If you Google the terms “constipation” and “heart attack” it’s not long before the name Elvis Presley crops up. Elvis had a longstanding history of chronic constipation and it’s believed he was straining very hard to poo, which then led to a fatal heart attack.

We don’t know what really happened to the so-called King of Rock “n” Roll back in 1977. There were likely several contributing factors to his death, and this theory is one of many.

But after this famous case researchers took a strong interest in the link between constipation and the risk of a heart attack.

This includes a recent study led by Australian researchers involving data from thousands of people.

Are constipation and heart attacks linked?

Large population studies show constipation is linked to an increased risk of heart attacks.

For example, an Australian study involved more than 540,000 people over 60 in hospital for a range of conditions. It 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 also found that people who were constipated had an increased risk of heart attacks and strokes.

It was unclear, however, if this relationship between constipation and an increased risk of heart attacks and strokes would hold true for healthy people outside hospital.

These Australian and Danish studies also did not factor in the effects of drugs used to treat high blood pressure (hypertension), which can make you constipated.

How about this new study?

The recent international study led by Monash University researchers found a connection between constipation and an increased risk of heart attacks, strokes and heart failure in a general population.

The researchers analysed data from the UK Biobank, a database of health-related information from about half a million people in the United Kingdom.

The researchers identified more than 23,000 cases of constipation and accounted for the effect of drugs to treat high blood pressure, which can lead to 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.

The researchers found a strong link between high blood pressure and constipation. Individuals with hypertension who were also constipated had a 34% increased risk of a major heart event compared to those with just hypertension.

The study only looked at the data from people of European ancestry. However, there is good reason to believe the link between constipation and heart attacks applies to other populations.

A Japanese study looked at more than 45,000 men and women in the general population. It found people passing a bowel motion once every two to three days had a higher risk of dying from heart disease compared with ones who passed at least one bowel motion a day.

How might constipation cause a heart attack?

Chronic constipation can lead to straining when passing a stool. This can result in laboured breathing and can lead to a rise in blood pressure.

In one Japanese study including ten 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.

One theory is that older people have stiffer blood vessels due to atherosclerosis (thickening or hardening of the arteries caused by a build-up of plaque) and other age-related changes. So their high blood pressure can persist for some time after straining. But the blood pressure of younger people returns quickly to normal as they have more elastic blood vessels.

As blood pressure rises, the risk of heart disease increases. The risk of developing heart disease doubles when systolic blood pressure (the top number in your blood pressure reading) rises permanently by 20 mmHg (millimetres of mercury, a standard measure of blood pressure).

The systolic blood pressure rise with straining in passing a stool has been reported to be as high as 70 mmHg. This rise is only temporary but with persistent straining in chronic constipation this could lead to an increased risk of heart attacks.

Some people with chronic constipation may have an impaired function of their vagus nerve, which controls various bodily functions, including digestion, heart rate and breathing.

This impaired function can result in abnormalities of heart rate and over-activation of the flight-fight response. This can, in turn, lead to elevated blood pressure.

Another intriguing avenue of research examines the imbalance in gut bacteria in people with constipation.

This imbalance, known as dysbiosis, can result in microbes and other substances leaking through the gut barrier into the bloodstream and triggering an immune response. This, in turn, can lead to low-grade inflammation in the blood circulation and arteries becoming stiffer, increasing the risk of a heart attack.

This latest study also explored genetic links between constipation and heart disease. The researchers found shared genetic factors that underlie both constipation and heart disease.

What can we do about this?

Constipation affects around 19% of the global population aged 60 and older. So there is a substantial portion of the population at an increased risk of heart disease due to their bowel health.

Managing chronic constipation through dietary changes (particularly increased dietary fibre), increased physical activity, ensuring adequate hydration and using medications, if necessary, are all important ways to help improve bowel function and reduce the risk of heart disease.

Vincent Ho, Associate Professor and clinical academic gastroenterologist, Western Sydney University

This article is republished from The Conversation under a Creative Commons license. Read the original article.

