updated 3/19/2007 11:29:58 AM ET 2007-03-19T15:29:58

Carrots, rich in beta carotene, long have been thought to sharpen eyesight, but a new study suggests that beta carotene pills are powerless against a common type of vision loss among older people.

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Age-related macular degeneration is the leading cause of blindness in people 65 and older. The condition blurs the center of the field of vision, making it difficult to read, drive, thread a needle and even recognize faces. It affects more than 10 million Americans and there is no cure.

An earlier large study had shown that beta carotene — when taken with certain vitamins and zinc — could slow or prevent vision loss in people with age-related macular degeneration. Commercial formulations of the eye-protecting combination vitamins are sold over the counter.

But the new study found no benefit for beta carotene supplements alone against the disease.

Comforting news for smokers
That may be a comfort for smokers with signs of macular degeneration. Smoking is a risk factor for the condition, but beta carotene has been shown in other research to raise the risk of lung cancer in smokers. So eye doctors have advised smokers concerned about macular degeneration to find a vitamin regimen without beta carotene.

“This study at least suggests that beta carotene might not be an important component of that (vitamin) formulation,” said Dr. Stuart Fine of the University of Pennsylvania’s Scheie Eye Institute, who was not involved in the new study.

The finding is based on data from more than 21,000 male doctors who were followed for an average of 12 years. The doctors were randomly assigned to take either 50 milligrams of beta carotene every other day or a dummy pill. The doctors didn’t know whether the pills they took contained beta carotene.

Roughly the same number of doctors in both groups developed the eye condition, suggesting beta carotene didn’t help or hurt. After 12 years, there were 162 cases of macular disease in the beta carotene group and 170 cases in the group taking the dummy pills. The difference in the numbers was not statistically significant, meaning it could have occurred by chance.

Study co-author Dr. William Christen at Harvard-affiliated Brigham and Women’s Hospital in Boston said it’s possible that beta carotene might be helpful only in combination with the other vitamins and zinc, but he said that’s unlikely.

Effects on women unknown
Christen said it’s unclear whether the latest findings would apply to women since the experiment only involved men; he said he’d like to see a similar study among women. The research, appearing in the March issue of the Archives of Ophthalmology, also says nothing about carrots and eyesight.

“Currently the best advice might be something you’ve heard before: Eat five or more servings of fruits and vegetables a day because it’s the combination of nutrients that seems to be the important factor,” Christen said.

The study was funded by grants from the National Institutes of Health. Some of the researchers reported receiving past funding from pharmaceutical and nutritional supplement makers.

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