At every stage of life, from birth through infancy to old age, changes occur in the body to support its development and proper functioning. The gut microbiota is an important player and has an influence on the physical and mental health of an individual throughout his life. Its composition and functions are dynamic and change with age. Therefore, what changes occur in the microbiota as we age? What are the consequences?
The key periods of life for the gut microbiota
The first months of life are the first key stage. From birth to feeding, from breastfeeding to solid food introduction, key events will contribute to shape the gut microbiota from 0 to 3 years old.
The transition from adulthood to old age is a second stage. This second phase (beginning between 65 to 70 years old) is characterized by numerous changes in the body, some of them may impact the gut microbiota, others result in more general difficulties in performing daily tasks. Indeed, on a daily basis, it is possible to witness situations where age becomes an obstacle to certain actions, particularly because of joint pain. This would be due to “a physiological and progressive reduction of the functional reserves of the organs and systems”. And this results in a loss of efficiency on several levels: kidneys, heart and blood vessels and/or nervous system, which is no longer in the best of shape. In addition, there may be a phenomenon of “senility” that can occur at times when intellectual and physical abilities are reduced.
Finally, the immune system also ages, resulting in a greater exposure to diseases : we speak of “immunosenescence“, defined as a “reduced activity of the innate and adaptive immune system, the two mechanisms that protect us from infections”.
Immunosenescence, an age-related loss of immune system effectiveness
The immune response can be defined by two types of responses: a first one called “innate” and a second one called “adaptive”. Both mechanisms act in cooperative and collaborative manners and the terminology gives us an indication of their respective functions. Innate immunity is part of the baggage we carry from birth, without prior learning. It acts fast but can prove insufficient. Adaptive immunity acts as a second shield and is acquired over time. In order to develop our adaptive immune system, several means exist:
- Active way: the immune system tends to have an immune memory during repeated contacts with the same infectious agent.
- Passive way: the mother transmits to her fetus antibodies that act as a weapon to fight against the target against which they were specifically created, even if the child has never encountered it before.
- Artificial way: through human voluntary interventions such as vaccines.
Under normal conditions of efficiency, the immune system reacts to certain factors with a proliferative response.In the case of immunosenescence, this response is reduced. There is also a reduction in the activity of cells such as Natural Killer cells and T lymphocytes, involved in innate and adaptive immunity respectively.
In addition, there is a relative increase in pro-inflammatory cytokines. Under physiological conditions, there is a balance between anti and pro-inflammatory cytokines. However, in immunosensitive conditions, the imbalance in favor of pro-inflammatory cytokines (e.g. TNF-α, IL-6 and IL-8) causes a state of chronic inflammation.
In this context of immunosenescence and possible chronic inflammation, the microbiota also undergoes alterations resulting in a phenomenon of dysbiosis.
Dysbiosis: what consequences for the microbiota of the elderly?
Dysbiosis is defined as a change in the quality and quantity of the intestinal microbiota due to several factors, starting with dietary changes.
It can occur at this delicate time of life. Indeed, with ageing, protein and fiber consumption is often reduced and may be accompanied by dehydration. Older adults may also have trouble chewing, and their gut becomes less efficient at absorbing nutrients. In addition, as we said before, elderly may suffer from an underlying pro-inflammatory state.
These elements can have cumulative effects and lead to states of malnutrition. They primarily lead to alterations in the intestinal microbiota which increase the risk of diseases. Thus, a relative reduction of protective and anti-inflammatory bacteria in the gut (e.g. Akkermansia municiphila, Faecalibacterium prausnitzii and Bacteroides fragilis) and an increase in aggressive pathobionts (Clostridium, Actinobacteria and Proteobacteria) is observed.
Gut dysbiosis would seem to potentially cause cognitive changes, characteristics of neurodegenerative diseases. Some studies have shown a link between gut dysbiosis and neurodegenerative diseases, such as Parkinson’s and Alzheimer’s. In view of these data, it is relevant to ask whether we could age in good health by maintaining a normal homeostasis to avoid the damage of dysbiosis.
In a context where the average lifespan is increasing and the population is aging, science is broadening its fields of research towards the promotion of healthy aging. It is thus turning to the microbiota to try to understand its potential role in this phase, where the phenomenon of dysbiosis seems to be correlated with neurodegenerative pathologies.
In this context, it is important to take care of one’s microbiota by adopting a healthy diet in terms of quantity and quality, in order to limit possible alterations.
This post is written on the basis of the book “Microbiota”.
“Microbiota” is published in english by the Danone Institute Italy and Danone Institute International. It gathers a mix of historical, anthropological and scientific concepts explaining why research on gut bacteria, from ancient texts to the most recent scientific evidence, is a sector of great interest for science. Thanks to a Q&A structure, 7 recognized experts explain several topics considering the different ages and conditions in life. The book is available in pdf and e-book format (on the Danone Institute International website)
