Women May Need More Folate
Chemist Robert Jacob discusses progress of a 12-week folate study with
participants Carol Garnett (right) and Maria Salazar.
More evidence that the current Recommended Dietary Allowance of 180
micrograms a day of the B vitamin folate (folic acid) for women is probably too
low has resulted from a new study by ARS researchers and their colleagues.
Adequate folate intake has been linked to decreased risk of spina bifida and
other birth defects, as well as reduced risk of cardiovascular disease and
"A very small amount of the powdered form of folate," says
Agricultural Research Service chemist
Robert A. Jacob, "provides the RDA. It's the quantity of this nutrient
found in 1-3/4 cups of orange juice or about 4/5 cup cooked red beans, for
example." Other foods rich in folate include dark-green leafy vegetables
like spinach and broccoli, peas and beans, nuts and seeds, eggs, and liver.
Jacob led the folate investigation of 10 healthy, post-menopausal
volunteers, age 49 to 63. They lived round-the-clock at the ARS Western Human
Nutrition Research Center in San Francisco. For 9 weeks, they ate meals that
provided 30 to 60 percent of the RDA for folate. For a final 3 weeks, they got
meals fortified with extra folate.
The center's dietary staff meticulously prepared and measured the
volunteers' meals. "We tried to provide familiar foods and to mimic the
eating patterns of women who don't get enough folate-containing fruits and
vegetables," says Jacob.
To remove about half of the folate from green beans, carrots, chicken,
turkey, and ham, the dietary staff boiled these foods three times, discarding
the water each time. Volunteers ate a standard menu of low-folate foods
throughout the study, supplementing it at breakfast and dinner during the last
7 weeks with pure, synthetic folic acid mixed with applesauce.
Technician Janet Chan adds a precise amount of B vitamin folate solution to a
dish of applesauce.
A typical day's menu might include applesauce and hash-browned potatoes or
applesauce and toast with jelly for breakfast; boiled chicken, noodles,
zucchini squash, and stewed tomatoes for lunch; and pasta, roast turkey,
carrots with Italian dressing, and applesauce for dinner. That day's evening
snack would be a light dessert made of carrots, margarine, sugar, and a
Women of childbearing age were excluded from the study because of the link
between low folate levels and increased risk of spina bifida and other neural
tube birth defects, that is, deformities of the brain or spinal cord. To help
prevent these birth defects, the U.S. Food and Drug Administration requires--as
of January 1, 1998--that enriched bread, flour, cornmeal, rice, pasta, and
other grain products be fortified with folate. [See "Foods To Be Fortified
With Folic Acid," Agricultural Research, June 1997, pp. 16-17.]
Another Measure of Folate Status
After the 9-week regimen of low folate, the researchers found that all of
the women had low levels of folate in their blood (plasma). And seven of the
women had a larger number of components called micronuclei in their white blood
Says Jacob, "An increase in micronuclei indicates damage to DNA in
chromosomes. DNA is the genetic blueprint for all cell growth. Damage and
repair to DNA is always occurring, but chronic DNA damage may overwhelm repair
mechanisms and increase the risk of cancer and birth defects.
"The micronucleus test," notes Jacob, "wasn't used to study
folate nutrition in 1989, when folate RDAs for adults were lowered from 400
micrograms to 200 micrograms for men and 180 micrograms for women."
The idea of raising the folate RDA isn't new. But the San Francisco test was
apparently the first to use white blood cell micronuclei counts in a controlled
study of moderate folate deficiency.
The scientists used a second technique to check the body's DNA. Explains
Jacob, "The body uses folate to supply one-carbon-units in many reactions,
a process called methylation. That happens during formation of DNA, for
instance. Methylation of white blood cell DNA decreased during the low-folate
regimen. Other researchers have seen that happen in animal tests. But our
experiment was the first to show that even a mild folate deficiency can reduce
methylation of DNA in humans."
Seven of the 10 volunteers had elevated levels of an amino acid,
homocysteine, in their blood by the time they completed the first 9 weeks of
the 3-month study.
"The body," Jacob says, "has a folate-based mechanism to keep
homocysteine from getting too high. It uses a form of folate called
methyltetrahydrofolate to convert homocysteine into a different amino acid,
methionine. It's another example of methylation. High homocysteine levels
increase risk of heart attack or stroke."
A typical meal served in the folate study included pasta, tomato sauce, and
triple-boiled green beans and chicken.
For 2 weeks following the low-folate stint, volunteers received 160 percent
of the RDA. That raised plasma folate, but homocysteine levels remained high in
half of the women.
Says Jacob, "This indicated that the current RDA may not be sufficient
to maintain safe homocysteine levels in women who consume low-folate diets
similar to what was fed in this experiment."
During the last week of the study, when the women were given nearly three
times the RDA, homocysteine levels decreased to normal, or near normal, in all
but one of the volunteers, whose level still remained above normal at the end
of the study. Plasma folate, white blood cell micronuclei counts, and DNA
methylation also returned to their pre-study levels.
Jacob did the work with ARS colleagues Denise Gretz and Peter C. Taylor at
the nutrition center; Marian E. Swendseid of the University of California at
Los Angeles; S. Jill James of the U.S. Food and Drug Administration, Jefferson,
Arkansas; Tsunenobu Tamura of the University of Alabama at Birmingham; and Nina
Titenko-Holland of the University of California at Berkeley.
Folate deficiency has been linked to increased risk of cancer of the cervix,
intestine, and other parts of the body that have a lining of epithelial cells.
So the team also examined micronuclei counts in epithelial cells from the
inside of the cheeks. Using a toothbrush, cells were gently scraped from the
cheeks of each volunteer. Cheek-cell tests are used in other nutrition and
Titenko-Holland found that cheek-cell micronuclei didn't increase during the
low-folate phase. But they decreased after the final 3 weeks of higher folate
In an earlier experiment, Jacob and Swendseid had shown that the RDA for
adult males may not be adequate. Four of the 10 volunteers who ate 12 percent
of the folate RDA showed moderately elevated homocysteine levels. These levels
remained elevated even when the volunteers received 84 percent of the RDA.
"Raising the RDA for men--as well as women," says Jacob,
"would increase the margin of safety for maintaining healthy homocysteine
levels. When the folate RDA was set 8 years ago, homocysteine levels weren't
measured. Nor was the connection of high homocysteine with heart disease known
at that time." By Marcia
Wood, Agricultural Research Service Information Staff, 800 Buchanan
St., Albany, CA 94710; phone (510) 559-6070.
Robert A. Jacob is at the
USDA-ARS Western Human
Nutrition Research Center, P.O. Box 29997, Presidio of San Francisco, CA
94129; phone (415) 556-3531; fax (415) 556-1432.
"Women May Need More Folate " was published in the March
1998 issue of Agricultural Research magazine. Click here to see this
issue's table of contents.