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Antioxidants May Reduce Risk of Age-Related Macular Degeneration

Dec. 28, 2005 - A diet with a high intake of beta carotene, vitamins C and E, and zinc is associated with a substantially reduced risk of age-related macular degeneration in elderly persons, according to a study in today's issue of JAMA.

Age-related macular degeneration (AMD) is a degenerative disorder of the macula, the central part of the retina, and is the most common cause of irreversible blindness in developed countries, according to background information in the article.

Late-stage AMD results in an inability to read, recognize faces, drive, or move freely. The prevalence of late AMD steeply increases with age, affecting 11.5 percent of white persons older than 80 years.

In the absence of effective treatment for AMD, the number of patients severely disabled by late-stage AMD is expected to increase in the next 20 years by more than 50 percent to 3 million in the United States alone. Epidemiological studies evaluating both dietary intake and serum levels of antioxidant vitamins and AMD have provided conflicting results.

One study (called AREDS) showed that supplements containing 5 to 13 times the recommended daily allowance of beta carotene, vitamins C and E, and zinc given to participants with early or single eye late AMD resulted in a 25 percent reduction in the 5-year progression to late AMD.

Redmer van Leeuwen, M.D., Ph.D., of Erasmus Medical Centre, Rotterdam, the Netherlands, and colleagues investigated whether antioxidants, as present in normal daily foods, play a role in the primary prevention of AMD. Dietary intake was assessed at baseline in the Rotterdam Study (1990-1993) using a semiquantitative food frequency questionnaire.

Follow-up continued through 2004. The Rotterdam Study included inhabitants aged 55 years or older from a middle-class suburb of Rotterdam, the Netherlands. Of 5,836 persons at risk of AMD at baseline, 4,765 had reliable dietary data and 4,170 participated in the follow-up.

Average follow-up of participants was 8.0 years. During this period, 560 persons (13.4 percent) were diagnosed as having new AMD, the majority of whom had early-stage AMD. A significant inverse association was observed for intake of vitamin E, iron, and zinc. After adjustment, a 1-standard deviation increase in intake was associated with a reduced risk of AMD of 8 percent for vitamin E and 9 percent for zinc.

An above-median (midpoint) intake of beta carotene, vitamins C and E, and zinc, compared with a below-median intake of at least 1 of these nutrients, was associated with a 35 percent reduced risk of AMD, adjusted for all potential confounders. In persons with a below-median intake of all 4 nutrients, the risk of AMD was increased by 20 percent. Adding nutritional supplement users to the highest quartile of dietary intake did not change the results.

“This study suggests that the risk of AMD can be modified by diet; in particular, by dietary vitamin E and zinc. A higher intake of vitamin E can be achieved by consumption of whole grains, vegetable oil, eggs, and nuts.

"High concentrations of zinc can be found in meat, poultry, fish, whole grains, and dairy products. Carrots, kale, and spinach are the main suppliers of beta carotene, while vitamin C is found in citrus fruits and juices, green peppers, broccoli, and potatoes.

"Based on this study, foods high in these nutrients appear to be more important than nutritional supplements. Until more definitive data are available, this information may be useful to persons with signs of early AMD or to those with a strong family history of AMD.

"Although in need of confirmation, our observational data suggest that a high intake of specific antioxidants from a regular diet may delay the development of AMD,” the authors conclude.

Mayo Clinic on Antioxidants

As you process food for energy, your body produces substances called free radicals. Free radicals are believed to contribute to aging and certain diseases.

To neutralize free radicals, your body uses antioxidants — certain vitamins, minerals and enzymes — that come from the food you eat. Proponents believe that antioxidants can prevent chronic diseases, such as heart disease and diabetes.

Some antioxidants you may have heard of include:

Vitamin A, Vitamin B-6, Vitamin B-12, Vitamin C, Vitamin E, Beta carotene, Folic acid and Selenium

The best way to give your body the antioxidants it needs is to eat a variety of fruits and vegetables. If you can't obtain all the nutrients you need from food, your doctor may recommend using supplements to make up for any deficiencies. Also, if you have certain medical conditions, such as macular degeneration, your doctor may recommend that you supplement your diet with antioxidants.

There's no proof that antioxidants in pill form can improve your general health or extend your life. In fact, they can have the opposite effect.

About Vitamin E - Statement by Brent Bauer, MD, general internal medicine, Mayo Clinic, Rochester, Minn.

"In the past, vitamin E has been touted as an antioxidant, meaning it helps counter the oxidation process that damages cells and can accelerate aging. Vitamin E has been said to prevent or treat numerous health conditions, such as cardiovascular disease, cancer, cataracts, diabetes and even Alzheimer's disease.

"Other than treatment of vitamin E deficiency, no evidence shows conclusively that taking more than the recommended daily allowance of vitamin E offers any medical benefits. Recent research actually has raised concerns that taking high doses of vitamin E supplements can be harmful.

"Researchers looked at 19 studies conducted from 1993 through 2004, involving more than 136,000 people. Nine studies looked at vitamin E alone and 10 looked at vitamin E in combination with other vitamin supplements. All compared vitamin use against a placebo (sugar pill). People who took more than 400 IU of vitamin E a day died at a higher rate than people who didn't take supplements. This was an unexpected finding that has generated a great deal of controversy.

"Vitamin E is found in many foods, such as vegetable oils, nuts and whole grains. Although vitamin E occurs naturally in eight forms, most supplements contain only one form of the vitamin (alpha-tocopherol). Research suggests that the other forms of vitamin E may be the ones that provide the beneficial effects. There is even some research that suggests alpha-tocopherol may decrease the benefit of these other forms.

"Basically, it's not clear which form or forms of vitamin E, or how much of each, may protect you against disease. Until more research is done that provides further information, you should not take more than 400 IU of vitamin E a day."

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