"Taking an overload of the amount of nutrient doesn't guarantee that you can avoid disease or see better," he said. "Your body can only use so much of the vitamins and pigments, so there's no evidence that taking more of it is beneficial for you."
A yellow pigment found in the eye, called Lutein, is one supplement now being studied by the AREDS2 trial, a followup to the first AREDS trial on antioxidant supplements.
Unlike other nutrients, although found in the eye, Lutein is not produced in the body and can only be found through the nutrient in foods and in supplements. Other supplements in the AREDS2 trial include Xeoxanthin, and Omega-3 fatty acids.
Researchers hypothesize that these supplements will slow the progression of mild AMD, said Dr. Barbara Blodi, associate professor at the department of ophthalmology at the University of Wisconsin and a lead researcher on the AREDS2 trial.
"These fatty acids are in the retina and help the cones and rods in the retina to help you see," Blodi said. "So the idea is that if you got more, it could save your sight."
The future implications, she said, could be big.
"Of the estimated 14 million people who have a mild stage of AMD, we hope a good proportion would benefit from taking supplements to prevent end stage AMD," Blodi said. "If you could prevent that, it would be an important step for older citizens to stay independent."
The trial is scheduled to end in the year 2013, but until then, Blodi said, supplement users should be warned against high hopes that marketers use to sell better vision.
"A dilated eye exam will show you if you have macular degeneration," she said. "Once you know what is causing your vision loss, then you know what supplements we know can help you -- so go from there."