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8 Benefits and Side Effects of L-carnitine (Please Pay Attention to the 4 Contraindications in Use)[Updated Feb/2023]

L-carnitine referred to as carnitine, is widely present in human tissues can produce an amino acid on its own, is an important factor in the energy production process, responsible for sending fatty acids into the mitochondria, in order to burn smoothly, produce energy, in addition to the metabolism of carbohydrates is necessary.

Carnitine is mainly formed by lysine and methionine, and ascorbic acid, ferrous iron, vitamin B6 and nicotinic acid are also the main cofactors in the synthesis process, and if one of the nutrients is lacking, it may cause carnitine deficiency.

For healthy people (including vegetarians), 75% of carnitine can be obtained through food (meat, dairy products, vegetables, fruits), but in some medical conditions, the body’s needs may exceed its own synthetic amount, so it is a conditional important nutrient.

What are the recommended proven benefits of L-carnitine?

  1. Good for non-alcoholic fatty liver

Non-alcoholic fatty liver disease (Non-alcoholic fatty liver disease) is a covering term with a wide range of histological manifestations, from very mild fatty degeneration (5% or more liver cell infiltration) to more aggressive liver lobules Or portal vein inflammation, liver cell swelling, fibrosis, and eventually liver cirrhosis.

Its incidence ranges from 20% to 30% in Western countries and 5% to 18% in Asia, and the prevalence of nonalcoholic fatty liver disease is increasing worldwide due to dietary refinement and sedentary lifestyles

A systematic literature review and meta-analysis (5 randomized controlled trials, 334 patients with nonalcoholic fatty liver disease) noted that carnitine supplementation (study duration ranged from 12 to 24 weeks, at doses of 300 to 2000 mg per day) significantly reduced insulin resistance index (HOMA-IR), aspartate aminotransferase (AST), alanine aminotransferase (ALT), and triglyceride (TG) levels. Note 1

The mechanism behind carnitine may be related to alteration of gene expression associated with insulin signaling pathways, reduction of expression of glycolytic enzymes and gluconeobiotic enzymes, regulation of the ratio of acylacyl-CoA in mitochondria and activity of pyruvate dehydrogenase complexes.

*Conclusion: For non-alcoholic fatty liver disease, carnitine supplementation may bring positive help, but limited by the small number of samples, more large-scale trials are still needed to support it

  1. Reduce inflammation indicators (C-reactive protein)

C-reactive protein (CRP) is an acute phase protein, which reflects the measurement of acute phase response. The plasma CRP level of most healthy subjects is usually 1 mg/L, and the normal value is defined as <10 mg/L. Plasma levels increase within 4 to 6 hours after the initial tissue injury, and continue to increase hundreds of times within 24 to 48 hours.

“Acute phase” refers to events that accompany local inflammatory reactions locally and systemically, including vasodilation, platelet aggregation, neutrophil chemotaxis, and the release of lysosomal enzymes.

People who smoke, hypertension, overweight, and do not exercise tend to have higher CRP levels, while people who are slender and like to exercise tend to have lower CRP levels.

A systematic literature review and meta-analysis (6 randomized controlled trials, 1087 participants) showed that oral carnitine significantly reduced C-reactive protein concentrations compared with controls. Note 2

*Conclusion: Supplementing carnitine may help reduce the concentration of C-reactive protein, but due to the small sample size and heterogeneity, more studies are needed for further verification

  1. Helps lose weight

Weight loss is an important topic for most people in modern times. In addition to increasing self-confidence, it is more important to get health. Studies have shown that compared with people of normal weight, obese people have a 7% increase in stroke rate, 49% increase in coronary artery disease, and heart failure. Risk increased to 96%.

