Risk for specific types of dementia varies in people with diabetes

People with type 2 diabetes (T2D) have a higher risk for developing vascular dementia than Alzheimer disease—especially those with poor glycemic control. In short, while diabetes is known to be associated with an increased risk for dementia, there is increasing evidence that the risk varies by the type of dementia, according to Dr. Naveed Sattar, a professor of cardiovascular and medical sciences at the University of Glasgow. He was coauthor of a large population study conducted by researchers from Sweden and the U.K. which investigated the relationship between diabetes and types of dementia. Findings were published in Diabetes Care. “We simply do not have enough studies on the links between these two important conditions, important now more than ever as rates of both appear to be rising,” he said. The topic is important for a number of reasons. One is that more people with diabetes are living longer, meaning more will develop other age-related diseases including cognitive decline and dementia. T2D accounts for 3.2% of all dementia cases. And previous studies show that dementia risk in individuals with T2D is 1.5 to 2.5 times greater than what is seen in people with no diabetes. “It is critical to improve our understanding of the links between type 2 diabetes and dementia and its subtypes,” the researchers wrote. However, the risk for Alzheimer disease was lower in the study cohort, which was a surprise, Dr. Sattar told the Medical Post. Read: Blood test for detecting early Alzheimer’s disease shows promise While some studies suggest that up to one-third of all dementia cases may be attributable to modifiable risk factors, including T2D, there is little detail on how much of the association between T2D and subtypes of dementia could be explained by modifiable factors—including glycemic control. Using data from the Swedish National Diabetes Register, the researchers identified all patients with T2D. They were divided into three groups: patients aged 40 years or over at the time of diagnosis and treated with insulin only; patients of any age 18 years and over, treated with diet only or oral hypoglycemic agents combined with diet; and patients 18 and over, treated with insulin combined with oral hypoglycemic agents. Each patient was matched to four controls without diabetes identified from the Swedish Total Population Register. Medical history including metabolic data, and sociodemographic details were attained. Data were from 1998 through 2013. A total of 378,299 patients with T2D and 1,886,022 age- and sex-matched control subjects were included. They had a mean age of 64 years, and 55% were male. The T2D patients generally had a lower income and lower education levels than controls. Average follow-up was 7.03 years. Dementia developed in 11,508 of the T2D patients (2,320 Alzheimer disease; 2,155 vascular dementia, and 7,033 nonvascular dementia). In comparison, 52,244 control subjects developed dementia (12,834 Alzheimer disease; 7,629 vascular dementia, and 31,781 nonvascular dementia). Patients with T2D were found to have a 34% higher risk for vascular dementia and 10% higher risk of nonvascular dementia than the controls without diabetes. This was independent of sex, income, education, country of birth and existing cardiovascular disease. However, the risk for Alzheimer disease was 6% lower in patients with T2D than in control subjects. But the researchers noted that those with T2D generally died earlier than control subjects, “which reduced the probability of Alzheimer disease developing in patients with type 2 diabetes.” The distinction between different times of dementia is important given they may have different risk factors, Dr Sattar said. The study also a linear association between HbA1c concentration and the risk for dementia. But the magnitude of the association differed by subtype of dementia, and the risk was strongest for vascular dementia. When compared to patients with HbA1c under 53 mmol/mol, patients who had HbA1c of 87 mmol/mol or more had a 93% higher risk for vascular dementia. This finding reiterates that keeping good glucose control will not only protect the heart, eyes and kidneys but also the brain in terms of stroke and cognitive performance, the study said. Associations were also seen with additional risk factors linked to vascular dementia in those with T2D. These included blood pressure, years with diabetes, existing CVD, BMI, and glomerular filtration rate. For nonvascular dementia the top risk factors after age were BMI and years with diabetes (2.0%). The study concluded that “poor glycemic control is associated with a higher risk of dementia in a dose-response manner, primarily vascular and nonvascular dementia.” The size of the study was helpful because it “has the statistical power to observe associations that we may not be able to identify in smaller cohorts,” said Nicole Anderson, PhD, from the Rotman Research Institute, and a professor of psychology and psychiatry at the University of Toronto. She was not involved in the study. And while the finding relating to Alzheimer’s disease was intriguing, it does not show that T2D is protective. “The authors are careful to point out that people with type 2 diabetes died earlier than those without type 2 diabetes, and so some of the 97% of people with type 2 diabetes who did not develop dementia during the period of observation may have died before they would have otherwise developed Alzheimer’s disease. The best way to interpret these results are that in the shorter lifespan of those with T2D, if they develop dementia, it is more likely to be vascular dementia than Alzheimer’s disease,” she said. She also noted that people are often clinically diagnosed with the most likely cause of dementia and that people with T2D tend to have other metabolic conditions such as hypertension, high cholesterol, and obesity that increase the risk of neurovascular disease. This sways doctors to diagnose people as having vascular dementia. “Yet, in the vast majority of cases, people have mixed dementia, with mixed Alzheimer’s disease -vascular dementia being the most common. This means that the majority of those diagnosed with vascular dementia in this study also likely had Alzheimer’s disease pathology,” she said.

Risk for specific types of dementia varies in people with diabetes

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