**Abstract**

Amyloidosis is a pathological condition which consists on the accumulation of fibrillar proteins. This disease is characterized by extracellular amyloid deposits with a clinical variability depending on the affected tissue. Histopathological evidence indicates that diabetes mellitus type 2 (DM2) induces dementia development, specifically Alzheimer's disease (AD). It has been demonstrated in animal subjects that there is a possibility that aberrant signaling of insulin is a key factor in the induction of the pathology of AD. Recently, there has been newly emerged evidence regarding the relationship between the pathogenesis of Parkinson's disease (PD) and insulin resistance. On another note, the importance of the amyloid deposits in the patients' pancreas with DM2 was evidenced by the discovery of islets of amyloid polypeptide. This has generated interest in the search of the etiopathogenic role of DM2 in the carbohydrates' metabolism. Finally, it is important to consider DM2 as a risk factor essential for the formation of deposits of amyloid-β in patients' brains with dementia.

**Keywords:** diabetes mellitus, insulin resistance, β-amyloid, dementia, Alzheimer's disease, Parkinson's disease

## **1. Introduction**

Dementia has become a worldwide public health issue that currently affects 50 million people. The impact of this disease not only affects the patient himself but also the family and caretaker. This neurodegenerative disorder is characterized by the loss of mental faculties in a progressive and irreversible way which includes language alterations, learning and memory, as well as loss of ethical judgment and social behavior.

Alzheimer's disease is the main cause of dementia, following vascular dementia, senil dementia, frontotemporal dementia, and even Parkinson's disease (P). Age is still the main risk factor to suffer from dementia, even though it is a multifactorial disorder. Smoking, alcoholism, lack of interest in education, and obesity are factors that can increase the risk of developing dementia in an old age [1].

Currently, obesity is another worldwide public health issue. According to the World Health Organization (WHO), the majority of the population lives in countries where overweight and obesity are the cause of more deaths than malnutrition. At the same time, obesity is one of the causes of diabetes mellitus (DM) which is a chronic disease derived from a failure in the pancreas to produce insulin, necessary hormone to process glucose [2].

Studies suggest that insulin is related with the formation of amyloid plaques which are histopathological structures, characteristics of some dementias such as Alzheimer's disease (AD) [3]. For this reason, in recent years, DM has been considered, specifically diabetes mellitus type 2 (DM2, in which the organism is unable to use insulin), as an important risk factor for the development of dementia. In this chapter, general data about DM and dementias, as well as the importance of DM in the formation of amyloid aggregates which converts it in a risk factor for AD and Parkinson's disease (PD), will be discussed.
