Nutrition, antioxidants and the eye: The connections are promising, but still tenuous

PORTLAND, Ore.—Although research is mounting to suggest that nutrition can help prevent and treat ocular diseases, the evidence is not yet conclusive. However, investigators agree that optometrists can and should play a role in helping patients onto a beneficial nutritional path.

Recent research has strengthened the connection between nutrition and ocular health. Diane Yolton, OD, PhD, a professor here at the Pacific University College of Optometry, said studies have focused on the role of antioxidants in age-related macular degeneration (AMD) and cataracts. "I'm not sure that with the rest of nutrition we're at a solid enough base to suggest nutritional treatment for eye disease," she said.

Oxidized molecules damage tissue

It is generally believed that AMD and cataracts are the result of the oxidation of molecules in the tissue of the retina or the lens, said Yolton. This oxidation leads to the formation of free radicals, and over a long period of time these free radicals can damage tissue. Free radicals may cause disease throughout the body, but it is thought they are a particular problem in the eye because of ultraviolet and blue light.

To combat oxidation, Yolton said, the body uses vitamins and minerals with antioxidant properties: vitamin C, vitamin E, carotenoids and a series of enzymes that require the minerals selenium, magnesium, copper and zinc. Research has focused on the effects of using nutrition to increase antioxidant levels, and whether or not such an increase can prevent disease. "Much evidence suggests that people who intake high levels of antioxidants or who have high levels of antioxidants in their blood have a decreased risk for macular degeneration and cataract," said Yolton.

Proving this has been difficult, she said, because it takes a lifetime to develop AMD or cataracts and the many variables in the nutrition equation. "Will we ever be able to prove prevention?" she said. "Probably not in our lifetime."

Kari Blaho, PhD, a clinical pharmacologist at the University of Tennessee in Memphis, said the problem has been that many studies are not well controlled and not longitudinal.

New studies are emerging that address those concerns. The National Eye Institute's Age-Related Eye Disease study is a huge, 10-year effort that may answer some of the nutritional questions about AMD. Other nutrition studies are being conducted, and research published in January's Journal of the American Optometric Association bolsters the role of antioxidants in stabilizing AMD.

Nutrition can play a crucial role

"There's enough clinical data available to show that good nutrition over a long period of time helps to at least minimize either the severity or the risk of diseases that are the result of long-term wear and tear," Blaho said. However, she cautioned, "There are some enticing studies out there, but the data is inconclusive as far as using nutritional supplements to prevent degenerative eye disease."

Because of the growing preponderance of evidence, researchers are suggesting that practitioners can play an important role by advising patients about nutrition, particularly because of the minimal risk involved. And Yolton said many practitioners, while waiting for more conclusive studies, are asking what they can do for their patients.

Srinivas Natrajan, OD, PhD, professor of physiology, pharmacology and nutrition at the New England College of Optometry, Boston, said ODs should definitely get more involved in suggesting to patients that antioxidants can help them with AMD and cataracts: "Optometrists can do wonders for patients, without doing any harm."

Yolton added: "I think we can prevent disease with antioxidants. There's so much information that points to the fact that we can prevent AMD, so we should start suggesting prevention strategies while the person's young."

While research is not conclusive, Natrajan said his own dry form of AMD has slowed its progression in the last 14 years. He feels this is mainly due to intake of a balanced diet with plenty of antioxidant-rich leafy, green vegetables combined with aerobic exercise. "You can prevent the progression—you can't prevent the onset—of AMD by taking antioxidants," he said. "I'm a living example."

Prevention and treatment

For prevention, Yolton said, the optometrist should take an either-or approach when considering dietary adjustments or supplements. To help patients with diet, the OD can follow the basic food pyramid: grains, fruits and vegetables are the dietary staples, with 8-11 servings of grain, 3-5 vegetables and 2-4 fruits per day. Vegetables and fruits that supply antioxidants should play a large role: carrots; leafy, green vegetables; and citrus fruits. For patients who cannot or choose not to monitor diet, the OD should recommend a nutritional supplement.

When disease is present, Yolton said, she first tries diet and then adds supplements. If a patient is already taking a multivitamin, she will add one antioxidant supplement. If the patient is not taking any vitamins, she adds two antioxidant pills per day, but no more than that. "You don't want them overdosing," she said.

When recommending a dietary regimen or supplements, optometrists should be careful to maintain a balance, Natrajan said. Too much of certain vitamins can interfere with the absorption and utilization of other vitamins. And he warned that vitamin A can be toxic, so intake should not exceed more than 5,000 IU per day.

Blaho said other factors should be considered when recommending supplements:

• Can the patient afford the nutritional supplement?
• Will the patient be compliant, and is the patient on many other medications?

  "There's some very good data to indicate that the more medicine you have to take the less compliant you become," Blaho said. "Is there a trade-off between asking people to take a supplement, and then they forget to take more important medications such as their antihypertension drug?"

• May drug interactions be a problem?

  "Vitamins, while they are considered nutritional supplements, are very much drugs, and they do interact with other medications," she said.

When considering supplements, Blaho advised caution. In some cases they have conclusively been shown to be beneficial: the calcium story in women and using folate supplements to prevent neural tube defects. But two recent studies—the Beta Carotene and Retinol Efficacy Trial and a Finnish study—indicated that they can worsen or increase the risk for some diseases.

Educate yourself, then your patients

Because of its potential significance, Yolton said, optometrists should become more educated about nutrition. "You're not going to hurt most patients by doing this, and you may help their overall health," she said. "If patients want to modify their lifestyle, you should have some answers for them."

Yolton added: "You can't tell patients with AMD or cataracts that supplements work. However, evidence suggests they might work. I think that's what you have to present to the patient: we can't guarantee it, but these might work to stabilize your vision."

Blaho said some ODs are starting to sell supplements out of their offices. "There's a great deal of responsibility associated with this," she said. "Selling products injudiciously from a medical office can undermine the integrity and credibility of the practice.

"You have to be realistic and you have to be very frank with patients. Tell them, 'The story isn't finished yet, but this might help.'"

Where to Find Antioxidants

VITAMIN C:	VITAMIN E:	CAROTENOIDS:	ZINC:	SELENIUM:
citrus fruits berries tomatoes peppers cabbage broccoli Brussels sprouts cauliflower	vegetable oils (wheat germ oil is especially rich) other cereal germs green plants egg yolk milk fat butter meat nuts	broccoli spinach cabbage cauliflower Brussels sprouts carrots collard greens sweet potatoes winter squash (most dark green, leafy vegetables containing carotenoids)	red meat liver eggs seafood (particularly oysters)	fresh vegetables cereals meat poultry fish dairy products