As with many areas of health, not all of these claims are backed by solid research. But while many eye health experts approach popularly marketed supplements, that tout better eye health, with skepticism, there is research that suggests at least some supplements may indeed benefit those at high risk of advanced eye diseases.
Much of this research has surrounded age-related macular degeneration, or AMD, a leading cause of vision loss. It's a big problem; 8 million people are at risk for experiencing AMD, and 1.75 million people have an advanced form of AMD, according to the National Eye Institute. It is expected that the number of people who have AMD will double by the year 2020.
So, when a large study called the Age-Related Eye Disease Study, or AREDS, found that people at high risk for advanced AMD lowered their risk of the disease by about 25 percent when treated with a high-dose combination of vitamin C, vitamin E, beta carotene, and zinc, eye health researchers took heed.
The 2001 clinical trial, sponsored by the National Eye Institute, also found that taking these supplements reduced the risk of vision loss caused by advanced age-related macular degeneration, or AMD, by about 19 percent.
Supplements Still No Magic Bullet for Eye Health
However, there is no evidence from this study to suggest that taking nutritional supplements can prevent people who currently do not have vision problems from getting AMD in the future, said Dr. Emily Chew, deputy director of the Division of Epidemiology and Clinical Research at the National Eye Institute, and a lead researcher in the AREDS study.
According to the study, 50 milligrams daily of beta carotene, 500 milligrams daily of vitamin C, 400 international units of vitamin E, and 80 milligrams of zinc were found to be effective doses of each supplement.
In general, many eye health experts may recommend supplements only for those who already experience specific types of vision loss, said Dr. Penny Asbell, director of the Cornea Service and Refractive Surgery Center at Mount Sinai Medical Center in New York.
For example, according to Asbell, supplements may have more benefit to those who suffer from dry age-related macular degeneration, a less severe form of AMD, because of the slower progression of vision loss, rather than the more severe wet AMD.
Supplements Will Not Cure All Eye Ills, Doctors Say
In fact, Chew said, ophthalmologists should only recommend supplements if an eye exam shows yellow spots in the eye, called drusen, which is a common sign of AMD.
"Only if you have those yellow spots do supplements work for you," said Chew. "You really have to be at that intermediate stage."
The common nutrient in most eye health supplements are antioxidants, because oxidative stress, the damaging effects of reactive oxygen and toxins, is implicated in AMD, as it is in most age-related diseases, and in the aging process itself. Researchers suggest that perhaps antioxidants may help slow the progression of vision loss.
However, other types of antioxidants that are currently marketed as nutritional supplements for eye health are not backed by significant research, many experts said.
"[The AREDS study] is the kind of study we need to actually say that a certain nutrient is good for your eye," said Dr. Timothy Stout, associate professor of ophthalmology at the Casey Eye Institute in Portland, Ore., and a scientific advisor for the nonprofit organization,Prevent Blindness America.
While the science is still out on some of these specific nutrients and their relation to eye health, some eye experts have weighed in on the purported benefits and warning signs of these most popularly marketed supplements:
The claim: Bilberry can improve low light vision and prevent macular degeneration.
The truth: During World War II, Royal Air Force pilots would eat a Bilberry jam to help improve their vision for overnight flights. It is thought that Bilberry is an antioxidant that can help improve night vision, and prevent macular degeneration.
However, just because a supplement is an antioxidant, and some antioxidants may improve eye health, does not mean that antioxidants are a "one size fits all," approach, according to Stout.
"The truth is we just don't know if it does what we're told it does," said Stout. "It could, but we just don't know."
The claim: taking a 50 mcg nutritional supplement daily can improve vision.
The truth: According to Chew, selenium is another form of antioxidant that has not yet been studied.
"We do know that we haven't found nutrients that can turn vision loss around completely," said Chew. "So I would be cautious about supplements that say they can protect against an eye disease."
The claim: two 500 mg capsules twice a day will help protect against cataracts.
The truth: While many people have reported better eyesight from taking turmeric supplements or from having a diet high in turmeric, the effects of the nutrient on eye health has not been studied in humans, said Stout. And while there may be benefits from taking antioxidants such as turmeric, Stout again cautioned against believing supplements with antioxidants work.
"Somewhere, all of these supplements hang their hats on the antioxidant peg," said Stout, "but don't think that just because the nutrient is an antioxidant, it must be good."
For Eye Health, It's Not All About the Pills
Indeed, antioxidants found as supplements on store shelves are also found naturally in the body and in many types of foods. And, previous research suggests that eating green leafy vegetables reduced the chance of vision loss.
Antioxidants in foods are much more numerous in foods than in individual supplements, according to Julie Mares, professor of nutrition the department of ophthalmology and visual sciences at the University of Wisconsin School of Medicine, who has studied the link between nutrition and eye health for more than a decade.
"We know that our body processes nutrient easier when it is given in the form of food rather than as a supplement," said Mares.
Stout added that for those who suffer from vision loss, relying on a healthy diet may not be enough.
"It's nearly impossible for someone who suffers from vision loss to receive the amount of nutrients he or she needs just from a healthy diet," he said.
But while many companies market high dose antioxidants, it is unclear whether taking larger doses of antioxidants are beneficial. Stout particularly cautioned against taking the "it can't hurt to take more" approach when taking supplements, since the body can only use a certain amount of nutrients.
"Taking an overload of the amount of nutrient doesn't guarantee that you can avoid disease or see better," he said. "Your body can only use so much of the vitamins and pigments, so there's no evidence that taking more of it is beneficial for you."
Research Continues on Supplements for Eye Health
A yellow pigment found in the eye, called Lutein, is one supplement now being studied by the AREDS2 trial, a followup to the first AREDS trial on antioxidant supplements.
Unlike other nutrients, although found in the eye, Lutein is not produced in the body and can only be found through the nutrient in foods and in supplements. Other supplements in the AREDS2 trial include Xeoxanthin, and Omega-3 fatty acids.
Researchers hypothesize that these supplements will slow the progression of mild AMD, said Dr. Barbara Blodi, associate professor at the department of ophthalmology at the University of Wisconsin and a lead researcher on the AREDS2 trial.
"These fatty acids are in the retina and help the cones and rods in the retina to help you see," Blodi said. "So the idea is that if you got more, it could save your sight."
The future implications, she said, could be big.
"Of the estimated 14 million people who have a mild stage of AMD, we hope a good proportion would benefit from taking supplements to prevent end stage AMD," Blodi said. "If you could prevent that, it would be an important step for older citizens to stay independent."
The trial is scheduled to end in the year 2013, but until then, Blodi said, supplement users should be warned against high hopes that marketers use to sell better vision.
"A dilated eye exam will show you if you have macular degeneration," she said. "Once you know what is causing your vision loss, then you know what supplements we know can help you -- so go from there."