Many
of us remember (or still watch!) the old Popeye cartoons where the title
character would instantly gain much greater physical strength by eating a can
of spinach. But did you know that it could also build the strength of the
macular pigment, a shield against vision loss?
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| Source: Robert Lynch |
Macular
degeneration is a common age-related complaint, partly because the macula in
the centre of our eyes can easily become damaged by prolonged bright light
exposure, or looking directly at strong light sources such as the sun, without
protection. As we rely on our eyes for so many things, including driving, any threat to our vision is rightfully a great concern. The risk of this damage, however, can be reduced by increasing the
amount of yellow pigment that shields the macula primarily from “blue” light.
This blue light is the dominant type of light emitted by computers and many
TVs, and is one part of sunlight. The yellow pigment that protects the macula
from blue light is made of three carotenoids: lutein, zeaxanthin and
meso-zeaxanthin. Zeaxanthin is 75%of the pigment in the central area of the
macula, while lutein makes up two-thirds of the macular pigment towards the
edges. This pigment can wear down with age, possibly due to poorer digestion,
or from poor dietary intake of these three carotenoids. The thickness of this
pigment is measured as Macular Pigment Optical Density, and is scored from 0 to 1. Less than 0.21 is considered
to be “low”, 0.22-0.44 is medium, and 0.45-1 is “high”, and the healthiest
range. A thicker pigmentation can not only protect against macular
degeneration, the most common form of blindness, but also prevent
photosensitivity, help us see at night and improve vision in natural
environments.
So
in theory, carotenoids may protect against blindness, but what about in
practice? In a Japanese study (Ozawa et al. 2016), 11 healthy non-smokers had
their macular thickness and vision (as visual acuity) tested, then were
instructed to eat 75 grams of frozen spinach, containing 10mg of lutein, every
day for two months. At both one and two months, visual acuity and macular
pigment density were significantly increased, and higher blood levels of lutein
helped to confirm the relationship. Despite appearances, spinach is a source of
yellow carotenoids, but the green chlorophyll overpowers the yellow
pigmentation. Additionally, a study testing the effect of kale extract on 20 patients with
macular degeneration also found a significant increase in pigment density.
After stopping the extract, macular pigment density dropped, showing the
importance of regularly eating these foods. Like the previous study the amount
of lutein in this extract was also 10mg, and was accompanied by 3mg of
zeaxanthin. Meso-zeaxanthin may strengthen the
effects of lutein and zeaxanthin, with a trial involving patients with early
age-related macular degeneration (AMD) showing greater improvements in pigment
density and contrast sensitivity, and continuing improvement in the second and
third year of supplementation. No supplemented patients progressed to AMD. As
for prevention, a meta-analysis of research on
carotenoid consumption and AMD found a 26% reduced risk of AMD in those
consuming the highest levels of carotenoids compared to those with the lowest
intake. Overall, the yellow carotenoids have an increasing amount of evidence
behind their effects on vision preservation, though increasing dietary intake
should be the first line of action. If you are looking to increase your intake
of the yellow carotenoids, spinach, kale, broccoli, green peas and collard and
turnip greens are the richest sources.
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