How Ageing Affects the Gut Microbiome

Does the Gut Microbiome Change With Age?

Yes, although there is no single microbiome that defines an older person.

During adulthood, the gut microbiome can remain relatively stable for long periods. As people move into later life, researchers tend to find greater differences in the types and proportions of microorganisms present.

Age itself is only part of the explanation.

Diet may change. Physical activity can increase or decrease. People may start taking different medicines, move home or experience changes in their general health. Each of these factors can influence the microbial community living in the gut.

This makes ageing particularly interesting to microbiome researchers.

When scientists compare a group of 30-year-olds with a group of 75-year-olds, they cannot automatically assume that every microbial difference is caused by those additional 45 years.

They have to consider the lives people have lived too.

What Happens to Microbial Diversity as We Get Older?

Microbial diversity describes the variety of microorganisms found within the gut and how evenly they are represented.

You will sometimes see greater diversity described as automatically better. Microbiome science is not quite that simple.

Some studies involving older populations have found differences in microbial diversity, particularly when comparing healthy adults living independently with people experiencing frailty or living in long-term residential care.

Other research has produced a more intriguing finding.

A study published in Nature Metabolism found that the gut microbiomes of healthy adults could become increasingly unique with age. This pattern was particularly noticeable from middle to later adulthood.

Rather than everybody's microbiome following the same path, the microbial community may therefore become more individual.

That is an important distinction.

Healthy ageing may not simply be about preserving the microbial composition found in younger adulthood.

Is Microbiome Age the Same as Your Actual Age?

Researchers have investigated whether patterns within the gut microbiome can be used to estimate chronological age. Some studies have even developed statistical or machine-learning models designed to identify age-associated microbial signatures.

That does not mean your microbiome has a simple biological age that can be read like the date on a birth certificate.

Two people born in the same year may have noticeably different gut microbiomes.

Geography, diet, medication, lifestyle, environment and health can all contribute to those differences. Researchers therefore have to distinguish between microbial features associated with chronological ageing and those associated with everything that tends to change alongside it.

This is one reason scientists increasingly study ageing as a process rather than looking for an individual "ageing bacterium".

Which Gut Bacteria Can Change With Age?

There are hundreds of bacterial species commonly detected in the human gut, alongside other microorganisms. Researchers therefore tend to look for patterns across microbial communities rather than concentrating on a single species.

One group that has received considerable attention is Bifidobacterium.

These bacteria are particularly abundant early in life, although different species remain present throughout adulthood. Studies have reported changes in their abundance and composition among older populations.

Researchers have also investigated bacteria involved in fermenting components of our diet and producing compounds known as short-chain fatty acids.

Results are not identical across every study.

Someone living in the UK may have a different microbial profile from someone of the same age living elsewhere. Diet and medication can introduce further differences.

This variation is one reason it is difficult to define exactly what an "older microbiome" should look like.

Why Are Short-Chain Fatty Acids Important?

Gut bacteria do more than simply occupy space in the digestive system. They are metabolically active.

One example is the fermentation of dietary fibre that reaches the large intestine.

Certain gut microorganisms can break down these compounds and produce short-chain fatty acids, often shortened to SCFAs.

The three commonly discussed SCFAs are:

• Acetate
• Propionate
• Butyrate

Butyrate is particularly interesting because cells lining the colon can use it as an energy source.

Researchers also study how SCFAs interact with the intestinal environment and other normal biological processes.

This creates an important connection between diet and microbial activity. What reaches the large intestine affects the substrates available to gut microorganisms and, in turn, the compounds those microbes produce.

Why Are Researchers Looking Beyond Individual Bacteria?

Early discussions about the microbiome often focused heavily on which bacteria were present.

Modern microbiome research is increasingly asking another question: what are those microorganisms actually doing?

Two people do not necessarily need identical collections of bacteria for some microbial functions to be similar.

Different microorganisms may possess genes that allow them to perform related metabolic tasks. Researchers can therefore study microbial genes, biochemical pathways and metabolites alongside the abundance of individual bacterial groups.

Techniques such as metagenomic sequencing have made this much easier.

Instead of only producing a list of microorganisms, researchers can investigate the genetic material contained within an entire microbial community.

That gives a much richer picture of how the microbiome may change throughout life. Our article on the future of gut health research explores where this kind of research may lead next.

Why Might Diet Affect the Ageing Microbiome?

Our eating habits rarely remain identical throughout adulthood.

Appetite may change. Dental problems can make certain foods less appealing. Changes in taste and smell can influence food choices, while living circumstances may affect how often someone shops or prepares fresh meals.

All of this matters because food provides nutrients and substrates that gut microorganisms can use.

Dietary fibre is one example. Much of it reaches the large intestine, where certain bacteria can ferment it.

Fruit, vegetables, pulses, wholegrains, nuts and seeds can provide different types of fibre as part of a varied, balanced diet.

There is no need to search for one perfect "gut food". Variety is a much more useful principle. For a broader explanation of how food is broken down and used, read the science of digestive health.

