You may have seen recent media reports about a scientific study suggesting that carnitine could be linked to heart disease. Carnitine – found in red meat, poultry, and fish and also available as a dietary supplement – is an amino acid that, unlike most amino acids, is not used in the body to make proteins. Instead, carnitine increases fat burning and improves energy metabolism.
The scientific study found that high plasma levels of carnitine in human subjects are associated with an increased risk of cardiovascular disease, including heart attacks and strokes. Furthermore, in a mouse model, increased levels of carnitine seemed to be a factor promoting atherosclerosis, the underlying cause of cardiovascular disease.
In addition, the study found that gut bacteria are converting carnitine into a substance called trimethylamine oxide (TMAO), which is absorbed into the body and seems to be causing the increased heart disease risk. In a related study published just a few days ago, the same authors reported that lecithin, abundant in meat and egg yolk, and choline, an essential nutrient available as a dietary supplement, also can give rise to TMAO in the body after conversion by intestinal bacteria.
Both studies were published in prestigious scientific journals, and the principal investigator and senior author, Dr. Stanley Hazen, is a highly respected, first-rate scientist.
Yet my immediate reaction to the carnitine study is that it is intriguing and novel but far from definitive. To call carnitine a culprit in heart disease in humans, as the press labeled it, is premature. I believe the main culprit in red meat for causing atherosclerosis and increasing cardiovascular risk is saturated fat. Additionally, a British study published in 1999 found that the consumption of 8 oz. of marine fish, such as cod, haddock, halibut, or herring, elevated urinary levels of TMAO and its precursor, trimethylamine, on average about 35 times, whereas eating 8 oz. of beef, other meats, or dairy products such as cheese, eggs and milk had no effect on the background levels of these compounds! And we know that the consumption of fish is associated with a lower risk for heart disease.
A large body of work, accumulated over decades, indicates that one form of carnitine called acetyl-L-carnitine is safe to use at appropriate doses. Acetyl-L-carnitine has been given clinically at very high doses – as much as 8 grams per day – with no observed side effects. Furthermore, we know from studies in rodents that acetyl-L-carnitine improves mitochondrial function, lowers lipid levels (which would lower cardiovascular risk), and improves muscle and brain function.
Therefore, based on current evidence, carnitine appears to have significant health benefits, and the balance – or “benefit-to-risk ratio”– favors the use of carnitine supplements.
Personally, I will continue to take a daily supplement containing 1,000 mg of acetyl-L-carnitine. In addition, I exercise regularly, eat a heart-healthy diet, and avoid red meat.
As a resource of trusted nutrition information for the public, we at the Linus Pauling Institute continually reassess our recommendations, based on new scientific information. We will let you know if we find compelling evidence against carnitine supplementation.
In addition to our Research Newsletter and Micronutrient Information Center (MIC), we are enhancing our communication efforts, such as with this new blog, to help you make informed personal decisions towards achieving optimum health.
To your health!
For more about LPI’s recommendations for a healthy diet and lifestyle, I refer you to our Rx for Health. You can also read my more detailed discussion of the scientific aspects of the carnitine study referred to in this post at this link, and the MIC article on L-carnitine.