Eating your greens may not give you Popeye-like strength, but it may help keep your eyes healthy and strong. According to a growing body of scientific evidence, the carotenoid zeaxanthin—found in a variety of fruits and vegetables, including leafy greens—may protect against certain eye diseases such as cataracts and age-related macular degeneration. Considering AMD is the leading cause of blindness in the aging population, it makes sense that consumers are eager to learn if eating zeaxanthin-rich foods or taking zeaxanthin supplements will keep their peepers healthy and their vision sharp.
What are carotenoids and where do they come from?
Carotenoids are a class of natural, fat-soluble pigments found in plants, algae and photosynthetic bacteria, as well as some yeasts and molds. Out of the 40 to 50 carotenoids typically found in the human diet, zeaxanthin—and its cousin, lutein—are the only two that are highly concentrated in the human macula, the part of the retina responsible for fine visual activities.1 The concentration of these two carotenoids is so high, in fact, that they are visible as a dark yellow spot called the macular pigment.
Although the exact role of the macular pigment is still unclear, there is evidence that it works like a good pair of sunglasses, absorbing light and reducing glare. Due to its yellowish color, the macular pigment also filters out harmful blue light that would otherwise damage the retina. And the high concentrations of zeaxanthin and lutein serve as powerful antioxidants that defend eye cells such as the rods, cones and photoreceptors against free-radical damage, which can lead to a host of debilitating conditions.2 With so much riding on the health of the macular pigment, it?s no wonder considerable research has been conducted on the role dietary levels of zeaxanthin play in the prevention and delay of eye diseases.
Does science suggest zeaxanthin protects eyes?
While some might argue the link between zeaxanthin intake and eye health is not yet definitive, there is certainly a growing body of evidence pointing in that direction.
One such recent animal study tested zeaxanthin?s ability to prevent light-induced damage to the photoreceptor cells of the eye—the cells that convert incoming light into signals the brain can understand.3 In the trial conducted by researchers at Harvard University in Boston, four groups of 16 quail were fed a diet completely devoid of carotenoids for six months. Three of the groups were then supplemented with 35 mg of zeaxanthin for one, three or seven days, respectively, while one group was not given zeaxanthin. Half of each group was then exposed to 10 one-hour sessions of 3,200-lux white light separated by two hours in the dark. After 14 additional hours in the dark, one retina of each quail in the study was collected for analysis. Results indicated the greater the zeaxanthin supplementation the more protection provided to photoreceptors, meaning zeaxanthin appears to play a strong role in protecting the eye.
Additional research suggests zeaxanthin may also protect sight by warding off cataracts—a cloudiness in the lens of the eye caused by damage to the protein contained there. Researchers at the University of Massachusetts, Amherst, evaluated the diets of more than 77,000 female nurses ages 45 to 71 over a 12-year period. According to their results, women who consumed the most zeaxanthin and lutein through their diets were 22 percent less likely to have cataract surgery.3 Similarly, trials have been conducted to evaluate the relationship between AMD and dietary intake of carotenoids and other antioxidants. AMD generally involves the thinning of the macular tissues or bleeding underneath the retina, both of which lead to vision loss.
In one study conducted at the Massachusetts Eye and Ear Infirmary in Boston, researchers examined the eating habits of 356 adults, aged 55 to 80 years, who, within one year prior to their enrollment in the trial, were diagnosed with the advanced stage of AMD. A total of 520 individuals with other ocular diseases were used as control subjects.
After controlling for risk factors such as smoking, the relative risk for AMD was estimated according to dietary antioxidant intake. Results showed those individuals eating the most carotenoids had a 43 percent lower risk for AMD compared with those eating the least. In particular, a higher intake frequency of zeaxanthin-rich spinach or collard greens was associated with a substantially lower risk for AMD.4
A number of other studies have demonstrated a similar connection between a lower risk of macular degeneration with an increased consumption of carotenoid-rich foods,5 as well as with the overall level of zeaxanthin in the diet or in the blood.6 In one trial, researchers examined the levels of zeaxanthin and lutein in the eyes of 56 people with AMD and 56 healthy subjects. Results showed those eyes with the greatest concentrations of these carotenoids were 82 percent less likely to have AMD.7 It should be noted, however, that not all studies have demonstrated these associations.8
Steering customers to carotenoids
Helping your customers boost their dietary intake of zeaxanthin is easy; just recommend they eat a rainbow of colorful foods. The best dietary sources of this carotenoid include greens such as spinach and collard; yellow/orange vegetables and fruits such as corn, peppers, squash, nectarines and papaya, as well as egg yolks; and dried lycii fruit (Lycium barbarum). Because vegetables and fruits contain other antioxidants that also help protect against eye disorders and other diseases, it is best to get zeaxanthin from these food sources.
However, for those who are partial to pills, stand-alone zeaxanthin supplements recently have become available. Prior to their release, consumers were encouraged to take lutein supplements, as some lutein is converted into zeaxanthin once in the body. The advantage of taking zeaxanthin rather than lutein supplements is not yet clear, as there have been no published studies focusing on zeaxanthin supplementation. Lutein supplementation studies, however, have shown increases in the macular pigment within a few months.9
In one such study, 16 participants with retinal degenerations completed a 26-week program of lutein supplementation (40 mg/day for nine weeks, 20 mg/day thereafter). In addition, 10 of those participants also took 500 mg of docosahexaenoic acid, or DHA, a day, a vitamin B complex and digestive enzymes. Ten of the 16 participants who had previously taken vitamin A and/or beta-carotene also continued those supplements throughout the study. During the 26-week trial, participants self-tested their visual abilities both on their computer screen and a wall chart; testing weekly for 14 weeks, and biweekly thereafter. Results showed improved visual activity and visual fields two to four weeks after lutein supplementation, particularly in blue-eyed individuals.10
Whether your customers choose zeaxanthin or lutein supplements, or simply choose to eat more carotenoid-rich foods, you can be certain they are taking steps to protect the health and longevity of their eyes. Certainly everyone can see the benefit of that effort.
Linda Knittel is a Portland, Ore.-based free-lance writer.
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