Cognitive decline and Alzheimer’s disease are ‘chronic’ conditions, meaning they develop over a relatively long period of time (years to decades). Like other chronic conditions, cognitive decline and ‘neurodegeneration’ are not caused by one thing, but by several potential processes. Some of the most important mechanisms that have relevance here are:


As time goes on, there is a tendency for brain cells to ‘wear out and die’. This process is to some degree a natural consequence of ageing. However, the more rapid the rate of brain atrophy, the more likely the risk of cognitive decline and dementia.

Of relevance here are what are known as ‘growth factors’ which stimulate growth and regeneration of brain cells. One of the most important growth factors is called ‘brain-derived neurotrophic factor’ (BDNF). A relative deficiency of BDNF and other growth factors increases the risk of brain atrophy over time.  


Inflammation is a healing response in the body, and can for example cause pain, tenderness, redness and swelling in, say, an injured joint. However, less obvious, lower-level inflammation can occur throughout the body in general, and this is sometimes referred to as ‘systemic inflammation’. This can affect the brain (‘neuroinflammation’), and can lead to damage to and death of brain cells (‘neurodegeneration’).


Certain proteins are integral to the structure and function of the body and brain. However, in Alzheimer’s disease, there is a tendency for specific proteins to build up in the brain. There are two main proteins involved here; ‘beta-amyloid’ (also sometimes referred to as ‘amyloid-beta’) and ‘tau’ (rhymes with ‘cow’). Beta-amyloid is deposited around brain cells, while tau accumulates within the cells. Either way, the end result is disruption to the normal and healthy functioning of neurones and a reduction in cognitive function.


Homocysteine is an amino acid (building-block of protein), and a normal constituent of the blood. However, relatively high levels of homocysteine are associated with an increased risk of chronic health issues including ‘cognitive impairment’ and Alzheimer’s disease. It is thought that homocysteine can be directly toxic to the brain, but can also predispose to compromised blood supply to this organ.


Maintaining stable levels of blood sugar is a key component in health, and this is especially true for the brain. There is evidence that generally raised levels of blood sugar (as is found in diabetes or 'pre-diabetes') and impaired functioning of the hormone insulin ('insulin resistance') can lead to impaired brain function and cognitive impairment over time. This association is why some researchers have dubbed some cases of Alzheimer's disease as 'Type 3 diabetes'.