L Carnitine effects ?What do we (not) know about the amino acid, whose name is often considered synonymous with weight loss?
Table of Contents
What is L-carnitine?
L-carnitine (L-carnitine) is a natural, non-protein amino acid. It was originally isolated from meat in 1905, and the Latin word for meat / table – carnis, is the source of its name. In the human body, the main action on carnitine is between cell membranes, helping to implement one of the mechanisms of energy production. To the greatest extent this is used in the organs, when used for energy, large amounts of fatty acids are used. It’s basically a muscle and a heart.
In the body, 99% of L-carnitine is found in the intracellular space and the main organs in which it is stored are skeletal muscles. The next most concentrated organ of L-carnitine is the liver. In recent years, the amino acid has been studied as part of solutions to combat the metabolic syndrome due to the good results it shows in improving insulin sensitivity.
L-carnitine is a non-protein amino acid that has always been associated with weight loss. Over time, the amino acid has earned the name of a vitamin-like substance or pseudovitamin, and more and more attention is being paid to its health benefits.
How do we get carnitine?
Like most amino acids, L-carnitine is found in the food we eat. Especially in animal products, among which meat is the richest source. To a much lesser extent, L-carnitine can also be found in milk, and in plant foods the amounts are practically insignificant. In the attached table you can see the content of L-carnitine in some major food sources.
Although through food we get about 75% of the total amount of L-carnitine for the day, the remaining 25% is synthesized by the body itself. The exceptions are vegetarians, who manage to get only 10% through food and synthesize the remaining 90%. Vegans and vegetarians may be more in need of L-carnitine, and you can read more about this in our article “Creatine, beta-alanine and L-carnitine in vegetarian diets.” Biosynthesis occurs in the brain, kidneys and liver with the help of two of the essential amino acids – lysine and methionine. Although skeletal muscle is the largest storehouse of L-carnitine, it does not have the ability to synthesize the amino acid.
Two enzymes involved in a number of chemical reactions are highly dependent on the presence of vitamin C and its deficiency can significantly disrupt the biosynthesis of L-Carnitine. The amino acid exists in the body in two forms – L-carnitine and the acetylated form acetyl-L-carnitine (Acetyl-L-Carnitine / ALCAR / ALCAR). ALCAR is obtained when L-carnitine binds to the acetyl group of acetyl-coenzyme A (Acetyl-CoA).
L-carnitine synthesis is lower in newborns, although this is covered by both breast milk (providing dietary L-carnitine) and infant formulas to which L-carnitine is added.
Assimilation, metabolism and elimination
L-carnitine, including ALCAR, is absorbed in the first part of the small intestine, mainly by the sodium-dependent transporter OCTN2. The absorption of L-carnitine from food is much more effective than when taken as a dietary supplement. Absorption from food is in the range of 54-87%, while orally taken food supplement, regardless of the form of carnitine, is in the range of 14-18%.
This difference is thought to be due to the body’s ability to absorb smaller doses of L-carnitine better. It is estimated that a 70 kg person gets between 20 and 200 mg of L-carnitine per day from food, while the concentration in food supplements starts from 500 mg upwards in one dose, and the total amount for the day is about 2-3 grams. And despite the difference in digestibility as a percentage, much more L-carnitine can be obtained through a dietary supplement than through food. Digestibility also depends to a very large extent on the already available L-carnitine in the body. In cases of deficiency and low levels of carnitine, intestinal digestibility is significantly increased.
This is seen when taking L-carnitine in vegetarians and vegans, who generally have much lower levels of amino acids in the body and are at risk of deficiency. Research shows about 10% higher absorption of L-carnitine in people with low levels than in people with normal levels. However, this group showed a lower conversion of L-carnitine to some of the subsequent metabolites, such as trimethylamine-N-oxide, which is a key component for heart health37.
