(USDA Agriculture Research Service) Studies at the Jean Mayer USDA Human Nutrition Research Center
on Aging at Tufts University in Boston suggest that consuming fruits and vegetables with a high-ORAC
value may help slow the aging process in both body and brain. ORAC--short for Oxygen Radical Absorbance
Capacity--measures the ability of foods, blood plasma, and just about any substance to subdue oxygen free
radicals in the test tube.
Early evidence indicates that this antioxidant activity translates to animals, protecting cells and
their components from oxidative damage. Getting plenty of the foods with a high-ORAC activity, such as
spinach, strawberries, and blueberries, has so far:
- raised the antioxidant power
of human blood,
- prevented some loss of
long-term memory and learning
ability in middle-aged rats,
- maintained the ability of
brain cells in middle-aged rats
to respond to a chemical
stimulus, and
- protected rats' tiny blood
vessels—capillaries—against
oxygen damage.
These results have prompted
Ronald L. Prior to suggest that "the
ORAC measure may help define the
dietary conditions needed to prevent
tissue damage."
Prior is coordinating this
research with Guohua (Howard) Cao,
James Joseph, and Barbara
Shukitt-Hale at the Boston center.
Science has long held that damage
by oxygen free radicals is behind
many of the maladies that come with
aging, including cardiovascular
disease and cancer. There's firm
evidence that a high intake of
fruits and vegetables reduces risk
of cancer and that a low intake
raises risk. And recent evidence
suggests that diminished brain
function associated with aging and
disorders such as Alzheimer's and
Parkinson's diseases may be due to
increased vulnerability to free
radicals, says Joseph, a
neuroscientist.
Such evidence has spurred
skyrocketing sales of antioxidant
vitamin supplements in recent years.
But several large trials testing
individual antioxidant vitamins have
had mixed results. "It may be that
combinations of nutrients found in
foods have greater protective
effects than each nutrient taken
alone," says Cao, a chemist and
medical doctor.
For example, foods contain more
than 4,000 flavonoids. These
constitute a major class of dietary
antioxidants and appear to be
responsible for a large part of the
protective power of fruits and
vegetables, Cao says.
By the year 2050, nearly
one-third of the U.S. population is
expected to be over age 65. If
further research supports these
early findings, millions of aging
people may be able to guard against
diseases or dementia simply by
adding high-ORAC foods to their
diets. This could save much
suffering, as well as reduce the
staggering cost of treating and
caring for the elderly.
Cao developed the ORAC test while
he was a visiting scientist at the
National Institute on Aging in
Baltimore, Maryland. After joining
Prior's group 5 years ago, the
researchers assayed commonly eaten
fruits, vegetables, and fruit juices
with ORAC. [See "Plant
Pigments Paint a Rainbow of
Antioxidants," Agricultural
Research, November 1996, pp.
4-8.]
"The ORAC value covers all the
antioxidants in foods," says Cao.
"You cannot easily measure each
antioxidant separately," he adds.
"But you can use the ORAC assay to
identify which phytonutrients are
the important antioxidants."
The researchers have been testing
whether antioxidants other than
vitamins are absorbed into the blood
and protect the cells. And the
results look promising.
Its in the Blood
Several laboratories have
reported that people can absorb
individual flavonoids thought to
have protective powers. Prior and
Cao now have good evidence that food
antioxidants not only are absorbed,
they boost the antioxidant power of
the blood.
In an earlier study at the Boston
center, 36 men and women ranging in
age from 20 to 80 had doubled their
fruit and vegetable intake.
According to the participants'
responses on a food frequency
questionnaire, they averaged about
five servings of fruits and
vegetables daily during the year
before the study. That intake was
doubled to 10 servings of fruits and
vegetables daily during the study.
To estimate ORAC intakes for the
participants, the two researchers
matched the questionnaire and the
diet data with their own antioxidant
values for each fruit and vegetable.
Before the study, says Prior, the
participants averaged 1,670 ORAC
units daily. Increasing their fruit
and vegetable intake to 10 a day
raised the ORAC intake to between
3,300 and 3,500 ORAC units—or about
twice the previous antioxidant
capacity.
Based on the participants' blood
samples, the antioxidants were
absorbed. The ORAC value of blood
plasma increased between 13 and 15
percent on the experimental diet.
This supports results of a
preliminary study in which Prior and
Cao saw a 10- to 25-percent rise in
serum ORAC after eight women ate
test meals containing high-ORAC
foods, red wine, or vitamin C. They
tested red wine because it has a
high ORAC value—higher than white
wine—and has been associated with a
lower risk of cardiovascular
disease.
Ten ounces of fresh spinach
produced the biggest rise in the
women's blood antioxidant
scores—even greater than was caused
by 1,250 milligrams of vitamin C. An
8-ounce serving of strawberries was
less effective than vitamin C but a
little more effective than 9.6
ounces of red wine.
Prior says the increase in plasma
ORAC can't be fully explained by
increases in plasma levels of
vitamin C, vitamin E, or carotenoids,
so the body must be absorbing other
components in these fruits and
vegetables. The antioxidant capacity
of the blood seems to be tightly
regulated, he says. Still, "a
significant increase of 15 to 20
percent is possible by increasing
consumption of fruits and
vegetables, particularly those high
in antioxidant capacity."
