L-carnitine is a derivative of the amino acid lysine. L-carnitine can be synthesized in the body from the amino acids lysine and methionine. L-carnitine can also be obtained through our diet and is mainly found in meat, fish, and dairy products. Some critically ill patients, people who follow a vegan diet, people that take certain medications (valproic acid), and people born with carnitine synthesis disorders might need to supplement L-carnitine to prevent deficiency. L-carnitine also acts synergistically with CoQ₁₀ because both are highly concentrated in our hearts, skeletal muscles, livers, and brains. L-carnitine also plays an essential role in mitochondrial energy production. Carnitine conjugates fatty acids for transport into our mitochondria across our inner mitochondrial membrane so that the activated fatty acids can then be metabolized for energy.[1] [2]

Long-chain fatty acids must become esters of L-carnitine first before our mitochondria can use them. The conversion enables fatty acids to enter our mitochondrial matrix and provide mitochondria with the source material for ATP (adenosine triphosphate) generation. Carnitine also works synergistically with coenzyme A to metabolize fatty acids and transport them within the individual cells. Finally, L-carnitine reduces oxidative stress in our mitochondria and reduces electron leakage in the electron transport chain, leading to enhanced mitochondrial function and health.[3] [4]

“Disruption of mitochondrial function is acknowledged as a critical event in a number of pathological conditions, including hypoxia-ischemic injuries, stroke, and diabetes. The carnitine acyltransferase pathway has been shown to be of critical importance for maintaining normal mitochondrial function. Fatty acids are transported via carnitine into mitochondria for their subsequent oxidation to generate ATP. Carnitines also remove the acyl groups from the mitochondria as acylcarnitines. Increase in free fatty acid levels can induce mitochondrial dysfunction resulting in cell death and/or enhanced secondary generation of reactive oxygen species. These effects can be attenuated with L-carnitine treatment. In addition, L-carnitine can suppress the palmitoyl-CoA induced dysfunction, membrane permeability transition (MPT), and cytochrome c release of isolated mitochondria as well as reduce the mitochondrial swelling and depolarization induced by long chain fatty acids (LCFAs) and palmitoyl-CoA through a protective mechanism thought to occur in and around the mitochondrial membrane. L-carnitine also suppresses oleic acid-mediated MPT by accelerating β-oxidation. Studies have also shown that carnitine has a protective effect both on mitochondria and in whole cells by inhibiting free fatty acid-induced mitochondrial membrane injury and/or its secondary effects. The protective effects of carnitine and related metabolites have been postulated to be due to improved energy metabolism and the inhibition of electron leakage from mitochondrial electron transport systems. Administration of carnitine has also been shown to decrease free fatty acids in serum and tissues and prevent tissue injury in juvenile visceral steatosis (JVS) mice that lack a carnitine transporter. Mitochondria are also emerging as important signaling transducers in the apoptotic pathway in a variety of disease states. Previous studies have shown a close relationship between carnitine and mitochondria. Cultured neonatal rat cardiac myocytes were studied to assess mitochondrial alterations during apoptosis. It was shown that CPT1 inhibition, ceramide accumulation, and complex III inhibition were downstream events in cardiac apoptosis mediated by long-chain fatty acids, such as palmitate. L-carnitine has also been shown to inhibit mitochondria-dependent apoptosis both in vivo and in vitro.”[5]

Different Forms of L-carnitine:

There are currently six recognized forms of L-carnitine, each serving a unique purpose. The six forms of supplemental L-carnitine are:

Standard L-carnitine and Its Chelations

L-carnitine – Standard L-carnitine supplementation is used in the body to increase energy production and improve the health of our mitochondria. L-carnitine should be used in people who are sensitive to acetyl L-carnitine, which may mentally overstimulate some people, leading to racing thoughts and mania.[6] [7]

The daily-recommended dose of L-carnitine for most people is 2,000 milligrams. I would not take more than 4,000 milligrams daily if possible because the excess L-carnitine might cause a fishy body odor and skin sensitivities at this large a dose.[8]

When You Should Take the Supplement: L-carnitine should be taken in divided doses when you first wake up and between breakfast and lunch for weight loss and energy. For example, if you take 2,000 milligrams of carnitine daily, you should take 1,000 milligrams upon waking and 1,000 milligrams between breakfast and lunch. Take it instead at breakfast and lunch if it is too stimulating or upsets your digestion.[9]

Recommended Brand: Jarrow Formulas L-carnitine (https://www.amazon.com/gp/product/B0020NC04Y/ref=as_li_ss_tl?ie=UTF8&camp=1789&creative=390957&creativeASIN=B0020NC04Y&linkCode=as2&tag=stac01-20), Now L-Carnitne Pure Powder (https://www.amazon.com/dp/B001B4JQP4/ref=cm_sw_r_as_gl_api_gl_i_26PESN47ECB869FN81J2?linkCode=ml1&tag=stac01-20)

