Glycaemic control influences dementia risk in type 1 diabetes

Lacy ME, Gilsanz P, Karter AJ et al (2018) Long-term glycemic control and dementia risk in type 1 diabetes. Diabetes Care 41: 2339–45

• Despite considerable research into the impact of type 2 diabetes and glycaemic control on cognitive health in older people, less is known about the possible impact of hypoglycaemia and hyperglycaemia on dementia risk in type 1 diabetes.
• Researchers in America followed a large group of patients aged 50 or older who had type 1 diabetes for a mean period of 6.3 years between 1996 and 2015. They obtained data on HbA_1c measurements, comorbidities and dementia diagnoses from patients’ medical records to determine the long-term effects of glycaemic control on cognitive function.
• During the study period, 155 out of the 3,433 participants (4.5%) received a diagnosis of Alzheimer’s disease, non-specific dementia or vascular dementia.
• There was a 45% lower risk of any form of dementia in patients whose HbA_1c measurements were 42–52 mmol/mol (6.0–6.9%) and 53–63 mmol/mol (7.0–7.9%) at least half of the time. In contrast, the risk of developing dementia was 79% higher in patients with HbA_1c measurements ≥75 mmol/mol (≥9.0%) and 65% higher in those with HbA_1c levels of 64–74 mmol/mol (8.0–8.9%) on ≥50% occasions. 
• Cumulative exposure to hypoglycaemia (<42 mmol/mol; <6.0%) resulted in a non-significant increase in the likelihood of being diagnosed with dementia.
• Prolonged exposure to higher HbA_1c levels increased the risk of older people with type 1 diabetes developing dementia by at least twofold; whereas longer exposure to well-controlled glycaemic levels resulted in a 60% reduction in the risk of dementia.
• This study demonstrated an association between chronic hyperglycaemia and decreased cognitive function, complementing the results of studies in children, adolescents and middle-aged people with type 1 diabetes, and in older adults with type 2 diabetes. 

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