Could losing excess weight help protect your eyesight in older age? A new study aims to find out, reports Claire O'Connell
BEING OBESE invites a raft of known health problems, including heart disease, diabetes and arthritis. But another ailment to add to that list could be progressive eye disease.
Researchers in Waterford are studying the possibility that by losing excessive body fat, you could help protect against age-related macular degeneration (AMD), where vision cells at the back of the eye are damaged.
"AMD is the leading cause of age-related blindness in the western world. It's estimated that it has affected more than 80,000 Irish adults to date with more than double that number not even registered yet," says Dr John Nolan, deputy director of the Macular Pigment Research Group at Waterford Institute of Technology.
"It's a problem because it's age related and we are living longer so the prevalence of this disease is known now to increase because of the ageing society we live in."
As the cells lose function in AMD, the central vision goes, he explains.
"So you lose the ability to see detail, to read, to write and to drive a car. Your social independence and quality of life are totally diminished.
"It's thought that the vision cells become damaged over time because of 'free radicals' that arise as a byproduct of normal cell function. It's not just something that happens overnight," says Nolan.
"It's believed that because it's an age-related eye disease, it's the cumulative and chronic damage caused by oxidative stress over our lifetime.
"We are exposed to light which produces free radicals, which are unstable molecules that break down stable cells within the body and the retina is an ideal site for such degeneration because of light exposure. And we are talking about visible light here, light in a room, not UV light."
However, our eyes may be able to stave off the degeneration if they have sufficient levels of protective "macular pigment" in the retina, he explains.
"The understanding is that the pigment is important because it protects the photoreceptors, it's an antioxidant," he says.
"The theory is that if you have enough pigment, you will protect against the damaging process of free radical damage."
Risk factors for developing AMD include age, smoking and a family history of the condition, but the good news is that lifestyle and diet can affect the levels of macular pigment in your eyes.
"You may be genetically predisposed to get this condition, but even if you are genetically identified to get this condition, there are things you can do with your lifestyle that can reduce the rate at which this disease presents itself," says Nolan.
Cutting out smoking reduces one major contributor. And eating a diet rich in leafy greens, fruit and vegetables and egg yolks helps provide the building blocks for making the pigment in our bodies, he explains.
"Lutein, zeaxanthin and meso-zeaxanthin are the three components of the macular pigment, they are three dietary carotenoids," explains Nolan.
"You are not born with them, they are entirely of dietary origin.
"So if you have a diet consisting of a high amount of fruits and vegetables, in general you will have high amounts of macular pigment and this has been studied in both humans and primates.
"They are also available as supplements - for example, you can go into a chemist and buy a concentrated form and we have performed studies showing significant augmentation of macular pigment following these supplements, so the retina does respond when somebody takes them."
So what's the link with obesity?
Population studies from the MPRG suggest an association between body fat and levels of the protective pigment, says Nolan: "High body fat equals low macular pigment levels.
"The body fat acts as a reservoir and takes up these important nutrients and, therefore, the retina is deprived of them."
Obese people also tend to have low levels of "good" cholesterol, or HDL, which is thought to bring macular pigment to the retina, he adds.
"It's believed that the are primarily carried around on the HDL. It's like a taxi system: there are not enough taxis to take you where you want to go, the retina in this case."
Now the MPRG is taking a new approach to the question - could reducing excessive body fat bump up the levels of macular pigment in the retina?
They have recruited 100 volunteers, mostly female, who have a BMI of over 28.
Half go off for a year and possibly lose weight under their own steam, and the researchers look at their macular pigment levels at the start and end of the year. The other half receive specific dietary and exercise support and advice and undergo testing of their macular pigment levels and dietary assessments at intervals over 12 months.
"This is the first time a study of this type has been performed, looking at the actual benefits of weight loss as opposed to looking at association," says Nolan, adding that participants have already shed weight on the programme.
"It's a win-win for everybody and it has been great so far."
And the researchers are already taking steps to keep themselves in shape. Both Nolan and MPRG's director, consultant ophthalmic surgeon Mr Stephen Beatty, are in training to run this year's Dublin City Marathon in support of the charity Fighting Blindness, which funds the obesity study.
• For more information, contact Fighting Blindness at info@fightingblindness.ie or tel: 01-709305