Spotlight on dementia and glycemic control

Prediabetes and diabetes were associated with development of dementia in a South Korean study, and poorly controlled diabetes was tied to increased risk of incident cognitive impairment or progression to dementia in a Swedish study.

Two recent studies looked at the relationship between diabetes and dementia, especially in the early stages of each condition.

The first study, published by Diabetes Care on Oct. 28, used information on 8,400,950 people in South Korea who were ages 40 years or older and underwent a health examination in 2009 to 2010. During follow-up through 2016, dementia developed in 4.2% and was more common in those with any elevation in glucose levels during the initial examination. Compared with normoglycemia, the hazard ratio (HR) for dementia was 1.01 (95% CI, 1.01 to 1.02) with impaired fasting glucose, 1.45 (95% CI, 1.44 to 1.47) with new-onset diabetes, 1.32 (95% CI, 1.30 to 1.33) with diabetes for less than five years, and 1.62 (95% CI, 1.60 to 1.64) with known diabetes for at least five years. Patients with a history of ischemic stroke and normoglycemia had a higher risk for incident dementia than patients with diabetes without ischemic stroke (HRs 1.90 [95% CI, 1.86 to 1.95] and 1.46 [95% CI, 1.44 to 1.47], respectively). “To the best of our knowledge, this study is the largest to find that dementia incidence was proportional to severity or duration of exposure to hyperglycemia and comorbidities rather than simply examining the presence of diabetes,” the authors wrote. “At least in terms of dementia prevention, prediabetes should no longer be considered an entirely benign condition.” They recommended that prediabetes interventions be considered for dementia prevention.

The other study, published by Alzheimer's & Dementia on Oct. 12, looked at two cohorts of older adults in Sweden, 1,840 who were cognitively healthy and 682 who had cognitive impairment-no dementia (CIND) at baseline. Over 12 years of follow-up, compared to participants with normoglycemia, patients with diabetes that was not well controlled (HbA1c level ≥7.5%) had double the risk of developing CIND (HR, 2.01; 95% CI, 1.13 to 3.58) and triple the risk of progressing to dementia if they already had CIND (HR, 2.87; 95% CI, 1.20 to 6.85). Well-controlled diabetes did not carry a significantly increased risk of CIND or dementia, which “suggests that it is the degree of hyperglycemia, rather than diabetes itself, that negatively impacts cognitive health,” the study authors noted. They also noted that systemic inflammation appeared to contribute to the diabetes-associated dementia risk. Having comorbid diabetes and heart disease was associated with increased risk of CIND and dementia. “Our findings highlight poorly controlled diabetes and its cardiovascular complications as ideal targets for interventions to prevent cognitive impairment or arrest its progression to dementia—conditions for which no curative treatment is available,” the authors concluded.