Homocysteine
Medical Author:
Dennis Lee, M.D.
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.
Why is it important to monitor homocysteine levels?
Elevated levels of homocysteine (>10 micromoles/liter) in the blood are
associated with atherosclerosis (hardening and narrowing of the arteries) as
well as an increased risk of heart attacks, strokes, 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.
How do elevated levels of homocysteine increase the risk of heart attacks and
strokes?
Elevated levels of homocysteine in the blood are believed to cause narrowing
and hardening of the arteries. This narrowing leads to diminished blood flow
through the affected arteries. Elevated levels of homocysteine in the blood also
increase the tendency to excessive blood clotting. Blood clots inside the
arteries further diminish the flow of blood. The resultant lack of blood supply
to the heart muscles causes heart attacks, and the lack of blood supply to the
brain causes strokes.
What causes elevated homocysteine levels?
Homocysteine is chemically transformed into methionine and cysteine with the
help of folic acid, vitamin B12, and vitamin B6. Therefore, insufficient amounts
of these vitamins in the body can hamper the natural breakdown of homocysteine.
This can cause homocysteine to accumulate in the blood. Conversely, a higher
folic acid intake and higher levels of body folate are associated with lower
blood homocysteine levels.
How can homocysteine levels be lowered?
The consumption of folic acid supplements or cereals that are fortified with
folic acid, and to a lesser extent vitamins B6 and B12, can lower blood
homocysteine levels.
Does lowering homocysteine levels prevent heart attacks and strokes?
Currently, there is no direct proof that taking folic acid and B vitamins to
lower homocysteine levels prevents heart attacks and strokes. However, in a
large population study involving women, those who had the highest consumption of
folic acid (usually in the form of multivitamins) had fewer heart attacks than
those who consumed the least amount of folic acid.
What should I do to prevent heart attacks and strokes?
Losing excess weight, exercising regularly, controlling diabetes and high
blood pressure, lowering the bad LDL cholesterol, and stopping cigarette smoking
are crucial steps in preventing heart attacks and strokes.
It is recommended that healthy adults eat more fresh fruits and vegetable,
eat less saturated fat and cholesterol, and take one multivitamin daily. One
multivitamin will supply 400 mcg/day of folic acid in addition to vitamins B6,
B12, and other important vitamins.
Who should undergo testing for homocysteine blood levels?
Currently, there are no official recommendations as to who should undergo
testing for homocysteine blood levels. There is also no consensus as to the
optimal dose of folic acid and other B vitamins for the treatment of elevated
blood homocysteine levels. (For example, treatment of patients with high
homocysteine levels may require higher doses of folic acid and other B vitamins
than the amounts contained in a multivitamin.) Therefore, a decision regarding
testing should be individualized after consulting with your doctor.
Some doctors screen for elevated homocysteine levels in patients with early
onset of heart attacks, strokes, or other symptoms related to atherosclerosis,
especially if these patients do not have typical heart attack risk factors, such
as smoking cigarettes, diabetes, or high LDL cholesterol levels.
For additional information, please visit www.MedicineNet.com
and review the
following topics:
Last Editorial Review: 3/15/2002
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