Supplement Series: Everything you need to know about L-carnitine
L-carnitine is an amino acid that is produced in the body and helps to turn food into energy. It can be found in red meat, poultry, fish and dairy products, as well as some vegetables. L-carnitine supplementation has been shown to improve heart health, increase energy levels and help with weight loss. This could explain why it has been an interest of the athletic community for quite some time.
What is L-carnitine?
The true chemical name of L-carnitine is quite the mouthful - β-hydroxy-γ-N-trimethylaminobutyric acid. It is derived from the amino acid lysine and was first isolated in 1905 from a slab of meat.[1] There are two different isomers of the amino acid as seen across the chemical world, D and L. L-carnitine is biologically active while D-carnitine will inhibit the activity of the L- form and can be toxic in higher concentrations.[1]
What is the role of this amino acid?
L-carnitine is foremost known for its role in in the metabolism of fats, as it is essential for the transport of fatty acids into the mitochondria for energy production. More specifically, long-chain fatty acids like those found in olive oil and nuts are broken down to produce ATP.
Studies have shown that L-carnitine can help to improve heart function in people with heart disease, and may also help to prevent heart disease in healthy people. Research as early as 1983 saw teams exploring the protective role of L-carnitine on animal heart tissues. They discovered early that there was a correlation between ATP levels and free carnitine.[2] Jumping ahead 35 years, another team completed a review that showed carnitine has favourable effects in everything from hypertension and diabetic ketoacidosis to cardiac arrhythmias and ischemic-reperfusion injuries.[3]
L-carnitine has also been shown to increase energy levels, and may be helpful for people who are struggling with fatigue. In addition, L-carnitine supplementation has been shown to be complementary for weight management efforts, and may help to reduce body fat. Carnitine is far from becoming the next magic weight loss pill, but studies are ongoing.
The connection with nitric oxide
Nitric oxide (NO) is a gas molecule that is produced by the body. It plays an important role in vasodilation, which is the widening of blood vessels. This allows more blood to flow through the vessels, which improves circulation. Researchers assessed a group of participants engaging in resistance training to see whether carnitine supplementation impacted oxygen delivery to muscles. A dose of 2 grams for 23 days was superior to a placebo for increasing oxygen supply and reducing muscle soreness.[4]
Nitric oxide can also help to protect the body against damage caused by free radicals. More technical, it reacts with peroxyl radicals as a sacrificial chain-terminating antioxidant.[5,6]
How to know if you're deficient.
L-carnitine deficiencies can cause a variety of symptoms, including fatigue, muscle weakness, nausea and vomiting, heart problems, and seizures. At a deeper physiologic level, carnitine deficiencies can cause declines in a variety of processes.[7]
gluconeogenesis - the ability of the body to convert amino acids and other non-carbohydrate substances into glucose to fuel the body. This usually happens when there is a lack of carb intake through the diet. 54% of glucose comes from gluconeogenesis after 14 hours of starvation, and this number continues to climb as the hours pass. [8, 9]
antioxidant status - as mentioned talking about nitric oxide, antioxidants help defend the body against damage caused by free radicals.
fatty acid metabolism - carnitine is necessary for the transport of long-chain fatty acids across the inner mitochondrial membrane so that they can be used for energy production. This process is called beta-oxidation.
ammonia detoxification - ammonia is a toxic waste product that is produced when protein is broken down. It can build up in the body and cause serious health problems. Carnitine helps to remove ammonia from the body. A deficiency in carnitine can therefore lead to a decline in these important processes, which can result in a variety of symptoms.
anti-inflammatory status - carnitine has also been shown to have anti-inflammatory effects. This is important because inflammation is a major contributing factor in many chronic diseases.
albumin synthesis - albumin is a type of protein that is found in the blood. It helps to keep fluid from leaking out of blood vessels. A carnitine deficiency can lead to a decline in albumin synthesis, which can cause problems such as fluid retention and edema (swelling).
Carnitine deficiencies are relatively rare, but they can occur in certain people, such as those with certain genetic disorders, those who are malnourished, or those who have certain medical conditions. For the average healthy individual, a robust diet should provide all of the necessary factors to generate enough carnitine to keep you fuelled.
Food sources and co-factors to consider
The compound can be obtained through diet, but it is also synthesized within the body from lysine and methionine.[10] This is why adequate amounts of lysine and methionine through diet are important for supporting your carnitine levels. Lysine can be found in fenugreek, spirulina, eggs and certain fish like cod and sardines. Methionine is highly concentrated in tuna and can also be found in plant-based sources like brazil nuts, quinoa, lentils and tofu.
Other co-factors involved in the synthesis of free carnitine include:
Vitamin C - an early symptom of vitamin C deficiency is fatigue, which makes sense now that you understand its role in generating energy. This extends to weight management efforts as well with studies showing those with healthy vitamin C levels lose more weight [11], oxidize 30% more fat during moderate exercise [12] and have lower body mass index, body fat and waist circumference.[13]
Vitamin B6 - this water-soluble vitamin is most often found in the form of pyridoxal 5' phosphate (PLP) and pyridoxamine 5' phosphate (PMP), both of which play a role in amino acid metabolism. It is also required for the synthesis of neurotransmitters and hemoglobin. Chickpeas, tuna, potatoes and bulgur are dietary sources to consider. Those battling alcohol use disorder are also at an increased risk of vitamin B6 deficiency and symptoms like a swollen tongue, scaling of the lips, cracks at the corner of the mouth, weakened immune function and even anemia.