The ORAC values of fruits and
vegetables cover such a broad range,
he adds, "you can pick seven with
low values and get only about 1,300
ORAC units. Or, you can eat seven
with high values and reach 6,000
ORAC units or more. One cup of
blueberries alone supplies 3,200
ORAC units."
Based on the evidence so far,
Prior and Cao suggest that daily
intake be increased to between 3,000
and 5,000 ORAC units to have a
significant impact on plasma and
tissue antioxidant capacity.
Rats High on ORAC
Rat studies are yielding even
more support for high-ORAC diets.
The animals live only about 2 1/2
years total, so it's possible to
follow the effects of high-ORAC
foods on the aging process.
Joseph and Shukitt-Hale have been
testing extracts of strawberry and
spinach, along with vitamin E, in
the rodents. And some of their
results wouldn't surprise Popeye. A
daily dose of spinach extract
prevented some loss of long-term
memory and learning ability normally
experienced by middle-aged rats. And
spinach was the most potent in
protecting different types of nerve
cells in various parts of the brain
against the effects of aging.
The researchers started
6-month-old rats on four feeding
regimens. Two groups got diets
fortified with either strawberry or
spinach extract, one ate the diet
containing an extra 500
international units of vitamin E,
while a fourth got the unfortified
diet. Shukitt-Hale, a behavioral
psychologist, had already put a
group of rats through their paces to
determine when they begin to falter
in memory and motor function. She
says the animals start to lose motor
function around 12 months and memory
at 15 months; the latter is
equivalent to a 45- to 50-year-old
human.
When the study rats reached 15
months, she had them doing
gymnastics—such as walking on rods
and planks and trying to stay
upright on a rotating rod—all tests
of motor function. She also had
these excellent swimmers paddle
around a deep pool until, using
visual cues, they found a submerged
platform on which they could rest.
With this test, she measures changes
in long- and short-term memory.
"None of the diets prevented
motor loss," says Shukitt-Hale. The
15-month-old rats performed like
middle-aged animals whether they got
the extra antioxidants or not. But
the spinach-fed rats had
significantly better long-term
memory than the animals getting the
control diet or the
strawberry-fortified diet. They
remembered how to find the hidden
platform better over time, she says,
showing they retained more of their
learning ability. The vitamin E-fed
rats were somewhat less protected
against memory loss than the spinach
group.
"That's significant," she notes.
"It's really difficult to effect a
change in behavior."
Where Aging May Reside
Joseph looks for age-related
changes in brain cell function,
focusing on an area of the brain
that controls both motor and
cognitive function—the neostriatum.
As people and animals age, the cells
become sluggish in responding to
chemical stimulation, he says. For
15-month-old rats, the striatal
cells have lost 40 percent of their
ability to respond to such signals.
Not so in the animals whose diets
were fortified with spinach or
strawberry extracts or vitamin E.
Their striatal cells performed
significantly better than those of
rats on the control diet—especially
the rats getting the spinach
extract. That group scored twice as
high as the control animals in
Joseph's test.
The spinach group also scored
best among the fortified diets in a
test of nerve cells in the
cerebellum, a part of the brain that
maintains balance and coordination.
The test was done by Paula Bickford,
a collaborating pharmacologist with
the University of Colorado Health
Sciences Center in Denver.
Why spinach is more effective
than strawberries is still a
mystery. The researchers conjecture
that it may be due to specific
phytonutrients or a specific
combination of them in the greens.
While this research is still in its
infancy, says Joseph, "the findings,
so far, suggest that nutritional
intervention with fruits and
vegetables may play an important
role in preventing the long-term
effects of oxidative stress on brain
function."
Prior and Cao also have early
evidence that these foods protect
other tissues. Subjecting rats to
pure oxygen for 2 days normally
damages cells lining the tiniest
blood vessels, or capillaries,
causing them to become leaky.
As a result, fluid accumulates in
the rats' pleural cavity—the space
surrounding the lungs. But that was
minimized when the animals were fed
blueberry extract for 6 weeks before
the oxygen stress. Of all the fruits
and vegetables tested with ORAC,
blueberries are one of highest in
antioxidant capacity.
In human terms, says Prior, the
animals got the equivalent of 3,000
ORAC units. "If we can show some
relationship between ORAC intake and
health outcome in people, I think we
may reach a point where the ORAC
value will become a new standard for
good antioxidant protection." —By
Judy McBride,
Agricultural Research Service
Information Staff.
This research is part of Human
Nutrition Requirements, Food
Composition, and Intake, an ARS
National Program described on at
http://www.nps.ar
s.usda.gov/programs/107s2.htm.
Ronald L. Prior,
James A. Joseph,
Guohua Cao, and
Barbara Shukitt-Hale are at the
USDA-ARS
Human Nutrition Research Center on
Aging at Tufts University, 711
Washington St., Boston, MA 02111;
phone (617) 556-3310, fax (617)
556-3299.
"Can Foods Forestall Aging?"
was published in the
February 1999 issue of
Agricultural Research magazine.
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