As shown in the table (Examine.com), vegetarians and omnivores have intestinal bacteria that successfully convert ingested L-carnitine to γ-butyrobetaine, but the subsequent conversion to trimethylamine-N-oxide and trimethylamine is completely absent. Another factor influencing digestibility may be the gene. It was in a study of the effect of carnitine on blood sugar and insulin that the substance was found to be 5 to 7 times more potent in subjects in Eastern Europe60. This means that the genotype can have a decisive effect.
L-carnitine is usually deficient in vegans and vegetarians, but is more absorbed by them. However, this group is characterized by lower conversion of the amino acid to other metabolites.
Serum levels of L-carnitine are in the range of 23–73 µmol / L, and those of the acetylated form – 3–14 µmol / L. Oral administration of 2 grams of L-carnitine, acetyl-L-carnitine or propionyl-L-carnitine (Propionyl-L-Carnitine / PLC) showed a peak serum Cmax concentration of L-carnitine (84.7 +/- 25.2 umol / L / h), followed by ALCAR (12.9 +/- 5.5) and PLC (5.08 +/- 3.08). The peak occurs about 3 hours after ingestion. Once in the blood, carnitine is directed to the appropriate cells where it is needed. Unfortunately, the body is not able to store large amounts of carnitine and regular supplementation does not increase the available reserves in the tissues, which effect is observed when taking other substances, such as creatine.
Studies show that after a single dose of 500 mg of intravenously injected ALCAR, most of the amino acid is hydrolyzed and blood levels return to normal within about 12 hours. The levels of L-carnitine in the blood are maintained within appropriate limits and by means of a very efficient process of reabsorption in the kidneys. The rate of reuptake is rapidly adapted to the levels of carnitine in the blood. Accordingly, as blood levels increase after intravenous or oral administration, the kidneys begin to eliminate more and more L-carnitine instead of returning it to the blood.
L-carnitine from food is better absorbed than from food supplements, and the second type still has good bioavailability. As the amount increases, so does the rate of absorption. Intravenous administration is most effective, while application to the skin is useless.
Physiological functions
Although it was not initially suspected how important L-carnitine was for the body’s work, in the 1950s, a number of studies conducted by and with the help of Irving Fritz revealed the essentiality of the amino acid in energy production in cells. . Carnitine plays an essential role so that fatty acids can be used for energy. In order for fatty acids to be used, they must go through a process called beta-oxidation in the cellular mitochondria.
Structurally, the mitochondria are divided into two compartments by an outer and an inner mitochondrial wall. L-carnitine plays a role in both places, using two enzymes called Carnitine Palmitoyltransferases. They are CPT1 and CPT2 respectively. In the outer mitochondrial wall, L-carnitine works with CPT1, and in the inner wall with CPT2. The beta-oxidation process itself takes place in the intramembrane space. The problem is that long-chain fatty acids cannot cross the inner membrane on their own. With the help of CPT1 and CPT2, L-carnitine binds to long-chain fatty acids and serves as a shuttle for their transport into the intramembrane space.
Once the intramembrane space is reached, CPT2 divides the molecule into its constituent parts. Then long-chain fatty acids can undergo the process of beta-oxidation, and the remaining free L-carnitine can play its second important role in energy metabolism. Using the enzyme carnitine acetyltransferase (CAT), L-carnitine in the intramembrane space can be converted to acetyl-l-carnitine. Subsequently, ALCAR may give up its acetyl group to participate in the Krebs cycle of energy production.
The need for L-carnitine for the use of fats for energy is particularly well observed in a scientific study in which a reduction in L-carnitine levels in muscle by 85% leads to a 75% reduction in palmitate oxidation levels, which is a marker. for energy production through beta-oxidation.
L-carnitine is an important component in the production of cellular energy and the use of fatty acids as an energy source. From these physiological properties comes the myth of the effectiveness of L-carnitine as a fat burning supplement.
