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The Gut Microbiome and Healthy Aging

Healthy aging is a significant area of research, which focuses on physiological changes and factors that are associated with healthy aging. For example, the connection between the gut microbiome and aging.

Worldwide populations are increasingly in an older age bracket. It is projected that globally there will be 1.6 billion individuals aged 65+ by the year 2050. A large elderly population could mean an increase in the prevalence of chronic diseases, requiring extensive resources from healthcare systems.

What is the gut microbiome?

Many terms are used in the study of the gut microbiome. Microbiome refers to the catalog of all of the microorganisms and their genes in a given environment. Microbiota refers to the specific types of microorganisms in a particular environment. The gut microbiota, therefore, describes the type of microorganisms present in the human gut, whereas the gut microbiome refers to the collective genome of the microorganisms present in the gut. 

The gut microbiota is made up of between 10 – 100 trillion microbial cells. The gut microbiome is made up of mostly bacteria, although archaea, viruses, and eukaryotic microbes are also present in smaller amounts.

The gut microbiota affects most physiological functions in the body, implicating it in human health and disease. It is known to help with digestion, interact with the immune system, and even act as a barrier against invading pathogens. The gut microbiota and humans are considered to have a mutually beneficial relationship. For example, certain food components are indigestible by humans if not for the gut microbiota.

The building of the microbiota begins at birth. Babies delivered vaginally will typically have similar microbiota to those found in their mother’s vagina shortly after being born. On the other hand, babies delivered via C-section will have microbiota that is often found on human skin.

The microbiome continues to develop during the first year of life. After a few years, a child’s microbiota resembles that of an adult. After the gut microbiota is well established, it is relatively stable over time until an individual reaches older age when it begins to change.

How does the gut microbiota change with age?

We all age with different levels of deterioration of physiological functioning over time. This deterioration even occurs with healthy aging but developing certain chronic diseases may be prevented or delayed with a healthy lifestyle.

Research on aging has found that people of all ages need a diverse, rich, and balanced gut microbiota to get the most out of their physical and mental health.

Research is now finding that the types of bacteria that make up the gut microbiota change during the aging process. For example, some studies have found that as a person ages, the levels of gram-negative bacteria present in the gut microbiota increase. These types of bacteria contain a component in their cell wall that is capable of inducing inflammation.

Overall, studies show that the diversity of the gut microbiota decreases during the aging process, which indicates an unhealthy gut microbiota. Research has revealed that some factors that are associated with aging have been linked to changes in the gut microbiota. Whether or not these age-associated factors cause changes in gut microbiota is still unknown.

Immune system

One age-related change is a decrease in immune system function called immunosenescence. This can cause long-term low-grade systemic inflammation.

Studies have found that immunosenescence can cause changes in gut microbiota composition and structure in older people, although it may be that the changes in microbiota cause immunosenescence.

An increase in inflammation over a long period of time can increase an older person’s risk of developing a number of chronic diseases. These can include inflammatory bowel syndrome (IBS), irritable bowel disease (IBD), type 1 and type 2 diabetes, and atherosclerosis, the buildup of plaque on artery walls, potentially restricting blood flow.

Another age-related change that impacts the immune system is a decrease in short-chain fatty acids (SCFAs) production by the gut microbiota. SCFAs not only play a role in maintaining gut homeostasis but have important anti-inflammatory properties. This change can negatively impact the immune system’s function and increase inflammation.

Diet

Diet is an important factor in maintaining beneficial gut microbiota. Older adults tend to have age-related changes in their diet, which influence the composition of their gut microbiota. For example, older people often have diets low in fiber that been found to negatively impact the diversity of gut microbiota.

High-fat diets have also been researched in association with changes in the gut microbiota. It is possible that these microbiota changes contribute to the development of certain chronic diseases, such as Alzheimer’s disease.

Another dietary factor that may change the gut microbiota is vitamin D deficiency, which can negatively impact the immune system. The exact mechanism of how diet impacts the gut microbiota is currently unclear.

Antibiotics

Studies demonstrate that antibiotics can alter gut microbiota. Broad-spectrum antibiotics can target the ‘good’ gut microbiota in addition to the ’bad’ bacteria that cause illness. Broad-spectrum antibiotics, as their name suggests, kill a variety of bacteria. This may reduce the range of different bacteria present in the gut. Often, after completing the course of antibiotics, the gut microbiota will return to its normal state.

