Carnitine

Purported Benefits, Side Effects & More

Carnitine

Purported Benefits, Side Effects & More
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Carnitine

Common Names

  • Vitamin BT
  • Vitamin B7
  • ALCAR

For Patients & Caregivers

Tell your healthcare providers about any dietary supplements you’re taking, such as herbs, vitamins, minerals, and natural or home remedies. This will help them manage your care and keep you safe.


What is it?

Carnitine is a chemical that your body makes to produce energy. It’s also found in foods such as meat, dairy products, beans, and avocados.

You can also take carnitine supplements as pills or capsules.

What are the potential uses and benefits?

Carnitine is used to treat:

  • Heart disease
  • Nerve pain from diabetes
  • Insulin resistance, which can increase your blood sugar
  • Fatigue (feeling more weak or tired than usual)
  • Fatigue due to cancer treatments
  • Male infertility

Carnitine also has other uses that haven’t been studied by doctors to see if they work.

Carnitine that you get from food is safe. Talk with your healthcare provider before taking carnitine supplements. Supplements are stronger than the carnitine you get from food. They can also interact with some medications and affect how they work.

For more information, read the “What else do I need to know?” section below.

What are the side effects?

Side effects of using carnitine supplements may include:

  • Nausea (feeling like you’re going to throw up)
  • Heartburn
  • Flu-like symptoms (such as a cough, fever, or chills)
  • Headache
  • Diarrhea (loose or watery bowel movements)
  • High blood pressure
  • Body odor
What else do I need to know?
  • Talk with your healthcare provider if you’re taking blood thinners such as warfarin (Coumadin®), clopidogrel (Plavix®), apixaban (Eliquis®), or rivaroxaban (Xarelto®). Carnitine can increase your risk of bleeding.
  • L-carnitine and acetyl-L-carnitine are not the same. Acetyl-L-carnitine can increase nerve pain caused by chemotherapy.

For Healthcare Professionals

Scientific Name
Beta-hydroxy-gamma-trimethyl-amino-butyric acid
Clinical Summary

Carnitine is a nutrient that plays an important role in fatty acid absorption and mitochondrial function. It is synthesized endogenously from lysine and methionine and is also found in meat and dairy products. Deficiencies can be caused by genetic disorders, malnutrition, malabsorption and kidney dialysis, and affect the heart, skeletal muscles, liver, nerve, and endocrine functions. Carnitine supplements are used to enhance physical performance and to treat fatigue, cardiovascular disease, diabetes, obesity, chronic fatigue syndrome, liver disorders, and cancer.

A meta-analysis determined that supplementation improves body weight and BMI in overweight and obese individuals (55). It also alleviated muscle damage in resistance trained and untrained groups (56), muscle wasting in patients with pemphigus vulgaris (61), and prevented cardiovascular disease in hemodialysis patients (24). Long-term supplementation has been correlated with improved myocardial mechanical performance, reduction in ventricular arrhythmias and increased exercise tolerance (7), and higher levels of carnitine were associated with lower risks of cardiovascular events and recurrent stroke after ischemic stroke (63). Carnitine also improved oxidative and inflammatory markers in patients with cardiovascular disease (62), but did not have any impact on blood pressure (66) or reduce risk of death or heart failure in patients with anterior acute myocardial infarction (36).

In critically-ill patients, supplements improved nutritional status indicators, which have a key role in prognosis of diseases (64) and adjunctive use improved symptoms of autism spectrum disorder in children and adolescents (65).

Preliminary findings also suggest improvement in symptoms of chronic fatigue syndrome  (22) and physical performance in patients undergoing dialysis for end-stage renal disease (9), but data on benefits against fatigue associated with multiple sclerosis are inconclusive (21). Some trials reported enhanced physical performance (17) (20), and improved aerobic capacity and exercise tolerance (32) whereas others yielded mixed results (37) (38) (39).

L-carnitine used by itself or in combination with clomiphene citrate may help treat idiopathic male infertility (25) and reduce lower urinary tract symptoms in those with benign prostatic hyperplasia (67) although it did not improve sperm count or motility (40). An antioxidant formulation containing L-carnitine was also ineffective in improving semen parameters or DNA integrity (57). In women with polycystic ovary syndrome, supplementation may reduce body mass (68), and improve mental health parameters and biomarkers of oxidative stress (2).

