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Poor blood glucose control linked to long-term cognitive decline

Deterioration associated with baseline HbA1c status irrespective of diabetes diagnosis

Caroline White

Friday, 26 January 2018

Poor blood glucose control is linked to long-term cognitive decline, finds a study* of some 5000 older people in the UK, published in Diabetologia, the journal of the European Association for the Study of Diabetes (EASD).
Greater efforts to better control blood glucose levels might stave off subsequent progressive deterioration, the findings suggest, as a high HbA1c at the start of the study was associated with greater deterioration, irrespective of whether an individual had diabetes.
The study draws on data from waves two (2004–2005) to seven (2014–2015) of the English Longitudinal Study of Ageing (ELSA).
Cognitive abilities were assessed at baseline (wave two) and then every two years at waves 3–7. Computer modelling was then used to establish any possible associatIn all, 5189 participants (55% women, mean age 66 years) with baseline HbA1c levels ranging from 15.9-126.3mmol/mol (3.6–13.7%) were included in the study. Current thresholds for defining diabetes using HbA1c are 6.5% and above.
The average monitoring period was eight years while the average number of cognitive assessments was five.
The analysis revealed that a 1mmol/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.
The results remained significant even after taking account of a range of potentially influential factors: age, sex, total cholesterol, HDL (good) cholesterol, triacylglycerol, high-sensitivity C-reactive protein, body mass index (BMI), education, marital status, depressive symptoms, current smoking, alcohol consumption, high blood pressure, heart disease, stroke, chronic lung disease and cancer.
While cognitive function declined with age, as would be expected, in all of the participants, the global cognitive decline associated with pre-diabetes and diabetes was significantly greater than among those with normal blood glucose levels.
Similarly, memory, executive function, and orientation z scores declined faster among those with diabetes. Significantly, the rate of cognitive decline was directly linked to a person’s HbA1c status at baseline (with higher HbA1c meaning higher rate of cognitive decline), irrespective of whether they were diabetic.
“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 authors write.

“Future studies are required to determine the long-term effects of maintaining optimal glucose control on cognitive decline in people with diabetes…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.”

*Zheng, F., Yan, L., Yang, Z. et al.. HbA1c, diabetes and cognitive decline: the English Longitudinal Study of Ageing. Diabetologia 2018. doi:10.1007/s00125-017-4541-7

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