Cognitive function was assessed at baseline and reassessed every two years.
People with high blood sugar may experience steep long-term cognitive decline than their healthy peers, a study suggests.
The study of about 5,000 older people in the UK has shown that efforts to delay the onset of diabetes and/or control blood sugar levels might prevent subsequent progression of brain function decline.
While other studies have linked cognitive decline with diabetes, the new study is one of the largest to establish the direct relationship between the levels of glycated haemoglobin (HbA1c) - a measure of overall blood sugar control - and subsequent risk of cognitive decline, researchers said.
The team from Imperial College London in the UK and Peking University in China used data from the English Longitudinal Study of Ageing (ELSA) for their analysis.
Cognitive function was assessed at baseline and reassessed every two years. Computer modelling was then used to establish any possible associations.
The study contained 5,189 participants (55 per cent women, mean age 66 years) with baseline HbA1c levels ranging from 15.9 to 126.3 mmol/mol (3.6-13.7 per cent).
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Current cut-offs for defining diabetes using HbA1c are 6.5 per cent and above, researchers said.
The mean follow-up duration was eight years and the mean number of cognitive assessments was five.
The analysis revealed that a one 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 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, researchers found.
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, researchers said.