By Christin L. Seher, MS, RD, LD
Today’s Dietitian
Vol. 15 No. 9 P. 76
Recent research indicates that maintaining sufficient levels of the amino acid L-carnitine may improve cardiac patients’ health.
Found naturally in red meat and synthetically as an over-the-counter nutritional supplement, L-carnitine plays an important role in energy metabolism and blood glucose regulation. In muscle tissue and the heart’s myocardium, L-carnitine helps transport long-chain fatty acids across the inner mitochondrial membrane where they become a primary substrate in energy production, metabolized through beta-oxidation.
In the heart, L-carnitine becomes especially important as the myocardium prefers to oxidize long-chain fatty acids for energy.1 In addition to its role in energy production, L-carnitine helps remove toxins from inside the mitochondria, mediate oxidative stress, inhibit fatty acid ester accumulation during ischemic events, and prevent cardiac cell apoptosis.1,2
Because of its importance in metabolic pathways, L-carnitine is widely marketed as a nutritional supplement, heralded as a way to boost energy production, promote weight loss, and improve athletic performance. At this point, however, these claims haven’t been substantiated by a consensus of clinical research studies. Most notably, studies of L-carnitine supplementation in athletes have been disappointing. While plasma levels have been shown to increase with supplementation, the intramuscular concentration of L-carnitine doesn’t always increase, and performance isn’t consistently affected.3
According to Janet Bond Brill, PhD, RD, LDN, a heart health expert and the author of Blood Pressure Down!, because L-carnitine is synthesized in the body from the amino acids lysine and methionine, “the body makes sufficient L-carnitine, so this isn’t an essential nutrient; we don’t need to eat it or take it in supplement form.” This holds true for the majority of the general population.
But recent research examining the effects of L-carnitine supplementation in cardiac patients appears promising, as studies indicate that maintaining sufficient levels of this amino acid in heart muscle appears to offer several protective benefits, prompting further consideration as to whether L-carnitine can effectively treat cardiac disease.
Meta-Analysis Review
Studies show that restoring myocardial carnitine—which can deplete rapidly during ischemic events such as a myocardial infarction (MI) and substantially decrease in diseased heart tissue—to adequate levels improves heart function and decreases left ventricle dilation, a key factor that may help avoid further cardiac problems, heart failure, and even death.2 Since heart disease remains the No. 1 cause of mortality in the United States, the potential for L-carnitine to attenuate further cardiac stress has far-reaching implications.
For these reasons, a team of researchers recently set out to more formally examine the effects of L-carnitine supplementation on cardiac health. The results of their meta-analysis, published in June in Mayo Clinic Proceedings, further indicate that L-carnitine is one dietary supplement worth watching.2
The researchers examined 13 clinical trials conducted in the last 30 years, representing more than 3,600 cardiac patients, to investigate the effects of L-carnitine supplementation on patients with a history of acute MI. The research team concluded that L-carnitine has potential as an inexpensive and safe therapy for cardiac patients after their analysis revealed a significant reduction in mortality from all causes (27%), a highly significant decline in ventricular arrhythmias (65%), and a significant decrease in the development of angina (40%).2 The analysis failed to show any association between supplemental L-carnitine and decreased occurrence of repeat MI or heart failure, though.
The study authors specifically attribute the potential protective effects of this supplement to the reestablishment of myocardial L-carnitine back to more optimal levels, which improves metabolic heart functioning.
According to the authors, a major limitation of the study was that the trials included in their analysis were conducted in a “less aggressive” treatment era, one in which dietary modifications were a focus of treatment for heart disease, and different medications were used than are recommended today. For this reason, the authors note that further research is needed that takes into account current treatment protocols for acute coronary syndrome and that standardizes the dosage of the L-carnitine used.
From the 13 trials examined, the study authors believe that a minimum dosage of 2 g of L-carnitine per day is needed, but an optimal amount is closer to 6 to 9 g/day. However, the exact dosage pattern remains unclear.
Renal Patients
Besides individuals with acute MI, other patient populations may benefit from supplemental L-carnitine as well. Studies of cardiac function in patients on hemodialysis for end-stage renal disease, for example, also have shown some improvement when L-carnitine levels increased.4,5 This includes improved blood flow and decreased arrhythmia without causing left ventricle hypertrophy or increases in end diastolic blood pressure.4
Since cardiovascular diseases such as coronary artery disease, MI, and heart failure account for almost 50% of mortality in this patient population,5 the potential for L-carnitine to improve cardiac function warrants further investigation. Furthermore, research indicates L-carnitine levels continue to decrease the longer a patient remains on dialysis, indicating that even patients with normal cardiac function may need supplementation while on dialysis.4
Conflicting Evidence
Despite the benefits certain individuals receive with supplementation, it remains important to explain that a chronic, high dietary intake of L-carnitine consistently has been linked with an increased risk of heart disease. “Another recent study raises concerns about the chronic intake of high amounts of carnitine from red meat,”6 Brill says. “L-carnitine is metabolized by the intestinal microbiotia to trimethylamine-N-oxide, an atherogenic substance which increases risk of cardiovascular disease.” Conflicting evidence such as this indicates that the benefits certain patient populations receive from L-carnitine supplementation may be best achieved by supplementing with synthetic vs. dietary sources.
For now, RDs working with cardiac patients should keep L-carnitine on their radar of supplements to watch. As Brill notes, while short-term supplementation in patients with acute coronary syndrome appears promising based on the current research, much more data are needed before the benefit of supplementation in acute MI patients becomes routinely incorporated into practice or before exact dosing protocols become clear.
Even more importantly, Brill tells practitioners to remember that “long-term exposure to L-carnitine from a diet high in red meat isn’t prudent, as a considerable body of research suggests this dietary pattern increases risk of cardiovascular disease and premature mortality.”
— Christin L. Seher, MS, RD, LD, is an instructor and nutrition consultant in northeast Ohio.
References
1. Oyanagi E, Yano H, Uchida M, Utsumi K, Sasaki J. Protective action of L-carnitine on mitochondrial function and structure against fatty acid stress. Biochem Biophys Res Commun. 2011;412(1):61-67.
2. DiNicolantonio JJ, Lavie CJ, Fares H, Menezes AR, O’Keefe JH. L-carnitine in the secondary prevention of cardiovascular disease: systematic review and meta-analysis. Mayo Clin Proc. 2013;88(6):544-551.
3. McArdle WD, Katch FI, Katch VL. Sports and Exercise Nutrition. 4th ed. Baltimore, MD: Lippincott Williams & Wilkins; 2012.
4. Khosroshahi HT, Habibi-Asl B, Toufan M, Ghabili K, Safarpour S. Effects of oral L-carnitine on cardiac abnormalities of maintenance hemodialysis patients. Biomed Int. 2010;1:30-33.
5. Molyneux R, Seymour AM, Bhandari S. Value of carnitine therapy in kidney dialysis patients and effects on cardiac function from human and animal studies. Curr Drug Targets. 2012;13(2):285-293.
6. Koeth RA, Wang Z, Levison BS, et al. Intestinal microbiota metabolism of L-carnitine, a nutrient in red meat, promotes atherosclerosis. Nat Med. 2013;19(5):576-585.
