Usefulness of Carnitine Supplementation for the Complications of Liver Cirrhosis L carnitine is a naturally occurring amino acid structure that is made in the human brain, liver, and kidneys. L carnitine plays a critical role in energy production, as it converts fat into energy. Serum L Carnitine Levels Are Associated With First Stroke in Chinese Adults With Hypertension Stroke L carnitine levels decrease with age, contributing to aging and a decline in mitochondrial function. The list doesn't stop there. L carnitine supports: Joint health L carnitine has been shown to support joint comfort L Carnitine Powder Fitness Support NOW Foods L Carnitine is Underrated. New Meta Review Reminds Us Why.