Author: Edward
Rosick, DO, MPH, DABIHM
The two leading causes of blindness are age-related
macular degeneration and cataract formation. While declining vision is
devastating in and of itself, new research shows that macular degeneration is
linked to development of Alzheimer’s disease.
Fortunately, two potent plant compounds, lutein and
zeaxanthin, have been found to not only reduce incidences of macular
degeneration and cataracts, but may also reduce Alzheimer’s risk. According to
a recent study, people with the highest intakes of lutein and zeaxanthin had a
40% reduced risk of developing advanced macular degeneration! When combined with a third carotenoid called
meso-zeaxanthin, the three have been found to provide even greater benefits for
people with early age-related macular degeneration. These low-cost natural
compounds are readily available so that everyone can benefit from their
potential to protect against vision loss and dementia.
Protection against
Age-Related Macular Degeneration
Age-related macular degeneration is a progressive, chronic
disease of the macula, which is the pigmented area near the center of the
retina. The macula is responsible for central vision. It is the part of the eye
that enables an individual to see fine details necessary for everyday
activities, such as reading, driving, and telling time. When the macula
deteriorates, it can lead to everything from blurred vision to the distortion
of central vision, and even to the complete loss of central vision. Sadly,
macular degeneration is projected to affect almost 300 million people worldwide
in the next 25 years. Prescription medications offer nothing in terms of
preventing macular degeneration.
The good news is that a recent article in JAMA
Ophthalmology confirms previous findings on two natural compounds, lutein and
zeaxanthin, and their ability to significantly reduce the risk of developing
this debilitating eye disease.
Lutein and zeaxanthin are carotenoids, natural compounds
found in vegetables that give them their color. Out of the hundreds of
carotenoids in nature, only lutein, zeaxanthin, and meso-zeaxanthin are
selectively present in high concentrations in the macula, giving this part of the
eye its distinctive yellow color.
Even more significantly, these three carotenoids play a
significant role in protecting the macula against UV light that causes
oxidative stress, a key culprit in the damage caused to the macula during
macular degeneration. In essence, these carotenoids function as natural
“sunglasses” for the eye, protecting it from harmful light and maintaining the
function of the macula.
As a result, multiple research studies have demonstrated
those who have the highest intakes of these eye-protective carotenoids have the
lowest risk of developing macular degeneration. Let’s take a look at the
studies.
A 40% Reduced Risk
of Macular Degeneration
The research detailed in the JAMA article previously
mentioned was a decades-long prospective cohort study that began in 1984 and
ended in 2010. During this time period, data from 69,443 women and 38,603 men
who participated in the Nurses’ Health Study and the Health Professionals
Follow-up Study were analyzed. All the participants were 50 years old or older
and did not have macular degeneration at the start of both studies. Intake of
carotenoids, including lutein and zeaxanthin, were calculated from food intake
data sheets and repeated food questionnaires at baseline and follow-up.
At the end of the study, researchers identified 1,361
cases of intermediate macular degeneration and 1,118 cases of advanced macular
degeneration. When the authors of the article compared these numbers with the
established levels of lutein and zeaxanthin, they found that those
participants, men and women alike, who had the highest intake of these
carotenoids, decreased their risk of developing advanced macular degeneration
by a significant 40% compared to those who had the lowest intake.
Benefits for Those
with Early Macular Degeneration
In addition to reducing the risk of developing macular
degeneration, other recent studies have demonstrated the beneficial impact of
lutein and zeaxanthin for those who already have early macular degeneration. A
randomized, double-blind, placebo-controlled trial examined the effects of
lutein and zeaxanthin on macular pigmentation and visual performance in 112 men
and women, aged 68 to 78, with early age-related macular degeneration.8
During the study, participants received lutein only, a
combination of lutein plus zeaxanthin, or a placebo daily. Scientists evaluated
the following important parameters of vision health:
* Serum concentrations of lutein and zeaxanthin (the
amount in the blood).
* Macular pigment optical density, which is a measurement
of the thickness of the macular pigment. Higher density reduces the risk of
macular degeneration, while lower density increases the risk.
* Best-corrected visual acuity, a test that measures the
sharpness or clarity of vision (not overall quality of vision). This determines
the degree to which vision can be corrected with glasses or contact lenses.