L-carnitine L-tartrate – L-carnitine L-tartrate is a chelation of L-carnitine and tartaric acid. Tartaric acid is a naturally occurring acid found within grapes. Tartaric acid is supposed to help with the stability and absorption of L-carnitine. L-carnitine L-tartrate has been shown in one study to reduce recovery time for athletes after workouts.[10] [11] [12]

The daily-recommended dose of L-carnitine L-tartrate for most people is 2,000 milligrams. I would not take more than 4,000 milligrams daily if possible because the excess L-carnitine L-tartrate might cause a fishy body odor and skin sensitivities at this large of a dose.[13]

When You Should Take the Supplement: L-carnitine L-tartrate should be taken in divided doses when you first wake up and between breakfast and lunch for weight loss and energy. For example, if you take 2,000 milligrams of carnitine daily, you should take 1,000 milligrams upon waking and 1,000 milligrams between breakfast and lunch. Take it instead at breakfast and lunch if it is too stimulating or upsets your digestion.[14]

Recommended Brand: Jarrow Formulas L-carnitine tartrate (https://www.amazon.com/gp/product/B0013OX9G4/ref=as_li_ss_tl?ie=UTF8&camp=1789&creative=390957&creativeASIN=B0013OX9G4&linkCode=as2&tag=stac01-20)

L-carnitine fumarate – L-carnitine fumarate is a chelation of L-carnitine and fumaric acid. Fumaric acid is a naturally occuring acid found within some mosses and mushrooms. Fumaric acid is also supposed to help with the stability and absorption of L-carnitine. Fumarate can help activate the nuclear factor erythroid 2-related factor 2 (NrF2) antioxidant response pathway, the primary cellular defense against the cytotoxic effects of oxidative stress. L-carnitine chelated with fumarate might provide greater mitochondrial protection from oxidative stress.[15] [16] [17] [18]

The daily-recommended dose of L-carnitine fumarate for most people is 2,000 milligrams. I would not take more than 4,000 milligrams daily if possible because the excess L-carnitine fumarate may create fishy body odor and skin sensitivities at this large of a dose.[19]

When You Should Take the Supplement: L-carnitine fumarate should be taken in divided doses when you first wake up and between breakfast and lunch for weight loss and energy. For example, if you take 2,000 milligrams of carnitine daily, you should take 1,000 milligrams upon waking and 1,000 milligrams between breakfast and lunch. Take it instead at breakfast and lunch if it is too stimulating or upsets your digestion.[20]

Recommended Brands: Doctor’s Best L-carnitine fumarate (https://www.amazon.com/gp/product/B0013HXKC4/ref=as_li_ss_tl?ie=UTF8&camp=1789&creative=390957&creativeASIN=B0013HXKC4&linkCode=as2&tag=stac01-20), Pure Encapsulations L-carnitine fumarate (https://www.amazon.com/dp/B0016RFXO4/ref=cm_sw_r_as_gl_api_gl_i_BNDHVJ8XCG37MHQQ2W42?linkCode=ml1&tag=stac01-20)

Specialized L-Carnitine Chelations

Acetyl L-carnitine – L-carnitine often does not cross our blood-brain barrier very well. Scientists discovered that carnitine could cross our blood-brain barrier more effectively by acetylating L-carnitine. Acetyl L-carnitine makes transporting fatty acids into our brain easier by allowing the acids to cross our blood-brain barrier easily and nourish our brain. In addition, the acetyl portion of the chelation helps increase acetylcholine levels in our brain by donating an acetyl group. Acetyl L-carnitine has been shown in studies to improve memory, cognition, and neuropathy, especially in people who are suffering from type two diabetes. It has been theorized that this brain function increase occurs because acetyl L-carnitine nourishes the brain with essential fatty acids for optimal functioning. Finally, low levels of L-carnitine in the brain have been linked to depression.[21] [22] [23] [24]

One of the only drawbacks that I know of acetyl L-carnitine supplementation is that, for some people, it can overstimulate their brain mitochondria so much that they develop racing thoughts or mania. If that occurs, switch to a standard L-carnitine chelation and receive some of the benefits of supplementation with carnitine.[25] [26]

The daily-recommended dose of acetyl-L-carnitine for most people is 2,000 milligrams. I would not take more than 4,000 milligrams daily if possible because the excess acetyl L-carnitine might cause a fishy body odor and skin sensitivities at this large a dose.[27]

When You Should Take the Supplement: Acetyl-L-carnitine should be taken in divided doses when you first wake up and between breakfast and lunch to support cognitive function. For example, if you take 2,000 milligrams of carnitine daily, you should take 1,000 milligrams upon waking and 1,000 milligrams between breakfast and lunch.

