The finding comes from a secondary analysis of a trial involving 3,640 adults between age 55 and 80 years of age with the retinal disease, macular degeneration. As treatment for their eye condition, the subjects were assigned to various treatments: daily antioxidant therapy with vitamin C, vitamin E and beta-carotene; zinc, 80 milligrams daily; antioxidants and zinc in combination; or inactive 'placebo' supplements.

In the Journal of Urology, Dr. Aaron R. Johnson and colleagues from the University of Wisconsin, Madison, report that there was a "significant increase in hospital admissions due to genitourinary causes in patients on zinc vs. non-zinc formulations (11.1 percent vs. 7.6 percent)" during the 6 years of the study.

These increased admissions were largely due to an increased number of urinary tract infections and urinary stones.

Zinc had no effect on the likelihood of developing a cancer of the urinary system. In fact, "a protective effect for high dose zinc was not demonstrated for any aspect of the genitourinary system," Johnson and colleagues say.

These results, they conclude, "suggest that patients receiving high dose zinc supplementation without a clear health indication should use caution until further trials are performed."