Have you ever wondered why most disinfectants indicate they kill 99.9% or 99.99% of germs, but never promise to wipe out all of them? Perhaps the thought has crossed your mind mid-way through cleaning your kitchen or bathroom.

Surely, in a world where science is able to do all sorts of amazing things, someone would have invented a disinfectant that is 100% effective?

The answer to this conundrum requires understanding a bit of microbiology and a bit of mathematics.

What is a disinfectant?

A disinfectant is a substance used to kill or inactivate bacteria, viruses and other microbes on inanimate objects.

There are literally millions of microbes on surfaces and objects in our domestic environment. While most microbes are not harmful (and some are even good for us) a small proportion can make us sick.

Although disinfection can include physical interventions such as heat treatment or the use of UV light, typically when we think of disinfectants we are referring to the use of chemicals to kill microbes on surfaces or objects.

Chemical disinfectants often contain active ingredients such as alcohols, chlorine compounds and hydrogen peroxide which can target vital components of different microbes to kill them.

The maths of microbial elimination

In the past few years we’ve all become familiar with the concept of exponential growth in the context of the spread of COVID cases.

This is where numbers grow at an ever-accelerating rate, which can lead to an explosion in the size of something very quickly. For example, if a colony of 100 bacteria doubles every hour, in 24 hours’ time the population of bacteria would be more than 1.5 billion.

Conversely, the killing or inactivating of microbes follows a logarithmic decay pattern, which is essentially the opposite of exponential growth. Here, while the number of microbes decreases over time, the rate of death becomes slower as the number of microbes becomes smaller.

For example, if a particular disinfectant kills 90% of bacteria every minute, after one minute, only 10% of the original bacteria will remain. After the next minute, 10% of that remaining 10% (or 1% of the original amount) will remain, and so on.

Because of this logarithmic decay pattern, it’s not possible to ever claim you can kill 100% of any microbial population. You can only ever scientifically say that you are able to reduce the microbial load by a proportion of the initial population. This is why most disinfectants sold for domestic use indicate they kill 99.9% of germs.

Other products such as hand sanitisers and disinfectant wipes, which also often purport to kill 99.9% of germs, follow the same principle.

Real-world implications

As with a lot of science, things get a bit more complicated in the real world than they are in the laboratory. There are a number of other factors to consider when assessing how well a disinfectant is likely to remove microbes from a surface.

One of these factors is the size of the initial microbial population that you’re trying to get rid of. That is, the more contaminated a surface is, the harder the disinfectant needs to work to eliminate the microbes.

If for example you were to start off with only 100 microbes on a surface or object, and you removed 99.9% of these using a disinfectant, you could have a lot of confidence that you have effectively removed all the microbes from that surface or object (called sterilisation).

In contrast, if you have a large initial microbial population of hundreds of millions or billions of microbes contaminating a surface, even reducing the microbial load by 99.9% may still mean there are potentially millions of microbes remaining on the surface.

Time is is a key factor that determines how effectively microbes are killed. So exposing a highly contaminated surface to disinfectant for a longer period is one way to ensure you kill more of the microbial population.

This is why if you look closely at the labels of many common household disinfectants, they will often suggest that to disinfect you should apply the product then wait a specified time before wiping clean. So always consult the label on the product you’re using.

Other factors such as temperature, humidity and the type of surface also influence how well a disinfectant works outside the lab.

Similarly, microbes in the real world may be either more or less sensitive to disinfection than those used for testing in the lab.

Disinfectants are one part infection control

The sensible use of disinfectants plays an important role in our daily lives in reducing our exposure to pathogens (microbes that cause illness). They can therefore reduce our chances of getting sick.

The fact disinfectants can’t be shown to be 100% effective from a scientific perspective in no way detracts from their importance in infection control. But their use should always be complemented by other infection control practices, such as hand washing, to reduce the risk of infection.

Hassan Vally, Associate Professor, Epidemiology, Deakin University

This article is republished from The Conversation under a Creative Commons license. Read the original article.