* Contrast sensitivity, a test that measures the ability
to distinguish between an object and its background. Having low contrast
sensitivity can lead to problems with night driving and can increase the risk
of falling.
* Vision-related quality of life.
After two years, researchers were able to show that serum
concentrations of lutein, zeaxanthin, and macular pigment optical density
significantly increased for all treatment groups receiving either lutein or the
combination of lutein-zeaxanthin. There were no adverse side effects. In terms
of visual performance, there was an increase in contrast sensitivity in the
active treatment groups. Compared to placebo, those taking lutein and
zeaxanthin showed a significant increase in the vision-related quality of life
score.
While there were no improvements seen in best-corrected
visual acuity, this study demonstrated that supplementation with lutein and zeaxanthin
have multiple benefits for those suffering from early macular degeneration.
How to Enhance the
Benefits of Lutein and Zeaxanthin
As beneficial as these two nutrients are, their impact is
even more dramatic when combined with a third compound: meso-zeaxanthin. Formed
in the macula from zeaxanthin, meso-zeaxanthin is one of the three carotenoids
we mentioned earlier that is present in the macula. Because all three are
present in the macula, it only makes sense that all three together offer the most
benefits to eye health, which is exactly what this next study found.
A randomized, single-blind trial examined the effects of
combinations of lutein, zeaxanthin, and meso-zeaxanthin in patients with early
macular degeneration. The study involved 52 men and women averaging 66 years of
age who were followed over 12 months and assigned to receive the combination
lutein and zeaxanthin or lutein, zeaxanthin, and meso-zeaxanthin.
Vision was assessed using two of the testing parameters
we mentioned earlier: macular pigment optical density and best-corrected visual
acuity. While there were significant improvements in vision in both groups at
the end of the study, the most statistically significant improvements were seen
in the group taking the combination of meso-zeaxanthin along with lutein and
zeaxanthin.
The same researchers did a three-year follow-up of the
original participants, and as in the first study, they found that those taking
meso-zeaxanthin in addition to lutein and zeaxanthin had the most significant
improvements in vision, specifically in terms of enhancing contrast sensitivity
and increasing macular pigment. This led the authors to conclude that taking
these three carotenoid nutrients together provided the most benefits for those
suffering from early age-related macular degeneration.
Types of Macular
Degeneration
Macular degeneration is generally grouped into two
categories: dry macular degeneration or wet macular degeneration. In dry
macular degeneration, which affects about 90% of people with macular
degeneration, the macula becomes progressively brittle and thin over time and
due to these changes, loses its ability to transmit images to the brain. Dry
macular degeneration is also called nonexudative macular degeneration because
there’s no leakage from surrounding blood vessels.
In wet macular degeneration, which affects approximately
10% of people with macular degeneration, new blood vessels develop in the
choroid, which is a layer of connective tissue and blood vessels underneath the
retina. Since these new blood vessels aren’t as strong as the original vessels,
they have a tendency to break and leak into the retina, including the macula,
causing scar tissue to form, which can damage and kill retinal cells. Wet
macular degeneration is also known as exudative macular degeneration, since
there’s exudate, or leakage, from the new choroid-layer blood vessels.
Protection against
Cataracts
In addition to battling age-related macular degeneration,
lutein and zeaxanthin have been found to significantly reduce the risk of
another cause of vision loss: cataracts. A cataract is a clouding of the lens
of the eye and is caused in large part by oxidative stress and glycation. In
America alone, it is projected that 50 million people will have cataracts by 2050.
A study out of Melbourne, Australia, examined the
relationship between lutein, zeaxanthin, and the risk of cataracts in 3,271
people aged 40 or greater over a two-year period. What they found is that the
men and women who ate a diet with foods high in lutein and zeaxanthin had a
statistically significant lower risk of developing cataracts.
This was confirmed in a more recent meta-analysis
published in 2014. After analyzing data from studies with 41,999 total
participants, 4,416 of whom had cataracts, the authors of the study determined
that the intake of dietary lutein and zeaxanthin was associated with a reduced
risk of developing age-related cataracts.
Additional Ways to
Protect against Macular Degeneration
In addition to lutein and zeaxanthin, two natural
compounds have also been found to be key players in preventing the underlying
damage that can lead to the development of age-related macular degeneration.