A systematic literature review and meta-analysis (9 studies, 911 participants) found that L-carnitine had a more significant weight loss and body mass index lowering effect (especially in people with chronic symptoms, such as diabetes or obesity) compared with the control group. Note 1

*Conclusion: Oral L-carnitine can reduce weight, but considering the heterogeneity of the included studies, more large-scale studies are still needed to confirm

  1. Good for diabetes

Affected by the aging population and the increasing obesity rate, diabetes has become the fastest growing disease. According to the U.S. Census, about 35% of the population over the age of 20 is pre-diabetic, and up to 50% after the age of 65, and if left untreated, 37% of patients will develop diabetes within 4 years. Note 2

A systematic literature review and meta-analysis (4 studies, 284 patients with type 2 diabetes) pointed out that oral L-carnitine improved fasting blood glucose and lowered blood lipids (including total cholesterol, LDL cholesterol, apolipoprotein B100, and AI). Note 3

The mechanism behind it is related to enhancing mitochondrial oxidation of long-chain acetyl-CoA, inducing glycolytic enzymes, and regulating the expression of insulin-related genes.

Another systematic literature review and meta-analysis (5 studies, 631 patients with type 2 diabetes) showed that L-carnitine helped improve insulin resistance, and the improvement increased with the duration of treatment. Note 4

*Conclusion: L-carnitine has a positive effect on insulin resistance and blood sugar, but it is limited by the number of samples and needs further confirmation

  1. Beneficial cognitive function

Cognitive ability generally refers to behaviors related to mental processing, including thinking, cognition, memory, judgment, problem-solving ability, etc.

Cognitive function is deteriorated to varying degrees due to many factors, including aging, stress and many medical conditions, such as high blood pressure, dementia, Parkinson’s disease, schizophrenia, bipolar disorder and other mental diseases.

A Cochrane Review (2 studies with 418 healthy adults) noted that L-carnitine had no effect on cognitive function (measures of reaction time, alertness, memory, or delayed recall). Note 5

*Conclusion: L-carnitine does not improve cognitive function in healthy people, but the evidence from the included studies is low, and more large, precisely designed studies are needed

  1. Prevent cardiovascular disease

Cardiovascular disease is the leading cause of death in humans, far ahead of malaria, AIDS and tuberculosis. In the United States, costs related to treating cardiovascular disease account for about 17% of total health care expenditure, and related costs increase 1-fold every 10 years.

A meta-analysis (13 randomized controlled studies involving 3629 participants with acute myocardial infarction) showed that carnitine use helped reduce all-cause mortality by 27%, ventricular arrhythmia by 65%, and angina by 40%. Note 6

The mechanism behind it may be related to carnitine’s ability to improve mitochondrial energy metabolism, remove toxic fatty acid products, and reduce infarction effect.

Conclusion: Considering the characteristics of low cost and high safety, L-carnitine may have a good secondary prevention effect for people at high risk of cardiovascular disease, but more research is needed to confirm it.

  1. Beneficial idiopathic oligospermia (male infertility)

Idiopathic oligoasthenoteratozoospermia is defined as an unexplained decrease in male semen parameters, the origin of spermatogenesis defects is unknown, and physical examination and endocrine examination do not reveal a possible cause.

This condition is characterized by sperm necrosis and apoptosis (oligospermia), decreased percentage of normal sperm morphology, decreased sperm motility (asthenospermia), e.g., sperm count <15×106 cells/ml, abnormal sperm morphology >4%, motility <40%.

Oxidative stress is one of the main factors involved in the pathogenesis, and in most patients, oxidative stress manifests itself as an increase in reactive oxygen species and a decrease in the total antioxidant capacity in seminal plasma.

A meta-analysis (7 studies, 693 patients with idiopathic oligospermia) pointed out that the combination of L-carnitine and acetyl-L-carnitine can increase the percentage of forward sperm motility, total motile spermatozoa, and forward motile compared with placebo spermatozoa) percentage and number of pregnancies. Note 1

*Conclusion: For patients with idiopathic oligospermia, carnitine therapy can help improve some semen parameters, but limited by small sample sizes, more high-quality trials are needed to provide more evidence

  1. Beneficial to renal anemia in hemodialysis patients

Due to an aging population, obesity and increasing rates of type 2 diabetes, the prevalence of chronic kidney disease (CKD) is gradually increasing, about 8% to 16% of the total population.

