AMD: diet may make a difference

One of the ailments that can cause failing eyesight in seniors is age-related macular degeneration (AMD). Caused by a breakdown of the eye's light-sensing cells in the macula--a small area of the retina--AMD results in a loss of central vision (the ability to distinguish details) in one or both eyes.

Although researchers are not yet sure what causes this disease, they suspect that the same kind of arterial plaque build-up that contributes to heart disease may also affect the delicate blood vessels in the eye. If that is the case, they reason, than a low-fat diet that helps to guard against heart disease may also help protect against AMD.

Diet's role in eye health

To test this theory, researchers assessed the usual food intake and health habits of almost 90,000 participants--all over the age of 50--who participated in the Nurses' Health Study (NHS) and Health Professional Follow Up Study (HPFS) several times over a 12-year period. The researchers found that participants who consumed a high-fat diet (providing 42% of total calories from fat) were more likely to suffer from AMD than those who consumed a lower-fat diet.

They then looked at the association between intakes of different kinds of fats and fat-containing food products on disease risk. High intakes of linolenic acid, a polyunsaturated fat found in beef, pork, and lamb, and trans fat, a type of fat found in some fried foods and margarine, appeared to increase the risk of AMD.

On the other hand, those who consumed fish, especially tuna fish, several times a week were about 35% less likely than those who rarely ate fish to develop AMD during the course of the study.

Additional considerations

The authors point out that not all of their results support a connection between AMD and cardiovascular disease. For instance, intakes of neither saturated fat nor cholesterol appeared to affect disease risk. Also, the researchers cannot explain why linolenic acid, a polyunsaturated fat, appeared to increase the risk of disease. They speculate that some polyunsaturated fats may contribute to oxidative stress within the macula, an area of the retina already susceptible to oxidative damage due to long-term exposure to sunlight.

The authors do suggest a plausible reason as to why omega-3 fatty acids may help to protect eye health independent of their proposed antithrombotic role in cardiovascular health. Omega-3 fatty acids, especially docosahexaenoic acid (DHA), are abundant in the retina and essential to the development of normal vision. Several studies have suggested an inverse association between omega-3 intake and retinitis pigmentosa, another degenerative eye disease.

As both the NHS and the HPFS are prospective cohort studies, the analyses captured effects other than the individuals' long-term intake of fat. Those who consumed the most fat were also the most likely to smoke, a habit that greatly increases the risk of AMD. They also had the lowest average intakes of lutein and zeaxanthin, carotenoids found in dark green vegetables that may help reduce the risk of AMD.

Prudent advice to patients

More research is needed in this area before scientists can definitively map the connection between diet and lifestyle factors and the development of AMD. Note, though, that the study participants at lowest risk for the disease were consuming what the American Heart Association considers to be a "heart healthy" diet:

• Less than 30% of their total calories came from fat
• They consumed less saturated fat from beef, pork, and lamb
• They consumed omega-3 fatty acid-rich fish at least 2 times per week
• They limited their intake of trans fats, which, like saturated fat, can increase blood cholesterol levels.

Source

Prospective study of dietary fat and the risk of age-related macular degeneration.
E. Cho, S. Hung, WC. Willett ,  et al., American Journal of Clinical Nutrition., 2001, vol. 73, pp. 209--218

Links

• Risk factors for age-related macular degeneration (AMD), including dietary fat and fish
• To quickly access additional accurate information on this and other nutrition-related topics, visit Tufts University's Nutrition Navigator http://www.navigator.tufts.edu