Diabetes Complications

Diabetes And Alzheimer’s Risk: Scientists Explore The Link

You will have certainly heard of both diabetes and Alzheimer’s disease, but did you know they were thought to be fundamentally linked?

Type 3 diabetes is a term that is sometimes used to describe Alzheimer’s disease, and there is growing evidence about how this most common cause of dementia is linked with diabetes.

In this article, we will explore the links between Alzheimer’s disease and diabetes, as well as looking at the symptoms, diagnosis criteria, and treatment options.

What is type 3 diabetes and the link between diabetes and Alzheimer’s?

Before we move on to look at the relationship between the two diseases, including the symptoms and treatment of type 3 diabetes, it is essential to explore some of the backgrounds.

While the term ‘type 3 diabetes’ appears commonly in literature, it has several different uses. Major diabetes charity Diabetes UK refers to type 3 c diabetes as being a unique type of diabetes that develops because of damage to the pancreas.

This can happen for a few different reasons. You can only get Type 3c diabetes because of an illness or condition that affects the pancreas, such as pancreatitis or pancreatic cancer.

While type 3c diabetes has been identified as a (less common) type of diabetes, ‘type 3 diabetes’ is not an officially recognized term.

Yet, there has been a significant amount of research conducted into the link between diabetes and Alzheimer’s disease. It was proposed in 2008 by two researchers, Suzanne M. de la Monte and Jack R. Wands, that Alzheimer’s itself could be referred to as type 3 diabetes.

As already mentioned, there is growing evidence in this field. The neurodegeneration that characterizes Alzheimer’s disease is thought to be linked with insulin deficiency and resistance.

The type of insulin resistance that occurs in Alzheimer’s, and is a key feature of the disease, happens specifically in the brain. De la Monte and Wands reported in their research that when neurons in the blood-brain barrier become unable to respond to insulin, or the insulin is deficient, this leads to the cognitive decline seen in Alzheimer’s.

While it may seem that the researchers have identified clear justifications for why Alzheimer’s disease is type 3 diabetes, there are several other possible mechanisms.

One 2014 review study highlighted the metabolic links between Alzheimer’s disease and type 2 diabetes and identified that these may also lead to an increased risk of this specific type of marked a decline in cognitive function. The risk factors identified included:

  • Obesity

  • Metabolic syndrome, which includes high blood pressure, elevated blood lipid and systemic inflammation

  • It is not fully understood which mechanisms link to type 2 diabetes to Alzheimer’s disease, but it is thought to include the above in addition to hyperglycemia and insulin resistance.

  • Other mechanisms that have been proposed include impaired insulin growth factor (IGF) signaling, glucose toxicity caused by damaged beta cells, cerebral vascular accident (stroke), and inflammation of the blood vessels (vascular inflammation).

While’ type 3 diabetes’ is not recognized as an official category of diabetes, there is no denying the link between the characteristics of diabetes and Alzheimer’s disease.

As is often the case, more research is needed. For this article, when referring to type 3 diabetes, we will be discussing insulin resistance that affects the brain, and as such, leads to Alzheimer’s disease.

Causes and risk factors for type 3 diabetes

Unsurprisingly, type 3 diabetes shares causes and risk factors with the more commonly recognized type 2 diabetes. In this large scale study, people with type 2 diabetes were identified as being at a higher risk of developing Alzheimer’s disease.

This particular study examined data from 14 studies, covered which over 2 million individuals and more than 102,000 people living with dementia.

Among the significant conclusions were the findings that people who had type 2 diabetes were at an increased risk of developing dementia. This increased risk was substantial, at around 60%. Women were found to be more at risk of vascular dementia than men, but this was not the case for nonvascular dementia.

Risk factors for type 2 diabetes are well documented. Currently, in the UK, around 90% of people with diabetes are clinically defined as being overweight or obese. Other risk factors include a socioeconomic class (as poverty levels increase, so does the risk of diabetes), age, gender, and family history.

Symptoms of type 3 diabetes

You can consider the symptoms of type 3 diabetes as the same as those characteristics of early dementia. Dementia is not a disease itself, but rather, is the name for a set of symptoms.

Dementia occurs due to damage to the brain from other diseases, such as Alzheimer’s disease. In fact, Alzheimer’s disease is the most common cause of dementia. Symptoms of Alzheimer’s disease include:

  • Memory loss

  • Difficulties with thinking or problem solving

  • Language difficulties

  • Newly arising problems doing familiar things, e.g., following well-known routes or keeping hold of possessions

Diagnosis of type 3 diabetes

There are no certain tests for diagnosing type 3 diabetes. If you have a confirmed diagnosis of type 2 diabetes, you must get a treatment plan agreed, and if necessary, take the medication prescribed for you.