The presence of chronic kidney disease increases an individual’s risk of cardiovascular disease, hyperlipidemia, mineral and bone disorders, and anemia.

The development of anemia in patients is driven by at least two factors, such as decreased erythropoietin and elevated levels of hepcidin (a hormone that impairs dietary iron absorption).

A meta-analysis of 18 randomized controlled trials involving 1090 patients with end-stage renal disease treated on hemodialysis showed that L-carnitine supplementation significantly increased plasma free L-carnitine levels, reduced erythropoietin responsiveness index, and required erythropoietin dose. Note 2

However, L-carnitine use was not associated with higher hemoglobin levels and hematocrit levels.

In addition, subgroup analyses found that the effect of L-carnitine supplementation on renal anaemia in hemodialysis patients was independent of treatment time and intervention route.

*Conclusion: For renal anemia in hemodialysis patients, L-carnitine supplementation may bring positive help, but more studies are needed to confirm its efficacy and safety in long-term use

What are the types of carnitine?

Carnitine is a broad term that describes several different compounds.
L-carnitine is a relatively common form of carnitine, found in the human body and in many supplements.

Other forms of carnitine include:

D-carnitine: This type is an optical isomer (mirror image) of L-carnitine. It is an inactive form of carnitine, which inhibits the absorption of other forms of carnitine, leading to carnitine deficiency in the body

Acetyl-L-carnitine: Usually called ALCAR (a combination of L-carnitine and an acetyl group), it also plays a role in metabolism. It has neuroprotective properties. Studies have shown that it may Neurodegenerative diseases are beneficial

L-carnitine tartrate: Because of its fast absorption rate, it is usually added to sports supplements. Studies have shown that it may help reduce muscle soreness and aid recovery.

Propionyl-L-carnitine: This form is very suitable for blood circulation problems such as peripheral vascular disease and high blood pressure. It can promote the production of nitric oxide, thereby improving blood flow

L-Carnitine Fumarate: This form is a combination of L-Carnitine and fumaric acid, which is a citric acid cycle intermediate that naturally exists in the body. It is widely used to promote athletic performance and help weight loss.

How to take carnitine (what is the dosage)?

The dosage varies from study to study, the following is an overview of the commonly used dosages in the study:

The standard dose of L-carnitine is 500 to 2000 mg per day.

Acetyl-L-carnitine: The dose ranges from 600 to 2500 mg per day.

L-carnitine L-tartrate: The dosage ranges from 1,000 to 4,000 mg per day.

Propionyl-L-carnitine: The dose ranges from 400 to 1000 mg per day.

It is best to check with professional medical personnel before use to ensure safety

Are there any side effects of L-carnitine?

According to the currently available literature, under instructions, proper use of carnitine health products is very safe without serious side effects, but adverse reactions that have been reported include nausea, vomiting, abdominal cramps, heartburn, and diarrhea

A daily dose greater than 3,000 mg may cause fishy smell in breath, urine and sweat.

The use of Acetyl-L-carnitine form may cause agitation in patients with Alzheimer’s disease and increase the frequency of seizures in patients with epilepsy.


Safety precautions

  1. Patients with poor liver and kidney function, pregnant women, breastfeeding mothers, peripheral vascular disease, diabetes, high blood pressure, and epilepsy, please consult a medical staff before use (because the relevant safety is unknown)
  2. Do not use for patients with hypothyroidism (may make symptoms worse)
  3. Do not use with anticoagulant drugs, which may affect the effect of the drug and increase the risk of bruising and bleeding
  4. It may affect the effect of thyroid hormone, please pay attention to those who use related thyroid therapy

Where to buy the most recommended L-carnitine capsules?

In recent years, food safety issues in various countries have exploded. What people spend money on is not healthy, but black-hearted products. Therefore, European and American products with relatively strict quality control have become popular products.


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