A New Look at Eye Health

This section is compiled by Frank M. Painter, D.C.
Send all comments or additions to:    Frankp@chiro.org

From The April 2001 Issue of Nutrition Science News

By Bill Sardi

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Many people with deteriorating vision are seeing nutritional therapy as a successful alternative to conventional medicine or surgery. An example is Mildred Frank of Ormond Beach, Fla., who experienced a dramatic improvement in her vision that was not the result of lasers or lens implants. Her vision improvement began with a can of kale.

Frank had two retinal disorders: macular degeneration, which is the loss of central vision, and retinitis pigmentosa (RP), which initially manifests as night blindness and progresses to a permanently constricted field of vision. Frank's friend said kale might help resolve her eye troubles, so she began eating a can of cooked kale a day. Within weeks she noticed some improvement in her vision.

Although anecdotal, Frank's success with nutritional therapy isn't unprecedented. The journal Optometry recently reported on 16 night-blind patients with retinitis pigmentosa who took 40 mg/day lutein for nine weeks and 20 mg/day for 17 additional weeks. Ten of the participants also took 500 mg/day docosahexaenoic acid (DHA), an essential component of retinal light-receptor cells, along with a vitamin B complex and digestive enzymes for the entire 26-week study. Although the research was a preliminary pilot study, with no placebo controls, improvements reportedly began two to four weeks after supplementation started and plateaued at six to 14 weeks. Visual acuity gains were four times greater in blue-eyed people compared to those with dark eyes. [1]

Vision researchers recognize that lutein and zeaxanthin—plant pigments plentiful in collards, kale, mustard greens and spinach—play important roles in maintaining a healthy visual system. Lutein supplements have been available since 1995; commercially, it is extracted from marigold flower petals. A February 2001 study between Johns Hopkins University and the Chinese University of Hong Kong indicates a new rich source of zeaxanthin with traces of lutein is an extract of the berry of Fructus Lycii (Lycium barbarum). [2]

Lutein and zeaxanthin work because they act like sunglass filters to protect the retina. The retina, about the size of a postage stamp, contains millions of light receptor cells. Normal, healthy retinas exhibit a yellow spot in their visual center, the macula. Lutein and zeaxanthin are concentrated in the central retina, overlying the macula, a pinpoint-wide zone where color vision and central vision is produced. Yellow pigmentation of the central retina of animals disappears when lutein and zeaxanthin pigments are removed from the diet. [3]

Both types of carotenoids—the carotenes such as beta-carotene and the xanthophylls such as lutein and zeaxanthin—are essential to maintain human vision. Beta-carotene converts to vitamin A in the liver and then travels to the retina where it is converted into rhodopsin, the night-vision chemical. Intense sunlight exposure can bleach out rhodopsin from the night-vision cells (called rods) during the day and prolong visual adaptation at dusk.

Foods such as cantaloupe, carrots, sweet potato, yams and yellow squash are rich in beta-carotene but provide no lutein. Dark-green leafy vegetables such as collards, kale, mustard greens and spinach are rich sources of beta-carotene as well as lutein and zeaxanthin. Blue-eyed individuals need more lutein and zeaxanthin because they have less of these protective pigments in their retinas.

Although kale therapy is far from mainstream, researchers are observing connections between nutrition and macular degeneration, cataracts, and glaucoma.

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Reverse Macular Degeneration?

Most patients with macular degeneration are given a poor prognosis for their failing central vision. This has been changing slowly since a 1994 report showed that the equivalent of 6 mg lutein/day obtained from a diet rich in dark-green leafy vegetables significantly reduces the risk of advanced macular degeneration. [4] In a pilot study with 14 patients at the North Chicago Veterans Medical Center, Stuart Richer, O.D., Ph.D., showed that blind spots, the ability to see shades of gray (contrast), and even visual acuity can be improved in the short-term by eating a three-quarters portion of dark-green leafy vegetables daily along with either 5 oz. spinach four to seven times a week or a lutein-based antioxidant. [5] Richer is now comparing a group taking 10 mg lutein/day against another group taking lutein plus mixed supplemental antioxidants.

