Homocysteine
Medical Author: Siamak Nabili, MD, MPH
Medical Editor: William C. Shiel, Jr., MD, FACP, FACR
What is homocysteine?
Homocysteine is an amino acid that is produced by the body, usually as a
byproduct of consuming meat. Amino acids are naturally made products, which are
the building blocks of all the proteins in the body.
Why is it important to monitor homocysteine levels?
Elevated levels of homocysteine (>10 micromoles/liter) in the blood may be
associated with atherosclerosis (hardening and narrowing of the arteries) as
well as an increased risk of heart attacks,
strokes,
blood clot formation, and
possibly Alzheimer's disease.
In 1969, Dr. Kilmer S. McCully reported that children born with a genetic
disorder called homocystinuria, which causes the homocysteine levels to be very
high, sometimes died at a very young age with advanced atherosclerosis in their
arteries. However, it was not until the 1990's that the importance of
homocysteine in heart disease and stroke was appreciated.
What are the possible symptoms or features of elevated homocysteine levels?
Theoretically, an elevated level of homocysteine in the blood
(hyperhomocysteinemia) is believed to cause narrowing and hardening of the
arteries (atherosclerosis). This narrowing and hardening of the vessels is
thought to occur through a variety of ways involving elevated homocysteine. The
blood vessel narrowing in turn leads to diminished blood flow through the
affected arteries.
Elevated levels of homocysteine in the blood may also increase the tendency
to excessive blood clotting. Blood clots inside the arteries can further
diminish the flow of blood. The resultant lack of blood supply to the heart
muscles may cause heart attacks, and the lack of blood supply to the brain
causes strokes.
Elevated homocysteine levels also have been shown to be associated with
formation of blood clots in veins (deep vein thrombosis and
pulmonary
embolism). The mechanism is complex, but it is similar to the way that they
contribute to atherosclerosis. In some studies, even moderate levels of
homocysteine level showed higher rates of repeated incidence of blood clot
formation. (1,2)
Next: What is considered a high level for homocysteine? »
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