Niacin - otherwise known as vitamin B3, niacin is required by over 400 enzymes, more than any other vitamin coenzyme in the body.[14] Dietary sources include marinara sauce, turkey breast, brown rice (cooked), sunflower seeds and beef liver. Grain sources can be limited as the niacin is largely bound within polysaccharides, meaning only about 30% is bioavailable.[15]
Ferrous ions - often found in the form of ferrous sulphate or ferrous gluconate due to its higher availability, iron is required for L-carnitine synthesis. Populations including young children, teenage girls and those currently pregnant are at higher risk of deficiencies. Adding dark leafy greens and beans (i.e. kidney, white) to the diet should be encouraged.
How to take it
L-carnitine supplements are available in a variety of forms, including capsules, tablets, liquids and powders. A care provider familiar with its use can help you figure out the best form for you.
Safety profile
L-carnitine as a supplement has a generally safe profile, and is well-tolerated by most. Doses as high as 2 grams per day have been investigated for a year in healthy adults with few ill effects like nausea and stomach discomfort.[16, 17] One biomarker to be mindful of is levels trimethylamine-N-oxide (TMAO). TMAO may increase with high doses of carnitine supplementation and could increase your risk of atherosclerosis.[18, 19]
In summary...
L-Carnitine is a compound that is synthesized in the body from lysine and methionine. It plays a role in energy generation and weight management, and can be obtained through diet or supplementation. Co-factors including vitamins C, B6, niacin and ferrous ions are important for carnitine synthesis and you may consider having your nutrient intake and blood levels assessed by your local ND.
References
Durazzo, Alessandra, et al. "The nutraceutical value of carnitine and its use in dietary supplements." Molecules 25.9 (2020): 2127.
Suzuki, Y., et al. "Effects of l-carnitine on tissue levels of free fatty acid, acyl CoA, and acylcarnitine in ischemic heart." Advances in Myocardiology. Springer, Boston, MA, 1983. 549-557.
Wang, Zhong-Yu, et al. "l-Carnitine and heart disease." Life sciences 194 (2018): 88-97.
Spiering, Barry A., et al. "Effects of L-carnitine L-tartrate supplementation on muscle oxygenation responses to resistance exercise." The Journal of Strength & Conditioning Research 22.4 (2008): 1130-1135.
ME, Shils. "Olson G. Roos AC. Modern nutrition in health and disease." (2006).
Hummel, Stephen G., et al. "Nitric oxide as a cellular antioxidant: a little goes a long way." Free radical biology and medicine 40.3 (2006): 501-506.
Hanai, Tatsunori, et al. "Usefulness of carnitine supplementation for the complications of liver cirrhosis." Nutrients 12.7 (2020): 1915.
Chourpiliadis, Charilaos, and Shamim S. Mohiuddin. "Biochemistry, gluconeogenesis." StatPearls [Internet]. StatPearls Publishing, 2021.
Chandramouli V, Ekberg K, Schumann WC, Kalhan SC, Wahren J, Landau BR. Quantifying gluconeogenesis during fasting. Am J Physiol. 1997 Dec;273(6):E1209-15.
Durazzo, Alessandra, et al. "The nutraceutical value of carnitine and its use in dietary supplements." Molecules 25.9 (2020): 2127.
Naylor, G. J., L. Grant, and C. Smith. "A double blind placebo controlled trial of ascorbic acid in obesity." Nutrition and health 4.1 (1985): 25-28.
Johnston, Carol S. "Strategies for healthy weight loss: from vitamin C to the glycemic response." Journal of the American College of Nutrition 24.3 (2005): 158-165.
Johnston, Carol S., et al. "Plasma vitamin C is inversely related to body mass index and waist circumference but not to plasma adiponectin in nonsmoking adults." The Journal of nutrition 137.7 (2007): 1757-1762.
Penberthy WT, Kirkland JB. Niacin. In: Erdman JW, Macdonald IA, Zeisel SH, eds. Present Knowledge in Nutrition, 10th ed. Washington, DC: Wiley-Blackwell; 2012:293-306.
Coates, Paul M., et al., eds. Encyclopedia of Dietary Supplements (Online). CRC press, 2004.
Villani, Rudolph G., et al. "L-Carnitine supplementation combined with aerobic training does not promote weight loss in moderately obese women." International journal of sport nutrition and exercise metabolism 10.2 (2000): 199-207.
Hathcock, John N., and Andrew Shao. "Risk assessment for carnitine." Regulatory Toxicology and Pharmacology 46.1 (2006): 23-28.
Koeth, Robert A., et al. "Intestinal microbiota metabolism of L-carnitine, a nutrient in red meat, promotes atherosclerosis." Nature medicine 19.5 (2013): 576-585.
Tang, WH Wilson, et al. "Intestinal microbial metabolism of phosphatidylcholine and cardiovascular risk." New England Journal of Medicine 368.17 (2013): 1575-1584.