Researchers at the Schapens Eye Research Institute in Boston report that 60-year-olds with normal levels of lutein and zeaxanthin in their retinas exhibit the visual sensitivity of 20-year-olds. [6]

Lutein and zeaxanthin are not limited to protective roles in the retina only. They may also prevent cataracts, a cloudy focusing lens, and glaucoma, an optic nerve disease.

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Protect Against Cataracts

The focusing lens of the human eye, about the size of an aspirin tablet, is the only organ that never sheds a cell. It receives nutrients indirectly via the aqueous fluid rather than the bloodstream. The lens of the eye is under unusual stress because it is exposed to constant bombardment by solar ultraviolet radiation through the transparent cornea. In order to maintain lens transparency and thus clarity, the protective antioxidant levels in the aqueous fluid of the eye must be higher than in the blood plasma. [7] The lens loses about 1 percent of its transparency each year, so if a person lives long enough, he or she will likely develop cloudy cataracts. But sufficient data exist that nutritional therapy may help prevent cataracts.

In 1990, James Robertson, of the Department of Epidemiology at the University of Western Ontario in Canada, compared adults with cataracts to those without. He found that taking 300 to 600 mg supplemental vitamin C reduced cataract risk by 70 percent and 400 IU supplemental vitamin E for more than a year reduced cataract risk by 50 percent. [8]

The focusing lens is also sensitive to high blood-sugar levels, which can cause inflammation, vision changes and eventually diabetic cataracts. Sugar can oxidize and harden in the lens, a destructive process among diabetics that can be countered by nutrients such as inositol. [9] Sulfur-bearing amino acids, such as taurine, can help to prevent diabetic cataracts. [10] Bioflavonoids such as quercetin are known to inhibit the enzyme that promotes diabetic cataracts. [11]

Diet plays a significant role in cataract risk. One study found that individuals who consume the highest amounts of butter and salt have double the cataract risk compared to those who consume the lowest amounts of these foods, while spinach, peppers, melons, tomatoes and citrus fruits halve the relative risk of needing cataract surgery. [12] Individuals who do not eat five servings of fruits and vegetables per day are 5 to 13 times more likely to develop cataracts. Insufficient dietary vitamin C intake also dramatically increases cataract risk 4 to 11 times. [13] The typical American diet provides about 110 mg/day of vitamin C, but the minimum amount of vitamin C required to prevent cataracts is closer to 300 mg/day—about five oranges. [14,15] It is unlikely that consumers will eat this much fruit, so vitamin C supplements are often more practical.

The potential to delay or avoid cataract surgery with lutein and zeaxanthin became evident in 1992. A prospective study at Harvard Medical School in Boston surveyed 50,828 nurses and found women who consumed spinach five or more times per week, as well as those who took vitamin C supplements for 10 years or more, reduced their risk of cataract extraction by more than 45 percent. [16] Although other carotenoids in spinach could have been at work, this study suggests the benefits of dietary lutein and zeaxanthin.

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Nutrition and Glaucoma

For decades, eye doctors have approached glaucoma as a loss of peripheral vision resulting from optic nerve damage caused by elevated fluid pressure in the eye. However, eyes with normal fluid pressure can also lose peripheral vision. Now researchers suspect a nerve toxin may be involved in the common form of glaucoma. Glaucoma patients exhibit an abnormally high concentration of glutamate in the vicinity of the optic nerve. [17] Glutamate is a primary chemical used in the transmission of optic nerve impulses. Housed inside the nerve sheath, it is innocuous. As optic nerves die off at a normal rate and release small amounts of glutamate, surrounding Muller cells detoxify the area. But glutamate may overwhelm the Muller cells and destroy surrounding cells, thus releasing more nerve-toxic glutamate, resulting in an accelerated loss of vision that is typically observed in the end stages of glaucoma.

While nerve-protective drugs may take years to develop, an array of natural nerve protectors may be able to minimize glutamate toxicity. These include vitamin B12 (methylcobalamin), [18] SAMe (S-adenosylmethionine), [18] ginkgo (Ginkgo biloba), [19] vitamin E, [19] coenzyme Q10, [19] folic acid, [20] and magnesium. [21]

Japanese researchers prescribed 28 glaucoma patients a high oral-dose of 1,500 mcg/day vitamin B12 for five years in an open-label study to evaluate the vitamin's influence on vision. The patients receiving B12 experienced less measurable loss of peripheral vision, more stable visual acuity, and better control of eye fluid pressure compared to a group that did not take B12. [22] The effects of vitamin B12 are attributed to the preservation of myelin, which insulates nerve cells. Results of this study were achieved with methylcobalamin, a readily absorbable form of vitamin B12.

