Carnitine, which we get from animal proteins like red meat and chicken, and produce from the amino acids lysine and methionine, has been a popular supplement in the fitness and bodybuilding world for years. Why? This compound—more than 95 percent of which can be found in our muscles—helps us turn fat (specifically long-chain fatty acids) into energy by transporting it to the mitochondria (a.k.a. energy generators) in our cells.
In fact, one 2011 Journal of Physiology study found that when healthy recreational athletes supplemented with two grams of carnitine and 80 grams of carbohydrates twice daily for six months, they increased the concentrations of carnitine in their muscles by 21 percent, which allowed them to use about 50 percent less glycogen—and thus more fat (like body fat)—to fuel low-intensity exercise. They were also able to work at a 35 percent higher intensity—while producing significantly less lactate, a biomarker of fatigue—in all-out cycling tests after their workouts. “Maximal exercise has been associated with a decrease in carnitine levels in trained athletes, so restoring levels through supplementation can have beneficial effects,” echoes Ginger Hultin, R.D., spokesperson for the Academy of Nutrition and Dietetics.
Given its fat-burning, endurance-boosting abilities, it’s no wonder carnitine has long been a favorite of gym junkies. But guess what? Carnitine’s benefits extend far beyond the walls of the weight room. Here are four other reasons to consider taking it.
1. Reproductive Health
Remember when we said 95 percent of carnitine is located in the muscles? In men, some of the other five percent is housed in the testes, and therefore in sperm. According to a 2016 Reproductive Biology and Endocrinology study of guys with subfertility (reduced fertility indicated by failed attempts to conceive), supplementing with 500 milligrams of carnitine twice daily for three months significantly improved sperm volume, density, and motility (ability to swim). How? Carnitine acts as an antioxidant (a.k.a. free radical catcher) and helps to ward off oxidative damage to reproductive cells, a major contributor to infertility.
Since nutrient insufficiencies have also been linked to fertility issues, a concoction that combined carnitine with other nutrients—including arginine, zinc, and vitamin E—was shown to have an even greater benefit for sperm health.
Carnitine’s antioxidant actions can impact female reproductive health, too. A recent Reproductive Biology and Endocrinology review concluded that carnitine supplementation supports healthy hormone levels and oocyte (immature egg) health, and may especially benefit women with reproductive issues such as polycystic ovary syndrome, endometriosis, and amenorrhea.
You already know that carnitine helps combat muscle fatigue—but its energy-boosting benefits don’t end there. “The reason carnitine could help decrease fatigue may have to do with its role in lipid metabolism and energy production in the body,” says Hultin. By transporting long-chain fatty acids and a compound called acetyl-CoA into the mitochondria, carnitine supports mitochondrial function and energy production on a cellular level.
Those with low carnitine levels—like people undergoing chemotherapy, which can lead to decreased carnitine consumption and affect the body’s ability to absorb carnitine—often experience fatigue. One recent Molecular and Clinical Oncology study found that chemo patients who supplemented with 500 milligrams of carnitine three times a day for eight weeks reported a decline in general fatigue.
Carnitine has also been shown to ward off fatigue in the elderly, with one study finding that supplementing with two grams a day for six months reduced physical and mental fatigue in older participants by 52 and 43 percent, respectively, says Hultin.
3. Heart Health
One of the most promising potential benefits of carnitine being explored by researchers these days is its role in improving heart health, specifically cholesterol and blood pressure.
One recent Lipids in Health and Disease study, for example, found that 12 weeks of supplementing with 1,000 milligrams of carnitine a day supported healthy HDL (‘good cholesterol’) and apolipoprotein-A (the substance that helps clear fat from cells) levels in people with coronary artery disease.
Meanwhile, a 2017 meta-analysis of 468 studies about carnitine and heart health concluded that carnitine supplementation may “improve factors associated with metabolic syndrome and cardiovascular disease, such as arterial hypertension, cholesterol levels, impaired glucose tolerance, and insulin resistance.”
The researchers cite carnitine’s transportation of fatty acids to the mitochondria as critical for the heart, which requires a constant flow of energy to function properly. They suggest that carnitine increases heart cells’ ability to produce energy, helping to increase how much blood the heart can process and pump out with each beat and lowering resting heart rate.
What’s more, carnitine can also increase the production of nitric oxide, which dilates blood vessels, and supports proper circulation.
4. Insulin Function
Insulin, the hormone secreted by the pancreas in response to rises in blood sugar or concentrations of certain amino acids (like leucine), helps shuttle glucose and amino acids into our cells. According to a review published in the European Journal of Nutrition, carnitine supplementation can improve glucose tolerance, or how quickly the body can clear sugar from the blood. The researchers noted that this effect was especially beneficial for those with insulin resistance, a condition in which the body has become resistant to insulin, and which can develop into prediabetes or type 2 diabetes if not addressed.
The buildup of the by-products created during energy production in the mitochondria has been implicated in insulin resistance—and carnitine helps clear these by-products from the mitochondria.