What Role Do Medicines Play?

Medication is another reason researchers need to be careful when studying the ageing microbiome.

Antibiotics are the most obvious example. Because they act against bacteria, antibiotic exposure can alter microbial populations within the gut.

But antibiotics are not the only medicines being investigated.

Research has found associations between several commonly used medicines and differences in gut microbiome composition.

This becomes especially relevant when studying older populations because medication use often increases with age.

If researchers find a particular bacterium is less common among older participants, they need to ask why. Is ageing responsible? Could medication be involved? Is diet different? Or are several factors acting together?

There is rarely a single explanation.

Does Where We Live Make a Difference?

It might, although living environment cannot be separated neatly from all the other things that come with it.

One influential study examined older adults living within the community, attending day hospitals, undergoing rehabilitation or living in long-term residential care.

Researchers found differences in dietary patterns and gut microbiome composition between these groups.

Dietary diversity was also associated with microbiome differences.

The study does not mean that moving somewhere new automatically changes the gut in a predictable way. People living in different environments may eat differently, move differently, take different medicines and have different levels of health.

What it does demonstrate is something microbiome research repeatedly encounters: our microbes are connected to the way we live.

What About the Gut and Immune System?

The gut and immune system interact throughout life.

The gastrointestinal tract is one of the body's major points of contact with substances from the outside world. Food components and an enormous microbial community are present within this environment, so immune activity around the gut needs to be carefully regulated.

Ageing is also associated with changes in immune function.

Researchers are consequently interested in how age-associated changes in the microbiome may interact with changes occurring elsewhere in the body.

There is still a lot we do not know.

Finding that a microbial pattern and an immune measurement change together does not prove that one caused the other. The microbiome could influence the process, respond to it, or both could be affected by another factor.

Understanding those relationships remains an active area of research. You can learn more about how the gut and immune system are connected in our dedicated guide.

What Have Scientists Found in People Who Live to 100?

Centenarians provide researchers with an unusual opportunity to study the microbiome at the far end of the human lifespan.

Interestingly, studies do not suggest that the microbiome simply becomes progressively depleted as people get older.

Researchers who have studied centenarians and other very old populations have found distinctive microbial patterns. Some studies have also identified differences in microorganisms involved in particular metabolic pathways.

Exactly what those findings mean is still being investigated.

People who reach 100 are a highly unusual population. Genetics, environment, diet, medical history and lifestyle could all contribute to the patterns researchers observe.

It would therefore be a mistake to identify bacteria found in centenarians and assume that increasing those bacteria would help someone live longer.

Instead, these studies demonstrate something more fundamental.

The gut microbiome can remain complex and distinctive even at very advanced ages.

Can Exercise Influence the Gut Microbiome as We Age?

Physical activity has also attracted attention in microbiome research.

Studies have reported associations between exercise, microbial diversity and the compounds produced by gut microorganisms. Separating exercise from other lifestyle factors is difficult, however.

People who exercise regularly may also eat differently or have different daily routines.

What is already well established is that appropriate physical activity is an important part of maintaining a healthy lifestyle as we age.

The relationship between that activity and the microbiome is an interesting additional area of research. We examine it more closely in how exercise supports gut health.

Can We Stop the Gut Microbiome From Ageing?

Trying to prevent the microbiome from ageing may be the wrong goal.

Change is normal.

The microbiome develops dramatically during childhood, becomes more established during adulthood and continues responding to diet, environment and lifestyle throughout life.

Growing older is another part of that process.

There is also no established "perfect" microbiome that everybody should try to maintain.

A more practical approach is to concentrate on habits that form part of a healthy lifestyle at any age. Eating a varied and balanced diet, including fibre-rich foods, staying physically active where appropriate and maintaining regular routines are sensible foundations.

The microbiome does not need to remain frozen in time.

What Does the Research Tell Us About Healthy Ageing and the Microbiome?

Even among people of similar ages, microbial communities can look remarkably different.

Scientists are also moving beyond simply cataloguing bacteria. Increasingly, research considers microbial genes, metabolic activity and the compounds microorganisms produce.

That shift should give us a better understanding of what changes in the gut as we get older and, importantly, which changes actually matter.

Supporting Your Gut Through Different Stages of Life

We cannot control every factor that influences the gut microbiome.

We can, however, build everyday habits around a varied diet, regular movement and a healthy lifestyle.

And those fundamentals remain relevant whether you're 25, 55 or 85.

The Bigger Picture

Ageing affects the gut microbiome, but it does not send everybody's microbial community down exactly the same path.

Some bacterial populations may change. Microbial activity can change too. Diet, medicines, activity and living environment can all become part of the picture.

Perhaps most interestingly, research suggests that our microbiomes may become increasingly individual as we grow older.

There is still much to discover, particularly around the difference between changes that simply accompany ageing and those that have wider biological significance.

For now, one thing is clear: the microbiome continues to change with us throughout life.