Note: The last update for this page was a partial update. We haven't yet added most studies for dementia, growth, neuropathy, and several other areas. We also haven't added most studies in hemodialysis and cardiovascular disease treatment, as these studies are largely only relevant to medical professionals and, for now, our efforts could be directed towards more directly applicable endeavors.
L-Carnitine is a compound produced by the body from lysine and methionine. It can be acetylated to produce acetyl-L-carnitine (ALCAR), which is similar but crosses the blood-brain barrier more efficiently. L-Carnitine is best known for its involvement in the mitochondrial oxidation of long-chain fatty acids.
It's found in food and is most prevalent in meat, and beef in particular.
It seems to have high utility in liver diseases where it reduces ammonia levels, the symptoms of hepatic encephalopathy, and various markers of poor liver function. An improvement in sperm quality has been found with supplementation of high doses, and improvements in male fertility have been noted in a small number of studies. It seems to help women with polycystic ovary syndrome by reducing some of the symptoms, and one study found an increase in fertility, but more research is needed.
Acetyl-L-carnitine (and possibly L-carnitine too, but studies only use ALCAR) shows efficacy in depression, though more research is needed to determine how useful it is. It seems to reduce fatigue in older adults with low muscular endurance, but its effects on athletes during physical activity aren't particularly consistent, though research supports small improvements. L-Carnitine may slightly limit muscle damage during resistance exercise.
It seems to have minor beneficial effects on blood pressure, blood glucose, insulin sensitivity, lipid profile, oxidative stress, and inflammation. Overall, it seems useful in metabolic syndrome but not a first choice.
When it comes to fat-burning, studies in isolation do not show very good results. Some studies have found minor fat loss, which is typically attributed to increased physical activity due to increased energy levels.
A few studies have noted a benign adverse effect of 'odd smell', which is said to be due to the formation of trimethylamines; it has occurred at a frequency of 4%.
Probably only if it helps to reduce fatigue and that leads to an increase in physical activity. It's possible that very low carnitine levels could lead to impaired fatty acid oxidation, but for most people, there isn't a notable increase in resting fatty acid oxidation when taking carnitine.