Taking vitamins E and C may do nothing to protect aging eyes from macular degeneration - the leading cause of vision loss in older adults, a new clinical trial finds.

Researchers had been hoping the vitamins, both antioxidants, could shield against the tissue erosion that occurs in macular degeneration. The condition involves damage to the center of the retina, which makes it hard to see fine details.

Studies have found that people who get more antioxidants in their diet have a lower risk of macular degeneration. But that doesn’t rule out other possible diet or lifestyle explanations behind the link.

And so far, clinical trials using vitamin E have come up empty.

This latest study is the longest-running one to test vitamin E for eyesight in men, and the first to try out vitamin C alone, said lead researcher William G. Christen, of Brigham and Women’s Hospital and Harvard Medical School in Boston.

It found no benefits of either vitamin in older men who took supplements for eight years.

No one study can be the final word on the vitamins and macular degeneration, Christen told Reuters Health in an email. On the other hand, the findings also offer no evidence to support taking vitamins E or C to ward off vision problems.

The report, which appears in the journal Ophthalmology, is part of an ongoing study of more than 14,000 U.S. male doctors age 50 and older.

The men were randomly assigned to take either 400 international units (IU) of vitamin E or a placebo pill every other day, along with a daily dose of either 500 milligrams of vitamin C or a placebo.

That meant the men were either taking both vitamins, only one of them, or neither.

After eight years, 193 men had developed macular degeneration that was serious enough to interfere with their vision. But the risk was nearly identical among vitamin and placebo users.

In the U.S., an estimated 7.2 million people have some degree of macular degeneration, and 890,000 of them have advanced disease.

But the rate of new cases may be on the decline.

A study last year estimated that less than seven percent of Americans age 40 and up have macular degeneration. That was down from more than nine percent in research from the early 1990s (see Reuters Health story of January 11, 2011).

The researchers were not sure of the reasons for the decline. But they speculated that a dip in smoking rates could be one factor.

“A large body of evidence supports cigarette smoking as an important cause of age-related macular degeneration,” Christen said.

“So avoiding or quitting cigarette smoking appears to be one way to lower your risk,” he added.

But based on the current results, Christen’s team writes, vitamins E and C are “unlikely to have an important effect on the incidence of early age-related macular degeneration.”

The researchers note, though, that their study group was a generally “well-nourished” bunch. They say it’s possible the results would be different in people who have vitamin-deficient diets.

SOURCE: Ophthalmology, online April 13, 2012.