Gut bacteria may play a role in the development of heart disease, a new study suggests.
The results show, when gut bacteria feed on certain foods, such as eggs and beef, they produce a compound that may in turn increase heart disease risk, the researchers said.
Participants in the study with high levels of the compound, called trimethylamine-N-oxide (TMAO), in their blood were 2.5 times more likely to have a heart attack, stroke or to die over a three-year period compared with those with low levels of the compound. Even among people with no traditional risk factors for heart disease, high levels of TMAO were linked with an increased risk of these cardiovascular events.
The findings suggest that blood levels of TMAO could serve as a marker for predicting heart disease risk, although future studies are needed to confirm this, said study researcher Dr. Stanley Hazen, a cardiologist at the Cleveland Clinic.
The results also reinforce existing dietary recommendations for lowering heart disease risk, which advise people to reduce consumption of foods high in fat and cholesterol (such as beef and eggs), Hazen said.
If, in the future, researchers could develop a drug that blocks the production of TMAO, this could be a "whole new pathway" to tackle heart disease, Hazen said.
Previous studies had found a link between high levels of TMAO and a history of heart disease. It's thought that bacteria convert the nutrient lecithin to TMAO.
In the new study, the researchers took blood samples from 40 adults before and after they ate two hard- boiled eggs, a common source of lecithin. After eating the eggs, their blood levels of TMAO were elevated. But if participants took antibiotics before eating the eggs, their TMAO levels were suppressed, the researchers said.
In a second study, the researchers followed about 4,000 people who were being evaluated for a heart condition. (For instance, about three-quarters had high blood pressure, and 42 percent had had a prior heart attack.)
Participants who had a heart attack, stroke or died during the study period had higher average TMAO levels than those who didn't experience a cardiovascular event. 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.
"This is going to be a landmark observation," said Dr. Scott Wright, a cardiologist at Mayo Clinic in Rochester, Minn., who was not involved in the study. If the findings are confirmed by future studies, it may result in a shift in dietary recommendations away from foods that may cause gut bacteria to produce TMAO.
The findings also provide an explanation for why some people are particularly susceptible to heart disease while others are not, said Dr. Sanjay Rajagopalan, a cardiologist at Ohio State University Wexner Medical Center. In additional to genetic and environmental factors, components of our "internal environment," such as gut microbes, may play a role in this risk, he said.
However, the new study cannot prove that high TMAO levels cause cardiovascular disease, and future studies are needed to examine the effect of lowering TMAO levels, Rajagopalan said.
Wright recommended people eat mainly lean meat, such as chicken and turkey, and limit consumption of beef to one or two times a week.
Earlier this month, the same group of researchers published a study that found a link between consumption of carnitine, which is found in red meat, and a risk of heart disease. Carnitine is also converted by bacteria to TMAO.
The new study is published in the April 25 issue of the New England Journal of Medicine.
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