Few threats to one’s physical well-being are more menacing
than blindness. And few subjects prompt more anxiety among
our patients than age-related
macular degeneration (AMD), the number one cause of significant
visual impairment and “legal” blindness in Americans
age 65 and older. By the year 2030, an estimated 70 million
Americans will be counted in the age group at highest risk.
Medical researchers are directing increased attention toward
biochemical substances, such as free radicals and growth factors,
which are suspected of playing a role in the mechanisms associated
with aging. Free radicals are unstable by-products of normal
body processes, as well as a byproduct of photic injury to
the eye’s lens and retina by UV light. Naturally occurring
antioxidants in body tissues are largely responsible for neutralization
of harmful free radicals. The abnormal accumulation of free
radicals is associated with certain diseases once dismissed
as resulting from the “aging process”—clouding
of the crystalline lens (cataracts) and age-related macular
degeneration (AMD), for example. Reducing the level of free
radicals in susceptible tissues by dietary supplements of
antioxidants is the rationale for so-called antioxidant “vitamin
therapy” of AMD.
The 2001 ten-year Age-Related Eye Disease Study1 (AREDS)
provides the first strong documentation of the effectiveness
of high doses of the antioxidant vitamins C, E, and beta-carotene,
together with zinc, to slow the progression of certain specific
stages of “dry” AMD to the more damaging “wet”
stage. AREDS recommends that people over 55 undergo a dilated
retina examination to ascertain their risk of developing advanced
AMD. According to the director of the National Eye Institute,
for those demonstrating high risk of developing advanced AMD,
the AREDS formula can significantly reduce the risk of progression,
saving the vision of many who otherwise would suffer severe
vision impairment. However, he cautions, the nutrients are
not a cure for AMD nor will they restore vision already lost
to the disease. While AREDS is very specific in its recommendations,
the study was necessarily limited by its design, excluding
other promising antioxidants such as lutein and zeaxanthin
which have recently attracted much attention. The daily vitamin
doses are as much as fifteen times the recommended dietary
allowances traditionally quoted and are very difficult to
achieve by diet alone.
With such high dosage levels, the potential for side effects
must be recognized. Long term side effects are not yet fully
appreciated. No biologically active agent taken in high doses
can be considered entirely risk-free—even if the agent
is a “natural” constituent of food. We know, for
example, that excessive vitamin A is toxic to the liver and
that, in lower doses, all caretenoids (including vitamin A,
lutein, and zeaxanthin) have the potential for yellowish discoloration
of the skin. Beta-carotene, a precursor of vitamin A, in large
concentrations can increase the risk of lung cancer in smokers—even
in those who have recently quit smoking. High doses of vitamin
C may contribute to formation of kidney stones. Vitamin E
may raise cholesterol levels in the blood or alter blood coagulation.
Zinc, an essential trace element which enhances the activity
of certain enzyme systems, in larger quantities may deplete
the body’s stores of copper. High dietary zinc (without
copper) may lead to anemia or contribute to urinary tract
problems. Each individual must carefully weigh the potential
risks vs. benefits of vitamin therapy.
While scientific investigation often confirms the effectiveness
and safety of proposed treatments, sometimes these investigations
serve to discredit such claims. In the AREDS study, for instance,
the use of high dose antioxidant vitamins and zinc is shown
to be of benefit for some with age-related macular degeneration.
These same substances, once thought to deter cataract formation
as well, were shown to be ineffective in this regard. It remains
yet to be determined if promising substances not studied,
such as lutein or zeaxanthin, will in fact slow the development
of cataracts or AMD. Other organ systems have also been evaluated
for the potential benefit of antioxidants in the diet. It
was recently reported in a five year study of thousands of
British patients that vitamins C, E, and beta- carotene, previously
thought to protect the heart, did not prevent heart attacks
or strokes at all. It is clear then that claims of safety
and effectiveness—even those based on seemingly sound
hypotheses—must be considered speculation unless they
are substantiated by scientifically sound investigation, such
as AREDS.
We will provide you with guidance in assessing your individual
needs, help you choose from available appropriate therapies
where indicated, and advise you regarding the safety and effectiveness
of vitamin supplement products.
1Arch Ophthalmol. 2001;119:1417-1436
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