Dr. Ed Blonz

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Incompatibility problems between calcium and vitamin C; Can supplements prevent blindness?

http://www.NewsAndOpinion.com -- DEAR DR. BLONZ: I am interested in learning about macular degeneration. In particular, I am looking for foods that contain lutein and zeaxanthin. I've heard that these nutrients might be able to slow the progression of the disease. What is your view on supplements as a preventive measure for macular degeneration? My father and both of his siblings suffer from the condition, but they weren't afflicted until they were 75 or older. -- D.L., Charlotte, N.C.

DEAR D.L.: The macula is the part of the eye where images are focused. At the center of the macula is the "fovea centralis," the focal point where our vision is at its best. It is in the macula where the electrical impulses that correspond to what we are looking at are initiated, and it is only after these signals make their way to the brain via the optic nerve that we are able to understand exactly what it is we have seen.

One of the unfortunate conditions associated with aging is a breakdown of these tissues, and macular degeneration is the leading cause of blindness in older Americans. The precise cause of macular degeneration is not yet known, but it is thought that the retina (and the lens) suffers oxidative damage. Some have suggested that dietary antioxidants, including zinc, vitamin C, vitamin E, vitamin A and selenium might be protective. The carotenoids, particularly the antioxidant compounds lutein (LOO-teen) and zeaxanthin (zee-uh-ZAN-thin), are known to be concentrated in the macula. In fact, they are the only carotenoids known to exist in the macular region of the retina, and they are referred to as macular pigments.

Spinach and corn are good sources of lutein and zeaxanthin. A study in the journal Investigative Ophthalmology and Visual Science (August 1997) reported how increased intakes of these foods elevated blood levels of the key macular pigment compounds. A study in the same journal in October 2000 reported increased levels of macular pigment after 12 weeks of supplemental lutein (10 milligrams of lutein per day). In the June 2000 issue of the American Journal of Clinical Nutrition, a study reported how servings of corn and spinach raised blood levels.

Given the evidence, it makes sense to pay special attention to lutein- and zeaxanthin-rich foods, and to antioxidant nutrients in general. Ingesting these nutrients is a win-win situation, because they can help reduce the risk of other chronic diseases.

Vegetables are the richest sources of lutein and zeaxanthin. The vegetables that contain the highest concentrations are kale, collard greens, spinach, cress leaf, Swiss chard, chicory leaf, mustard greens, beets greens, red peppers, okra, endive, celery, romaine lettuce, leeks, broccoli, leaf lettuce, green peas, pumpkin, iceberg lettuce, Brussels sprouts, yellow corn, yellow pepper and green beans. Fruits contain lesser amounts, but the best of the lot include avocados, plums, kiwis, pears and grapes.

As for the supplement question, it is a reasonable option, but it does not eliminate the need for healthful foods. If you use supplements, lutein is better absorbed when taken with meals that contain fat.

Be aware that there are many multipurpose supplements claiming that they contain lutein (or zeaxanthin), but there may be little present. Check the label, and compare with the 10 milligrams per day used in the study cited above.

DEAR DR. BLONZ: Periodically, I read articles stating that combining calcium and vitamin C at a meal is not advantageous, as one counteracts the other. This notion creates a problem for me at breakfast. I like to drink orange juice with a serving of yogurt or cottage cheese. If these nutrients are incompatible, why do some orange juices contain added calcium? -- D.W., San Diego, Calif.

Dear D.W.: There are no incompatibility problems between calcium and vitamin C. If anything, the vitamin C can help keep calcium in solution and facilitate absorption.

JWR contributor Ed Blonz, Ph.D., is a nutrition scientist and author of Power Nutrition and the "Your Personal Nutritionist" book series. Send questions to him by clicking here.