Taking additional antioxidant supplements on top of vitamin C, vitamin E and beta carotene does little to ward off macular degeneration among older adults, new research suggests.
Researchers found a combination of lutein and zeaxanthin only provided extra protection for people who started out getting the smallest amount of those nutrients in their diets, such as from green, leafy vegetables.
"Overall, people were hoping it would be a bigger bang," said Dr. Jack Cioffi, head of ophthalmology at Columbia University Medical Center in New York, who wasn't involved in the new research.
Still, Cioffi said he would probably recommend people at risk for macular degeneration take lutein and zeaxanthin instead of the previously-prescribed beta carotene - which was linked to an increased risk of lung cancer among smokers in the new study.
"If anything, this speaks to the fact that you can use antioxidants other than beta carotene," he said.
Macular degeneration is a chronic eye disease that causes blurred vision and blind spots, which become worse over time. According to the U.S. Centers for Disease Control and Prevention, about 1.8 million Americans age 40 and older have age-related macular degeneration.
Previous research showed a combination of vitamins C and E, beta carotene and zinc could reduce the risk of advanced macular degeneration by about one quarter.
"We wanted to see if we could improve upon the result - make it a little better, make it a little safer," said Dr. Emily Chew, who led the new study at the National Eye Institute in Bethesda, Maryland.
So she and her colleagues added a combination of lutein and zeaxanthin or two types of omega-3 fatty acids to the supplement regimens of some of the original 4,203 study participants, age 50 to 85, who were still taking their initial vitamins and minerals.
Over the next five years, the researchers found, macular degeneration progressed in 29 to 31 percent of study participants, regardless of whether they were given the extra supplements.
In a separate analysis, the proportion of people who had to undergo cataract surgery for other vision problems was also similar across groups, at about 24 percent.
People in the study were relatively well-educated and tended to have good-quality diets before taking supplements, the researchers noted.
"It could be that the addition of more antioxidants, and different antioxidants, doesn't convey any additional benefits, which is probably the truth," Cioffi said.
Chew said she does believe lutein and zeaxanthin have an important role in protecting against vision loss. Among study participants who ate the fewest green, leafy vegetables, taking those antioxidants was tied to a 26-percent lower risk of progression to advanced macular degeneration, the study team reported in the Journal of the American Medical Association.
"People at risk for macular degeneration - they're the ones who will benefit the most," she said.
The cataracts finding was published in JAMA Ophthalmology, and the data were presented collectively at the Association for Research in Vision and Ophthalmology's annual meeting in Seattle.
Cioffi said the possible link between lung cancer and beta carotene was "somewhat confusing." In the new study, 2 percent of people taking beta carotene developed lung cancer, compared to 1 percent not using that antioxidant. Most of those cancers were in former smokers.
Still, he said it would probably make sense going forward to substitute other antioxidants for beta carotene in recommended formulations with vitamin C, vitamin E and zinc, as lutein and zeaxanthin weren't tied to any complications.
Lutein and zeaxanthin supplement combinations can be bought over the counter for about $10 to $15 per month.
"I think if you're at all health-conscious and have a well-rounded diet that includes dietary supplements of these antioxidants, you're probably doing good for more than just your eyes," Cioffi said.