Nutritional Supplements and the Eye
Herbal and nutritional supplements have gained considerable attention over the past few years, with many people hoping to maintain or improve their eyesight. Other people might try to treat a medical condition of their eyes using these supplements. In many cases, herbal and nutritional supplements appear to be helpful in preventing such conditions as cataract and age-related macular degeneration (see below).
However, in other cases, the use of supplements has virtually no benefit, and in some cases, may be harmful. This section will discuss which herbal and nutritional supplements may be beneficial of eye health based on scientific studies. There is also a section on commonly used herbal supplements and possible adverse effects.
Read this important information before proceeding further:
Nutritional supplements, herbal preparations, and vitamins have definite potential for complications, side effects, and toxicity, and can interact with prescription medications. Supplements and herbal medications should be taken under the supervision of a physician, and generally should not be taken in abnormally high doses (mega-doses) unless directed by a physician.
- Ginkgo biloba
- St. John's Wort
- Results of the AREDS study concerning vitamins C, E, beta carotene, and zinc
- Vitamins A, E, and C
- Other Anti-oxidants
- Omega-3 and -6 fatty acids
Herbal Supplements and Eye Health
Bilberry is often used by individuals who believe that it improves night vision. Bilberry extract contains anthocyanosides which are hypothesized to support blood vessel elasticity and permeability, and to prevent leakage of vessels. An April 2000 study¹ looked at contrast sensitivity and night vision in a double-blind, crossover, controlled study where subjects took either placebo or bilberry extract (160 mg three times a day) for 3 weeks. After a washout period, the medication was reversed. Contrast sensitivity and night vision measurements were taken throughout the 3 month study. There was found to be no difference in night vision or contrast sensitivity between the treatment groups and control groups during any part of the experiment. Thus, the use of bilberry was felt to be ineffective in modifying these visual qualities. The weaknesses of the study include the small group size (15), and the short duration of the study.
Others have postulated that bilberry may be effective at preventing capillary leakage in conditions such as diabetic macular edema, but no controlled studies nor case reports have demonstrated this.
Overall, there is very little evidence in reputable medical literature that Bilberry has any effect in improving night vision or eye health in general. Furthermore, it is fairly expensive. Some have recommended a regimen of 3 pills taken twice a day. Over a period of a year, this could add up to as much as $525.
¹Altern Med Rev 2000;5(2):164-173 ER Muth et al.
Ginkgo biloba may have a benefit in protecting the optic nerve of the eye in certain vascular conditions. Increasing evidence is pointing to glaucoma being more than simply an intraocular pressure dependent degeneration of the optic nerve. A recent study showed that even after maximal ocular pressure lowering by surgery, 10% of glaucoma patients continued to lose peripheral vision over a 10 year period. The existence of "normal tension glaucoma", where damage occurs with no history of elevated eye pressure, also indicates other mechanisms of damage to the nerve that cause a loss of vision. Possible vascular risk factors may include systemic LOW blood pressure (especially during sleep), cardiovascular disease, spasm of blood vessels, elevated endothelin levels, autoimmune disease, hematological abnormalities, and cerebral microvascular ischemia (mini-strokes). A role for excitatory neurotransmitters and free radicals may also be present in cellular death in glaucoma.
Ginkgo biloba extract has numerous properties which may be beneficial in treating non-pressure related mechanisms of damage in glaucoma². These include increased ocular blood flow, antioxidant activity, platelet activating factor and nitric oxide inhibition, and neuroprotective activity. Some researchers are beginning trials where ginkgo biloba extract is used in selected glaucoma patients, especially in those with "normal tension glaucoma" or those with progressing glaucomatous damage in spite of adequate ocular pressure control.
²Ophthalmology Times 2000;Apr. 15:14-15 R Ritch MD
St. John's Wort
St. John's Wort, which is commonly taken for anxiety, depression, and sleep disturbances, may be potentially damaging to the lens and retina of the eye. The active ingredient in St. John's Wort (hypericin) has demonstrated potential for phototoxicity due to its absorption spectrum of light in both the ultraviolet and visible light ranges. This can lead to toxic retinal and lens effects, especially with outdoor sunlight exposure.
Patients using St. John's Wort should avoid sun exposure (not just UV exposure) for at least 2 days after taking the medication. Cataract and retinal damage may take 1 to 5 years to develop after exposure.
Eyebright has been used in the past to treat allergic problems of the eye, and as an astringent. The herb is thought to be effective due to the open flower resembling an eye. This, of course, has no scientific basis, and herb itself has not been found helpful in treating seasonal eye allergies, except through a "placebo" effect.
