Written by Rudy Mawer, MSc, CISSN on November 6, 2018

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.

What Is L-Carnitine?

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, 2, 3).

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.

For your body to produce it in sufficient amounts, you also need plenty of vitamin C (4).

In addition to the L-carnitine produced in your body, you can also obtain small amounts by eating animal products like meat or fish (5).

Vegans or people with certain genetic issues may be unable to produce or obtain enough. This makes L-carnitine a conditionally essential nutrient (6).

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 may cause a carnitine deficiency in your body by inhibiting the absorption of other, more useful forms (7, 8).
  • 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 (9).
  • Propionyl-L-carnitine: This form is well-suited for circulatory issues, such as peripheral vascular disease and high blood pressure. It may boost production of nitric oxide, which improves blood flow (10, 11).
  • 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 (12, 13, 14).

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 (3, 15, 16).

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

About 98% of your L-carnitine stores are contained in your muscles, along with trace amounts in your liver and blood (17, 18).

L-carnitine may help increase mitochondrial function, which plays a key role in disease and healthy aging (19, 20, 21).

Newer research illustrates the potential benefits of carnitine’s different forms, which may be used for various conditions, including heart and brain diseases (22, 23).