L-carnitine deficiency
Deficiency is not observed in healthy people. Even vegans, who are a risk group for deficiency and have many times lower levels of carnitine, rarely suffer from health consequences due to deficiency. However, L-carnitine deficiency exists in certain health and genetic diseases and is divided into two types:
Primary systemic L-carnitine deficiency
Primary systemic deficiency (PSD) is a rare autosomal recessive disease of fatty acid oxidation. The disease is expressed in the much more difficult absorption of L-carnitine by the cells, accompanied by a defective process of reuptake in the kidneys. Together, they lead to systemic depletion of L-carnitine levels in the body, reaching below 10% of normal levels. PSD occurs in every 1-5 out of 10,000 people and most often occurs between 1 and 7 years of age. PSD affects three main organs:
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heart muscle – leading to progressive cardiomyopathy;
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central nervous system – leading to hypoketonic hypoglycemic encephalopathy;
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skeletal muscle – leading to myopathy.
In PSD, administration of L-carnitine in injectable or oral form is life-saving.
Secondary L-carnitine deficiency
Secondary L-carnitine (VD) deficiency is much more common than PSD, although there are no good statistics on the number of diseases. Secondary deficiency results in increased urinary excretion of L-carnitine. Unlike the primary, the cause of the secondary deficiency is associated with another health disease, such as liver or kidney. VD can be caused by a defect in fatty acid metabolism or taking certain medications, such as pivampicillin or valproic acid. Some treatments, such as hemodialysis, also significantly reduce L-carnitine levels, with a drop of up to 60%.
VD can also be caused by other serious diseases. Scientists have found a direct link between cancer and low levels of the amino acid38,39,40. In a study using an increasing dose (500 mg for 2 days, 1000 mg for 2 days and 2000 mg for 10 days), it was found that taking the food supplement normalized L-carnitine levels in cancer patients with a deficiency. Normalization of levels leads to improvement of the general condition, regulation of fatigue and body functions directly affected by the disease. There is also an increase in muscle mass.
The Stayfitlonger – team listed three different situations in which L-carnitine deficiency directly depends on a previous condition, which directly affects the levels of amino acids in the body. These forms of deficiency differ from the deficiency caused by suboptimal nutrition.
Proven and potential health benefits in humans
L-carnitine and acetyl-L-carnitine have been subjected to numerous studies in various fields of human health.
Metabolic syndrome
Research with normal and overweight people, as well as people with diabetes, has shown a significant effect on insulin sensitivity and glucose uptake by cells. Glucose uptake is improved by stimulating AMPK. Reducing the amount of acyl and acetyl groups in the cell, the accumulation of which has been shown to reduce insulin sensitivity, helps to improve insulin sensitivity.
The reduction of these groups can be done by removing them from the cell, followed by their excretion in the urine. A possible mechanism is the introduction of these groups into the mitochondria, where they can be used during beta-oxidation. As an additional effect we can note the lowering of blood sugar, so people with low blood sugar should be careful with the intake of the amino acid.
Reduction of Alzheimer’s symptoms
Carnitine, mostly ALCAR at doses of about 3 grams per day, has been studied in a number of scientific experiments to improve mental ability and slow cognitive function in elderly people with Alzheimer’s disease. While half of the studies show good and statistically significant positive results, unfortunately the other part of the studies do not find a difference between the studied groups of people.
However, it should be mentioned that even when positive results are observed, their potency is not high enough for ALCAR to be recommended as a stand-alone anti-disease agent, but may be a good option to supplement drug treatment.
Attention Deficit Hyperactivity Disorder
There are currently two well-conducted studies. In 2002, a German team of researchers found a significant improvement in symptoms in children diagnosed with ADHD, ranging between 20 and 65% in different participants. A 2007 study of 112 children looked at different results according to the type of ADHD. No improvements have been observed in mixed-type ADHD, but they are present in inattentive type disease. Doses of 3-4 grams of ALCAR per day were used in both studies.
