Zinc Intake and Risk of Prostate Cancer: Case-Control Study and Meta-Analysis

Abstract

Zinc is an essential dietary element that has been implicated in the pathogenesis of prostate cancer, a cancer that disproportionately affects men of African descent. Studies assessing the association of zinc intake and prostate cancer have yielded inconsistent results. Furthermore, very little is known about the relationship between zinc intake and prostate cancer among African Americans. We examined the association between self-reported zinc intake and prostate cancer in a hospital-based case-control study of African Americans. We then compared our results with previous studies by performing a meta-analysis to summarize the evidence regarding the association between zinc and prostate cancer. Newly diagnosed African American men with histologically confirmed prostate cancer (n = 127) and controls (n = 81) were recruited from an urban academic urology clinic in Washington, DC. Controls had higher zinc intake, with a mean of 14 mg/day versus 11 mg/day for cases. We observed a non-significant, non-linear increase in prostate cancer when comparing tertiles of zinc intake (OR <6.5 vs 6.5-12.5mg/day 1.8, 95% CI: 0.6,5.6; OR <6.5 vs >12.5mg/day 1.3, 95% CI: 0.2,6.5). The pooled estimate from 17 studies (including 3 cohorts, 2 nested case-control, 11 case-control studies, and 1 randomized clinical trial, with a total of 111,199 participants and 11,689 cases of prostate cancer) was 1.07hi vs lo 95% CI: 0.98-1.16. Using a dose-response meta-analysis, we observed a non-linear trend in the relationship between zinc intake and prostate cancer (p for nonlinearity = 0.0022). This is the first study to examine the relationship between zinc intake in black men and risk of prostate cancer and systematically evaluate available epidemiologic evidence about the magnitude of the relationship between zinc intake and prostate cancer. Despite of the lower intake of zinc by prostate cancer patients, our meta-analysis indicated that there is no evidence for an association between zinc intake and prostate cancer.

Fig 1. Flow diagram of systematic literature search on zinc and the risk of prostate cancer.

Fig 2. Forest plot of included studies for the highest versus lowest meta-analysis, stratified by zinc intake (dietary, supplement, and total) or zinc status (serum, nail, and hair).

Fig 3. Funnel plot of studies examining the association between zinc and prostate cancer incidence as a test for publication bias.

Fig 4. Sensitivity analysis investigating the influence of each individual study on the overall meta-analysis of zinc and risk of prostate cancer.

The meta-analysis of all studies except the “omitted” study named on the left margin is presented as a horizontal confidence interval. The full, “combined” results are shown as the solid vertical lines.

Fig 5. Dose-response relations between zinc intake and RR of prostate cancer (P for nonlinearity = 0.0022).

The fitted nonlinear trend is represented by the solid line with the 95% confidence intervals line in long dashes. Lines with short dashes represent the linear trend.