Dementia is a broad term used to describe a decline in mental ability that is severe enough to interfere with daily life. It is not a specific disease, but rather a group of symptoms caused by various diseases or conditions. Diabetes, especially when poorly controlled, has been linked to an increased risk of certain types of dementia, including Alzheimer’s disease and vascular dementia.
The Link Between Diabetes and Dementia
Several studies have found that people with diabetes, especially type 2 diabetes, are at higher risk of eventually developing dementia. For example, a 15-year study published in the New England Journal of Medicine found that older adults with diabetes had a 65% higher risk of developing dementia compared to those without diabetes. The risk was even greater for people who used insulin – they were over 3 times more likely to develop dementia.
The connection is likely complex, involving several aspects of how diabetes impacts the body and brain over time. Here are some of the leading theories behind why diabetics may be more prone to dementia:
- Chronic high blood glucose levels – High levels of blood glucose (sugar) can damage blood vessels and nerves over time. This can reduce blood flow and oxygen to the brain.
- Vascular disease – Diabetes significantly increases the risk of vascular diseases like stroke, which can lead to vascular dementia or make Alzheimer’s worse.
- Insulin resistance – Type 2 diabetes is characterized by insulin resistance, which has been linked to brain changes that can increase dementia risk.
- Advanced glycation endproducts (AGEs) – High blood sugar leads to production of AGEs, proteins that are harmful to blood vessels and nerves in the brain.
- Increased inflammation – Chronic inflammation is common in diabetes and may promote dementia.
Mechanisms Behind the Link
Let’s explore some of the key mechanisms that help explain the connection between diabetes and increased dementia risk:
One of the most well-established links is the fact that diabetes significantly increases the risk of various vascular diseases, including stroke, heart disease, and atherosclerosis (hardening of artery walls). These diseases damage blood vessels, reducing blood flow to the brain. Reduced blood flow deprives brain cells of vital oxygen and nutrients, which can lead to cell death. This vascular damage is a major cause of vascular dementia.
People with diabetes also tend to have higher rates of high blood pressure, high cholesterol, and obesity – all additional risk factors for vascular disease. Vascular disease and vascular dementia may also contribute to Alzheimer’s disease progression.
Type 2 diabetes involves insulin resistance, meaning the body’s cells become less responsive to insulin over time. Insulin resistance in the brain may cause changes that promote dementia.
For example, insulin enhances certain enzymes that help break down beta-amyloid proteins. Beta-amyloid clumps into plaques, one of the hallmarks of Alzheimer’s. With insulin resistance, less amyloid is cleared away, potentially contributing to plaque accumulation.
Insulin also helps regulate neurotransmitters like acetylcholine. Lower acetylcholine is linked to dementia symptoms. Changes in insulin signaling have also been shown to lead to inflammation and tau protein tangles, the other key Alzheimer’s brain change.
AGEs (Advanced Glycation Endproducts)
High blood sugar promotes formation of molecules called AGEs. AGEs form through a process called glycation, when sugars like glucose bond to proteins and lipids, changing their structure and function. AGEs can damage blood vessels, nerves, and other tissues throughout the body, including the brain.
The accumulation of AGEs may directly inflict damage or induce inflammation in the brain over many years, leading to dementia. AGEs have specifically been found in the beta-amyloid plaques and neurofibrillary tangles that are hallmarks of Alzheimer’s disease.
Chronic inflammation appears to be a key mechanism linking diabetes to dementia. People with diabetes tend to have higher levels of inflammatory cytokines like interleukin-6 (IL-6) and C-reactive protein (CRP). Inflammation promotes damage to blood vessels and brain cells.
Inflammatory cytokines may also impact signaling of insulin and amyloid proteins, exacerbating insulin resistance and amyloid clumping. Long-term use of anti-inflammatory medications has been associated with a reduced risk of dementia, especially among diabetics.
