Mom was right after all.
When she said, "Eat your carrots, they’re good for your eyes," she didn’t have the benefit of new research into the role that vitamins and minerals play in preserving good eyesight. But as we know today, it’s great advice.
Science has known for some time that a diet rich in orange and green leafy vegetables – those rich in anti-oxidant vitamins and minerals like C, E and zinc – was good for vision and particularly beneficial in preventing age-related macular degeneration (AMD), the leading cause of blindness among adults aged 50 or older in the Western world.
Now a study has proven that supplementation with a multi-vitamin containing those anti-oxidants can reduce the risk and progression of the disease.
"This is the first really potent evidence we've got to suggest that we now have an effective prevention to slow progression of AMD in the form of dietary supplements," says Dr. Alan Cruess, head of the department of ophthalmology at Queen's University in Kingston and a specialist in retinal diseases at Hotel Dieu and Kingston General hospitals. "I think this is very, very exciting news for patients who are at risk for this disease. Or who have early stages of the disease."
The Age Related Eye Disease Study (AREDS), an ongoing multi-centre clinical trial conducted by the American National Eye Institute and published in October in the Archives of Ophthalmology, showed a 25-per-cent risk reduction or reduced progression of AMD in patients who were already in early stages or showed risk indicators of developing the disease. The trial followed participants, ranging from 55 to 80 years old, for more than six years, comparing results from a vitamin supplement containing vitamin C (500 mg), vitamin E (400 IU), beta carotene (15 mg) and zinc (80 mg) with copper (2 mg of cupric oxide) against a placebo control. Anti-oxidants are the body's protection against unstable oxygen molecules, the by-product of generating energy, referred to as free radicals, that combine with other compounds to cause cell damage and contribute to many chronic and age-related conditions.
A noteworthy aspect of the trial results, says Cruess, is that the greatest benefit was seen in those who were most at risk of losing their sight to the disease. The participants were divided into groups, or strata, depending on the severity of the AMD, ranging from no symptoms to more severe forms. "Those strata that actually benefitted the most were patients who had a moderate degree of change already."
In the past, a diagnosis of AMD often meant that loss of sight was on the horizon. The best advice doctors could give their patients was to make some lifestyle changes. A major one, Cruess says, was to stop smoking, which alone could reduce the risk of AMD 2 1/2 times. Another was to adopt a diet rich in fruits and vegetables containing the anti-oxidants.
"We knew those patients who had higher blood levels of beta carotene and other anti-oxidants did better and had a lower risk of disease progression," he says. "What we didn't know in the 1990s was whether supplementing with anti-oxidants in pill form would be beneficial. So we weren't in a position to give our patients positive, clear-cut advice. Now we can recommend these dietary supplements in addition to a healthy lifestyle."
While the AREDS trial did not include carotenoids such as lutein and zeaxanthin in its vitamin formulations, there is evidence to suggest that these may also be beneficial for AMD sufferers, Cruess says.
Carotenoids are naturally occurring pigment compounds that give fruits and vegetables their distinctive colours, tastes and odours and are particularly plentiful in green, yellow and orange vegetables. About 20 carotenoids – of some 600 detected in nature – are found in human tissues. Lutein and zeaxanthin are the dominant pigments found in the macula of the eye.
"There is evidence that increasing macular pigment density may have a protective effect and we know that lutein and zeaxanthin are the yellow pigment that's concentrated in the centre of the macula, the very centre of the reading vision portion of the retina, the seeing film in the back of the eye," Cruess explains. This yellow pigment filters out blue light – "the more toxic end of the visible spectrum" – and the carotenoids also act as anti-oxidants, "possibly quenching free radicals in the tissues and preventing retinal damage in that way."
Regardless of why they work, Cruess says it's clear that they are important. As a result many vitamin manufacturers will be adding these protective agents to their formulations, he says.
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diagram: Lutein and zeaxanthin are the yellow pigment that's concentrated in the centre of the macula, the centre of the reading vision portion of the retina, which is the seeing film in the back of the eye."