Diet May Improve Cognition, Slow Aging, And Help Protect Agai
nst Cosmic Radiation
Society for Neuroscience via the Science Daily
November 11, 2003
Eating certain foods can help protect
you from heart disease, some types of cancers and other illnesses. But can
your diet also help protect your brain if you should suffer a stroke or
accidental head injury? Or keep your thinking and memory skills strong as
you age?
Some scientists believe it might. They
even think eating the "right" foods --specifically, those high
in antioxidants -- may help defend astronauts from brain-damaging cosmic
rays on future manned missions to Mars.
New research also suggests that some of
the environmental chemicals that have gotten into many of our foods --
through the application of herbicides and insecticides, for example, or
from the leaching of plasticizers from plastic food containers -- may be
harmful to children. This is because of the chemicals' effect on
reproductive development and their impact on brain areas involved in
thinking and learning. Still other studies are beginning to shed some
light on the neurological reasons why men tend to have an easier time than
women at losing unwanted weight.
"The role of diet in cognitive
function is one of the vastly understudied areas in the
neurosciences," says Carl W. Cotman, PhD, of the University of
California-Irvine. "As these recent studies show, significant new
findings are appearing which highlight the importance of this research on
diet and cognitive function."
Eating an antioxidant-rich diet may help
keep cognitive skills strong during old age, according to a recent animal
study conducted at the
University
of
Toronto
. "We found that old dogs that were on an antioxidant diet
performed better on a variety of cognitive tests than dogs that were not
on the diet," says P. Dwight Tapp, PhD, now of the
University
of
California Irvine
, "In fact, the dogs eating the
antioxidant-fortified foods performed as well as young animals."
Antioxidants include vitamin E, vitamin
C, and beta carotene (a form of vitamin A), as well as other minerals and
compounds found in food. These nutrients have been shown to help reduce
oxidation, a process that can cause damage to cells and may contribute to
aging, including the reduced cognitive decline that typically develops
with age. Studies suggest that antioxidants may also protect against
certain cancers, heart disease and other non-neurological age-related
diseases.
Tapp and his colleagues used 39 beagles
in their current study. Dogs, like humans, develop a range of cognitive
impairments as they age. They lose some of their ability to learn new
information, for example, and experience more difficulty retaining
information in both short-term and long-term memory.
"Although we found that not all
cognitive functions respond to antioxidant treatment, our data suggests
that antioxidants play an important role in preventing or slowing
age-related cognitive impairments," says Tapp. Interestingly,
although eating antioxidant-fortified food improved the cognitive skills
of the older dogs, we found no improvement in the younger animals. This
suggests, Tapp says, that the diet is most effective in animals that
already have some degree of cognitive impairment. The study is currently
ongoing in the younger dogs to determine if the diet has a protective
effect on age-related cognitive decline in general.
Two years ago, researchers at the
Universidad Nacional Autуnoma de Mexico (UNAM) and the University of
Houston-Clear Lake (UHCL) reported that a blueberry-enriched antioxidant
diet may prevent age-related deterioration of object recognition memory in
aged rats. Now, new findings from the same research group reveal that, in
the brains of the same rats, the diet also prevents an age-related
increase in a protein (NF-kappaB) that responds to oxidative stress, a
probable cause of brain aging.
"Our findings fit into an emerging
pattern of data from many laboratories that point to a buildup of
oxidative damage as one of the key factors in brain aging," says
Pilar Goyarzu, a doctoral student at UNAM under the direction of David
Malin, PhD, and Francis Lau. "The findings also suggest that diets
rich in natural antioxidants have the potential to slow down this
damage."
For the current study, Goyarzu fed rats
a blueberry-enriched diet. NF-kappaB levels were then assayed in five
different brain regions involved in memory processes (the hippocampus,
frontal cortex, striatum, basal forebrain, and cerebellum). The aged rats
on the blueberry-enriched diet had lower NF-kappaB levels than aged rats
fed a control data. Young control rats also had lower NF-kappaB levels
than the aged control rats.
"We also found that among the aged
rats, the higher the NF-kappaB levels, the poorer their memory
scores," says Goyarzu. The UNAM and UHCL researchers are now studying
the effects of aging and diet on other proteins that mediate the effects
of oxidative stress in the brain.
At the National Institute on Aging's
(NIA)
Gerontology
Research
Center
in
Baltimore
,
Maryland
, scientists have found that blueberries
can help lessen some of the functional damage caused by a brain injury.
"Our results suggest that the consumption of blueberries and perhaps
other fruits and vegetables could have a positive neurological impact on
the aging brain, Alzheimer's disease, and other neurological
disorders," says Edward L. Spangler, the lead author of the study.
Spangler and his colleagues fed one
group of young rats a diet supplemented with a 2 percent blueberry
extract; another group was fed the same diet, but without the extract.
After two to three months, all the animals received chemically-induced
lesions in their hippocampus, a region deep within the brain that plays an
essential role in learning and memory. Damage to the hippocampus results
in an inability to remember recent events. The researchers then tested the
animals' ability to learn a complicated maze task. The rats that had been
fed the blueberry extract were significantly less impaired at performing
the task than those that didn't receive the extract.
"We believe the blueberries contain
a particular group of as-yet unidentified bioactive chemicals that
ameliorate the functional consequences of brain damage, including a loss
of the ability to learn or remember recent events," says Spangler.