Nutritional Supplements and Eye Health
The eye is at risk of damage from ultraviolet radiation, and sunlight exposure has been linked to cataract and age-related macular degeneration. It is hoped by many that vitamin supplements might be able to help minimize or prevent damage to the ocular structures that happen over a lifetime exposure. Many studies have been done looking at whether or not dietary habits, vitamin supplement consumption, and other factors such as medical health and tobacco use are associated with eye health and disease. Large populations of people (thousands) are studies to help sort out all of the different variables that might lead to a false conclusion. This section discusses possible beneficial effects of certain nutrients through well designed scientific studies.
AREDS Results: Beneficial Effects Found with Antioxidant and Zinc Supplements in those at High Risk for Age-Related Macular Degeneration
The Age-Related Eye Disease Study (AREDS) was an 11 center double-masked clinical trial looking at the possible beneficial effects of antioxidant and zinc supplementation in reducing the risk of vision loss from age-related macular degeneration (AMD). This well done study, published in 2001, showed that there is a definite benefit to taking supplements of vitamin C, E, beta carotene and zinc in the prevention of vision loss in those at high or moderate risk of vision loss from age-related macular degeneration. The actual supplements used were:
Antioxidants (500mg vitamin C, 400 IU vitamin E, 15 mg beta carotene)
80 mg zinc, as zinc oxide, and 2mg copper, as cupric oxide
Both antioxidants plus zinc together
This combination of supplements is now available as Bausch and Lomb Preservision with beta carotene or with Lutein. Taking the supplements had a beneficial effect in preventing the progression to advanced macular degeneration:
In those at high or moderate risk for vision loss from macular degeneration, there was a beneficial effect of antioxidant use alone (vitamins C, E, and beta carotene), in zinc use alone, and a combination of antioxidants and zinc, when compared to placebo:
The risk of significant worsening of vision by year 5 was 29% in the placebo group (categories 3 and 4).
The risk of visual loss was 10% lower in those taking antioxidants only, at 26% by year 5.
The risk of visual loss was 14% lower in those taking zinc only, at 25% by year 5.
The risk of visual loss was 21% lower in those taking antioxidants AND zinc, at 23% by year 5.
The trend of decreasing risk with the use of antioxidants and zinc alone or in combination continues to increase with increasing time in the study, being even lower at 7 years.
It is now generally recommended for those at moderate to high risk of vision loss from macular degeneration to take a vitamin supplement such as above. Note that the amounts of vitamins C, E, beta carotene, and zinc are much higher than typically found in multivitamin preparations. Prior to starting supplementation use, one's primary care physician should be consulted to determine if there are any medical problems, contraindications, or interactions which would make supplementation dangerous (such as the finding that beta carotene use in smokers leading to an increased risk of lung cancer). For more information about this study, go to the Eye News Section.
Lutein May be Protective in Macular Degeneration
Lutein is a dietary carotenoid found primarily in leafy green vegetables such as spinach. It has received considerable media attention recently, with well known brands of vitamins adding lutein into their products. The significance of lutein is that it, along with the related carotenoid zeaxanthin, are dominant pigments found in the macula (the part of the retina giving the sharpest vision). Other carotenoids such as beta carotene and lycopene (found in tomatoes) are virtually absent in the macula. It is felt that these yellow pigments (lutein) may serve to filter blue light from reaching the retina, which has been established as a major cause of photic damage to the retina. Furthermore, carotenoids are well known to have anti-oxidant properties. The outer retina's photoreceptor layer, with its high proportion of polyunsaturated fatty acids, is subjected to constant photochemical insults leading to oxidation and free radical formation. Carotenoids may play a role in preserving normal retinal and vascular function.
A study published in 1994 as part of the Eye Disease Case-Control Study¹ looked at relationships between dietary intake of carotenoids, and vitamins A, C, and E and the risk of neovascular (wet) age-related macular degeneration in Caucasians. (Age-related macular degeneration is the leading cause of irreversible blindness in those over 65). 356 patients with AMD and 520 matched control subjects were divided into groups based on their intake of different nutrients from foods. Those in the highest fifth of carotenoid intake (from foods) had a 43% lower risk of developing AMD than those in the lowest fifth. Foods especially rich in lutein and zeaxanthin had the strongest associated protective effect, with the highest fifth of consumption giving a 57% lower risk of advanced AMD than the lowest fifth. When specific foods were evaluated for a beneficial effect, spinach and collard greens consumption were associated with an astounding 86% reduction in risk. Spinach and collard greens are known to be especially high in lutein and zeaxanthin. In the study, those consuming 1/2 cup of spinach or collard greens 5-6 times per week had the 86% reduction is AMD risk, while those consuming the vegetables once per week had only a 39% reduction in risk.
