Can Foods Forestall Aging?
To determine the motor function of middle-aged test rats, behavioral
psychologist Barbara Shukitt-Hale and technician George Mouzakis monitor the
performance of these 15-month-olds walking a rotating rod.
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
- maintained the ability of brain cells in middle-aged rats to respond to a
chemical stimulus, and
- protected rats' tiny blood vesselscapillariesagainst oxygen
These results have prompted Ronald L. Prior to suggest that "the ORAC
measure may help define the dietary conditions needed to prevent tissue
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.
Neuroscientist Jim Joseph and behavioral psychologist Barbara Shukitt-Hale
estimate the memory capacity of test rats required to swim to a submerged
platform in a pool. Software quantifies their performance by tracking swimming
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
The researchers have been testing whether antioxidants other than vitamins
are absorbed into the blood and protect the cells. And the results look
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
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 unitsor 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 valuehigher than white wineand 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 scoreseven 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
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."
Fruits with high oxygen radical absorbance capacity are freeze-dried by
technician John McEwen for feeding in experimental fat diets.
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
gymnasticssuch as walking on rods and planks and trying to stay upright
on a rotating rodall 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 functionthe
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.
To better understand cellular activity within the brain, technician Derek
Fisher views fluorescent images of calcium in cells that are affected by
oxidative stress. The calcium binds to a fluorescent dye that the imaging
system can measure.
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 dietespecially the rats getting the spinach
extract. That group scored twice as high as the control animals in Joseph's
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
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 cavitythe 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
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
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.