Alzheimer’s disease can only be accurately diagnosed following a post-mortem. Such examinations would be looking for significant neurofibrillary ‘tangles’ and neurotic ‘plaques’ that are a hallmark of Alzheimer’s disease.

In order to confirm a diagnosis of Alzheimer’s disease, these tangles and plaques would also be present alongside amyloid precursor protein and amyloid-β (APP-Aβ) deposits, which would be present in specific regions of the brain.

Despite this barrier to confirming a definitive diagnosis, a working diagnosis can be made. A working diagnosis of Alzheimer’s disease can be made with the following information/examinations:

  • Testing of cognitive capacity

  • Memory loss testing

  • Clinical observations, which will include medical history and questions such as how the person’s symptoms are affecting their life

Research is now indicating that brain scanning techniques are useful for identifying the likelihood of Alzheimer’s disease. Scans included in the below list can be used as they can reveal atrophy (degeneration) of the brain.

  • Magnetic Resonance Imaging (MRI)

  • Computed Tomography (CT), and

  • Positron Emission Tomography (PET)

These scans are also thought to be useful for identifying the build-up of amyloid deposits, which, as mentioned, are characteristic in Alzheimer’s.

Before investigations into suspected Alzheimer’s, the person’s doctor should aim to rule out any conditions with similarities in symptoms. These may include but are not limited to, infections, depression, and side effects of certain medications.

Treatment

If you have diagnosed type 2 diabetes, you must attend regular medication reviews and follow your treatment plan as advised. Doing so can help you to maintain good blood glucose control, reduce your risk of diabetes complications, and could also lower your risk of brain damage caused by diabetes.

In one 2014 study, 365 older adults living with diabetes mellitus were followed up via the population-based Singapore Longitudinal Ageing Study.

When appropriate adjustments were made for factors such as age, fasting blood sugar levels, and duration of diabetes, it was found that long term treatment with metformin may reduce the risk of cognitive decline. Among those included in the study who took metformin, they were significantly lowered levels of cognitive decline.

In the influential study that lay claim to Alzheimer’s disease being type 3 diabetes, hopeful treatment methods were also explored. Anti-diabetic agents called peroxisome proliferator-activated receptor (PPAR) agonists were given in various concentrations in animal studies, and the effects examined.

This drug approach helped with the treatment of type 3 diabetes in various ways, including preventing brain atrophy and deficits in learning and memory.

Outlook

Put simply; type 3 diabetes is a way of describing insulin resistance that affects your brain, which in turn leads to a diagnosis of Alzheimer’s disease. If you or a loved one has been giving a working diagnosis of Alzheimer’s disease, the outlook will depend on several factors. These include, but are not limited to:

  • The efficiency in which the diagnosis was made

  • The severity of your symptoms and how long your doctor thinks you have been living with the condition

  • The type of diabetes treatment you are on

  • If you are concerned about your diabetes, a diagnosis of Alzheimer’s disease, or the link between the two, you must speak with your doctor. They can carry out a clinical assessment if necessary and advise on treatment and the next stages where needed. As with most medical conditions, it is best for your outlook to start treatment as soon as possible.

Conclusion

Type 3 diabetes has not been recognized as an official form of the overall disease category of diabetes. Yet, it is important to be aware that there is a growing body of research linking diabetes with the characteristics of Alzheimer’s disease, and many experts believe them to be very closely connected.

More research is needed into insulin resistance in the brain to help guide advice on prevention, treatment, and the hope of a cure in the future.

Sources

  1. Li X, Song D, Leng S. Link between type 2 diabetes and Alzheimer’s disease: from epidemiology to mechanism and treatment. Clin Interv Aging. 2015;10:549-560
    https://doi.org/10.2147/CIA.S74042
  2. Alzheimer’s society, United Against Dementia (online). Available at: https://www.alzheimers.org.uk/ accessed on 16/2/20
  3. De La Monte, S, M and Wands, J, R. Alzheimer’s Disease is Type 3 Diabetes – Evidence Reviewed. Journal of Diabetes Science and Technology Volume 2, Issue 6, November 2008
  4. Chatterjee S, Peters SA, Woodward M, et al. Type 2 Diabetes as a Risk Factor for Dementia in Women Compared With Men: A Pooled Analysis of 2.3 Million People Comprising More Than 100,000 Cases of Dementia. Diabetes Care. 2016;39(2):300–307. doi:10.2337/dc15-1588
  5. Australian Alzheimer’s Research Foundation, diagnosing Alzheimer’s (online). Available at: https://alzheimers.com.au/about-alzheimers/diagnosing-alzheimers/ accessed on 18/2/20

 

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