Lycopene and Risk of Prostate Cancer: A Systematic Review and Meta-Analysis

Abstract

Prostate cancer (PCa) is a common illness for aging males. Lycopene has been identified as an antioxidant agent with potential anticancer properties. Studies investigating the relation between lycopene and PCa risk have produced inconsistent results. This study aims to determine dietary lycopene consumption/circulating concentration and any potential dose-response associations with the risk of PCa. Eligible studies published in English up to April 10, 2014, were searched and identified from Pubmed, Sciencedirect Online, Wiley online library databases and hand searching. The STATA (version 12.0) was applied to process the dose-response meta-analysis. Random effects models were used to calculate pooled relative risks (RRs) and 95% confidence intervals (CIs) and to incorporate variation between studies. The linear and nonlinear dose-response relations were evaluated with data from categories of lycopene consumption/circulating concentrations. Twenty-six studies were included with 17,517 cases of PCa reported from 563,299 participants. Although inverse association between lycopene consumption and PCa risk was not found in all studies, there was a trend that with higher lycopene intake, there was reduced incidence of PCa (P = 0.078). Removal of one Chinese study in sensitivity analysis, or recalculation using data from only high-quality studies for subgroup analysis, indicated that higher lycopene consumption significantly lowered PCa risk. Furthermore, our dose-response meta-analysis demonstrated that higher lycopene consumption was linearly associated with a reduced risk of PCa with a threshold between 9 and 21 mg/day. Consistently, higher circulating lycopene levels significantly reduced the risk of PCa. Interestingly, the concentration of circulating lycopene between 2.17 and 85 μg/dL was linearly inversed with PCa risk whereas there was no linear association >85 μg/dL. In addition, greater efficacy for the circulating lycopene concentration on preventing PCa was found for studies with high quality, follow-up >10 years and where results were adjusted by the age or the body mass index. In conclusion, our novel data demonstrates that higher lycopene consumption/circulating concentration is associated with a lower risk of PCa. However, further studies are required to determine the mechanism by which lycopene reduces the risk of PCa and if there are other factors in tomato products that might potentially decrease PCa risk and progression.

FIGURE 1

Flowchart of literature searches.

FIGURE 2

Forest plot for the association of highest vs. lowest categories of dietary lycopene consumption and the risk of prostate cancer (PCa). The association was indicated as relative risk (RR) estimate with the corresponding 95% confidence interval (CI). The RR estimate of each study is marked with a solid black square. The size of the square represents the weight that the corresponding study exerts in the meta-analysis. The CIs of pooled estimates are displayed as a horizontal line through the diamond. RR <1 indicates decreased risk of PCa.

FIGURE 3

Forest plot for dose–response association of highest vs. lowest categories of dietary lycopene consumption and the risk of prostate cancer (PCa) after sensitivity analysis and removing one Chinese study. The association was indicated as relative risk (RR) with the corresponding 95% confidence interval (CI). The RR estimate of each study is marked with a solid black square. The size of the square represents the weight that the corresponding study exerts in the meta-analysis. The CIs of pooled estimates are displayed as a horizontal line through the diamond. RR <1 indicates decreased risk of PCa.

FIGURE 4

Forest plot for dose–response association of each 5 mg/day increase of lycopene intake with the risk of prostate cancer (PCa). The association was indicated as relative risk (RR) with the corresponding 95% confidence interval (CI). The RR estimate of each study is marked with a solid black square. The size of the square represents the weight that the corresponding study exerts in the meta-analysis. The CIs of pooled estimates are displayed as a horizontal line through the diamond. RR <1 indicates decreased risk of PCa.

FIGURE 5

Forest plot for dose–response association of each 5 mg/day increase of lycopene intake with the risk of prostate cancer (PCa) after sensitivity analysis and removing one Chinese study. The association was indicated as relative risk (RR) with the corresponding 95% confidence interval (CI). The RR estimate of each study is marked with a solid black square. The size of the square represents the weight that the corresponding study exerts in the meta-analysis. The CIs of pooled estimates are displayed as a horizontal line through the diamond. RR <1 indicates decreased risk of PCa.

FIGURE 6

Dose–response analysis of lycopene consumption and risk of prostate cancer. The solid black line and 2 dotted black lines are the restricted cubic spline for the published relative risks (RR) and 95% confidence intervals (CIs); the short dash straight line is the linear fitting curve used for linear and nonlinear analysis.

FIGURE 7

Forest plot for dose–response association of highest vs. lowest categories of circulating lycopene concentrations and the risk of prostate cancer (PCa). The association was indicated as relative risk (RR) with the corresponding 95% confidence interval (CI). The RR estimate of each study is marked with a solid black square. The size of the square represents the weight that the corresponding study exerts in the meta-analysis. The CIs of pooled estimates are displayed as a horizontal line through the diamond. RR <1 indicates decreased risk of PCa.

FIGURE 8

Forest plot for dose–response association of each 10 μg/dL increase of circulating lycopene concentrations with the risk of prostate cancer (PCa). The association was indicated as relative risk (RR) with the corresponding 95% confidence interval (CI). The RR estimate of each study is marked with a solid black square. The size of the square represents the weight that the corresponding study exerts in the meta-analysis. The CIs of pooled estimates are displayed as a horizontal line through the diamond. RR <1 indicates decreased risk of PCa.

FIGURE 9

Dose–response analysis of circulating lycopene concentrations and risk of prostate cancer. The solid black line and 2 dotted black lines are the restricted cubic spline for the published relative risks (RRs) and 95% confidence intervals (CIs); the short dash straight line is the linear fitting curve used for linear and nonlinear analysis.