In this same study, the intake of supplemental vitamin A, E, and C were not shown to offer a statistically significant reduction in risk for AMD. Total vitamin A (foods and supplements) was associated with a reduced risk, but the use of supplements did not improve the risk reduction over food alone. Vitamin C intake from food, excluding supplements, had a weak protective effect against AMD.
Lutein Protective Against Cataract Also
A prospective study² looking at the association between dietary intake of carotenoids, vitamins A, C and E, and riboflavin with cataract extraction in women included 50,800 nurses aged 45 and older, over an 8 year follow-up period. 493 cataracts were extracted over the course of the study. Total vitamin A intake (including carotenoids but excluding supplements) was associated with a significant 39% reduction in risk of cataract extraction comparing the highest to the lowest fifths of consumption. Spinach consumption (lutein and zeaxanthin), rather than carrots (beta carotene), was associated with the risk reduction. Dietary consumption of riboflavin, and vitamins E and C were not associated with cataract extraction. Long term vitamin C supplementation (10 years or more) was associated with a 45% lower risk of cataract extraction. However, multivitamin use was not associated with a reduced risk (multivitamins contain 60-90 mg of vitamin C, while vitamin C supplements contain 250-500 mg).
Overall, these and other studies apparently point to increased dietary consumption of foods high in lutein and zeaxanthin as being protective of age-related macular degeneration and cataract. In general, additional vitamin supplementation in these studies did not improve the reduction in risk. Thus, it is not known whether or not lutein supplementation will improve the risk of developing macular degeneration and cataract compared to eating the foods themselves. Future prospective studies will attempt to answer this question. The foods highest in lutein are kale, collard greens, spinach, mustard greens, and turnip greens.
¹JAMA 1994;272:1413-1420 JM Seddon, MD et al.
²BMJ 1992;305:335-339 SE Hankinson et al.
Vitamins A, E, and C
Evidence for Protection from Cataract and Age-related Macular Degeneration
Several studies have looked at associations between vitamin intake (as food, with or without supplements) and the presence or development of cataract or age-related macular degeneration. These studies tend to be population based studies, where a given eye disease is correlated with a dietary history questionnaire. While studies such as these are important, they do not establish a definite cause and effect relationship. One ongoing, randomized study evaluating the relationship of cataract and age-related macular degeneration with actual vitamin supplementation is the National Eye Institute's Age-Related Eye Disease Study (AREDS). The results of that study are discussed above, on this page.
A number of well designed and significant studies have correlated dietary vitamin consumption as well as supplementation mainly with cataract prevention. The Longitudinal Study of Cataract¹, published in 1998, found a significant reduction in nuclear cataract development over a 4.5 year follow-up period with regular users of multivitamins (31% reduced risk), and regular user of vitamin E (57% reduced risk). The actual visual significance of the cataract was not measured (surgery or vision).
A prospective study looking at cataract progressing to extraction in nurses (also discussed in the section on Lutein) found a significant reduction in cataract risk associated with dietary total vitamin A (including carotenoids, but excluding supplements), and with a long term history of vitamin C supplementation (10 years).
A March 2000 population-based cross-sectional study in Australia² found that higher intakes of protein, vitamin A (including carotenoids), niacin, thiamin, and riboflavin were associated with a reduced prevalence of nuclear cataract (again, through masked grading of photographs of the lens, not through visual significance). No evaluation of vitamin E, or of supplementation as a separate variable was made. Spinach (high in lutein) was especially found to be associated with a reduced cataract risk.
Studies evaluating age-related macular degeneration have mainly pointed to dietary habits, rather than vitamin supplementation, as being preventative. A 1994 report from the Baltimore Longitudinal Study of Aging³ found that vitamin supplementation was generally not beneficial. Plasma levels of vitamin E, C, and beta carotene were moderately inversely related with non-severe (dry) macular degeneration. Other cross-sectional studies have shown that low intake of foods rich in vitamin A to be a risk factor for macular degeneration. Consumption of foods rich in the carotenoids lutein and zeaxanthin was found to be highly protective of macular degeneration, as discussed in the Lutein section.
