High homocysteine levels is undesirable and known to be an indicator of heart disease and stroke risk. Free homocysteine in the blood causes sclerosis of the arteries, putting strain on the vascular system and the heart. One of the primary reactions of methylcobalamin is to convert homocysteine to methionine, reducing the potential for damage. Outcomes from this reaction include the formation of cysteine, a precursor to the super-antioxidant glutathione. Methionine also contributes to the formation of adenosylcobalamin, the other form of B12 used by the body in mitochondrial energy creation, the foundation for all human energy.