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Eyes & Nutrition. SISITYSO? (Archive in eyes.)

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Scientists Link Nutrition & Eye Health

About 16 million people in the United States over age 45 report some
vision loss. This group may find hope in a growing body of evidence
that diet can influence eye health. ARS has several scientists
studying the possibility of reducing-by way of dietary modification-
the risk of two common sight-robbing disorders: cataract formation
and age-related macular degeneration.

About 20 years ago, scientists were hard-pressed to find published
research studies on correlations between nutrition and risk of eye
disease. But steady efforts by government and academic researchers
over the years have led to a clearly established discipline of
ophthalmologic nutrition and epidemiology.

A Cloudy Matter
For baby boomers reaching an age at which steady vision can no
longer be taken for granted, many are wishing they'd worn sunglasses
when young. Sunlight is somewhat of a natural enemy to the eye's
lens.

"Lens cells make a specific, predominant set of proteins called
crystalline," says bio-organic chemist Allen Taylor. He is chief of
the Laboratory for Nutrition and Vision Research at the Jean Mayer
USDA Human Nutrition Research Center on Aging (HNRCA) at Tufts
University in Boston, Massachusetts. "Those proteins act like fiber
optics, allowing light to pass through the lens and onto the
retina," he says. They must function over decades with little
opportunity for repair.

Red, blue, green, yellow, and ultraviolet (UV) wavelengths penetrate
the transparent lens. But UV light appears to be particularly
damaging to the lens, and blue light appears to damage the retina-a
complex, sensory membrane that lines the eye and receives the images
formed by the lens. Normal byproducts of metabolism, called oxygen
free radicals, also cause damage. If not neutralized by an
antioxidant, over time such oxidation damages the lipids, proteins,
and other components of the lens. The result is a clouding of the
lens in a gradual slide from transparent to opaque. These opacities
are called cataracts.

Antioxidants are compounds in foods that help maintain healthy cells
and tissues in the eye and other organs. Inside the lens are high
levels of vitamins C and E as well as some lutein and zeaxanthin.
The latter two fall within a class of phytochemicals called
carotenoids, and they are concentrated in the retina.
"As damaged proteins gather, they result in lens opacities," says
Taylor. His research suggests that protective, antioxidant-rich
nutrition could be the least costly and most practical means to
delay cataracts. "The accumulation of oxidized or modified proteins
we've observed is consistent with the failure of protective systems
to keep pace with the insults that damage lens proteins," he says.
The protective systems include protein-digesting enzymes, which may
seek out and destroy damaged proteins, as well as antioxidants,
which can lessen initial damage and may keep protective enzymes
functioning longer.

In economic and human terms, damage to lens proteins is costly.
About half of those over 75 in the United States will experience a
visually significant cataract. The costs of cataract-related
disability and cataract surgery now total $6 billion annually
worldwide.

Various Causes
Three distinguishable areas of the lens can be affected by
cataracts: the nuclear, cortical, and posterior subcapsular (PSC)
areas. The nuclear and cortical areas are associated with age-
related cataracts, while the PSC area is associated with diabetes-
related cataracts.

Nuclear lens opacity has been the most widely studied of the three
lens areas. Paul F. Jacques, Taylor, and colleagues reported in 2001
that antioxidant nutrients play a role in the prevention of nuclear
cataracts. Jacques is chief of HNRCA's Nutritional Epidemiology
Program.

The scientists looked at 478 nondiabetic women from Boston, aged 53
to 73 years and not previously diagnosed with cataracts. These women
were sampled from the Nutrition and Vision Project (NVP), a substudy
of the federally funded Nurses' Health Study. Researchers conducted
eye exams to study the relationship between newly diagnosed nuclear
opacities and nutrient intake over time. Food intake was assessed
from multiple food frequency questionnaires completed over 13 to 15
years.

The study showed that women with the highest intakes of vitamins C
and E, riboflavin, folate, beta carotene, lutein, and zeaxanthin had
a lower prevalence of nuclear opacification than did those with the
lowest intakes of those nutrients. Moreover, those who used vitamin
C supplements for 10 or more years were 64 percent less likely to
have nuclear opacification than those who never used vitamin C
supplements.

Taylor, Jacques, and colleagues reported similar findings in 2002
when they looked for cataracts in the cortical and PSC regions of
the lens in some NVP participants. Those findings support a role for
vitamin C in reducing the risk of cortical cataracts in women
younger than 60. The data also indicated that women who consumed
higher amounts of carotenoids had a lower risk of PSC cataracts if
they had never smoked.

In the same NVP population, women who regularly took vitamin E had
less progression of eye lens damage, as Taylor reported during last
year's Association for Research in Vision and Ophthalmology
proceedings in Fort Lauderdale, Florida. "The increase in nuclear
opacification-over 5 years of follow-up after their initial
examination-was 30 percent lower among women who used vitamin E
supplements for at least 10 years than among those who had never
used vitamin E supplements," says Jacques.

Another recently completed study explored the relationship between
body mass index, waist circumference, diabetes, and the presence of
age-related cataracts in women. The study supports other findings
that diabetes is a strong risk factor for PSC opacities and that
abdominal fat and obesity may also be associated with PSC.
Several variables complicate a comprehensive evaluation of the
existing evidence linking nutrition and age-related vision
loss. "Definitions of cataract may differ from one study to another,
and the various methods for assessing the intake or status of
nutrients, such as antioxidants, certainly complicate matters," says
Jacques. "There are several questions that still need to be
resolved."

