Carnitine: Its Function, Sources, and Side Effects

Carnitine is a compound similar to an amino acid that the body produces from lysine and methionine. It is found in nearly every cell and plays a part in cellular energy production. While the body can produce sufficient amounts, it is also obtained from food.

The Function of Carnitine in the Body

Carnitine’s primary function is in energy metabolism. It acts as a transport system, moving long-chain fatty acids into the mitochondria, the powerhouses of the cell where energy is generated. Without carnitine, the entry of these fatty acids into the mitochondria is restricted.

Inside the mitochondria, these fatty acids undergo beta-oxidation. This process breaks them down to produce acetyl-CoA, which is used to generate adenosine triphosphate (ATP). ATP is the main energy currency of the cell, powering biological activities.

This process is important in tissues with high energy demands, such as skeletal and heart muscles, which rely heavily on fatty acid oxidation for energy. The liver also utilizes this pathway for its metabolic functions. Carnitine ensures these tissues receive the fuel they need to function properly.

How the Body Obtains Carnitine

The body acquires carnitine by synthesizing it or absorbing it from food. The liver and kidneys are the main sites of synthesis, a process requiring the amino acids lysine and methionine. Several micronutrients, including vitamin C, vitamin B6, niacin, and iron, are also necessary as cofactors for this process.

Dietary intake complements the body’s production. Animal products are the most concentrated sources, with red meat like beef and lamb containing high amounts. Fish, poultry, and dairy products are also good sources, and the bioavailability of carnitine from food is high.

Plant-based foods like avocados, asparagus, and whole wheat products contain carnitine in much smaller quantities. Because the body produces what it needs, carnitine is considered a conditionally essential nutrient. This means dietary intake becomes important only when the body’s needs exceed its production capacity.

Understanding Carnitine Supplements

Carnitine is available as a dietary supplement in several forms. The most common include:

• L-carnitine: The biologically active form found in the body and food.
• Acetyl-L-carnitine (ALCAR): Often studied for its potential effects on the brain.
• L-carnitine L-tartrate: Noted for its rapid absorption rate and used in sports supplements.
• Propionyl-L-carnitine: Thought to improve blood flow.

People take these supplements to enhance athletic performance, support weight loss, or address certain health conditions. It has been explored for benefits in heart health, managing nerve pain from diabetes, and improving male infertility. Research also suggests it may help reduce muscle damage and fatigue in some populations.

Evidence for the effectiveness of carnitine supplements is mixed. While some studies show positive outcomes, like modest weight reduction or improved heart function, others find little benefit. Its role in improving exercise performance remains under investigation, and effectiveness can vary by form, dosage, and the individual’s health.

Carnitine supplements are considered safe for most healthy adults at recommended dosages. High doses, around 3 grams per day, can lead to side effects, including:

• Nausea
• Vomiting
• Abdominal cramps
• Diarrhea
• A “fishy” body odor

Carnitine may also interact with certain medications, such as some antibiotics and anticonvulsants.

Carnitine Deficiency Conditions

Carnitine deficiency occurs when the body lacks enough carnitine to transport fatty acids for energy. The condition is categorized as either primary or secondary. Primary carnitine deficiency is a rare genetic disorder caused by a defective protein that moves carnitine into cells, impairing the body’s ability to process fats.

Secondary carnitine deficiency is more common and arises from other medical conditions or treatments. For example, chronic kidney disease, especially in patients on dialysis, can lead to a deficiency. Certain metabolic disorders or medications can also deplete the body’s carnitine levels.

Symptoms of carnitine deficiency reflect the body’s struggle to produce energy. Common signs include muscle weakness, fatigue, and heart muscle problems (cardiomyopathy). Other issues can include liver problems and low blood sugar. A diagnosed deficiency is managed with prescription L-carnitine supplementation under a doctor’s guidance to restore adequate levels.