Recommended Brands: Jarrow Formulas acetyl L-carnitine (https://www.amazon.com/gp/product/B0027DWNHQ/ref=as_li_ss_tl?ie=UTF8&camp=1789&creative=390957&creativeASIN=B0027DWNHQ&linkCode=as2&tag=stac01-20), Life Extension acetyl L-carnitine (https://www.amazon.com/gp/product/B0001KFD0G/ref=as_li_ss_tl?ie=UTF8&camp=1789&creative=390957&creativeASIN=B0001KFD0G&linkCode=as2&tag=stac01-20), Pure Encapsulations – acetyl L-carnitine (https://www.amazon.com/gp/product/B00169P3OC/ref=as_li_ss_tl?ie=UTF8&camp=1789&creative=390957&creativeASIN=B00169P3OC&linkCode=as2&tag=stac01-20)

Acetyl L-carnitine arginate – This specially chelated form of acetyl L-carnitine is acetyl L-carnitine bonded with the amino acid L-arginine. It is believed that the extra arginine in which the carnitine is bonded can cross our blood-brain barrier and increase nitric oxide production, which improves brain circulation. Acetyl L-carnitine arginate is also an excellent form of carnitine for bodybuilders because the arginine chelation enhances nitric oxide production with our body and acts as a vasodilator. Increased arginine supplementation has also been theorized to increase blood flow to our muscles. Finally, I recommend avoiding acetyl L-carnitine arginate if you are suffering from viral reactivation (herpes outbreak, shingles, chronic fatigue syndrome caused by Herpesviridae) because excessive arginine may increase viral replication.[28] [29] [30]

“The role of mitochondria in cardiovascular pathologies is being extensively scrutinized. In cardiovascular diseases, there is increased production of reactive oxygen species (ROS). This leads to endothelial dysfunction and impaired endothelium dependent vasodilation by reducing the bioavailability of nitric oxide (NO). Studies on the mechanism(s) underlying the effects of L-carnitine in cardiovascular diseases have demonstrated that the chronic administration of L-carnitine can reduce blood pressure and attenuate the inflammatory process associated with arterial hypertension. Carnitine treatment has also been shown to increase post-ischemic blood flow in patients with peripheral vascular disease, indicative of an improvement in functional circulatory reserve. L-carnitine has been shown to limit ischemia reperfusion injury by preventing long-chain acyl-CoA accumulation and subsequent production of ROS by damaged mitochondria. L-carnitine also improves repair mechanisms for oxidative-induced injury to membrane phospholipids and reduces the ischemia-induced apoptosis and the consequent remodeling of the left ventricle. L-carnitine restores endothelial dysfunction present in spontaneously hypertensive rats (SHR) and has the ability to increase the release of the vasodilator PGI₂ and enhance the production of TXA₂ in normotensive rats. An acute L-carnitine treatment to SHR was also able to restore endothelium-dependent relaxations of aortic rings.

NO production and availability plays a major role in determining endothelial cell functions. Decreases in endothelial nitric oxide synthase (eNOS) expression and/or activity leading to decreased bioavailable NO generation has been linked to endothelial dysfunction and vascular remodeling. We have observed reduced mitochondrial function as measured by increased lactate/pyruvate ratios, increased uncoupling protein-2 (UCP-2) and decreased mitochondrial superoxide dismutase (SOD-2) protein levels in a lamb model of pulmonary hypertension. Further, the mitochondrial dysfunction was associated with decrease in interaction of HSP90 with eNOS, which correlated with a progressive decrease in relative eNOS activity, and increased NOS-dependent superoxide levels. Thus, L-carnitine supplementation may help to maintain eNOS-HSP90 interactions, NO signaling, and normal endothelial function.”[31]

The daily-recommended dose of acetyl L-carnitine arginate for most people is 2,000 milligrams. I would not take more than 4,000 milligrams daily if possible because the excess acetyl L-carnitine arginate might cause a fishy body odor and skin sensitivities at this large of a dose.[32]

When You Should Take Acetyl L-carnitine Arginate: Acetyl L-carnitine arginate should be taken in divided doses when you first wake up and between breakfast and lunch for increased cognitive function. For example, if you are taking 2,000 milligrams of carnitine daily, you should take 1,000 milligrams upon waking and 1,000 milligrams between breakfast and lunch.[33]

Recommended Brand: Supersmart acetyl L-carnitine arginate (https://www.amazon.com/dp/B00LPJJLG4/ref=cm_sw_r_as_gl_api_gl_i_M5KTRRR5CSY1PPMBVBAA?linkCode=ml1&tag=stac01-20)