¹Ophthalmology 1998;105:831-836 MC Leske, MD et al.
²Ophthalmology 2000;107:450-456 RG Cumming PhD et al.
³Arch Ophthalmol. 1994;112:222-227 S West PhD et al.
Other Anti-oxidant Nutrients
There are other anti-oxidant nutrients that are commonly found in the diet or in supplements, especially those marketed toward the eyes. These include Vitamin A, Beta-carotene, and selenium. Most studies have not determined conclusively that these particular nutrients are independently protective for age-related macular degeneration or cataract. For patients with certain sub-types of retinitis pigmentosa, Vitamin A supplementation may be helpful.
Omega- 3 and Omega-6 Fatty Acids
There have been some reports that omega-3 and -6 fatty acids can have a beneficial effects on the functioning of the oil glands that open at the margin of the eyelid (the meibomian glands). These glands produce an oil layer that helps to prevent tear evaporation from the surface of the eye. An abnormal oil layer can lead to symptoms and findings of dry eye, even in cases of normal tear production.
These fatty acids are found in high concentrations in flax seed oil (available in capsules) and cod-liver oil. These fatty acids have also been used to treat acne rosacea effectively. Improvement in symptoms usually takes one to three months when these supplements are used. Randomized studies are being undertaken to evaluate these effectiveness of these fatty acids in cases of dry eye. Usual recommended starting dosages are 1000 mg per day (or 2 capsules).
Complications and Adverse Reactions of Commonly Used Herbs
Many herbal supplements can interact with prescription medications or other over-the-counter drugs, can cause complications with certain medical conditions, or can have adverse reactions themselves. For this reason, a physician should be consulted prior to using herbal supplements. This section discusses side effects and contraindications of commonly used herbal supplements.
Ginkgo biloba is commonly used to increase circulation, improve memory, and to treat vertigo. Adverse reactions include gastrointestinal irritation, headache, reduced platelet function (bleeding or bruising tendency), blood pressure problems, and vein inflammation. It should not be taken if anticoagulants are being taken, including aspirin and non-steroidal anti-inflammatories, and it may interfere with anticonvulsive. It should not be taken by those at risk for intracranial hemorrhage.
St. John's Wort
St. John's Wort is often taken for anxiety, depression, and sleep problems. Adverse reactions include gastrointestinal irritation, restlessness, skin hypersensitivity to light, as well as possible lens and retinal light damage as mentioned above. This drug may interfere with a number of medications, including MAO inhibitors, oral contraceptives, general anesthetics, antiretroviral protease inhibitors, digoxin, levodopa, and warfarin (Coumadin).
Ginseng is used to boost energy and improve concentration. It has been associated with episodes of hypertension and tachycardia, and hypoglycemic effects in diabetics. Other adverse effects include insomnia, headache and nervousness. It should be taken with caution in diabetics, and in those with cardiovascular disease. It may interact with MAO inhibitors, estrogen, insulin, and steroids.
Kava kava is commonly taken for stress, anxiety, and insomnia. Adverse reactions include skin discoloration, scaly skin eruptions, dizziness, drowsiness, visual impairment, and balance disturbances. It may interfere with MAO inhibitors, lithium, warfarin (Coumadin), levodopa (Sinemet), alcohol, barbiturates, anticonvulsants, muscle relaxants, tricyclic antidepressants, and benzodiazepines (Valium).
Echinacea is used for the treatment and prevention of viral, bacterial, and fungal infections, especially those of the upper respiratory tract. There have been cases of allergic reactions to Echinacea, including one case of anaphylaxis. It should be used with caution in people with asthma or seasonal allergies. There are some concerns with toxicity to the liver, and it may reduce the effectiveness of immunosuppressive drugs. Short term use of Echinacea is associated with stimulation of the immune system, but long term use may lead to immunosuppression, and could reduce wound healing after surgery.
Garlic appears to improve the risk of developing atherosclerosis (hardening of the arteries) by reducing blood pressure, clotting, and cholesterol levels. It also blocks platelet function, thus acting as an anticoagulant (blood thinner). Caution should be exercised in using garlic with other blood thinning agents, and it should be stopped at least 7 days prior to surgery.
Valerian has been used as a sedative, particularly in the treatment of insomnia, and most herbal sleep aids contain valerian. It should be expected to magnify the sedative effects of other sedating medications, as well as anesthetics. Heavy use of valerian may result in physical dependence, with a risk of withdrawal symptoms if abruptly stopped.