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2016-09-06 09:42:28
Many people suffer declining eyesight as they get older, but is there something
we can eat to improve it, asks Michael Mosley.
My eyesight has never been good. I've worn glasses most of my life and as I get
older that's a situation that I've only expected to get worse. When the Trust
Me, I'm A Doctor team suggested that I try taking supplements to improve my
eyesight, though, I was sceptical, particularly as I am not a fan of
supplements.
Nonetheless I headed off to meet Prof John Barbur of City University in London
to have my eyesight thoroughly tested. He was particularly interested in my
retina, the light sensitive part of the eye, and made me stare at a computer
screen in the dark for hours, having tests flashed up at me which thoroughly
and precisely measured the limitations of my perception of different colours,
my night vision and my detection of faint and small objects.
He also measured the level of protection that the most delicate area of my
retina - the macula - had against damage from high energy blue and UV light.
This protection is, in effect, a kind of natural sunscreen that we have
covering the light-detecting cells, and is made up of yellowish "macular
pigments".
The results of my tests were both fascinating and depressing. My detection of
yellow and blue colours was extremely poor - something that Prof Barbur said
was likely the result of my brush with diabetes many years ago. My night vision
and perception of details were also poor compared with younger people - but
consistent with my age.
The Trust Me team then handed me a 90-day supply of supplement pills that were
supposed to help. They contained concentrations of certain compounds found in
coloured plants. These were extracted from marigolds, but two of the key
chemicals - lutein and zeaxanthin - are also found in a range of things we eat
more commonly.
A team in the United States devised a recipe for a daily smoothie for us that
they hoped could supply a similar level of lutein and zeaxanthin. It was a
heady mix of fruits and veg such as kale and kiwi fruit, along with fats such
as milk and wheat germ oil which help the absorption of the key compounds.
Twelve weeks later, I returned to City University to see whether my daily
pill-popping had made any difference to my eyesight. The results surprised even
Prof Barbur. There were significant improvements in several different aspects -
my blue and yellow colour perception was back to normal and my night vision was
much better. The levels of my protective macular pigments were also boosted.
The results were less of a surprise to Prof John Nolan, who I went to meet in
Waterford, in south-east Ireland. His team has been studying macular pigments
for many years, and recently completed a year-long trial with over 100
participants in which they had seen similar results to mine.
They found that boosting the diet with the three macular pigments - lutein,
zeaxanthin and meso-zeaxanthin - led to significant improvements in the
protection of the delicate macula, as well as improved eyesight.
There is also some evidence that such supplementation may help slow or possibly
even prevent, age-related macular degeneration (AMD) - the leading cause of
vision loss in the UK. However, this is still controversial.
Should we all, then, be taking supplements to protect and even improve our
eyesight?
Well, the research certainly shows that supplements work. Even for someone like
me, who has a relatively healthy diet with plenty of fruit and vegetables, and
whose blood levels of the compounds that weren't particularly low, the
supplements helped. However, some researchers believe that diet can simply be
enough, if we eat the right things.
More research needs to be done on the best dietary sources for each of the
three macular pigments.
Lutein is a yellow compound made only by plants. They make it in order to
absorb blue light, as part of their mechanism to capture energy from sunlight
through photosynthesis. Animals then get it from eating plants - good sources
are green kale and spinach, or the yellow yolks of eggs.
It is used as a supplement to feed industrially-reared chickens to make their
yolks a more attractive yellow (and, being fat-soluble, ends up turning their
skin and fat yellow too).
Zeaxanthin is another yellow compound, almost identical to lutein, made by
plants to absorb light. It is the chemical that gives corn, bell peppers and
saffron their yellow colour.
Meso-zeaxanthin is a form of zeaxanthin not generally found in plants, but it
is made in the body from lutein. More research needs to be done on how
efficient this process is. It is found in some fish (particularly in the
skins), but in supplements containing marigold extract, it appears that the
industrial processing that the marigolds undergo can create meso-zeaxanthin
(and it has been found to be in some marigold-extract supplements, even when
not listed on the label).
Our volunteers taking the smoothie containing amounts of plant sources
calculated to give them a boost of lutein and zeaxanthin did indeed boost their
lutein levels, but not their zeaxanthin. Clearly more work needs to be done to
refine the recipe. So, this might be a rare occasion where, given the current
state of research, I might end up on the side of supplements - especially for
those who don't eat as many leafy greens as they should, and for older people
(who absorb nutrients less efficiently).
However, for all of those whose mothers and grandmothers told them that carrots
would improve their vision the message is this - although lutein, zeaxanthin
and meso-zeaxanthin are all chemicals known as "carotenoids", and carrots do
owe the yellow portion of their colour to them, these particular key compounds
are found mainly in the green parts of plants above ground.
So, if you want to improve your eyesight, I'm afraid it's munching on leafy
greens (taken with some fats to help absorb these fat-soluble chemicals) that
will do the best job.