L-Carnitine - A Review of Benefits, Side Effects and Dosage (2024)

L-carnitine is an amino acid produced by the body that’s also found in food and supplements. Some studies suggest it may offer some health benefits, including increased weight loss, improved brain function, and more.

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L-carnitine is a naturally occurring amino acid derivative that’s often taken as a supplement. It is used for weight loss and may have an impact on brain function.

However, popular claims about supplements don’t always match up with the science.

This article examines the potential risks and benefits of L-carnitine supplements and explains how this nutrient functions in your body.

L-carnitine is a nutrient and dietary supplement. It plays a crucial role in the production of energy by transporting fatty acids into your cells’ mitochondria (1).

The mitochondria act as engines within your cells, burning these fats to create usable energy. Your body can produce L-carnitine out of the amino acids lysine and methionine (2).

For your body to produce it in sufficient amounts, you also need plenty of vitamin C (3).

In addition to the L-carnitine produced in your body, you can also obtain small amounts by eating animal products like meat or dairy products (2).

Vegans or people with certain genetic issues may be unable to produce or obtain enough. This makes L-carnitine a conditionally essential nutrient (2).

Different types

L-carnitine is the standard biologically active form of carnitine, which is found in your body, foods, and most supplements.

Here are several other types of carnitine:

  • D-carnitine: This inactive form has been shown to reduce blood levels of carnitine and increase fat buildup, leading to liver inflammation and oxidative stress (4).
  • Acetyl-L-carnitine: Often called ALCAR, this is possibly the most effective form for your brain. Studies suggest that it may benefit people with neurodegenerative diseases (5).
  • Propionyl-L-carnitine: This form is well-suited for circulatory issues, such as peripheral vascular disease and high blood pressure. According to some older research, it may boost the production of nitric oxide, which improves blood flow (6, 7).
  • L-carnitine L-tartrate: This is commonly added to sports supplements due to its rapid absorption rate. It may aid muscle soreness and recovery in exercise (8, 9).

For most people, acetyl-L-carnitine and L-carnitine seem to be the most effective for general use. However, you should always pick the form that’s best for your personal needs and goals.

Role in your body

L-carnitine’s main role in your body involves mitochondrial function and energy production (1).

In cells, it helps transport fatty acids into the mitochondria, where they can be burned for energy.

More than 95% of your L-carnitine stores are contained in your muscles, along with trace amounts in your blood, liver, heart, and kidneys (2).

L-carnitine may help increase mitochondrial function, which plays a key role in disease and healthy aging (1, 10, 11).

Newer research illustrates the potential benefits of carnitine’s different forms, which may be used for various conditions, including heart and brain diseases (12, 13).

Summary

L-carnitine is an amino acid derivative that transports fatty acids into your cells to be processed for energy. It is made by your body and also available as a supplement.

Because L-carnitine helps move more fatty acids into your cells to be burned for energy, it’s sometimes used as a weight loss supplement.

One review of 37 studies found that L-carnitine supplementation significantly reduced body weight, body mass index (BMI), and fat mass. However, it had no effect on belly fat or body fat percentage (14).

Another analysis of nine studies — mostly in individuals with obesity or older adults — found that people lost an average of 2.9 pounds (lbs), or 1.3 kilograms (kg), more weight while taking L-carnitine (15).

What’s more, a meta-analysis of six studies showed that L-carnitine could reduce body weight, BMI, and belly fat in people with polycystic ovary syndrome (16).

Still, more research is needed to understand how it may impact long-term weight loss.

Furthermore, while it may aid in weight loss for some people, you may wish to consult with a dietician to develop a thorough diet and exercise regimen first.

Summary

Some studies suggest that L-carnitine could help promote weight loss and fat loss. However, more studies are needed.

L-carnitine may benefit brain function.

Some research suggests that the acetyl form, acetyl-L-carnitine (ALCAR), may help prevent age-related mental decline and improve markers of learning (13).

In fact, according to one 2018 study, taking 1,500 milligrams (mg) of ALCAR daily for 28 weeks significantly improved brain function in people with dementia (17).

However, other studies have turned up mixed results.

For instance, a 2017 review of two studies showed that taking L-carnitine for 3 days had no effect on markers of brain function — including reaction time, vigilance, immediate memory, and delayed recall — in young adults without cognitive impairment (18).

Therefore, more research is needed on the potential benefits of supplementation.

Summary

L-carnitine — specifically acetyl-L-carnitine — may have beneficial effects on brain function. Still, more research is needed.

A few more health benefits have been linked to L-carnitine supplements.

Heart health

Some studies demonstrate that L-carnitine could benefit several aspects of heart health.

For example, one review of 10 studies found that L-carnitine significantly reduced diastolic blood pressure, especially in people with overweight and obesity (19).

Another analysis of 17 studies showed that L-carnitine could improve heart function and decrease symptoms in people with congestive heart failure (20).

Additionally, a 2020 review showed that L-carnitine could reduce total and LDL (bad) cholesterol while increasing HDL (good) cholesterol in people at risk for heart disease (21).

Exercise performance

The evidence is mixed when it comes to the effects of L-carnitine on sports performance, but it may offer some benefits.

Keep in mind that L-carnitine’s benefits may be indirect and take weeks or months to appear. This differs from supplements like caffeine or creatine, which can directly enhance sports performance (22, 23).

