Some dietary supplements once thought to slow the progression of age-related macular degeneration (AMD) have been proven to either show no effect or may even be harmful to some segments of the population.

AMD destroys cells in the retina, a layer of tissue in the back of the eye that provides sharp central vision necessary for tasks such as reading, driving, and recognizing faces. In some cases, abnormal vessels grow under the retina leading to bleeding, scarring, and further vision loss. Advanced AMD can lead to significant vision loss and is the leading cause of blindness in the United States. About 2 million Americans have advanced AMD; another 8 million are at risk.

The Age-Related Eye Disease Study (AREDS), led by the National Institutes of Health’s National Eye Institute, concluded in 2001 that daily high doses of vitamins C and E, along with beta-carotene and the minerals zinc and copper—called the AREDS formulation—can help slow the pace toward advanced macular degeneration.

A follow up five-year study (AREDS2), which ended in 2012, tested whether the original formulation of supplements could be improved by adding omega-3 fatty acids, adding a lutein/zeaxanthin combination, removing beta-carotene, or reducing the zinc.

The new study is available in the April 2013 journal Ophthalmology.

Researchers at 82 sites across the country conducted research for the study. James Folk, M.D., professor of ophthalmology and visual sciences at the University of Iowa, was the principal investigator at the Iowa site. Stephen R. Russell, M.D., professor of ophthalmology and visual sciences, was also an investigator and Barbara Taylor was the study coordinator.

Folk said in the Iowa study, 43 study participants were split into four groups and took a different variation of the AREDS formulation daily for five years: one group received the original formulation of vitamins C and E, beta-carotene, zinc and copper; one group received the original formulation with no beta-carotene; one received the original formulation with a reduced amount of zinc; and one group received the original formulation with no beta-carotene and a lower amount of zinc.

In addition, participants in each group took one of four additional supplements or combinations: lutein/zeaxanthin alone; omega-3 fatty acids alone; lutein/zeaxanthin and omega-3 fatty acids; or a placebo.

“It was important to take a look at these supplements because previous research had indicated that they may be helpful and because so many people have this disease,” Folk says. “If one or two of the supplements could reduce advanced AMD by even 10 percent at five years, this would save vision in many people in the United States, Europe and Australia. ”

In the first AREDS trial, participants with AMD who took the AREDS formulation were 25 percent less likely to progress to advanced AMD over the five-year study period, compared with participants who took a placebo. In AREDS2, researchers found no overall additional benefit from adding omega-3 fatty acids or a 5-to-1 mixture of lutein and zeaxanthin to the formulation. However, the investigators did find some benefits when they analyzed two subgroups of participants: those not given beta-carotene, and those who had very little lutein and zeaxanthin in their diets but then received both as supplements.

Folk said the overall AREDS2 study showed that removing the beta-carotene from the original AREDS formulation didn’t change its effectiveness in slowing advanced AMD. This is significant. Smokers should not take beta-carotene since it increases the risk of lung cancer.

In this present study, even ex-smokers who took beta-carotene had an increased risk of lung cancer although the numbers were small.

"There is also a developing hypothesis that supplementing with extra beta-carotene may be 'overfeeding' the eye which might actually cause more damage," Folk says. "For all these reasons, most experts recommend that people with AMD should not take supplement containing beta-carotene. They should though continue to eat healthy leafy green vegetables and fruits."

Although there was no overall benefit of the lutein/zeaxanthin combination, there was a hint that it could be worthwhile in the group that didn't take beta-carotene. People with AMD could consider and formulation of AREDS supplements in which the beta-carotene is replaced with lutein or a lutein/zeaxanthin combination.

Folk says the addition of the omega-3 fatty acids, so called fish oils, showed no benefit, He says that’s indicative of the small effect that vitamin supplements—as opposed to overall lifestyle change—has on a person’s health.

“You try to pick out any one of those factors, and when you do a study on them you find out that it’s not just one vitamin or food that will suddenly cure a disease. It's taking care of your overall health to prevent the disease,” Folk says. “It’s changing your lifestyle, exercising, eating right, getting enough rest, all of those things.

"It’s hard, but you know you have to do it," Folk says. "Some people just get the bad genes and they are in a tough spot. But most of us get a mixed bag and can stave off this disease if we take care of ourselves, but, unfortunately we shouldn't expect that a magic pill is going to make everything better if we haven't taken care of ourselves for 70 years.”