Cyanocobalamin, the more common form of vitamin B12 present in vitamin supplements, has not been effective in other studies of optic nerve disorders. [23]

Various studies reveal that Greenland Eskimos have lower rates of glaucoma than other Caucasian populations, an observation attributed to the consumption of omega-3 fish oil. Omega-3 fats appear to help prevent optic nerve disorders. A proprietary combination of DHA-rich fish oil, vitamin E, and vitamin B complex widened the visual field of 30 glaucoma patients within 90 days in an open-label, nonrandomized study. [24]

In animal studies, researchers were able to lower ocular fluid pressure, a measure of glaucoma, by injecting a very large dose of 0.2 mL/day cod liver oil. Reduction was from 21 mmHg to 18, with injections of 1 mL/day lowering pressure to 14.5 mmHg. [25]

There is also evidence that lutein and zeaxanthin also help protect the optic nerve. The nerve layer of the retina, near where nerve cells exit the eye and connect to the brain, is protected from oxidative damage by lutein. Researchers have found that a lack of lutein in this nerve bundle may be an early sign of glaucoma. [26]

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Other Eye Disorders

The aqueous fluid in the eye delivers antioxidants to the front of the inner eye, which helps to keep the fluid drain unobstructed. This fluid drains out of the eye in a controlled manner that maintains the shape and fluid pressure inside the eye. When drainage is blocked, fluid pressure rises and can impinge upon peripheral optic nerve cells at the back of the eye, narrowing side vision.

Glucosamine sulfate and vitamin C may counter fluid drain swelling. In a preliminary, uncontrolled 1998 U.S. pilot study of two patients, an unreported daily amount of glucosamine sulfate substantially reduced abnormally high fluid pressure over the short term. [27] Vitamin C may help by maintaining the collagen structure of the fluid drain. [28,29] Taking 500 mg vitamin C four times a day moderately and significantly reduces eye fluid pressure in humans. [30,31] Typical recommended dosages of glucosamine for collagen support are 1,500 mg/day.

Dry eye, which causes eye redness, itching, and burning, can be bothersome. It is common among women and is often accompanied by dry skin and brittle nails. Essential fatty acids (1,500 mg/day) derived from evening primrose, borage or black currant seed, combined with vitamin B6 (50­75 mg/day) and vitamin C (375­1,000 mg/day), have been shown to improve tear production and provide symptomatic relief. [32]

With advancing age, the likelihood of macular degeneration, cataracts, and glaucoma increases. The baby boomers will soon swell the population of retirees in the United States, with inevitable increases in eye disease and sight loss. The best answer to stem the tide of age-related vision problems is prevention. Nutrition tops the list of preventive measures for age-related eye disorders.

Sidebars:

Glutathione: The Eye Healer Within

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Bill Sardi, president of Knowledge of Health in San Dimas, Calif, is a health journalist.

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References

1. Dagnelie G, et al. Lutein improves visual function in some patients with retinal degeneration: a pilot study via the Internet. Optometry 2000;71:147-64.

2. Leung IY, et al. Absorption and tissue distribution of zeathanthin and lutein in Rhesus Monkeys after taking fructus lycii (GouQiZi) extract. IOVS 2001 Feb;42(2):466-71.

3. Malinow MR, et al. Diet-related macular anomalies in monkeys. Inv Oph 1980;19:857-63.

4. Seddon JM, et al. Dietary carotenoids, vitamins A, C, and E, and advanced age-related macular degeneration. J Am Med Assoc 1994;272:1413-20.

5. Richer S. Part II: ARMD—pilot case series environmental intervention data. J Am Optom Assoc 1999;70:24-47.

6. Hammond BR, et al. Preservation of visual sensitivity of older subjects: association with macular pigment density. Inv Ophthamol 1998;39:397-406.