L-carnitine may benefit:

  • Recovery: It may improve exercise recovery (24, 25, 26).
  • Muscle oxygen supply: It can increase the oxygen supply to your muscles (27).
  • Stamina: It might increase blood flow and nitric oxide production, helping delay discomfort and reduce fatigue (27).
  • Muscle soreness: It could reduce muscle soreness after exercise (24).
  • Red blood cell production: It may increase the production of red blood cells, which transport oxygen throughout your body and muscles (28, 29).
  • Performance: It could improve high intensity exercise performance when taken 60–90 minutes before working out (30).

Type 2 diabetes

L-carnitine may be beneficial for people with type 2 diabetes.

A recent review of 41 studies concluded that L-carnitine supplementation could reduce fasting blood sugar and hemoglobin A1c (a marker of long-term blood sugar levels) while also improving insulin sensitivity in people with diabetes, overweight, or obesity (31).

According to the authors of the review, L-carnitine is believed to work by altering insulin receptors and changing the expression of specific genes that regulate sugar metabolism (31).

It may also help improve the function of beta cells, which are cells in the pancreas that are responsible for producing insulin (31).

Depression

Some research suggests that L-carnitine could be beneficial for the treatment of depression.

In one review of 12 studies, acetyl-L-carnitine significantly reduced symptoms of depression compared with placebo (32).

Interestingly, several of the studies included in this review also found that acetyl-L-carnitine was as effective as antidepressant medications but caused fewer adverse effects (32).

Still, more research is needed to understand how L-carnitine may affect depression.

Summary

Research suggests that L-carnitine may aid exercise performance and treat health conditions like heart disease, depression, and type 2 diabetes.

For most people, taking 2 grams (g) or less per day is relatively safe and free from any serious side effects (33).

Some research has also used doses of up to 4,500 mg per day (33).

In one review of L-carnitine’s safety, doses of approximately 2 g per day appeared to be safe for long-term use. However, there were some mild side effects, including heartburn and indigestion (33).

However, L-carnitine supplements may raise your blood levels of trimethylamine-N-oxide (TMAO) over time. High levels of TMAO are linked to an increased risk of atherosclerosis — a disease that clogs your arteries (34).

More studies on the safety of L-carnitine supplements are needed.

Summary

Doses of 2 g or less per day seem to be well tolerated and safe for most people. However, L-carnitine may increase levels of TMAO, which could be linked to an increased risk of plaque build-up.

You can get small amounts of L-carnitine from your diet by eating meat and dairy products (35).

The best sources of L-carnitine are (35):

  • Beef: 139–143 mg per 3.5 ounces (oz), or 100 g
  • Pork: 25–61 mg per 3.5 oz (100 g)
  • Chicken: 13–34 mg per 3.5 oz (100 g)
  • Milk: 40 mg per 3.5 oz (100 g)
  • Hard cheese: 3 mg per 3.5 oz (100 g)

Interestingly, food sources of L-carnitine have a greater absorption rate than supplements.

According to one older study, 57–84% of L-carnitine is absorbed when it’s consumed from food, compared to only 14–18% when taken as a supplement (36).

As noted before, your body can also produce this substance naturally from the amino acids methionine and lysine if your stores are low.

For these reasons, L-carnitine supplements are only necessary in special cases, such as disease treatment.

Summary

The main dietary sources of L-carnitine are meat and some other animal products, such as milk. A healthy individual can also produce sufficient amounts within the body.

Your L-carnitine levels are influenced by how much you’re eating and how much your body is producing.

For this reason, L-carnitine levels are often lower in vegetarians and vegans since they restrict or avoid animal products (37).

Therefore, vegetarians and vegans may want to consider L-carnitine supplements, which can help normalize carnitine levels in the blood and muscles (37).

Older adults may also benefit from L-carnitine supplements.

In fact, one study found that taking 1.5 g of L-carnitine per day for 10 weeks improved functional status and frailty in older adults (38).

On the other hand, another study showed that L-carnitine supplementation had no effect on muscle strength or markers of inflammation in older women (39).

The risk of deficiency is also higher for those with diseases like cirrhosis and kidney disease. If you have one of these conditions, a supplement may be beneficial (40, 41).

However, as with any supplement, you should speak with a doctor before taking L-carnitine.

Summary

Specific populations may benefit from L-carnitine supplements. This includes older adults and people who rarely or never eat meat.

Studies on the potential benefits of L-carnitine have used a wide range of doses.

Although dosage varies from study to study, here is an overview of the use and dose for each form (13, 19, 33):

  • Acetyl-L-carnitine: This form is best for brain health and function. Doses vary from 500–3,000 mg per day.
  • L-carnitine L-tartrate: This form is most effective for exercise performance. Doses vary from 1,000–4,000 mg per day.
  • Propionyl-L-carnitine: This form may help improve blood flow in those with high blood pressure or related health conditions. One study used a dose of 2 g per day.
Summary

Although the recommended dose varies, around 500–4,000 mg (0.5–4 g) seems to be both safe and effective.

Though more research is needed, L-carnitine may help increase weight loss and fat burning.

Studies also support its use for health, brain function, and disease prevention. Supplements may also benefit those with lower levels, such as older adults, vegans, and vegetarians.

Of the different forms, acetyl-L-carnitine and L-carnitine are the most popular and seem to be the most effective.

L-Carnitine - A Review of Benefits, Side Effects and Dosage (2024)
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