Herbal and
Nutritional Supplements for 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.
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Herbal Supplements and Eye Health
Bilberry
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 (160mg 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
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
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.
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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 Ocuvite
Preservision, or 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
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).
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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
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
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
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 (Sinimet), alcohol, barbiturates,
anticonvulsants, muscle relaxants, tricyclic antidepressants, and
benzodiazepines (Valium).
Echinacea
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
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
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.
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