Researchers at the
University
of
Maryland
, Baltimore County (UMBC) and the U.S. Department of Agriculture in
Boston
have found that an antioxidant-rich diet
may help stave off the harmful, immediate effects of certain cosmic
radiation. "These findings may help protect future astronauts from
the dangerous physical and mental effects produced by extended radiation
exposure on long-term space missions," says UMBC's Bernard M. Rabin,
PhD.
One of the biggest obstacles facing a
future manned mission to Mars is the hazard that an extended,
three-years-long space flight poses to the human nervous system. Highly
radioactive, subatomic particles known as cosmic rays can cause severe
damage to an astronaut's brain and central nervous system.
To see if antioxidants might provide
future space travelers some protection, Rabin and his colleagues fed one
group of rats a control diet and another group a diet containing either a
2 percent blueberry or a 2 percent strawberry extract for two months.
Then, using facilities at the Brookhaven National Laboratory (the NASA
Space Radiation Laboratory), the researchers exposed the rats to the
equivalent of space radiation -- 1.5 Gy of 56Fe particles. Afterwards, the
rats were put back on the antioxidant diet for one more week before being
shipped to UMBC and trained to press a lever to receive food.
Seven months later, all the radiated
animals were tested to determine whether they were able to respond
appropriately to increases in work requirements. The control rats and
those fed the antioxidant-rich diets responded similarly. When tested
again at 12 months, however, the radiated rats that had been fed either
the control or the blueberry extract diet performed less well than those
fed the strawberry extract diet. In fact, the "strawberry" rats
performed as well as non-irradiated rats.
"These results suggest that certain
antioxidant diets can prevent some of the cognitive changes that occur
with exposure to cosmic rays," says Rabin. He and his colleagues are
now studying the effect of different antioxidant diets on other tasks and
behaviors.
New studies from Florida State
University (FSU) in
Tallahassee
,
Florida
, may help explain why women are more prone
to weight gain and shed fewer pounds through exercise than men. In studies
involving male and female rats, Lisa A. Eckel, PhD, and graduate student
Shelley Moore found that females were much more susceptible than males to
overeating when presented with a sweet-tasting diet. They also discovered
that exercise helps males overcome their urge to overeat such foods, but
not females.
"When given access to running
wheels, only the male rats decreased their food intake," says Eckel.
"The female rats continued to overeat. This suggests that females are
more vulnerable than males to over eating a palatable, sweet-tasting
diet."
In the past, few animal studies of
overeating have involved females, although obesity is greater in women
than in men. According to the Centers for Disease Control (CDC), 33
percent of women in the
United States
are overweight compared to 28 percent of
men. For both sexes, however, obesity has become a growing and serious
health problem. CDC statistics released in 2002 showed that the number of
obese people in the
United States
has doubled over the past two decades.
Obesity has been linked to a host of potentially deadly health problems,
including heart disease, stroke, diabetes and certain cancers.
One of the next steps in this research,
says Eckel, is to determine the hormonal basis for why female rats are
more susceptible to overeating than their male counterparts. "We
intend to investigate the sex differences in the release of
neurotransmitters and neuropeptides that regulate appetite and the
preference for sweet tastes," she says.
Researchers at
Mississippi
State
University
have found that early exposure to
environmental chemicals that mimic or block the action of the sex hormones
estrogen and testosterone may disrupt normal differences in the brain
between males and females -- differences that affect thinking and learning
as well as sexual behavior. These findings add more scientific support to
the growing concern that exposure to environmental chemicals is harmful,
particularly to children.
In recent years, scientists have
increasingly linked environmental chemicals to certain reproductive
abnormalities, particularly premature or delayed sexual development.
"In the last decade, we've also come to understand that sex hormones
play an important role in the maturation of other, non-reproductive
systems," says Russell Carr, PhD. "It's now known that estrogen
is a key player in the development of the nervous system, and that the
presence or absence of estrogen during development causes significant
differences in the brains of both male and female animals." These
gender-related differences are connected to areas of the brain involved in
cognitive as well as reproductive functions.
In their recent study, Carr and his
colleagues administered several environmental chemicals orally to newborn
rats for two weeks, beginning one day after the animals' birth. The
chemicals selected for the study were the sex hormone estradiol (E2); the
synthetic estrogen diethylstilbesterol (DES); the plasticizer bisphenol A
(BPA), which has been shown to leach out of plastics into food; the
herbicide atrazine (ATR), which has been suggested to be estrogenic; and
the insecticide methoxychlor (MC), which mimics estrogen once it's
metabolized in the body. During and after the exposure period, the
researchers measured the effects of the chemicals on the animals' brain
development. They specifically looked for changes in the levels of the
neurotransmitters dopamine, serotonin and norepinephrine, as well as some
of their metabolites, in various regions of the brain. These levels were
then compared to levels in control animals.
At one week following the end of
exposure, no significant changes were detected in the overall levels of
neurotransmitters between the treated and the control groups. The
scientists did, however, make a startling discovery: In the control
animals, there was a significant difference between males and females in
the levels of neurotransmitters observed in two areas of the brain, the
cerebellum and hippocampus. In the treated animals, no such differences
were found.
These findings support earlier studies
from MSU that had shown a similar gender-dependent effect of an
environmental chemical (the plasticizer BPA) on cognitive function.
"This suggests that the main effect of developmental exposure to
these chemicals is the disruption of the normal differences between males
and females," says Carr. "It's a subtle effect because exposure
to these chemicals doesn't produce any significant effects on brain
neurochemistry within each sex."
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