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Scientists have discovered what may be an important new risk factor for heart disease, and there's a surprising twist. It appears to come from bacteria in our digestive systems. As NPR's Rob Stein reports, the discovery could lead to new ways to prevent heart attacks and strokes.
ROB STEIN, BYLINE: We all know there are lots of things that are bad for our hearts - high blood pressure, cholesterol. But Stanley Hazen of the Cleveland Clinic says some people make it clear there's more, a lot more we don't know.
STANLEY HAZEN: People who have high cholesterol seem to never go on and develop heart disease, and then others who have more modest levels of cholesterol and then have a very early heart attack.
STEIN: So Hazen started hunting around for other risk factors, and he found a compound called TMAO. But it wasn't clear TMAO had anything to do with heart disease. So he tested more than 4,000 people for their TMAO levels and followed them for three years to see what happened. He reports what he found in this week's New England Journal of Medicine.
HAZEN: What we saw is that the blood level of TMAO strongly predicted who is at risk for experience a heart attack, stroke or death in that ensuing three-year period.
STEIN: Those with the highest levels had about double the risk of those with the lowest. Now, a lot more research is still needed to prove TMAO actually causes heart disease, and it remains unclear exactly how it might cause heart disease. But if it does, the next question is: Where does TMAO come from?
Well, Hazen had a theory that he tested in mice. Here's the theory: That when we eat certain foods, like red meat and eggs, bacteria in our digestive system basically belch out something, something that gets turned into TMAO.
HAZEN: We had kind of proven that TMAO in the blood was coming from bacteria in the mice, but it had not been proven in humans.
STEIN: So the researchers conducted another experiment. They fed 40 volunteers things they thought would make TMAO rise in their blood, like hard-boiled eggs. Sure enough, their TMAO levels spiked.
HAZEN: But if then subjects were placed on a cocktail of antibiotics that are good at eradicating bugs in the intestines, now, absolutely no TMAO appears in the bloodstream.
STEIN: Next, when the antibiotics were stopped, the bacteria and the TMAO came roaring back. That, Hazen says, proves we can blame the bacteria for TMAO.
HAZEN: This is like, if you will, the waste product that the bacteria is not digesting.
STEIN: Joseph Loscalzo of the Harvard Medical School says the research opens up a whole new way of thinking about heart disease.
JOSEPH LOSCALZO: I think it's an incredibly big deal. It really provides completely new insight into a mechanism for heart disease and stroke that we didn't appreciate previously.
STEIN: And the hope is that new insight could lead to totally new ways to prevent heart attacks and strokes.
LOSCALZO: Perhaps a probiotic approach that would involve the intentional ingestion of certain types of bacteria that might alter the population of bacteria in the gut to one that is beneficial.
STEIN: Or perhaps people could change the bacteria in their guts by changing what they eat, or scientists could develop drugs that block TMAO. Wherever the research eventually leads, Hazen says the work focuses attention on the complicated relationship that humans have with the microbes that inhabit our bodies.
HAZEN: They require us. We require them. And we have coevolved over the eons together. And they play an essential role in eating and digestion, but no one had really appreciated until very recently that they also can sometimes participate in disease processes.
STEIN: In fact, evidence has been mounting that microbes in our bodies do play a role in many diseases, including obesity, diabetes and others. Rob Stein, NPR News.
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