Glycine propionyl L-carnitine – Propionyl L-carnitine is the primary recommended form of L-carnitine for people with arterial blood flow problems and heart disease. Propionyl is also an extra donor to the coenzyme A cycle. Since L-carnitine works synergistically with coenzyme A, taking a propionyl L-carnitine supplement is a great way to increase natural coenzyme A production within our body.[34] [35] [36]

Propionyl L-carnitine has been shown in studies to increase nitrate/nitrite production in the body, as well. Extra nitrates/nitrites in our body have been shown to theoretically increase nitric oxide production, which is why propionyl L-carnitine promotes proper arterial blood flow, as increased nitric oxide production is a potent vasodilator. Propionyl L-carnitine is the preferred form of L-carnitine for people with poor blood flow in their extremities, including those with intermittent claudication. Finally, I recommend avoiding propionyl L-carnitine if you are experiencing viral reactivation (herpes outbreak, shingles, chronic fatigue syndrome caused by Herpesviridae), nitric oxide may increase viral replication.[37] [38] [39] [40]

“Finally, GPLC (a novel form of carnitine) supplementation with exercise has been shown to elevate NO levels in human subjects. Besides, decreasing oxidative stress, GPLC supplementation was associated with normalization/enhancement of circulating NO levels.”[41]

The daily-recommended dose of propionyl L-carnitine for most people is 2,000 milligrams. I would not take more than 4,000 milligrams daily if possible because excess propionyl L-carnitine might cause a fishy body odor and skin sensitivities at this large a dose.[42]

Propionyl L-carnitine should be taken with breakfast and lunch in divided doses. For example, if you are taking 2,000 milligrams of carnitine daily, you should take 1,000 milligrams with breakfast and 1,000 milligrams with lunch.[43]

Recommended Brand: bilor propionyl-L-carnitine (https://amzn.to/401XZs4)

L-carnitine Supplementation Side Effects

L-carnitine is safe for most people to supplement daily and has few known side effects. In some people, L-carnitine can cause upset stomach and indigestion, which can be relieved when it is taken with a meal rather than on an empty stomach. L-carnitine supplementation may also rarely cause nausea, vomiting, and diarrhea. L-carnitine can cause some people to develop a fishy body odor when taken in quantities greater than 4,000 milligrams daily. There are also infrequent systemic allergic reactions caused by L-carnitine supplementation in some people.[44] [45]

Trimethylamine (TMAO) is obtained from daily dietary ingestion of foods or supplements that contain choline, glycine, carnitine, or betaine and their interaction with differing microbes in our digestive system. Varying amounts of trimethylamine are produced, person to person, because of the differences within our microbiomes and diets. Certain microbes in our gut may have excessive amounts of trimethylamine from ingesting foods that are elevated in carnitine, choline, betaine, or glycine (animal products are a rich source) or from supplementation of these components. Escherichia coli, for example, normally resides in small amounts harmlessly in our gut microbiome and produces the enzyme choline Trimethylamine-lyase (CutC), which metabolizes choline into trimethylamine.

Trimethylamine converts into trimethylamine-N-oxide by both microbes within our digestive tract and by our liver. Increased trimethylamine-N-oxide levels in our blood may be associated with an increased risk of excessive arterial inflammation and the development of atherosclerosis. However, TMAO might also benefit the cardiovascular system. Since seafood contains elevated amounts of trimethylamine and trimethylamine-N-oxide, you would think that ingesting seafood would be bad for your cardiovascular system. Instead, most evidence shows that ingesting seafood frequently is good for the health of your cardiovascular system. I recommend that if you are dealing with gut dysbiosis (especially Escherichia coli dysbiosis) or if your Viome (https://www.viome.com/) gut test results show that you have elevated TMAO production pathways you should avoid L-carnitine supplementation.[46] [47] [48]

L-carnitine should be used cautiously in people with an underactive thyroid (hypothyroidism). L-carnitine supplementation can worsen the symptoms of hypothyroidism. Finally, L-carnitine was once believed to trigger or worsen seizures. However, multiple recent studies have disproven this claim, and supplementation may help prevent seizures and improve cognitive function.[49] [50] [51]

[1] http://lpi.oregonstate.edu/infocenter/othernuts/carnitine/

[2] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2905823/

[3] http://lpi.oregonstate.edu/infocenter/othernuts/carnitine/

[4] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2905823/

[5] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2905823/

[6] http://lpi.oregonstate.edu/infocenter/othernuts/carnitine/

[7] https://journals.sagepub.com/doi/full/10.1177/1039856216658831

[8] http://lpi.oregonstate.edu/infocenter/othernuts/carnitine/

[9] http://lpi.oregonstate.edu/infocenter/othernuts/carnitine/

[10] http://lpi.oregonstate.edu/infocenter/othernuts/carnitine/

[11] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4924324/

[12] https://www.ncbi.nlm.nih.gov/pubmed/12930169