Gut bacteria may be responsible for thousands of heart attacks - particularly in people who have no obvious risk factors for heart disease, such as high cholesterol.
Scientists have discovered that certain gut flora turn a nutrient found in egg yolks, liver, beef, pork, pork and wheatgerm into the compound Trimethylamine N-oxide (TMAO).
TMAO makes blood cholesterol build up on artery walls, causing hardening of the arteries.
If this buildup breaks away and blocks an artery, it usually results in a stroke or heart attack.
The study found that organisms in our gut may be responsible for converting some foods into toxic chemicals
The new study built on a 2011 research on lab mice.
Carried out by the Cleveland Clinic's Lerner Research Institute, scientists asked 40 healthy adults to eat two hard-boiled eggs, which are rich in a fatty substance called lecithin.
After eating the eggs, the blood levels of TMAO became raised.
But if participants took antibiotics - which kill bacteria in the gut - before eating the eggs, their TMAO levels were suppressed, the researchers found.
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‘This showed that intestinal bacteria are essential for forming TMAO,’ Dr. Stanley Hazen, a cardiologist at the Cleveland Clinic, told Reuters.
Next, to see whether TMAO predicts cardiovascular events, the researchers measured its levels in 4,007 heart patients.
After taking age and a past heart attacks into account, they found that high levels of TMAO were predictive of heart attack, stroke and death over the three years that the patients were followed.
Participants who had a heart attack, stroke or died during the study had higher than average TMAO levels than those who didn't.
In fact, those who possessed the highest TMAO levels had more than twice the risk of a heart attack or stroke compared to people in the bottom quartile.
The study asked volunteers to eat eggs, which contain high levels of lethicin, a precursor to harmful TMAO
And even people with high TMAO levels and no cardiovascular risk factors were 1.8 times more likely to experience a cardiovascular event than those with low levels.
The findings suggest TMAO could serve as a marker for predicting heart disease although more studies are required to confirm the link, said the paper published in the New England Journal of Medicine.
If the findings are confirmed, it is hoped that researchers will be able to develop a drug that blocks the production of TMAO.
Earlier this month, the same researchers published a study that found a link between consumption of a chemical called carnitine, which is found in red meat, and a risk of heart disease.
Carnitine is also converted by bacteria to TMAO.
The study joins a growing list of findings that link microbes in the gut, nose and genital tract, and on the skin to health and disease.
Research has shown that certain species of gut bacteria protect against asthma while others affect the risk of obesity. Last week scientists reported that circumcision alters bacteria in the penis, and that this helps protect men from sexually transmitted disease.