Small studies in oncology settings found supplementation to improve nutritional status and quality of life in pancreatic cancer patients (27), and to reduce vismodegib-associated muscle spasms (52). L-carnitine by itself (15) (23) or in combination with Coenzyme Q10 (33) may also relieve chemotherapy-related fatigue, reduce fatigue in both younger hypothyroid patients receiving levothyroxine, and in thyroid cancer patients who have hypothyroidism, post-surgery (41). But it did not improve fatigue in patients with invasive malignancies (28). Confirmatory data are also needed to determine if chemo-induced carnitine insufficiency increases malaise or fatigue (58) (59)
Current guidelines do  not recommend L-carnitine for cancer-related fatigue (69).

In prostate cancer patients initiating androgen deprivation therapy (ADT), a low-carb diet reversed ADT-induced metabolic abnormalities which included reductions in acylcarnitine  (60)

Acetyl-L-carnitine, an ester derivative available as a supplement, is often used as a neuroprotective agent. It may help reduce diabetic neuropathy (42) (43) and improve cognition in patients with severe hepatic encephalopathy (44). In elderly patients with dysthymic disorder, it was found comparable to fluoxetine (45), but ineffective against Alzheimer’s disease (46) (47).
In cancer settings, acetyl-L-carnitine increased chemotherapy-induced peripheral neuropathy (CIPN) (35), which persisted at the 2-year follow-up (53). Current guidelines do not recommend this supplement for preventing CIPN (54).

Food Sources

Meat, dairy products, beans, avocado

Purported Uses and Benefits
  • Cardiovascular disease
  • Diabetic neuropathy
  • Insulin resistance
  • Chronic fatigue syndrome
  • Chemo-induced fatigue
  • Male infertility
Mechanism of Action

Carnitine is a non-essential amino acid, with only the L-isomer utilized in human bodies. It is available in many foods, and bioavailability from dietary sources is much higher (54%–87%) than from oral supplements (14%–18%) (48). L-carnitine plays a role in the transport of long chain fatty acids across the inner mitochondrial membrane, facilitating beta-oxidation of fatty acids and acting as an intracellular energy reservoir of acetyl groups. In deficiencies, these acyl esters accumulate and cause deleterious effects including inhibition of adenine nucleotide translocase, which impedes ATP production (5). Carnitine supplementation prevents oxidative stress and ameliorates mitochondrial function (29). L-carnitine may protect against statin-induced cellular damage via antioxidative properties in rat hepatocytes (31).

Animal studies show L-carnitine has cardioprotective effects by preventing skeletal muscle myopathy (14) and may improve myocardial metabolic patterns, reduce necrosis, diminish enzymatic infarct size, and preserve left ventricular function (8). Effects on congestive heart failure-associated myopathy may be due to caspase inhibition and decreased TNF-alpha levels (14). Metabolism of dietary L-carnitine by intestinal microbiota produced trimethylamine-N-oxide, a proatherogenic species, which accelerated atherosclerosis (30). Anticatabolic effects may occur by improving nitrogen balance either via increased protein synthesis or reduced protein degradation. Other studies show it prevents oxidative stress and ameliorates mitochondrial function (29). Carnitine is often proposed for the treatment of obesity and metabolic syndrome. Possible mechanisms include inhibition of stearoyl-CoA desaturase-1 activity, β-oxidation of fatty acids, and increased storage in the body tissues (49). It may help cancer-related cachexia by reducing proteasome activity (50), but studies in humans are needed.

In one clinical trial, carnitine reversed hyperthyroidism by acting as a peripheral antagonist of thyroid hormone action (3). In hemodialysis patients, carnitine has anti-inflammatory and anticoagulation effects which may contribute to its cardioprotective activity (24).

Adverse Reactions

Rare: Dyspepsia, heartburn (5).

Reported: Flu syndrome, injection-site reaction, pain, pharyngitis, headache, diarrhea, and hypertension (6) (9). High oral doses may cause unpleasant body odor (5).

Case Report
Hypoglycemia: In a patient with a rare genetic metabolic disorder after taking carnitine supplements (11).

Herb-Drug Interactions

Warfarin: L-carnitine may have additive anticoagulant effects when used with warfarin (24) (51).

Dosage (OneMSK Only)
References
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  3. Benvenga S, et al. Usefulness of L-carnitine, a naturally occurring peripheral antagonist of thyroid hormone action, in iatrogenic hyperthyroidism: a randomized, double-blind, placebo-controlled clinical trial. J Clin Endocrinol Metab 2001:86:3579-94.
  4. Breitkreutz R, et al. Effect of carnitine on muscular glutamate uptake and intramuscular glutathione in malignant diseases. Br J Cancer 2000:82;399-403.
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  10. Food and Drug Administration. Carnitor® (levocarnitine).
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