Blood Pressure
Several studies have also shown significant potential for L-carnitine in the fight against high blood pressure. In one study, the combination of 1 g of acetyl-L-carnitine and 400 mg of alpha-lipoic acid resulted in nearly 10 units of systolic blood pressure decline in people over 55 years of age diagnosed with ischemic heart disease. 8 Similar results are observed in younger people suffering from high blood pressure. There is also a significant improvement in insulin sensitivity.
Intermittent claudication
Propionyl-L-carnitine has shown serious positive results in people suffering from intermittent claudication. Prolonged use of this form in doses of about 2-3 grams per day, several times shows an improvement in symptoms and an increase in the distances that can be walked by patients. The standard form of L-carnitine also shows good results in this regard, but weaker than propionyl-L-carnitine. It is possible that the results will be uniform if the dose of the standard form is increased.
Secondary prevention in people who have had a heart attack
People who have had a myocardial infarction are also likely to benefit from taking a standard dose of about 3-4 grams of L-carnitine per day. There are many scientific studies that show a significant reduction in mortality in the studied groups receiving L-carnitine. There is also a reduction in side effects caused by heart attack.
A 2013 meta-analysis conducted by DiNicolantonio JJ and his team, which included 13 well-conducted studies, confirmed the benefits of taking L-carnitine in people who have had a heart attack. There are no studies in which no positive results are observed, but also no negative ones are observed.
Prevention of hemodialysis deficiency in humans
Hemodialysis often leads to a deficiency of certain substances. L-carnitine is one of them and this can lead to worsening of existing or new side effects of this type of treatment. This is the reason why the intake of L-carnitine in people on hemodialysis is approved and recommended by the US Food and Drug Administration (US FDA).
Treatment of liver conditions The intake of L-Carnitine leads to a decrease in ammonia in the body, and this effect is manifested both in people with hepatic encephalopathy and in healthy individuals. Three of the four main studies used 2 grams of ALCAR daily. An additional effect should be noted a small decrease in liver enzyme levels in a condition of hepatic encephalopathy.
Semen quality
L-Carnitine has a positive effect not only on blood flow, but also on the quality and quantity of semen54,55,56. Data to date show that a daily intake of 3000 mg of L-Carnitine increases sperm quality and especially morphology. At this stage, the effect on sperm motility has not been fully established, but it is thought to have a small positive effect.
Anti-fatigue
L-Carnitine appears to be an effective means of regulating fatigue in the elderly who suffer from poor muscular endurance or chronic fatigue syndrome57,58. At this stage, there is insufficient data to potentially regulate exercise fatigue in healthy individuals.
Effects on Autism Spectrum Disorders (ASD)
Although not fully proven and lacking a sufficient scientific basis, one study found the potential of L-Carnitine to treat autism59. The impact is extremely large and a shock dose of 50 mg / kg body weight is used, but more data are needed on the efficacy and safety of such therapy.
L-carnitine and its role in sports
L Carnitine effects
Carnitine is still one of the best-selling supplements to help lose weight and improve athletic performance. Still, L-carnitine is the first thing that comes to mind of almost everyone who decides to lose a few extra pounds and reduce their subcutaneous fat. Carnitine is also often used to improve endurance and reduce fatigue during aerobic exercise. Unfortunately, carnitine also remains one of the most controversial scientific data behind when it comes to confirming its effectiveness in this context.
These contradictions can be clearly seen in Eric P Brass’s 2000 analysis. It selected 17 scientific experiments, the earliest conducted in 1985 and the last in 1996. All studies track the effect of taking standard doses of L-carnitine (3-4 g) on various training parameters. Markers such as maximal oxygen intake (VO2 max), lactate accumulation, respiratory rate (RQ) and others are monitored. Most studies have not found a positive effect of L-carnitine intake, but a few do just the opposite. These controversies continue and are found in more recent research conducted in the last few years.
