Your gut microbiome and heart health

Your gut microbiome — the trillions of microorganisms living in your gut — is essential for good health.

Although research into the microbiome is young, scientists have identified multiple links between a thriving community of “good” bugs and positive health outcomes.

These miniature life-forms help us digest food, synthesize vitamins, and much more. They have links with many parts of your body, including your heart.

In this article, we’ll take a look at how your gut microbiome can influence heart health.

We'll dig deep into the science, so hold on to your hats.

What is cardiovascular disease?

Cardiovascular disease is a catchall term for conditions that affect your heart and/or blood vessels. This includes well-known conditions like angina, heart attack, stroke, and high blood pressure.

Globally, heart disease is the number one cause of death, accounting for an estimated 17.9 million deaths yearly.

The most common type of heart disease is coronary artery disease, which affects more than 20 million adults in the United States.

Coronary artery disease is caused by a buildup of fatty plaques on the inside lining of blood vessels. This process — which is called atherosclerosis — makes blood vessels narrower. 

Over time, these plaques can partially or totally block blood vessels. And, unsurprisingly, that causes significant trouble.

Are there links to gut bacteria?

The heart and gut seem like very separate bits of the body. So, in some ways, it’s surprising that they're linked at all.

However, studies have found a number of links between your resident microbes and heart conditions. Here, we’ll dig into some of the details.

Early studies noted some tantalizing hints that gut bacteria and cardiovascular disease might be related. 

For instance, a study from 2012 found differences between the gut microbiomes of people with atherosclerosis and those without.

Specifically, people with significant atherosclerosis were more likely to have more bacteria from the Collinsella genus.

Interestingly, ZOE’s research has shown that members of this genus are more common in people who eat a lot of processed foods.

Conversely, participants without atherosclerosis were more likely to have higher levels of “good” bacteria from the Roseburia and Eubacterium genera. 

Similarly, ZOE’s research has shown that some bacterial species in these genera — namely, Roseburia sp. CAG:182 and Eubacterium eligens — are associated with lower levels of inflammation. 

And inflammation appears to play a significant part in atherosclerosis.

As another example, a small study from 2015 found that people (and rats) with high blood pressure had a less diverse gut microbiome than controls without high blood pressure. 

Again, these studies don’t prove changes in gut bacteria cause high blood pressure, but it’s further evidence of some kind of link. 

Looking for a mechanism that might directly cause heart disease, scientists first zoned in on a compound called trimethylamine N-oxide (TMAO).

What's TMAO?

Foods such as red meat, egg yolks, and many other animal products contain high levels of choline and L-carnitine. 

Choline is an essential nutrient, and L-carnitine naturally occurs in nearly all your cells. So, on their own, they’re important for good health.

However, as some gut bacteria break down these compounds, they produce trimethylamine (TMA). 

TMA enters the blood and travels to the liver. Once there, the liver converts it into TMAO. And here’s the link to heart disease:

Studies have shown that, compared with individuals with low levels of TMAO in their blood, those with higher levels are 62% more likely to experience “major adverse cardiovascular events,” which include heart attack and stroke. 

Also, elevated levels of TMAO are associated with increased mortality rates.

Only certain species of gut bacteria produce TMA. These include a few members of the Clostridium genus.

So, scientists believe a gut microbiome in an unbalanced state with increased numbers of TMA-producing bacteria might increase levels of TMAO in the blood.

Finally, we have a plausible mechanistic link between gut bacteria and cardiovascular disease risk. More research is needed before the theory is set in stone, but the evidence is building.

However, some scientists think that gut microbes can influence heart health in other ways, too.

Leaky gut

The walls of your intestines don’t just let things pass through into your blood willy-nilly. They tightly control what gets out. 

For instance, nutrients from your food can pass through into your blood, but toxins are kept inside your gut to be moved along and shunted out in your poop.

However, if your gut lining becomes “leaky,” toxins — for instance, those produced by certain gut bacteria — can enter your bloodstream. In response, your immune system triggers inflammation.

For example, an early study showed that people with heart failure had higher levels of a bacterial toxin called lipopolysaccharide in their blood. 

Along similar lines, another group of scientists focused on participants with atrial fibrillation — an irregular, fast heart rate. 

They also found that individuals with higher levels of lipopolysaccharide in their blood were more likely to have a major adverse cardiovascular event than those with lower levels.

Interestingly, they also showed that participants who closely followed the Mediterranean diet had lower levels of lipopolysaccharide.

Scientists haven’t definitively shown that having a leaky gut is linked to heart disease. It seems that if there is a link, it’s probably pretty complicated.

For instance, as the authors of a review explain, a leaky gut is a feature in several conditions, but not all come with an increased risk of heart disease.

Another angle

Globally, high blood pressure, or hypertension, affects 1.28 billion adults aged 30–79. 

Although it often has no discernible symptoms, it increases the risk of developing other cardiovascular problems.

Some scientists have spotted links between gut bacteria and hypertension. For instance, one study identified significant differences in the gut microbiome of people with hypertension compared with people without hypertension.

As we always note: Spotting an association between the gut microbiome and hypertension doesn’t prove that gut bacteria cause high blood pressure. 

However, the authors of the study went one step toward filling that gap. They took poop from people with hypertension and transplanted it into germ-free mice — these are animals that scientists have carefully reared to lack a gut microbiome.

After the fecal transplant from people with hypertension, the mice developed hypertension. 

At the same time, mice that received a fecal transplant from people without hypertension did not develop high blood pressure. 

Of course, mice are certainly not biologically the same as you, but that’s a fairly striking finding.

A role for cholesterol

Having high levels of “bad” cholesterol in your blood increases the risk of cardiovascular disease.

And gut bacteria can influence cholesterol levels in a number of ways. We’ll outline three here.

1. Bile acids

Many types of gut bacteria play a part in the production of bile acids. These compounds help you digest fats, and they’re partially made from cholesterol.

Some gut bacteria can make changes to bile acids. They convert them into secondary bile acids. And some of these secondary bile acids prevent bile from being absorbed back into your body, so it exits in your poop.

Because bile is partially composed of cholesterol, if it's pooped out rather than reabsorbed, cholesterol levels in the blood decrease because the body removes it from your blood.

2. Coprostanol

Another way your gut bugs influence cholesterol levels is by converting cholesterol into coprostanol. 

Once cholesterol has been converted, it can no longer be absorbed back into the body and, once again, it comes out in your poop and has to be replaced.

In this way, blood cholesterol levels decrease. 

3. SCFAs again

As we learned earlier, some bacteria produce SCFAs as they ferment fiber. And these metabolites play a whole host of roles in the body.

Among their special powers, SCFAs can reduce the amount of cholesterol the liver produces.

SCFAs can also redirect cholesterol from the blood back to the liver. Both of these actions reduce the amount that’s circulating in your blood.

What should you do?

Researchers are still investigating the full range of connections between gut bacteria, heart health, and nutrition.

But, as with the other systems in the body, your gut microbiome appears to be playing an important part.

Because scientists are still working out the details, there are no recommendations about how to nurture your gut bugs to maintain heart health, specifically.

However, a thriving, varied gut microbiome is linked to both overall good health and a healthy diet, and ZOE knows a lot about that. If you’d like to read Prof. Tim Spector’s top 5 tips for maintaining a healthy gut microbiome, look here.