Beta-carotene supplements not proven beneficial

Q. Does drinking carrot juice help with cataracts?

A cataract is a clouding of the lens, the clear part of the eye that helps focus images like the lens in a camera. Cataracts can blur images and discolor them. Most cataracts are related to aging. More than half of Americans over age 65 have a cataract.

I suspect this reader's question was inspired by the common belief that carrots are good for your eyes. And yes, carrots are good for your eyes.

Carrots contain beta-carotene, an orange pigment that is also found in spinach, sweet potatoes, green leaf lettuce, winter squash, cantaloupe, and broccoli. The body converts beta-carotene into vitamin A, which is necessary for normal vision. A lack of vitamin A may cause problems seeing in the dark.

The results of studies of beta-carotene supplementation for cataract prevention are not clear. More study is needed before a conclusion can be drawn.

(Warning: Don't take any over-the-counter supplements such as beta-carotene without consulting your physician.)

Harvard University researchers examined whether taking beta-carotene supplements protects against age-related cataracts. There were 22,071 volunteers in a large, ongoing health study. After 12 years, about 2,000 cataracts and almost 1,200 cataract surgeries were reported. In most cases, beta-carotene did not appear to lower the risk of getting cataracts.

Beta-carotene is an antioxidant. Antioxidants are substances that may protect your cells against damage. Antioxidants are found in many foods including fruits and vegetables, nuts, grains, and some meats, poultry and fish.

Beta-carotene has been studied to determine its effect upon a variety of disorders, not just cataracts.

Here are some of the results:

Alzheimer's disease: Intake of dietary or supplemental beta-carotene has been shown not to have any effect on Alzheimer's disease risk.

Angioplasty: There is some concern that when antioxidants, including beta-carotene, are used together they might have harmful effects in patients after angioplasty. Additional research is needed to determine the effect of beta-carotene specifically.

Cancer: Diets high in beta-carotene have been shown to potentially reduce the incidence of certain cancers. Beta-carotene supplements may have an adverse effect on the incidence of lung cancer.

Cardiovascular disease: The American Heart Association states that the evidence does not justify the use of antioxidants such as beta-carotene for reducing the risk of cardiovascular disease.

Chronic obstructive pulmonary disease (COPD): Beta-carotene supplements have not been proven to benefit COPD and may increase cancer rates in smokers.

Cognitive performance: Long term, but not short term, beta-carotene supplementation appears to benefit cognition.

Osteoarthritis: Beta-carotene supplementation does not appear to prevent osteoarthritis, but it might slow progression of the disease. More study is needed.

Stroke: Taking synthetic beta-carotene orally has been reported to have no effect on the overall incidence of stroke in male smokers. There is some evidence that beta-carotene increases the risk of intracerebral hemorrhage by 62 percent in patients who also drink alcohol.

Sunscreen: A combination of antioxidants may help protect the skin against irradiation. Long-term supplementation with beta-carotene appears to modestly reduce the risk of sunburn in individuals who are sensitive to sun exposure. However, beta-carotene is unlikely to have much effect on sunburn risk in most people.

Ulcers: Infection with Helicobacter pylori bacteria in the gut can lead to gastric ulcers. Dietary supplementation with beta-carotene has not been found to be effective for treating this condition.

The American Heart Association recommends obtaining antioxidants, including beta-carotene, from a diet high in fruits, vegetables, and whole grains rather than through supplements, until more information is available from randomized clinical trials. Similar statements have been released by the American Cancer Society and other cancer organizations.