The idea of straining too hard to poo and causing a fatal cardiac event is most commonly associated with the final moments of Elvis Presley.

And according to a fascinating explainer at The Conversation, after Presley’s fatal toilet visit, researchers were moved to look more closely at the link between constipation, higher blood pressure and an increased risk of heart attack or stroke.

A new study led by Monash University found that people with constipation were twice as likely to have a cardiac event.

In the study, constipation was defined as having less than three stools a week.

The researchers analysed data from the UK Biobank, a large-scale biomedical database and research resource.

Using medical records or via a questionnaire, they identified more than 23,000 cases of constipation.

They found a significant link between constipation and high blood pressure.

Participants with hypertension and constipation had a 34 per cent increased risk of a major heart event compared to those with just hypertension.

Unlike previous studies, the researchers took into account risk factors such as smoking and high cholesterol, but also the effect of drugs to treat high blood pressure, which can lead to constipation.

“This was independent of having other risk factors such as high blood pressure or high cholesterol, diabetes or smoking,” Professor Francine Marques said. “It is also independent of medication that can cause constipation.”

People with constipation (identified through medical records or via a questionnaire) were twice as likely to have a heart attack, stroke or heart failure as those without constipation.

A 2023 large-scale Australian study – in people over 60, sick in hospital – found constipated patients had a higher risk of high blood pressure, heart attacks and strokes compared to non-constipated patients of the same age.

A Danish study of more than 900,000 people from hospitals and hospital outpatient clinics had similar findings.

A 2016 Japanese study investigated more than 45,000 men and women in the general population.

It found that people who produced a stool once every two to three days had a higher risk of dying from heart disease. That was compared with people who passed at least one stool a day.

These studies indicate something profound is going on with constipation and cardiac events.

But is constipation actually causing strokes and heart failure? Is it more complex that that?

For example, a high-fibre diet is good for the heart, a lack of fibre is not.

So, with a chronically constipated person, they are presumably consuming a poor amount of fibre. This causes constipation, but also puts the heart at greater risk of catastrophe.

In other words, constipation and heart attacks can go hand in hand, rather than one causing the other.

Evidence that straining can be dangerous

According to The Conversation piece, the straining involved in passing a stool when chronically constipated “can result in laboured breathing and can lead to a rise in blood pressure”.

In a small Japanese study involving 10 elderly people, “blood pressure was high just before passing a bowel motion and continued to rise during the bowel motion”.

This increase in blood pressure “lasted for an hour afterwards, a pattern not seen in younger Japanese people”.

Why not? Because older people have stiffer blood vessels – which means “their high blood pressure can persist for some time after straining”.

In contrast, younger people have more elastic blood vessels. and their blood pressure returns to normal more quickly.

As we know, when blood pressure rises, the risk of heart disease increases. It may be temporary.

But the persistent straining in chronic constipation can “lead to an increased risk of heart attacks”.

Researchers are also investigating the imbalance in gut bacteria in people with constipation.

Short version: You have waste material just sitting there, with unhealthy bacteria throwing the gut microbiome out of whack.

The nasty stuff can end up leaking through the gut barrier into the bloodstream. This triggers an immune response which leads to low-grade inflammation, increasing the risk of a heart attack.