At this point, what scientists do know is that oxidative damage
within the eye is harmful to several eye tissues.

The Yellow Spot
Among Americans who are 55 or older, age-related macular
degeneration (AMD) is reported to be a leading cause of blindness
and vision impairment. According to the National Eye Institute
(NEI), more than 1.6 million Americans in that age group have
advanced AMD. Some experts estimate up to 7 million more may be at
the intermediate stage. They see fine now, but they are at high risk
for developing the advanced form, which causes vision loss.
Among the causes of AMD, scientists describe a breakdown of light-
sensitive cells within the retina. The focus is on a 3-millimeter-
wide yellow spot, called the macula lutea, toward the back and
center of the eye. The macula plays a key role in the central part
of visual images. But as the eye ages, oxidized proteins, or debris
called drusen, begin to pile up and cause trouble. Taylor and other
scientists are seeking to unravel the mystery of why this process
happens.

Scientists have long known that the yellow color, or pigment, inside
the macula comes from the carotenoids lutein and zeaxanthin. Many
scientists believe that these plant chemicals help protect the eye
by absorbing blue light and neutralizing free radicals. But as the
body ages, the importance of carotenoids in the macula may increase
because of the lifelong exposure to damaging light.

These two carotenoids circulate in the food supply and in blood
plasma at a ratio of about one part zeaxanthin to about six or seven
parts lutein. As blood passes by the macula through retinal blood
vessels, these pigments pass through the macula's outer layer to
rest in high concentrations inside its center. Perhaps most
interesting is that people with macular degeneration have been found
to have lower levels of zeaxanthin and lutein in the macula than
people without-which supports the premise that these antioxidants
provide some protection.

Absorbing Research
Nutritional biochemist Elizabeth J. Johnson, who is with HNRCA's
Carotenoids and Health Laboratory, is now leading a study aimed at
determining differences in the body's absorption and use-known as
bio-availability-of lutein from eggs, spinach, and supplements.
After study volunteers-healthy adult men-consumed cooked spinach,
eggs, and lutein supplements, Johnson measured levels of lutein and
triglyceride-rich lipoproteins in their blood serum. The study,
which is supported by the Egg Nutrition Center, in Washington, D.C.,
used eggs from chickens that had been fed marigold petals, which are
high in lutein. Consumption of these eggs considerably increased the
lutein in volunteers' blood.

"After volunteers ate eggs as a source of lutein, their blood serum
level of lutein was two to three times greater than it was after
they ate the same amount of lutein from other sources," says
Johnson. These preliminary results provide compelling evidence that
eggs can be a more bioavailable source of lutein than more
conventional sources, such as spinach and supplements. "We don't
know why the lutein in egg yolks is more bioavailable, but we think
it's due to other components in the yolks, such as lecithins."
The "designer" eggs used in the study had about six times-about 1.5
milligrams-the lutein of standard eggs. Still, spinach has about 11
milligrams per 2-ounce serving. "Even though the lutein in the eggs
is a comparatively tiny amount, it goes right into the bloodstream,"
says Johnson.

She has also studied and will soon report the effects of lutein and
zeaxanthin supplementation on carotenoid levels in the blood,
adipose (fat) tissue, and macula of monkeys. That research has led
to new findings about the source of an important form of zeaxanthin,
called meso zeaxanthin. Curiously, that form is found in the macula,
but not in food or blood. It may be better than lutein at reducing
damage from light entering the eye. Johnson believes meso zeaxanthin
could actually be formed from lutein once it's inside the macula
itself.

Diminishing Risk
In 2001, NEI researchers reported results from the 7-year Age-
Related Eye Disease Study, or AREDS. Results showed that people
lowered their risk of developing advanced AMD by about 25 percent
when they took a high-dose combination of vitamins C and E,
betacarotene, and zinc for more than 6 years.

NEI defines high risk as having intermediate or advanced AMD in one
eye. In those with advanced AMD, the nutrients reduced their risk of
further vision loss by about 19 percent. NEI concluded that while
the nutrients will not restore vision already lost from the disease,
they may play a key role in helping high-risk people keep their
remaining vision.

Lutein supplements were not available at the study's inception, but
NEI is starting to study it now. "Lutein is compelling because of
evidence that it neutralizes free radicals," says Johnson. "Since
it's in the macula, it's right where it needs to be to protect
against damage." In the meantime, during regular examinations, eye
doctors can see the telltale signs of early, intermediate, and
advanced AMD.

The AREDS supplements had no significant effect on cataract
development or progression. But intervention was only for about 6
years, and some people in the control group had already taken, or
continued to take, antioxidant supplements.
Cataract surgery is the most expensive outpatient surgery covered by
Medicare. While some see surgery as a stopgap intervention for
cataracts, there is as yet no known surgical remedy for AMD, making
optimal nutrition all the more attractive.
Researchers focusing on eye health today agree that for some,
nutrition will play an important role in lessening the risk of
developing these sight-robbing eye disorders.

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