New Study Links L-Carnitine to Cardio Problems

A team of scientists have reported L-carnitine consumed by frequent red meat eaters may contribute to increase risk of cardiovascular disease (CVD). The research, a collaborative effort led by researchers from the Cleveland Clinic, was published online April 7 by Nature Medicine and details  how gut bacteria metabolize L-carnitine, resulting in a byproduct being studied as a biomarker for increased risk of cardiovascular problems, including atherosclerosis and heart attack.

The researchers noted intestinal bacteria metabolize choline and phosphatidylcholine producing trimethylamine (TMA), which is further metabolized to, trimethylamine-N-oxide (TMAO), a proatherogenic biomarker.  L-carnitine is also metabolized by gut bacteria to produce TMA and TMAO. They theorized TMAO helps cholesterol infiltrate artery walls and prevents the body from excreting excess cholesterol.  

In their small study, the researchers looked at the effect of carnitine in red meat eatersred meat is a rich source of carnitineand non-meat eaters (vegetarians and vegans). As part of their research, TMAO levels were measured in a handful of meat eaters and a vegan who ate steaks and took L-carnitine capsules. In frequent meat eaters, TMAO levels were increased after carnitine supplementation, while TMAO appeared to pass right through the vegan, without producing TMAO. These results were supported by an analysis of data from 2,595 adults undergoing cardiac evaluation, which revealed plasma carnitine levels were associated with increased risk of both CVD and related major events including heart attack and stroke. This correlation was only found in regular meat eaters, not vegetarians or vegans.  Researchers followed up the steak portion of the study by giving the frequent meat eaters antibiotics to wipe out the bacteria responsible for producing TMAO, and they noticed the TMAO levels in those subjects were no longer present in the blood.