L-Carnitine is an amino acid naturally produced by the body and is found in dietary sources like meat, fish, and dairy products. It plays an important role in shuttling nutrients from outside the mitochondria to the inside where they are oxidized to produce energy. There is an abundance of human studies performed on the untrained and trained population that illustrate the benefits of supplementing with l-carnitine, let's analyze them.
Improving Athletic Performance
Considering the role l-carnitine plays in energy metabolism, it has been marketed as a dietary supplement for athletes seeking to enhance their athletic performance. Studies suggest supplementing with l-carnitine promotes recovery after exercise, and enhances both the performance of endurance and weight-trained athletes.
Keep in mind that the form of l-carnitine used to benefit athletic performance and recovery is l-carnitine-l-tartrate(LCLT).
Recovery
First, a study found that l-carnitine l-tartrate(LCLT) supplementation at 1000mg to 2000mg doses per day beneficially affects markers of postexercise metabolic stress and muscle damage by reducing postexercise serum hypoxanthine, serum xanthine oxidase, serum myoglobin, and perceived muscle soreness(1). A later study examined the influence of LCLT on markers of free radical formation and muscle tissue disruption after 5 sets of 15 repetitions of squats. 10 resistance-trained men consumed a placebo or 2000mg of LCLT for 3 weeks. Through an assessment using an MRI, muscle disruption during LCLT treatment was 41%-45% compared to the placebo, thereby being effective in assisting recovery from high-repetition squat exercises(2). A study with the same method examined the hormonal responses to resistance exercise and recovery when supplementing with l-carnitine. Blood samples were obtained pre, during, and post-exercise. Although the expected exercise-induced hormonal increases occurred, in the recovery period, there was a reduction in the amount of exercise-induced muscle tissue damage(3).
Also, a study investigated the effects on pain, tenderness, and creatine kinase release on 6 untrained subjects. Over 7 weeks, participants were given 3000mg of placebo the first 3 weeks, with a week break, and given 3000mg of oral l-carnitine for the last three weeks. During treatment, after a 20-minute eccentric focused quadriceps workout, l-carnitine significantly reduced pain, tenderness, and creatine kinase release, thus illustrating the effect against pain and damage from eccentric efforts(4). An upregulation of androgen receptor responses also occurred promoting recovery in post-resistance exercise(5).
Therefore, l-carnitine l-tartrate may have a beneficial effect on exercise recovery which is a great addition to a supplement regimen to increase exercise output!
Endurance Athletes
l-carnitine plays a crucial role in the metabolism of fatty acids, which are one of the primary sources of fuel during endurance exercises. The data suggest that there is a decrease in free and total carnitine in the muscles when performing endurance-type activities, thus, supplementing with l-carnitine l-tartrate may benefit individuals looking to boost their endurance.
The first reported use for l-carnitine as a dietary supplementation gave patients 1000mg of l-carnitine twice daily during 6 months of exercise which led to an increase in both free and total carnitine levels in the muscles(6).
In a different trail, 7 top junior cyclists received 2000mg of l-carnitine for 10 days prior to a cycling competition. After the competition, researchers reported an enhancement in exercise capacity and endurance(7). This is likely due to the increase in both free and total carnitine.
Furthermore, 26 professional footballers were given 3000mg and 4000mg of l-carnitine and executed exercise tests. Their heart rate and blood samples were registered pre and post-treatment which showed that running speed increased whilst lactate and heart rate decreased in a dose-dependent manner of intaking l-carnitine(8).
Moreover, 12 males were given 1036 mg of l-carnitine 2 times daily for 12 weeks. This increased total carnitine, energy expenditure, and body composition over a prolonged period(9).
Lastly, for 1 month, aerobically fit young adult women took a mineral combination of iron, zinc, and copper with 2000mg of l-carnitine. They executed tests on a stationary bike, a step platform, and a 3-mile run. After analyzing the tests pre and post-treatment, the participants increased stationary bike distance and steps in the step test, as well as decreased the time to complete a 3-mile run(10).
Therefore, there are many studies that illustrate the benefits of supplementing with l-carnitine-l-tartrate to increase endurance due to the increase in free and total carnitine in the blood to transport fatty acids into the mitochondria to produce more energy output.
Weight Trained Athletes
Asides from the benefits in recovery already mentioned above, a double-blind, randomized, and placebo-controlled treatment examined 23 men for 9 weeks in conjunction with resistance training. At weeks 6 and 9 there was a significant increase in bench press lifting volume and an increase in power output on the leg press compared to a placebo group. There was also a reduction in post-exercise blood lactate levels(11). This shows that l-carnitine supplementation not only helps with recovery but also assists in increasing lifting volume and strength.
Overall, regarding athletic performance, studies support that supplementing l-carnitine promotes recovery after exercise and enhances endurance and weight training performance. Due to the various studies emphasizing its benefits, we can confidently recommend this product for athletic performance!
Supporting weight loss
L-Carnitine has been studied for its potential to support weight loss by increasing fat metabolism and decreasing weight, BMI, and fat mass.
A systematic review and meta-analysis of nine studies examined the effect of l-carnitine on adult weight loss. Results revealed that subjects who received carnitine lost significantly more weight and showed a decrease in the body mass index in comparison with a control group(12). A placebo-controlled randomized study also found a reduction in fat mass after giving 2000mg of oral l-carnitine to their participants compared to a placebo group(13).
Another study looked at protein turnover and fat oxidation in twelve slightly overweight volunteers who received 3000mg of l-carnitine for 10 days. Supplementation led to a significant increase in fat oxidation whereas protein breakdown rates remained unchanged. This indicated that the increase in fat oxidation was not accompanied by protein catabolism during weight loss(14).