When it comes to losing weight, things get even darker. Scientific data conducted on humans or even rats in this direction are almost completely missing. There were two studies in rats, with negative results 23, 24 and three in humans, one with negative results and two with positive results.
| 0 hours | 24 hours | 48 hours | 72 hours | 96 hours | |
Muscle fatigue |
Decrease | Decrease | Decrease | Decrease | Decrease |
Creatine kinase |
Unchanged | Decrease | Unchanged | Unchanged | Unchanged |
Myoglobin |
Unchanged | Decrease | Unchanged | Unchanged | Unchanged |
| Lactate dihydrogenase | Unchanged | Decrease | Unchanged | Unchanged | Unchanged |
Eric Trexler of MASS analyzes these results and suggests that the amino acid may have real benefits, but more research is needed on the subject. Carnitine reduces muscle damage not only through its effect on some biomarkers, but also due to additional properties such as the effect on nitric oxide, improved vasodilation and antioxidant effect.
L-Carnitine can improve strength and endurance, but this is just a theory and not fully confirmed. It can happen with training programs with a long-term effect (over 3 months).
L-Carnitine as a dietary supplement
L Carnitine effects
L-carnitine is considered to be the main form of the substance carnitine. Because carnitine has a chiral (mirror) center, a similar compound called D-carnitine also exists41. The D-carnitine molecule cannot correct carnitine deficiency because it is biologically inert and can practically act against L-carnitine. The two forms compete not only in absorption in the small intestine, but also in absorption by the kidneys. For the other varieties of carnitine, the BB-Team has prepared some interesting facts.
Acetyl L-Carnitine Acetyl
L Carnitine effects
L-Carnitine or ALCAR is a carnitine molecule attached to an acetyl group. It is no coincidence that this form is called the neurological version of carnitine. ALCAR has more functions in the brain, as it manages to cross the blood-brain barrier. ALCAR is primarily associated with improved focus, memory and mental fatigue
Glycylpropionyl-L-Carnitine
L Carnitine effects
GPLC is the amino acid glycine linked to the carnitine molecule and short chain fatty acids. When GPLC reaches the mitochondria, the substance is metabolized to L-carnitine and propionyl coenzyme A. Due to its different metabolism, GPLC has some unique properties. The compound can improve blood flow, nitric oxide levels and blood pressure.
L-Carnitine-L-Tartrate
It is a compound of a carnitine molecule linked to a tartaric acid molecule. It is claimed that this form of carnitine has a faster absorption than the others45. Despite faster absorption, there is no difference in total bioactivity and L-carnitine-L-tartrate does not have unique properties.
The form of L-carnitine can be of great importance due to some unique properties. For example, tartrate is absorbed faster, ALCAR affects cognitive abilities, and GPLC affects blood flow.
Dosage, possible side effects and contraindications
In general, L-carnitine is a safe substance and in the recommended doses has no side effects. The standard recommended dosage is in the range of 3-4 grams of L-carnitine per day, divided into 2-3 doses during the day. Given the peculiarities above in the article, you can experiment and take doses around meals rich in carbohydrates when insulin levels will be high. The method of administration and dose applies to all popular varieties of carnitine. It does not matter if the product is taken in the form of a liquid, capsule, tablet, dragee or powder.
In some people, high intake of L-carnitine can lead to fishy odor syndrome – a strange smell of fish in sweat, breath or urine. The reason for this is the increase in the levels of the substance trimethylamine in the metabolism of L-carnitine and its elimination from the body. It is safe and occurs with high intakes of other substances, such as trimethylglycine (TMG) and choline. In people diagnosed with Hashimoto’s disease and hypothyroidism, L-carnitine intake is contraindicated due to evidence that oral L-carnitine prevents thyroid hormones from entering the cell nucleus.
L-carnitine is a substance that is characterized by low toxicity and no serious side effects. Its reception is permissible among the mass population.
What should I combine L-carnitine with?
