Betaine is a nutrient that is important for functioning of the heart and blood vessels. Betaine works in the body by preventing the build-up of an amino acid called homocysteine. This amino acid can harm blood vessels and contribute to heart disease, stroke, or circulation problems. Betaine is a byproduct of sugar beet processing. Betaine is used to reduce homocysteine levels in people with a genetic condition called homocystinuria, in which the amino acid builds up in the body. Betaine is not a cure for homocysteinuria. Betaine may also be used for purposes not listed in this medication guide.