Are there contradictions to the studies that depict weight loss in relation to supplementing with l-carnitine?
The weight loss may be attributed to the increase in energy output and free carnitine levels in the blood as an increase in free carnitine permits a larger quantity of free fatty acids to enter the mitochondria to be more extensively used as an energy source(15). Thus, enabling more work to be executed during exercise.
Also, analyses also show the anti-obesity effects of l-carnitine only occurred in overweight and obese subjects and when combined with other lifestyle modifications(16).
Therefore, enhancement in athletic performance and lifestyle modifications indirectly affect weight loss in a positive manner.
Cognitive enhancement
Some studies have also suggested that l-carnitine, specifically in the form of acetyl-l-carnitine(ALCAR) has been shown to enhance cognition as it may exert neuroprotective, neurotrophic, and anti-depressive effects in older adults(17).
For instance, 30 patients with mild to moderate dementia with probable Alzheimer's disease were administered memory, attention, language, and constructional ability tests. Patients were then randomly given 2500mg of ALCAR daily for 3 months followed by 3000mg daily for another 3 months. After 6 months, the acetyl-l-carnitine group demonstrated significantly less deterioration in timed cancellation tasks, verbal fluency tasks, and verbal memory tasks compared to the placebo group. These results show that the deterioration in cognitive areas was mitigated with the supplementation of l-carnitine(18).
Another study evaluated the efficacy and tolerability of acetyl-l-carnitine therapy in 40 patients who were divided into a therapy and a placebo group. The results in the therapy group confirmed improvements in the main mental parameters of the senile brain without side effects(19).
In the treatment of cognitive deficits attributed to chronic alcoholism, recovery of cognitive areas accelerated due to the administration of 2000mg of acetyl-l-carnitine(20).
Thus, according to several studies, supplementing with acetyl-l-carnitine may alleviate cognitive decline and recover damaged cognitive areas of the brain.
In regard to depression, a study found improvements in emotional and mental health when analyzing 67 patients with impairments in daily functions(21). However, this was likely caused by lifestyle modifications that improved their quality of life.
Overall, while there are studies that show evidence to suggest that l-carnitine supplementation may exert neuroprotective and neurotrophic benefits, more research is needed to fully understand the efficacy of this supplement on cognitive functions.
Blood flow
Note: In the cardiovascular system, nitric oxide helps to dilate blood vessels, which can increase blood flow and lower blood pressure. This is because nitric oxide acts as a vasodilator, meaning it relaxes the smooth muscle cells that surround blood vessels, allowing them to widen and increase blood flow.
Studies have acknowledged that l-carnitine, specifically glycine propionyl-l-carnitine(GPLC), may positively affect blood flow by increasing nitric oxide levels in the blood.
For example, 30 untrained adults performed 8 weeks of supervised aerobic exercise while supplementing with 2 doses of 1000mg or 3000mg propionyl-l-carnitine per day. Blood samples were analyzed at rest post-training which led to elevated nitric oxide levels(22). In another study, 15 healthy men were assigned 3000mg of propionyl-l-carnitine per day for 4 weeks. Blood samples were again, taken at rest which resulted in 12 out of the 15 men experiencing an increase in nitric oxide levels demonstrating that there exist both responders and non-responders to treatment(23).
With this said, we must consider the indirect benefit of improving one's exercise capacity and muscle function, which can support cardiovascular health and blood flow. Ultimately, l-carnitine does not directly increase nitric oxide, thus, more research is needed to fully understand its benefits on blood flow.
Does l-carnitine supplementation raise blood levels of trimethylamine-n-oxide (TMAO)?
Over time it does, which may cause an increased risk of atherosclerosis a disease that clogs your arteries(24). This is strongly associated with cardiovascular disease.
You can offset this by intaking raw garlic as it decreases serum TMAO levels validating its benefits to offset the risk of cardiovascular disease(25).
Low Bioavailability
The bioavailability of dietary l-carnitine is 54%-87% depending on the amount in a meal(26). Dietary sources include beef, pork, milk, chicken, and fish.
On the other hand, the bioavailability of l-carnitine supplementation is 14%-18%(26).
Types of l-carnitine supplements include Acetyl-l-carnitine, propionyl-l-carnitine, and l-carnitine-l-tartrate.
Generally, acetyl-l-carnitine is used for cognitive enhancement(17), glycine propionyl-l-carnitine is used to improve blood flow(23), and l-carnitine-l-tartrate is used for physical performance and recovery(27).
Recommended Doses
Generally, the standard dose of l-carnitine is around 500mg to 2000mg. According to Examine.com doses of ALCAR are around 630mg to 2500mg, LCLT is around 1000mg to 4000mg, and GPLC is around 1000 to 4000mg.
All in all, we would definitely recommend this supplement for individuals who want to improve their athletic performance. Anecdotally, we have taken l-carnitine-l-tartrate and found that we had more energy in our training sessions, and had less muscular discomfort post-training.
However, in regard to enhancements in weight loss, cognition, and blood flow, more studies are needed to fully understand its benefits and the efficacy of supplementing with acetyl-l-carnitine and glycine propionyl-l-carnitine.
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Also, all content contained within this article is for informational purposes only and is not intended to substitute the advice, diagnosis, or treatment from a qualified medical professional. Before taking l-carnitine, you should talk to your healthcare provider, especially if you have any medical conditions or are taking any medications. Your healthcare provider can help you determine a safe and effective dose for your individual needs.
References
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