Lutein intake decreases risk of late but not early AMD
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zeaxanthin is not significantly associated with a reduced risk of
early AMD, whereas an increase in the intake of these carotenoids may
be protective against late AMD.
Dietary antioxidants, particularly lutein and zeaxanthin, are
hypothesized to have the capacity to modulate defense and repair
systems that operate in response to oxidative damage and inflammation.
As the major components of macular pigment, lutein and its structural
isomer, zeaxanthin, are thought to have the beneficial effects on
preventing the onset and progression of AMD. Laboratory data suggested
an important role for these two carotenoids in protecting the neural
retina from photo-oxidative damage and the development of common
visually disabling disorders by absorbing blue light and by quenching
reactive oxygen species through powerful antioxidant activity.
Lutein and zeaxanthin are thought to decrease the incidence of
age-related macular degeneration (AMD); however, findings have been
inconsistent.
Methods & Results
The researchers conducted a systematic literature review and
meta-analysis to evaluate the relationship between dietary intake of
lutein and zeaxanthin and AMD risk. Relevant studies were identified
by searching five databases up to April 2010. Reference lists of
articles were retrieved, and experts were contacted. Literature
search, data extraction and study quality assessment were performed
independently by two reviewers and results were pooled quantitatively
using meta-analysis methods. The potential sources of heterogeneity
and publication bias were also estimated.
The search yielded six longitudinal cohort studies. The pooled
relative risk (RR) for early AMD, comparing the highest with the
lowest category of lutein and zeaxanthin intake, was 0.96 (95 % CI
0.78, 1.17). Dietary intake of these carotenoids was significantly
related with a reduction in risk of late AMD (RR 0.74; 95 % CI 0.57,
0.97); and a statistically significant inverse association was
observed between lutein and zeaxanthin intake and neovascular AMD risk
(RR 0.68; 95 % CI 0.51, 0.92). The results were essentially consistent
among subgroups stratified by participant characteristics.
Discussion & Conclusions
The present meta-analysis involved data on evaluating the effects of
lutein and zeaxanthin on AMD prevention published in six cohort
studies. Results suggested that high intake of lutein and zeaxanthin
was significantly associated with a reduction in risk of late AMD
(FIGURE). No significant relationship was found for dietary intake of
these carotenoids and early AMD (FIGURE).
Several biological mechanisms have been proposed for the potential
protective effect of lutein and zeaxanthin on preventing the onset of
AMD. As the major components of macular pigment, lutein and zeaxanthin
are uniquely concentrated at the macula, indicating that these
carotenoids may exert their effects on protecting the macula from
age-related loss of visual function and macular disease. Both lutein
and zeaxanthin, possessing a series of unconjugated double bonds, are
believed to be very effective antioxidants. They have been shown to
help quench singlet oxygen, scavenge reactive free radicals and
inhibit lipid peroxidation of membrane phospholipids, and thus may
prevent or delay the development of AMD. In addition, the spectrum of
lutein and zeaxanthin includes a broad absorption band, with a peak at
approximately 450 nm; therefore, these carotenoids have an important
role in absorbing and attenuating the damaging blue light before it
reaches the photoreceptors.
As there were no randomised clinical trials regarding the effect of
dietary lutein and zeaxanthin on AMD prevention at present. It is
generally considered that cohort studies provide stronger evidence for
evaluating a relationship than other observational studies, because
the cohort studies could largely reduce the likelihood of selection
bias and reverse causation. Therefore, only cohort studies were
included in the present systematic review and meta-analysis.
Results from the present analysis showed that lutein and zeaxanthin
intake was not significantly associated with a decrease in the risk of
developing early AMD. Among the six available studies, only one found
a significant association between dietary lutein and zeaxanthin and
the incidence of early AMD, whereas the others found no associations
that were consistent with the present finding.
In contrast with the findings for early AMD, we found a statistically
significant relationship between lutein and zeaxanthin intake and the
risk of late AMD. These inconsistent relationships from different
stages of AMD might be partly explained by differences in the degree
of macular pigment damage and ascertainment of AMD. Previous studies
had shown that no significant differences in macular pigment optical
density were found between eyes with and without early AMD or between
the various stages of early AMD. Results from studies that compared
the macular pigment optical density of eyes with and without late AMD
were not consistent; however, most indicated declines in the optical
density of macular pigment among subjects with late AMD. Similar
results had also been found in the peripheral retina of autopsy
specimens from donor eyes with AMD, indicating that the loss of
macular pigment might reflect the accumulation of damage accrued over
an entire lifespan.
In conclusion, the present systematic review and metaanalysis
demonstrates that, on the basis of evidence available to date, dietary
intake of lutein and zeaxanthin is not significantly associated with a
decrease in the risk of developing early AMD, whereas an increase in
the intake of xanthophylls may have beneficial effects for late AMD.
Br J Nutr. 2012 Feb;107(3):350-9
http://www.ncbi.nlm.nih.gov/pubmed/21899805
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