Purpose: Zinc is a common dietary supplement that is widely believed to have beneficial health effects. To assess the impact of high dose supplemental zinc on genitourinary diseases we analyzed a recent randomized trial comparing zinc, antioxidants and their combination to placebo for complications related to the genitourinary tract.
Materials and methods: In a further analysis of the recent Age-related Eye Disease Study we examined the data pool for primary International Classification of Diseases, 9th revision codes given for hospital admissions related to urological problems. The Age-Related Eye Disease Study randomized 3,640 patients with age related macular degeneration to 1 of 4 study arms, including placebo, antioxidants (500 mg vitamin C, 400 IU vitamin E and 15 mg beta-carotene), 80 mg zinc and antioxidant plus zinc. Statistical analyses using Fisher's exact test were performed.
Results: We found a significant increase in hospital admissions due to genitourinary causes in patients on zinc vs nonzinc formulations (11.1% vs 7.6%, p = 0.0003). The risk was greatest in male patients (RR 1.26, 95% CI 1.07-1.50, p = 0.008). In the study group of 343 patients requiring hospital admission the most common primary International Classification of Diseases, 9th revision codes included benign prostatic hyperplasia/urinary retention (benign prostatic hyperplasia), urinary tract infection, urinary lithiasis and renal failure. When comparing zinc to placebo, significant increases in urinary tract infections were found (p = 0.004), especially in females (2.3% vs 0.4%, RR 5.77, 95% CI 1.30-25.66, p = 0.013). Admissions for urinary lithiasis approached significance in men on zinc compared to placebo (2.0% vs 0.5%, RR = 4.08, 95% CI 0.87-19.10). There was no increase in prostate or other cancers with zinc supplementation. A significant decrease in prostate cancer diagnoses was seen in patients receiving antioxidants vs placebo (RR = 0.6, 95% CI 0.49-0.86, p = 0.049). Subgroup analysis revealed that this finding was significant in men who smoked but not in nonsmokers.
Conclusions: Zinc supplementation at high levels results in increased hospitalizations for urinary complications compared to placebo. These data support the hypothesis that high dose zinc supplementation has a negative effect on select aspects of urinary physiology.