As the elderly population increases in countries worldwide, there is a greater portion of the population at risk for Alzheimer’s Disease (AD). AD, characterized by abnormal plaques and fiber tangles in the brain, is a progressive brain disorder wherein the connections between brain cells undergo degeneration and eventually die. This progression slowly causes worsening memory and cognition in the afflicted person as the neurons capable of transmitting messages between the brain and body lessen in numbers. In order to understand this condition, currently affecting more than six million Americans over 65 years old, research efforts have been dedicated towards the condition in hopes of identifying a particular cause and treatments. Though no treatment has yet been found, the many potential causes and risk factors found offer possible avenues for treatment.
One such influence on the progression of AD is one’s gut microbiome, the various microorganisms that live in the digestive tract. Though it may seem unexpected for the gut of all locations in the body to have an impact on the brain, the research doesn’t lie. A connection between the gut and the brain, aptly termed the gut-brain axis, was well known prior to research connecting the gut microbiome and AD. The gut-brain axis is a two-way communication pathway between the central nervous system and the enteric nervous system, the part of the nervous system in charge of the gut. This pathway, which uses neurons and hormones as messengers, isn’t in our control but rather is automatically taken care of by our brains to link certain emotional and cognitive regions to the gut. It’s what causes the stomach to release juices after seeing a delicious meal or what causes butterflies in the stomach before going onstage. Considering how important the gut microbiome is to the digestive system, this microbiome is thought to influence the gut-brain axis through interactions between the bacteria or abundance of certain flora.
However, as previously mentioned, the gut microbiome doesn’t just affect the gut-brain axis; it affects AD progression, too. Even people in the earliest stage of Alzheimer’s disease have markedly different gut microbiomes in comparison to healthy individuals. The difference was found prior to cognitive symptoms and was present all the way into the last stages of AD. It is unsure whether this relationship between the gut microbiome and AD stems from the microbiome triggering or exacerbating AD, or the presence of AD causing these changes in the gut. If the former is true, then an opportunity for treating or slowing the progression of AD is present; by providing patients diagnosed with AD probiotics, thus changing their gut microbiome intentionally, the patient’s condition could improve or not worsen as quickly. The relationship present between the gut microbiome and AD diagnosis offers the avenue of using one’s gut microbiome as part of AD diagnoses or indicators. Though it would be tricky to make a diagnosis solely by looking at data on a gut microbiome, the results of abundance and type of species present could act as an indicator for AD, signaling the need to visit a medical professional. Such screening would be particularly accessible, and thus useful, for people at greater risk of AD, such as the elderly or those genetically predisposed to early onset AD.
Concerns can easily arise about the unreliability of gut microbiomes--and for good reason. A person’s diet or environment can easily impact their gut microbiome, meaning that people who live in different countries or prefer certain cuisines over others are likely to have dissimilar gut flora. Though this factor wouldn’t impact the change in gut microbiomes between healthy to AD diagnosis, it does mean that the abundance of a certain enteric bacterial species cannot yet be used in a reliable diagnosis of AD globally. The connection between the gut microbiome and the progression of AD is still under research, especially with the recent growth of bioinformatics as a field allowing for cheaper and quicker sequencing and analysis of the gut microbes’ genomes. As research continues to increase and more data is available, more conclusions can be drawn regarding the influence and importance of this relationship--potentially leading to new treatment options for those diagnosed with AD.
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