One is astaxanthin, a red carotenoid found in seafood and algae, and the other
is cyanidin-3-glucoside (C3G), a purple plant-based pigment in the class of
compounds called anthocyanins.
In a study, researchers examined the protective effect of
astaxanthin against light-induced retinal damage. This is the kind of damage
that is a key component of damage to the macula, ultimately leading to macular
degeneration.
In this study, scientists gave mice astaxanthin and then
exposed them to very bright light (8,000 lux) for three hours in order to
induce retinal oxidative damage. The researchers found that astaxanthin
protected the retina against light-induced oxidative damage. This led them to
conclude that dietary astaxanthin could help prevent and inhibit the
progression of dry macular degeneration, as well as retinitis pigmentosa, a
group of inherited diseases that cause retinal damage.
In another recently published study on the protective
effects of anthocyanins, specifically C3G, on light-induced retinal pigment
epithelial cell damage, researchers determined that multiple anthocyanins
protected human retinal pigment epithelial cells against oxidative damage and
found C3G to be significantly superior. The study authors concluded that
anthocyanins in general, and C3G specifically, are promising candidates for the
prevention of pathological changes in the retina.
The Link between
Macular Degeneration and Alzheimer’s
Scientists have long known that the retina is a direct
extension of the brain. With this knowledge, researchers have been examining
the eyes, retina, and macula to determine if changes in the macular pigment
optical density might be an indicator of something more than vision problems.
Specifically, they wanted to determine if these changes might reflect
pathological processes, like Alzheimer’s disease, and cognitive impairments in
the brain.
The first study examined whether or not macular pigment
optical density, along with lutein and zeaxanthin, is related to cognitive
functioning in older adults.24 Researchers tested 108 men and women with an
average age of 77 years for serum carotenoid levels, macular pigment optical
density, and cognition, including memory and brain processing speed. Results of
the study showed that macular pigment optical density was significantly
associated with cognition. Those with higher macular pigment optical density
showed better cognition, as well as verbal learning and fluency, recall, and
processing speed. Higher serum levels of lutein and zeaxanthin were associated
with a statistically significant level to verbal fluency.
Other research has shown a link between macular
degeneration and the risk of developing Alzheimer’s specifically. In an
eight-year-long population-based cohort study, researchers examined 4,993 men
and women aged 65 or older with macular degeneration. For the control cohort,
they recruited 24,965 participants matched for age and gender. At a mean
follow-up time of 4.4 years, the researchers discovered that the patients with
macular degeneration had a statistically higher risk of developing Alzheimer’s
than those participants without macular degeneration.
Because of studies like this, scientists are now
investigating whether or not increasing lutein and/or zeaxanthin intake could
be beneficial in decreasing the risk of developing Alzheimer’s. While more
research needs to be done, a recent study from France provides evidence that
these carotenoids could do just that.
French researchers followed 1,092 men and women, aged 65
or older, for up to 10 years and took baseline readings of multiple serum
carotenoids, including lutein and zeaxanthin. At follow-up, researchers found
that low lutein concentrations were significantly associated with Alzheimer’s
disease. This led the researchers to conclude that maintaining higher amounts
of lutein in the blood could moderately decrease the risk of Alzheimer’s.
It is important to point out that the association between
macular degeneration and onset of Alzheimer’s may relate to the lack of brain
activity that occurs in aging individuals who lose their eyesight. One method
of staving off dementia is to keep one’s neurons highly active via mental and
physical exercises. The blinding impact of advanced macular degeneration limits
one’s ability to maintain healthy stimulation of one’s neurons.
Summary
Age-related macular degeneration and cataracts are two of
the leading causes of vision loss in the elderly.
Lutein and zeaxanthin, carotenoids found in high
quantities in the macula of the eye, have been shown in multiple studies to
reduce the risk of developing both of these eye diseases. Adding a third
carotenoid, meso-zeaxanthin, has been found to produce even greater benefits.
Now, research has shown that having macular degeneration
puts people at higher risk for developing Alzheimer’s disease. Fortunately,
studies have shown that one of the nutrients that helps protect vision, lutein,
may also reduce the risk of developing Alzheimer’s.
Ultimately, the carotenoids lutein, zeaxanthin, and
meso-zeaxanthin may not only help people protect their vision, but could also
help protect cognitive function.
