Serum Lycopene Levels and Prostate Cancer Mortality: An 18-Year Follow-Up Study of a National Cohort

Lycopene is a carotenoid abundant in fruits and vegetables such as tomatoes, guava, etc. Several in vitro and animals studies have indicated that lycopene may have chemo-preventive effects for various cancers including prostate, skin, breast, lung and liver. However, reports on human trials linking lycopene and these chemo-preventive effects are inconsistent in their findings. The objective of this study was to determine whether serum lycopene levels influence prostate cancer mortality. A retrospective cohort study was conducted with 14,358 adults who participated in phase II of the National Health and Nutrition Examination Survey III (1991–1994) (NHANES III). This served as baseline and was cor-related with the National Death Index database for a 15-yr (1991–2006) follow-up study. The primary outcome measure was mortality; and serum lycopene levels were categorized as low, medium and high. Other variables such as family income, educational attainment, marital status, race and ethnicity, alcohol consumption, cigarette smoking, self-reported health, cancer status at baseline, vegetable consumption, and fruit/juice consumption were also considered. Estimates of the crude and adjusted hazard ratios (HRs) of dying from prostate cancer and all cancers for individuals with different levels of serum lycopene were derived from Cox Proportional Hazard Regression models using the SAS software. Proportionality assumption of the models were checked by visual inspection of plots of log [-log(S)] against time. Results indicate that mortality from all cancers increased among individuals with low versus high serum lycopene levels [Hazard ratio = 1.39 (1.19-1.63) for unadjusted rates] and [1.27 (1.08-1.49) for adjusted rates]. For prostate cancer mortality, however, no significant differences were detected between low versus high serum lycopene levels [Hazard ratio = 1.01 (0.57-1.79) for unadjusted rates] and [0.96 (0.53-1.73) for adjusted rates]. While lycopene reduces the risk of developing prostate cancer, this study suggests that serum lycopene does not prevent prostate cancer mortality. A major limitation of the study is that serum lycopene levels were measured only once during the study duration.