A Snapshot of Blood Homocysteine
Cholesterol isn't the only blood component associated with the risk of heart
disease and stroke. Since the early 1990s, the amino acid homocysteinea
byproduct of amino acid metabolismhas emerged as another important risk
Researchers believe that when body cells dump too much homocysteine into the
blood, artery linings become irritated, encouraging the formation of
plaquefatty deposits that cling to artery walls.
One cause of this dumping is a low intake of folate, vitamin B6, or vitamin
B12, according to earlier findings by researchers at the Jean Mayer USDA Human
Nutrition Research Center on Aging at Tufts University in Boston,
Massachusetts. Body cells need these three B vitamins to convert the amino acid
methionine to cysteine. When any one is lacking, the intermediate product in
the conversion, homocysteine, builds up.
In 1993, the Boston researchers were first to report homocysteine levels in
any populationmore than 1,100 elderly in the original Framingham
(Massachusetts) Heart Study. Even in this relatively narrow age range67
to 96 yearshomocysteine levels increased with age. Men had higher levels
than women, but the difference narrowed at the upper ages.
Two years later, Norwegian researchers reported similar age and gender
differences among the middle-aged population in their country. Smaller
population samples in the United States and Europe generally support these
"We wanted to describe serum homocysteine concentrations across our
population and test for differences among sex, age, race, and ethnicity,"
says Paul F. Jacques, an epidemiologist at the USDA center involved in the
But the studies covered specific age groups and were not representative of
the U.S. population as a whole.
In the current study, Jacques and his Boston colleagues collaborated with
scientists affiliated with the Centers for Disease Control and Prevention in
Atlanta, Georgia, and Hyattsville, Maryland. Using blood serum samples from the
latest National Health and Nutrition Examination Survey, they measured
homocysteine levels for 3,766 males and 4,819 females from age 12 up.
The results "confirm the age and sex differences reported in
nonrepresentative samples," says Jacques. Homocysteine levels increased
with age. They were also significantly higher in males than females, regardless
of whether the subjects were white or black with no Hispanic or
Mexican-American background. Levels were closest between the two genders in the
young and old, diverging around puberty and converging after menopause.
The researchers suspect that impaired kidney function may contribute to the
higher levels in older people.
Body size, estrogen, and vitamin status may explain the difference between
genders, they say. Larger people have more creatininea protein breakdown
productcirculating in their blood. And studies show a strong correlation
between circulating creatinine and homocysteine levels. Also, "estrogen
seems to protect against high homocysteine," says Jacques, judging by the
lower levels in premenopausal women. Further, women are more conscious about
nutrition. The women in the study had a higher folate status than the men.
Mexican-American females had the study's lowest homocysteine
levelssignificantly lower than non-Hispanic black and white subjects.
Jacques says nutrition may explain part, but not all, of the difference. He has
not yet analyzed the data to look for other factors.
"It's crucial we understand the basis for these age and gender
differences," he adds, "because fairly modest increases in
homocysteine are strongly associated with higher risk of vascular
McBride, Agricultural Research Service Information Staff.
This research is part of Nutrient Requirements, Food Composition, and
Intake, an ARS National Program described on the World Wide Web at
Paul F. Jacques is at the Jean
Mayer USDA Human Nutrition Research Center
on Aging at Tufts University, 711 Washington St., Boston, MA 02111; phone
(617) 556-3322, fax (617) 556-3344.
"A Snapshot of Blood Homocysteine Levels" was published in
the March 1999 issue of
Agricultural Research magazine.
Summaries of new ARS findings in nutrition, food safety, and health are
available in the Food & Nutrition Briefs. This quarterly publication is
available electronically at http://www.ars.usda.gov/is/np/fnrb/. For a free
subscription, contact Judy McBride, nutrition editor, at (301) 504-1628; or
write to her at 5601 Sunnyside Ave., Beltsville, MD 20705-5129; e-mail