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Diet is believed to impact on the development and course of age-related macular degeneration (AMD) mainly by influencing the strength of the body's antioxidant defenses. zinc is found in high concentrations in the retinal pigment epithelium and plays a role in the metabolic function of several important enzymes in the chorioretinal complex. It may be a cofactor for the activity of enzymes providing oxidant defense. Severe zinc deficiencies have been associated with retinal pathology in animal models and in humans.

Treatment Effect of Zinc Supplements:
In a 1988 study, Newsome and coauthors documented the treatment value of zinc supplements in lessening both visual loss and maculopathy (1). In this prospective study, 150 patients with drusen or varying degrees of macular degeneration were randomized to receive zinc sulfate tablets (200 mg) or placebo tablets. Patients were followed 2 years. Visual acuity loss was significantly less (p<0.001) among zinc-treated patients than among placebo patients (mean letters lost was 2.5 vs 6.4 at 1 year). The amount of visual loss was also related to treatment compliance. Furthermore, there was a lessened increase of drusen and macular atrophy among zinc-treated cases over the 2-year period.

Protection of Macular Health:
Mares-Perlman and colleagues conducted an epidemiological study of patients from the Beaver Dam Eye Study to evaluate the effect of zinc and antioxidant nutrients as preventive of AMD (2). This was a retrospective longitudinal cohort study. Patients were examined to determine the AMD status (none, early or late AMD). They were interviewed regarding known risk factors and were given dietary interviews to determine intake of various nutrients of interest through the diet and of dietary supplements during a one-year period 10 years prior to the eye exam. Their methods of analyzing nutrient intake were rigorous, following validated systems used by the National Cancer Institute. Following logistic regression analysis to control for other confounding risk factors, the authors reported that patients with reported dietary intake of zinc in the upper 5th quintile had a 40% lower risk (p<0.05) of having early AMD 10 years later compared with those in the lowest quintile. The group in the highest quintile of zinc intake through food plus supplements had a measured 30% decreased risk which was not statistically significant. Patients in the upper quintile of zinc intake through food plus supplements showed a significant 40% decrease in risk of early AMD lesion in the form of increased retinal pigment. The authors considered the data to be weakly supportive of a protective effect of zinc. The authors point out that the fact that the decrease in risk was not more strongly documented may very likely be due to the retrospective nature of the study: patients were interviewed regarding food and supplement intake 10 years earlier and may not have continued at the same levels over the next 10 years. Furthermore, only 5% of study participants reported taking supplements containing zinc during the period making it difficult to detect a stronger association.

References

1. Newsome DA, Swartz M, Leone NC et al: Oral Zinc In Macular Degeneration. Arch Ophthalmol 1988;106:192-198.
2. Mares-Perlman JA, Klein R, Klein BEK et al: Association of Zinc and Antioxidant Nutrients With Age-Related Maculopathy. Arch Ophthalmol 1996;114:991-997.