Eye health is a major concern of U.S. consumers, and several consumer studies suggest that interest in eye-health nutrients is expected to grow in the years ahead. According to data from a 2001 study by Sloan Trends and Solutions (Escondido, CA), 81% of consumers are somewhat or very concerned about their vision.
Although much of the demand for eye-health products is fueled by the aging population, younger consumers, particularly those with diabetes-related vision problems, are also drawn to these products. For instance, the American Diabetes Association (Alexandria, VA) notes that people with diabetes are more likely to develop cataracts, glaucoma, and retinopathy than the average population.
Most natural eye-health products on the market today contain an assortment of antioxidant ingredients, such as vitamins, carotenoids, flavonoids, and other herbal extracts. These ingredients are thought to preserve vision in at least one of three ways. The first is by offering protection against free radicals that can harm the eyes. The second is by blocking damaging ultraviolet (UV) rays. The third is by maintaining or repairing weak capillaries and blood vessels in the eye.
Because the delicate tissues of the eye contain significant amounts of polyunsaturated fatty acids and mitochondria, they are particularly vulnerable to damage caused by oxidative stress and free radicals. In healthy eye tissue, an abundance of antioxidants exists to counteract free-radical damage. If the eye’s stores of these antioxidants are diminished, eye tissues can become harmed.
Numerous studies suggest that dietary intake of foods rich in antioxidants and carotenoids is associated with a lower incidence of eye problems. For instance, data from the Second National Health and Nutrition Examination Survey (NHANES II) show that people with high plasma concentrations of vitamin C have a lower incidence of cataracts.
Data from other studies indicate that antioxidant supplementation may also be beneficial. The Roche European American Cataract Trial (REACT), for example, showed that supplementation with beta carotene (18 mg) and vitamins C (750 mg) and E (600 IU) slowed the progression of lens clouding.
Similarly, the Age-Related Eye Disease Study (AREDS), a large clinical trial organized by the National Eye Institute (NEI) of the National Institutes of Health (Bethesda, MD), demonstrated that supplementation with copper (2 mg), zinc (80 mg), beta carotene (15 mg), and vitamins C (500 mg) and E (400 IU) could slow the progression of age-related macular degeneration (AMD) in people with the advanced stages of the disease.
Although antioxidant vitamins and minerals are well-known for their ability to scavenge free radicals, several other ingredients also possess strong antioxidant properties. Lutein and zeaxanthin, two carotenoids found mostly in dark yellow and green vegetables, have emerged over the past few years as important eye-health nutrients.
“At one time, most people thought that beta-carotene was the most important nutrient for vision, but lutein is the most frequently found carotenoid in the eye,” explains Robert Abel, MD, author of The Eye Care Revolution.
Abel adds that the center of the retina is also called the macula lutea—a name derived from the Latin word for yellow, which is the same color as lutein.
One of the first major studies on lutein was published in 1994 in the Journal of the American Medical Association (JAMA). In the study, Harvard University researcher Johanna Seddon, MD, found that an intake of 6 mg per day of lutein led to a 57% lower incidence of AMD. In a more recent study, researchers from Florida International University (Miami) found that supplementation of 2.4 mg per day of lutein resulted in an increase of serum concentrations of lutein and an average increase in macular pigment density of 14%.
UV light is one of the greatest threats to delicate eye tissues such as the lens and retina. In general, the more that people are exposed to UV light, the more likely they are to develop eye problems later on. In fact, a report in the August 26, 1998, issue of JAMA indicated that exposure to UV-B radiation from sunlight can increase the risk of cataracts in people who have had fairly low exposure to sunlight throughout their lifetime.
According to Abel, lutein and zeaxanthin prevent harmful wavelengths of UV radiation from reaching the retina, counteracting UV-induced free-radical damage. Normally, UV light that reaches the eye is filtered out by the cornea or absorbed by the lens. However, if the damaging effects of UV light that reaches the lens aren’t absorbed by antioxidants, the protein structure of the lens can change, leading to cloudiness.
“The retinal photoreceptors in the eye are extremely fragile and constantly break down when stimulated by light,” explains Abel. “Lutein and its isomer zeaxanthin are the plant world’s natural UV blockers.”
Abel notes that lutein and zeaxanthin appear to be particularly effective at filtering out blue UV light, the part of the spectrum most damaging to visual acuity. Of the three types of eye cones necessary for color vision, the blue cones are the most sensitive and have the highest amount of lutein, according to Abel. “They look blue because they reflect blue UV light,” Abel says.
Capillary repair and maintenance is of particular importance to many people with eye problems, particularly those with diabetes-related eye complications. Diabetic retinopathy, which is caused by a breakdown of tiny capillaries and blood vessels under the retina, is the leading cause of vision loss in the industrialized world for people between the ages of 25 and 74, according to NEI data.
“In diabetic retinopathy, the capillaries nourishing the retina are damaged,” explains Frank Schonlau, PhD, director of scientific communications at Horphag (Geneva). “The damage is a result of elevated glucose levels in the blood, which causes the sugar to chemically react with proteins of the blood vessel walls. This changes the properties of the proteins and subsequently causes the capillaries to swell and get brittle, allowing blood to leak into the retina.”
“Diabetic retinopathy develops without symptoms, is not painful, and doesn’t show any other signs until the disease has progressed to a point where people notice that their vision is getting worse,” says Schonlau. “The damage that has occurred to this point then is largely
Pycnogenol®, a standardized extract from the bark of French maritime pine (Pinus pinaster), contains antioxidant phenolic compounds such as catechin, epicatechin, and taxifolin, and flavonoids such as procyanidins and proanthocyanidins. However, the extract, which is manufactured by Horphag and distributed in the United States by Natural Health Science (Chicago), also has another beneficial property.
“Although it is widely known to be a powerful antioxidant, its role for reducing bleeding in the eye is a result of another basic action,” Schonlau says. “It binds to certain proteins, such as those exposed in damaged areas of capillaries, and thus seals them to stop further outflow of blood. It has been shown in various clinical studies as well as in pharmacological studies to enhance the integrity of capillaries.” Schonlau notes that Pycnogenol® has been tested in five clinical studies using a total of more than 1000 participants.
In a 2001 study published in Phytotherapy Research, researchers examined the extract’s effect on retinopathy. “Efficacy was evaluated by measuring the visual acuity of patients, the response of photoreceptors, as well as the sealing of leaky capillaries,” Schonlau says. “While the placebo-treated patients showed further reduction of visual acuity, the Pycnogenol®-treated patients had improved vision. It was also found to significantly reduce leakage of blood from retinal capillaries.”
AN EYE FOR THE FUTURE
Although much more research is needed to fully understand the properties of these ingredients, the early results are promising. Several nutrients, such as lutein, zeaxanthin, and Pycnogenol®, appear to protect vision through more than one mechanism of action. As more research data become available, greater consumer interest can also be expected.
“The interest in eye-health products is appearing to grow dramatically,” says Horphag’s Schonlau. “The emphasis is clearly on ingredients that are clinically tested.”
“Interest in eye health is growing at a very healthy pace,” agrees Ross. “The continued aging of the population bodes well for eye-health supplements.”
Source: Nutritional Outlook online
http://www.nutritionaloutlook.com. April 2003.