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LE Magazine May 2002
Page 2 of 2
Carotenoids and macular pigment
Scientific evidence is mounting to demonstrate the power of
dietary antioxidants in maintaining eye health and warding off
age-related macular degeneration. The most recent study to
raid the headlines was the Age-Related Eye Disease Study
(AREDS), which was carried out by the National Eye Institute.
The large, multicenter study showed that a daily intake of 500
mg of vitamin C, 15 mg of beta carotene, 400 IU of vitamin E
and 80 mg of zinc reduced the risk of developing advanced
disease in those with intermediate damage by about 25%.[21]
Other research has more specifically set its sights on
examining the protective role of the carotenoids, lutein and
zeaxanthin, against macular degeneration. Why? With several
hundred carotenoids to be found, consider that only lutein and
zeaxanthin are found in the retina.[22,23] Compared to other antioxidant
concentrations found in the eye, German researchers found that
lutein and zeaxanthin did not break down nearly as fast as
lycopene and beta-carotene when exposed to free radical or UV
light induced oxidative stress.[24] The authors suggest that perhaps
the slow degradation of lutein and zeaxanthin may explain the
strong presence of these carotenoids in the retina. Also, the
quick breakdown of lycopene and beta-carotene may suggest why
these carotenoids are lacking in the same retinal tissues.
Researchers have also found that lutein and zeaxanthin are
more highly concentrated in the center of the macula. There,
the amounts of lutein and zeaxanthin are much greater than
their concentrations in the peripheral region. At the Baylor
College of Medicine, in Houston, scientific investigators
demonstrated, using retinas from human donor eyes, that the
concentration of lutein and zeaxanthin were 70% higher in rod
outer segment (ROS) membranes where the concentration of
long-chain polyunsaturated fatty acids, and susceptibility to
oxidation is highest, than in residual membranes.[25] The fact that lutein and zeaxanthin
are particularly concentrated in these parts of the eye
suggests that they may act as a shield or filter that helps to
absorb harmful UVB light and dangerous free-radical molecules,
both of which threaten the retinal tissue.[26,27]
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Moreover, while macular pigment density decreases with age,
and the risk of AMD increases-a coincidence that cannot be
overlooked-researchers have also found that older folks with
higher lutein and zeaxanthin concentrations in their macula
tend not to develop the disease. Researchers at Arizona State
University suggested that increasing macular pigment through
dietary intake of lutein and zeaxanthin may retard age-related
declines in visual function, and that high macular pigment
density was associated with the retention of youthful visual
sensitivity.[28] After measuring
the macular pigment density and visual sensitivity of 27 older
subjects (aged 60 to 84 years) and 10 younger ones (aged 24 to
36 years), results showed that older subjects with high levels
of lutein and zeaxanthin had visual sensitivity comparable to
younger subjects. Conversely, older subjects with low lutein
and zeaxanthin in their macula had lower visual
sensitivity.
Weighing all the evidence to date, it stands to reason that
increasing or maintaining levels of the carotenoids that make
up the pigment, namely lutein and zeaxanthin, would support
the protective role of macular pigment. While larger and
longer trials will bear out what research now seems to
suggest, increasing our lutein and zeaxanthin intake through
diet seems to be a safe bet. However, nutritional scientists
have not yet pinned down ideal amounts to recommend for lutein
and zeaxanthin supplements. Bernstein explains that we
currently hear much more about lutein, "since it is much more
common in our diet, and commercial supplements of lutein have
been available for a much longer time. Zeaxanthin supplements
have been approved for human use only recently." For the time
being, though, Bernstsein suggests consuming a diet high in
fruits and vegetables. He adds that daily supplementation with
at least 4 milligrams of lutein per day may be beneficial, but
further studies are needed.
References
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