Dysbiosis

Dysbiosis refers to an imbalance of the gut microbiota composition and diversity, which may be caused by the factors described previously. Some definitions describe dysbiosis as the gut microbiota associated with a diseased state, which is in contrast to the gut microbiota associated with a healthy individual. Dysbiosis is associated with numerous conditions, including cardiovascular disease (CVD), IBD, obesity, and neurodegenerative diseases.

Animal studies have found that dysbiosis associated with aging may alter the innate immune response and cause gut dysplasia, which in turn can cause defective epithelial cell functioning. Gut dysplasia is thought to promote unhealthy aging, such as a greater risk of infections and increased mortality rates.

Chronic diseases associated with aging

As previously mentioned, certain chronic diseases are associated with aging. The development of many of these conditions is thought to be influenced by changes to the gut microbiota in older people.

For example, age-related changes to the gut microbiota are associated with an increased risk of developing IBS, IBD, and CVD in the elderly. However, researchers are still unsure if the changes in gut microbiota are a direct cause of developing these diseases.   

Alzheimer’s disease  – a neurodegenerative disease – involves progressive memory loss and significant changes in behaviour and character. Risk factors include obesity, diabetes, and CVD – all of these are influenced by the intestinal microbiota. Both human and animal studies have reported that changes in gut microbiota may influence brain functions and might be linked to the development of Alzheimer’s disease. More research is required to better understand this association.

Maintaining beneficial gut microbiota

A nutritious diet with adequate fiber content may help to maintain a beneficial gut microbiota, which could prevent or reduce the risk of developing chronic diseases linked to age-related changes in the gut microbiota.

Fiber-rich diets also help to reduce inflammation and may improve both cognitive and motor capabilities in old age. Including fiber in your diet may help to balance the gut microbiota.

Adding a prebiotic – fermented ingredients or non-digestible food ingredients –can help grow certain bacterial species in the gut microbiota that maintain health in old age. Also, probiotics, which are live microbe supplements, may help maintain the balance of the gut microbiota to support healthy aging.

Always talk to your healthcare provider before taking any vitamins or supplements to make sure they are right for you.

References

Askarova, S., Umbayev, B., Masoud, A. R., Kaiyrlykyzy, A., Safarova, Y., Tsoy, A., Olzhayev, F., & Kushugulova, A. (2020). The links between the gut microbiome, aging, modern lifestyle and alzheimer’s disease. Frontiers in Cellular and Infection Microbiology10, 104. https://doi.org/10.3389/fcimb.2020.00104

Badal, V. D., Vaccariello, E. D., Murray, E. R., Yu, K. E., Knight, R., Jeste, D. V., & Nguyen, T. T. (2020). The gut microbiome, aging, and longevity: A systematic review. Nutrients, 12(12), 3759. doi: 10.3390/nu12123759. PMID: 33297486; PMCID: PMC7762384

Deng, F., Li, Y., & Zhao, J. (2019). The gut microbiome of healthy long-living people. Aging11(2), 289–290. https://doi.org/10.18632/aging.101771

Kim, S., & Jazwinski, S. M. (2018). The Gut Microbiota and Healthy Aging: A Mini-Review. Gerontology64(6), 513–520. https://doi.org/10.1159/000490615

Kumar, M., Babaei, P., Ji, B., & Nielsen, J. (2016). Human gut microbiota and healthy aging: Recent developments and future prospective. Nutrition and healthy aging4(1), 3–16. https://doi.org/10.3233/NHA-150002

Nagpal, R., Mainali, R., Ahmadi, S., Wang, S., Singh, R., Kavanagh, K., Kitzman, D. W., Kushugulova, A., Marotta, F., & Yadav, H. (2018). Gut microbiome and aging: Physiological and mechanistic insights. Nutrition and healthy aging4(4), 267–285. https://doi.org/10.3233/NHA-170030

Shreiner, A. B., Kao, J. Y., & Young, V. B. (2015). The gut microbiome in health and in disease. Current Opinion in Gastroenterology31(1), 69–75. https://doi.org/10.1097/MOG.0000000000000139

Ursell, L. K., Metcalf, J. L., Parfrey, L. W., & Knight, R. (2012). Defining the human microbiome. Nutrition reviews70 Suppl 1(Suppl 1), S38–S44. https://doi.org/10.1111/j.1753-4887.2012.00493.x

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