Depending on the form of L-carnitine, the BB-Team can offer you several basic combinations.
Acetyl L-Carnitine and cognitive support
ALCAR is used to improve memory and improve cognitive function. ALCAR can be successfully combined with cholinergics such as CDP-Choline and Alpha-GPC or choline sources such as choline bitartrate and DMAE. To improve memory is a good combination with fish oil and ginkgo biloba.
GPLC and improved blood flow
L Carnitine effects
GPLC can be used before training or in high blood pressure. Its combination is appropriate with citrulline malate and beet nitrates.
L-Carnitine L-Tartrate and energy during exercise
L Carnitine effects
This form of the amino acid is used primarily for sports and pre-workout intake. In this situation, combination with citrulline malate or caffeine is appropriate
How to choose L-Carnitine?
L Carnitine effects
This topic is not new to our team and we have already covered it in two detailed articles on the Stayfitlonger website. In the article “Which is the best L-Carnitine?” We discuss the difference between different forms – liquid, powder and capsules. Most consumers believe that the liquid form is faster to digest and more effective, but this is far from the case. However, there is no scientific evidence behind this claim. The best option is anyone who is comfortable for you. All forms have the same digestibility and effectiveness.
One study compared the bioavailability of a single oral intake of three oral forms of L-carnitine – liquid, tablet and chewable tablet. In conclusion, the study declares the three forms to be bioequivalent, which in pharmacokinetics means that the substances are the same and do the same job47. When choosing the form, the compactness and convenience of taking the product should be taken into account. In another article, “Lonza, Carnipure® and the Best L-Carnitine,” we look at the difference between the patented Swiss form and the ordinary forms of the amino acid.
Carnipure® is manufactured by Lonza and at this stage is considered the purest and highest quality raw material on the market. The raw material has a number of certificates on the three continents and a special permit for use in baby food. Carnipure® is actually established as one of the best raw materials L-Carnitine on the market. This does not mean that the other products are of poor quality, but that the Lonza product guarantees its quality.
The form of L-Carnitine is not important for its effectiveness. Carnipure® is considered the established standard in the industry and guarantees its quality. The choice for the other parameters of L-Carnitine falls to convenience.
Conclusion
L-carnitine is one of those substances. One of those supplements – well researched, but still with a lot of questions in front of you. It is clear that carnitine has serious potential and can be part of the solution to many of the diseases we are currently fighting. Most of you are probably used to associating L-carnitine with weight loss and improving endurance, but as we noted, the data at this stage are very contradictory. However, carnitine is safe, and if you judge, there’s nothing stopping you from experimenting and judging for yourself.
Sources used for L – Carnitine effects :
- Obesity, Inflammation, and the Potential Application of Pharmaconutrition
- Ameliorating hypertension and insulin resistance in subjects at increased cardiovascular risk: effects of acetyl-L-carnitine therapy
- Effect of L-Carnitine Supplementation on Metabolic Status in Obese Diabetic Women With Hypocaloric Diet
- Alzheimer’s Disease: The Pros and Cons of Pharmaceutical, Nutritional, Botanical, and Stimulatory Therapies, with a Discussion of Treatment Strategies from the Perspective of Patiens and Practitioners
- Efficacy of carnitine in the treatment of children with attention-deficit hyperactivity disorder
- Acetyl-L-carnitine (ALC) in attention-deficit/hyperactivity disorder: a multi-site, placebo-controlled pilot trial
- The effects of L-carnitine supplementation on glycemic control: a systematic review and meta-analysis of randomized controlled trials
- A Prospective Double-blind, Randomized Clinical Trial Of Levocarnitine To Treat Autism Spectrum Disorders
- L-Carnitine Treatment Reduces Severity Of Physical And Mental Fatigue And Increases Cognitive Functions In Centenarians: A Randomized And Controlled Clinical Trial
- Effects Of Citric Acid And L-Carnitine On Physical Fatigue
L Carnitine effects.
