Inflammaging and the role of gut bacteria

The average lifespan of people in many countries is slowly increasing. Although this is a positive trend, it does come with challenges. 

For instance, older adults are more susceptible to a range of conditions, including neurodegenerative diseases, cancer, heart disease, diabetes, autoimmunity, and infections. 

As a result, many scientists are focused on keeping us healthier during our steadily lengthening lives. And this includes maintaining a healthy immune system.

As you age, your immune system changes, making it harder for your body to fight off bugs. This is called immunosenescence, and it contributes to long-term inflammation, which scientists call inflammaging. 

Several other factors also play a part in inflammaging, including dietary changes, a lack of physical activity, repeated infections, hospitalization, medications, and changes in your resident gut bacteria.  

Your gut microbiome is a thriving community of bacteria and other microbes that live in your intestines. Not long ago, scientists believed that these microbes simply helped us digest certain compounds in our food. Now we know that they play a vital role in our health.

For instance, ZOE scientists have identified 15 “good” bacteria associated with positive health measures and 15 “bad” bacteria linked to poor health measures.

If you’d like to know about the gut microbes that live in your gut, start by taking our free quiz.

In this article, we'll explore what inflammaging is, why it happens, and how your gut microbiome is involved.

What is inflammaging?

There are many reasons why older adults are more susceptible to certain diseases, and experts believe that one of these factors is inflammation.

Inflammation in itself is not a bad thing. It’s a healthy response to an injury or infection and forms part of your body’s defense mechanism. However, if inflammation persists, it increases the risk of diseases such as heart disease, cancer, and type 2 diabetes. It's also linked with mortality. 

Additionally, scientists have linked long-term inflammation to a loss of muscle mass and reduced strength with age.

Your immune system

Your immune system is broadly made up of two parts:

• Innate: This part of the immune system is the first line of defense against infections and injuries. One of its tools to protect the body is inflammation.

• Adaptive: This part of the immune system is more specific. It holds “memories” of things that have made you sick in the past — such as disease-causing bacteria — and destroys them when it finds them.

Because inflammation is healthy when it happens at the right time but damaging when it happens for too long, the innate immune system has to keep it carefully balanced. The aging immune system finds this balancing act more difficult, which leads to long-term inflammation, or inflammaging.

The adaptive immune system also plays a part in inflammaging. Over a lifetime, this part of the immune system builds up a huge library of molecules that it recognizes as a threat. 

Because of its lifetime of “memories,” the adaptive immune system finds it harder to tell the difference between healthy cells that make up the body and cells that are a genuine threat. 

In its confusion, the innate immune system might attack healthy cells by mistake, triggering more unnecessary inflammation.

Now that you’ve been introduced to inflammaging, let's investigate where gut bacteria come in.

The microbiome as we age

Many factors influence your unique gut microbiome profile, including diet, physical activity, and sleep. And scientists have also shown that your gut microbiome changes with age.

Experts believe that a healthy gut microbiome is diverse, with a range of beneficial bacteria. But studies show that the number of these “good” bacteria drops as we get older. On the other hand, we see an increase in “bad” opportunistic bugs. Experts call this microbial dysbiosis. 

Although your gut microbiome is significantly different from everyone else’s, humans do share some similarities. For instance, around 90% of the bacteria in a healthy adult’s gut are Bacteroidetes and Firmicutes.

Specifically, Bacteroidetes and Firmicutes become less dominant, and bacteria that are less common in adulthood become more prevalent.

Some of the “bad” bacteria that increase with age can drive inflammaging. According to the authors of a review on the topic:

“These bacteria have the potential to induce inflammation when allowed to proliferate uncontrolled and can promote the onset of chronic diseases in older adults.”

The main changes to the microbiome in older age are:

1. Your community of gut bacteria becomes less diverse, although there is some evidence that the reverse might be true.

2. The number of potentially harmful “bad” bacteria increases.

3. There are reduced numbers of “beneficial “bacteria that produce metabolites, such as butyrate, which have anti-inflammatory properties.

Butyrate is a short-chain fatty acid (SCFA). You’ll learn more about why SCFAs are important in the next section.

Changes to the gut lining

Alongside shifts in gut bacteria composition and the metabolites they produce, there are also changes in the lining of the gut, which is called the epithelium. The epithelium helps regulate the transport of compounds between your gut and your blood vessels. 

“Good” gut bacteria help keep the epithelium healthy. As you age, your gut epithelium becomes less effective, and compounds can move more easily from your gut into circulation. Scientists call this “gut leakage.”

If you would like to know which bacteria are living in your gut, ZOE can help. With our at-home test, we analyze your gut microbiome and then provide you with information about the best foods to eat to boost your gut health.

We’ll also let you know how your blood sugar and blood fat levels respond to food so you can tailor your diet to suit your body.

A shift in metabolites

As the types of bacteria in the gut microbiome change, so do the compounds, or metabolites, that these bacteria produce. These metabolites carry out a number of roles. For instance, they help regulate metabolism, act as a source of energy, and regulate immune function. 

As the production of these important metabolites dips with age, it can increase the risk of inflammation in your gut and the rest of the body. 

For instance, “good” bacteria produce SCFAs — such as butyrate — as they break down dietary fiber. SCFAs help nourish your gut lining and help damp down inflammation.

Some scientists think that inflammaging might be driven by a vicious cycle: 

Inflammation helps promote the survival of “bad” bacteria. And as the “bad” bacteria increase in number, “good” bacteria get pushed out so that fewer SCFAs are produced. With lower levels of SCFAs to keep inflammation in check, inflammation increases. And increased inflammation completes the cycle by encouraging the growth of more “bad” bacteria.

However, there is some evidence from studies in mice that gut leakage may directly cause inflammaging. 

Why does the microbiome change with age?

Scientists have shown that a range of factors influence changes in the gut microbiome as we age. 

For instance, one study found a modest link between gut bacteria diversity and levels of physical activity.

Another study also concluded that changes in the gut microbiome are linked to diet. The scientists also found that changes were associated with where the person was living — for instance in the community, a day hospital, or in long-term residential care. 

Diet also plays a factor in how our gut microbiome changes with age. Our diet tends to change over time, which might be due to changes in our sense of smell or taste. Or it might be because it gets harder to chew certain foods, so we eat fewer uncooked fresh vegetables and fruits.

Fresh plant-based foods are often packed with fiber. And fiber fuels gut bacteria that produce SCFAs.

Immunosenescence might also play a part in changing your gut microbiome as you age. As your adaptive immune system functions less accurately, it might accidentally attack “good” bacteria.

Because these beneficial bacteria help support the immune system and produce SCFAs, with less of them to help, it might provide an opportunity for “bad” bacteria to step in and expand. Again, this can help drive inflammaging.

The future of inflammaging

There is still much more to learn about inflammaging and its role in health and disease.

Inflammaging refers to an ongoing state of inflammation that occurs in many older adults. Over time, it increases the risk of chronic diseases. Although changes to the microbiome are not the only factor involved in inflammaging, evidence is mounting that they play an important role. 

As a relatively new field of study, scientists are exploring inflammaging from many angles.

For instance, some researchers are investigating whether inflammaging might be influenced by microbiomes beyond the gut — such as the lung microbiome and skin microbiome.

Other scientists are asking how inflammaging affects moms before, during, and after pregnancy. No doubt, fascinating insights are likely to come from these studies.

At ZOE, we are at the forefront of microbiome research. We know that everybody is different and that the gut microbiome plays a vital role in health and disease, whatever your age. 

If you would like to get detailed information about the bacteria that live in your gut, take our free quiz today.