Dementia Risk Increased in Seniors With Newly Diagnosed Diabetes

Veronica Hackethal, MD

August 05, 2015

Seniors with newly diagnosed diabetes may have up to 16% increased risk of dementia, according to a Canadian study published online on July 27 in Diabetes Care.

The study represents the first large, populationwide study in North America to find a link between newly diagnosed diabetes and dementia in seniors.

"Our findings add to a growing understanding that diabetes is an independent risk factor for Alzheimer's disease and vascular dementia," commented first author Nisha Nigil Haroon, MD, PhD, of the University of Toronto, Ontario.

"Severe hypoglycemia, stroke, and vascular disease increased the risk of dementia," she added. "Other aggravating factors include coronary events such as heart attacks, peripheral vascular disease, hypertension, and chronic kidney disease."

Growing research supports a link between diabetes and dementia, with some studies pointing to abnormalities in insulin signaling within the central nervous system. Epidemiology studies have linked diabetes with a 1.5 times higher risk of Alzheimer's dementia and 2.5 times higher risk of vascular dementia. Perhaps for these reasons, some experts have suggested that Alzheimer's disease could be termed "type 3 diabetes," according to background information in the article.

Dementia and diabetes seem to share cardiometabolic risk factors like hypertension, dyslipidemia, and obesity, which complicates the picture. Another school of thought holds that vascular complications of diabetes increase the risk for dementia.

Furthermore, whether diabetes onset in later life affects cognitive decline has also remained an open question. People who develop diabetes in later life may have been healthy for longer, so they may have had less exposure throughout life to risk factors for dementia.

Cerebrovascular Disease Strong Predictor: Stroke Prevention Key

The researchers set out to examine whether incident diabetes is a risk factor for dementia in elderly individuals and also to identify factors that predict a higher risk of dementia in elderly patients with diabetes, as an aid to individualized risk assessment and prevention.

The cohort study used administrative databases from Ontario, Canada, and included seniors aged 66 to 105 years (median age, 73 years) with (n = 225,045), and without (n = 668,070) newly diagnosed diabetes. The researchers matched each patient with newly diagnosed diabetes to three patients without diabetes. They identified new diagnoses of dementia using hospitalization records and outpatient billing claims and followed participants until March 2012.

Over an average follow-up of 7.2 years, 169,114 new cases of dementia were reported. Patients with diabetes had "modestly higher incidence" of dementia, compared with patients without diabetes (2.68 vs. 2.62 per 100 person-years).

After adjustment for baseline cardiovascular disease, chronic kidney disease (CKD), hypertension, and other risk factors, participants with diabetes had 16% higher risk of dementia (hazard ratio [HR], 1.16; women, 1.14; men, 1.20).

Further analyses showed that those with diabetes had increased risk for dementia very early (< 180 days), and this risk remained increased over time (> 180 days) (P < .05 for differences in HR between the very early and late periods). Earlier time periods (30, 60, 90 days) revealed similar results.

The risk of diabetes on dementia increased by about 1% per year. After about 10 years after diagnosis, patients with diabetes had an almost 30% increased risk of dementia.

Having a history of cerebrovascular disease doubled the risk of dementia (HR, 2.03) and proved to be its strongest predictor, and this finding underscores "the importance of stroke prevention," say the researchers.

Patients with a history of peripheral vascular disease (HR, 1.47), CKD (HR, 1.44), and one or more hospital visits for hypoglycemia (HR, 1.73) also had higher risk of dementia, compared with those without.

Analyses controlling for duration of medication exposure found that only statins (HR, 0.78) and calcium-channel blockers (HR, 0.80) were linked to lower risk of dementia. People on insulin had a much higher risk of dementia (HR, 1.74).

"Prevention of vascular events including stroke and avoidance of severe hypoglycemic events might be beneficial in preventing or delaying the onset of dementia," Dr Haroon pointed out. "Potential benefits of good glycemic control may have been partly negated by a greater exposure to severe hypoglycemia."

The authors note that other clinical trials have also suggested that current medications for controlling blood glucose levels, blood pressure, and abnormal lipids do not prevent the development of dementia in seniors with diabetes, suggesting a need for more effective therapies to decrease dementia risk in this population.

The databases used in this study lacked information about certain variables, like actual blood-pressure levels and dementia subtypes, which could have limited the study.

Some patients may have had undiagnosed cognitive decline at baseline, which could muddy the picture about whether diabetes onset is linked to the development of dementia or accelerates its onset.

Primary-care practitioners in Canada also receive incentives for diabetes management and may have been more likely to list diabetes as a diagnosis rather than dementia.

Dr Haroon reports grant support from Amgen. The coauthors report no relevant financial relationships.

Diabetes Care. Published online July 27, 2015. Abstract



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