High blood glucose levels can lead to oxidative stress, an imbalance between free radicals and antioxidants in the body. Oxidative damage to lipids, proteins, and DNA occurs more readily in the presence of uncontrolled diabetes. Oxidative stress and free radical damage is a contributor to brain aging and neurodegeneration.
Types of Dementia More Common in Diabetics
While many types of dementia can occur in people with diabetes, two major types are particularly increased:
Vascular dementia is cognitive impairment caused by cerebrovascular disease that damages the blood supply to parts of the brain. It is sometimes termed “mini-strokes” when caused by multiple infarcts or blockages of small vessels. As discussed earlier, diabetics are at high risk for vascular disease. Vascular dementia may occur alone or alongside Alzheimer’s dementia.
Alzheimer’s disease is the most common cause of dementia overall. It involves the hallmark brain changes of beta-amyloid plaques and tau tangles. Several major studies have found diabetes increases risk of Alzheimer’s dementia by 50-100%. Insulin resistance and inflammation typically start years before any memory problems appear, supporting the link between diabetes and Alzheimer’s.
Other Factors That Increase Dementia Risk
While diabetes is an important risk factor for dementia, several other factors also come into play. Having multiple risk factors will compound the risk. Here are some additional factors more common in diabetics that also promote dementia:
- Physical inactivity
- High blood pressure
- High cholesterol
- Sleep apnea
- Genetic risk factors like APOE4 allele
The development of dementia and Alzheimer’s in particular is impacted by a complex interaction of age, genetics, lifestyle factors, and chronic diseases like diabetes.
Poor Blood Sugar Control Worsens Risk
Multiple studies indicate that the risk of dementia appears to be higher when type 2 diabetes is poorly controlled compared to well-managed:
- In a study following over 2,000 people for 15 years, those with poorly controlled diabetes had a nearly 3-fold increased risk of dementia compared to those with good control.
- Having high A1C levels (over 7%) is associated with impaired cognitive function and greater brain atrophy.
- Large fluctuations in blood sugar may also predict higher dementia risk.
This highlights the importance of controlling diabetes through medication, diet, exercise, and blood sugar monitoring. Sticking to prescribed treatment helps reduce complications.
Can Dementia Lead to Diabetes?
While diabetes clearly raises dementia risk, researchers have also been studying whether dementia could reciprocally increase the risk of diabetes. There are a few reasons why this link is plausible:
- Alzheimer’s disease and vascular dementia can damage the brain regions involved in metabolizing glucose and regulating insulin, potentially leading to diabetes.
- Some of the risk genes for Alzheimer’s disease also appear to impact diabetes risk.
- Behavior changes from dementia can make managing medications, diet, exercise, and blood sugar testing more difficult.
A meta-analysis of 16 studies found that dementia increased the relative risk of developing diabetes by 39%. While more research is still needed, it’s possible that dementia contributes to diabetes, and this interplay forms a vicious cycle.
Preventing Dementia in Diabetics
There are several steps diabetics can take to reduce the increased risk of developing dementia:
- Control blood glucose levels through diet, exercise, medications, regular testing, and working closely with your doctor.
- Monitor and treat high blood pressure if present.
- Check cholesterol levels and use statins as needed.
- Quit smoking and consume alcohol only in moderation.
- Treat sleep apnea if present.
- Stay mentally and socially active to strengthen cognitive reserves.
- Consider using cinnamon, curcumin, vitamin D, fish oil and other supplements that may benefit both diabetes and brain health.
Beyond managing diabetes itself, many healthy lifestyle choices like staying active, eating well, lowering stress, and engaging in brain-stimulating activities apply to all looking to prevent cognitive decline with age.
Diabetes, especially type 2 diabetes, significantly raises the risk of dementia including Alzheimer’s disease and vascular dementia. The mechanisms behind this heightened risk are complex, but involve vascular disease, insulin resistance, inflammation, oxidative stress, and AGEs. Controlling blood sugar and related health factors appears key to reducing, though not eliminating, the excess dementia risk. More research is still needed on preventing and treating dementia in people with diabetes.