7. Stahl E, et al. Regulation of glutathione level in venous plasma and aqueous humor in cataracta senilis provecta. Ophthalmologe 1996;93:54-8.

8. Robertson JM. Cataract prevention: time for a clinical trial. Br J Clin Pract 1990;44:475-6.

9. Ramakrishnan S, et al. Two new functions of inositol in the eye lens: antioxidation and antiglycation and possible mechanisms. Ind J Biochem Biophys 1999;36:129-33.

10. Devamanoharan PS, et al. Prevention of lens protein glycation by taurine. Mol Cell Biochem 1997;177:245-50.

11. Varma SD, Kinoshita KH. Inhibition of lens aldose reductase by flavonoids—their possible role in the prevention of diabetic cataracts. Biochem Pharm 1976;25:2505-13.

12. Tavani A, et al. Food and nutrient intake and risk of cataract. Ann Epidemiol 1996;6:41-6.

13. Jacques PF, Chylack LT. Epidemiological evidence of a role for the antioxidant vitamins and carotenoids in cataract prevention. Am J Clin Nutr 1991;53:352S-5S.

14. Taylor A. Cataract and macular degeneration: relationship to long-term ascorbate intake. Clin Chem 1993;39:1305.

15. Jacques PF, et al. Long-term vitamin C supplement use and prevalence of early age-related lens opacities. Am J Clin Nutr 1997;66:911-6.

16. Hankinson SE, et al. Nutrient intake and cataract extraction in women: a prospective study. Br Med J 1992;305:335-9.

17. Dreyer EB, et al. Elevated glutamate levels in the vitreous body of humans and monkeys with glaucoma. Arch Ophthamol 1996;114:299-305.

18. Akaike A, et al. Protective effects of a vitamin B12 analog, methylcobalamin, against glutamate cytotoxicity in cultured cortical neurons. Eur J Pharm 1993;241:1-6.

19. Ritch R. Neuroprotection: is it already applicable to glaucoma therapy? Curr Opinion Ophthamol 2000;11:78-84.

20. Sattayasai J, Ehrlich D. Folic acid protects chick retinal neurons against the neurotoxic action of excitatory amino acids. Exp Eye Res 1987;44:523-35.

21. Reynolds IJ. Intracellular calcium and magnesium, critical determinants of excitotoxicity. Prog Brain Res 1998;116:225-43.

22. Sakai T, et al. Effect of long-term treatment of glaucoma with vitamin B12. Glaucoma 1992;14:167-70.

23. Foulds WS, et al. The optic neuropathy of pernicious anemia. Arch Oph 1969;82:427-32.

24. Cellini M, et al. Fatty acid use in glaucomatous optic neuropathy treatment. Acta Oph Scand 1998;227:41-2.

25. Mancino M, et al. A comparative study between cod liver oil and liquid lard intake on intraocular pressure on rabbits. Prost Leuko Ess Fatty Acids 1992;45:239-43.

26. Schweitzer D, et al. Spectrometric investigations in ocular hypertension and early stages of primary open angle glaucoma and of low tension glaucoma—multisubstance analysis. Int Ophthamol 1992;16:251-7.

27. McCarty MF. Primary open angle glaucoma may be a hyaluronic acid deficiency disease: potential for glucosamine in prevention and therapy. Med Hypoth 1998;51:483-4.

28. Higginbotham E, et al. Effects of ascorbic acid on trabecular meshwork cells in culture. Exp Eye Res 1988;46:507-16.

29. Chang S, et al. Effects of ascorbic acid on the production of firbonectin laminin and collagen type I by bovine trabecular meshwork cells in organ culture. Inv Ophthamol 1994;35:Arvo Abstracts.

30. Linner E. The pressure lowering effect of ascorbic acid in ocular hypertension. Acta Ophthamol 1969;47:685-9.

31. Fishbein SL, Goodstein S. The pressure lowering effect of ascorbic acid. Ann Ophthamol 1972 Jun:487-9.

32. Giuffrida S, et al. Essential fatty acids (linoleic and gamma-linolenic acids) on tear deficient dry-eye treatment. Inv Ophthamol 2000;41:Arvo Abstract 1447

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