cognitive decline with diabetes.
Significantly, the rate of cognitive decline was directly linked to a person’s HbA1c status (with higher HbA1c meaning higher rate of cognitive decline), whether or not they were diabetic according to their HbA1c status at baseline.
“Future studies are required to determine the long-term effects of maintaining optimal glucose control on cognitive decline in people with diabetes,” the study authors said.
“Our findings suggest that interventions that delay diabetes onset, as well as management strategies for blood sugar control, might help alleviate the progression of subsequent cognitive decline over the long-term.”
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Fanfan Zheng et al. HbA1c, diabetes and cognitive decline: the English Longitudinal Study of Ageing. Diabetologia, published online January 28, 2018; doi: 10.1007/s00125-017-4541-7
