This 2020 review subject was carnitine, acetyl-L-carnitine, and its other molecular forms:
“Carnitine is necessary to deliver long-chain fatty acids from cytosol into mitochondria. Carnitine homeostasis is maintained by diet and renal absorption, as only a small amount (about 25%) is obtained by endogenous biosynthesis.
Defective fatty acid oxidation occurs with reduced intracellular levels of carnitine, leading to glucose consumption instead of lipid consumption, resulting in hypoglycemia. Non-metabolized lipids accumulate in tissues such as heart, skeletal muscle, and liver, resulting in myopathy and hepatic steatosis.
2000 mg/day is unlikely to provoke unwanted side effects and is safe for humans. In-depth studies are needed to identify a unique method of analysis which can guarantee efficient monitoring of supplement active component amounts.”
https://www.mdpi.com/1420-3049/25/9/2127/htm “The Nutraceutical Value of Carnitine and Its Use in Dietary Supplements”
The review listed animal studies of L-carnitine alone and in combination with:
- Vitamin D3;
- Coenzyme Q10;
- Nicotinamide riboside;
- Anti-histamine drugs cetirizine hydrochloride and chlorpheniramine maleate; and
- Hypertension drug olmesartan.
Human studies of its effects included:
- Muscle soreness, damage biomarkers, and cramps;
- Osteoarthritis knee pain and inflammation markers;
- Ischemic cerebrovascular injury;
- Peripheral neuropathy;
- Nonalcoholic fatty liver disease;
- Insulin resistance and Type 2 diabetes;
- Kidney diseases;
- Inherited diseases phenylketonuria and maple syrup urine;
- Stress, depression, and anxiety;
- Male infertility; and
- Hepatitis C.