Scientists Link Nutrition & Eye Health

[Guest guest]

I would be curious as to the amounts of the nutrients used in this study. I

suspect that some of them were low level amounts and still produced benefits.

What would happen with a study that used optimal amounts?

 

Frank

 

http://healthy.net/scr/news.asp?Id=7461

 

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.