What's the relationship between diabetes and dementia? - Harvard Health

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What’s the relationship between diabetes and dementia? - Harvard Health

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Mind & Mood

July 12, 2021

Due to increasing rates of obesity, inactivity, and an aging population, type 2 diabetes is more prevalent in our society than ever before. In high-income countries, death from diabetes dropped from 2000 to 2010, but then increased from 2010 to 2016 — leading to an overall 5% increase in premature deaths since 2000. Particularly troubling is that type 2 diabetes is now being seen frequently in children, due to their obesity and inactivity.

It has been known for many years that type 2 diabetes increases your risk for strokes and heart disease. More recent studies have shown that diabetes also increases your risk of dementia. What has not previously been investigated, however, is whether the age of onset of diabetes makes a difference in your risk of developing dementia.

New research about age at diabetes onset and the risk of developing dementia

A newly published study examined the association between age of onset of diabetes and the development of dementia using a large, ongoing cohort study. The cohort was established in 1985–88 among 10,308 employees aged 35 to 55 years (33% women, 88% white) in London-based government departments. Data on diabetes exposure, including fasting glucose and the Finnish Diabetes Risk Score, were obtained at ages 55, 60, 65, and 70. (The Finnish Diabetes Risk Score includes age, family history of diabetes, personal history of elevated blood glucose, fruit and vegetable consumption, blood pressure medication, physical activity, body mass index, and measured waist circumference.)

Dementia due to any cause was the primary outcome measure. In addition to diabetes, they also examined the effects of age, sex, race, smoking, alcohol consumption, physical activity, fruit and vegetable consumption, high blood pressure, body mass index, coronary heart disease, heart failure, stroke, medications, and the Alzheimer’s risk factor gene, apolipoprotein E.

The long-term effects of diabetes on dementia

From 1985 to 2019, 1,710 cases of diabetes and 639 cases of dementia were recorded. For every 1,000 people, examined yearly, the rates of dementia were 8.9 in those without diabetes at age 70. Comparable rates of dementia for those with diabetes were 10.0 for those with onset up to five years earlier, 13.0 for six to 10 years earlier, and 18.3 for more than 10 years earlier. These striking results clearly show that the earlier you develop diabetes, the greater your risk is for developing dementia.

How diabetes can lead to dementia

There are multiple reasons why years of type 2 diabetes may lead to dementia. One reason is related to the effects that diabetes has on the heart, as heart health is related to brain health. Heart disease and elevated blood pressure are both associated with strokes that, in turn, can lead to dementia. However, strokes do not appear to be the complete answer, as some studies found that diabetes led to an increased risk of dementia even when strokes were controlled for.

Another factor relates to the episodes of hypoglycemia that commonly occur in diabetes. Although tight control of blood sugars has been proven to reduce the long-term risks of heart disease and strokes, tight control can also lead to hypoglycemia, memory loss, and dementia. Here, the reason is likely because low blood sugars are known to damage the hippocampus — the memory center of the brain.

One of the more intriguing hypotheses is that diabetes directly causes Alzheimer’s disease. Indeed, Alzheimer’s disease has even been called "type 3 diabetes" because of shared molecular and cellular features among diabetes and Alzheimer’s. For example, insulin plays a critical role in the formation of amyloid plaques, and insulin is also involved in the phosphorylation of tau, which leads to neurofibrillary tangles. In other words, whereas insulin resistance in the body can lead to type 2 diabetes, insulin resistance in the brain can lead to the plaques and tangles of Alzheimer’s disease.

Reduce your risk of diabetes and dementia

The good news is that you can reduce your risk of type 2 diabetes — and your risk of dementia. Speak with your doctor today about whether the following lifestyle modifications would be right for you. Note that these life changes are helpful even if you have a diagnosis of diabetes or prediabetes.

Lastly, social activities, a positive attitude, learning new things, and music can all help your brain work at its best and reduce your risk of dementia.

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