Many epidemiologic studies have investigated the association between carotenoids intake and risk of Prostate cancer (PCa). However, results have been inconclusive.
We conducted a systematic review and dose-response meta-analysis of dietary intake or blood concentrations of carotenoids in relation to PCa risk. We summarized the data from 34 eligible studies (10 cohort, 11 nested case-control and 13 case-control studies) and estimated summary Risk Ratios (RRs) and 95% confidence intervals (CIs) using random-effects models.
Neither dietary β-carotene intake nor its blood levels was associated with reduced PCa risk. Dietary α-carotene intake and lycopene consumption (both dietary intake and its blood levels) were all associated with reduced risk of PCa (RR for dietary α-carotene intake: 0.87, 95%CI: 0.76–0.99; RR for dietary lycopene intake: 0.86, 95%CI: 0.75–0.98; RR for blood lycopene levels: 0.81, 95%CI: 0.69–0.96). However, neither blood α-carotene levels nor blood lycopene levels could reduce the risk of advanced PCa. Dose-response analysis indicated that risk of PCa was reduced by 2% per 0.2mg/day (95%CI: 0.96–0.99) increment of dietary α-carotene intake or 3% per 1mg/day (95%CI: 0.94–0.99) increment of dietary lycopene intake.
α-carotene and lycopene, but not β-carotene, were inversely associated with the risk of PCa. However, both α-carotene and lycopene could not lower the risk of advanced PCa.
PCa is the second most abundant male cancer . Owing to the improved screening and early detection procedures, rising incidence rates of PCa have been observed over the last few decades . However, the success in treating advanced PCa remains poor, drawing attention to dietary factors that may influence risk of this malignancy, particularly carotenoids . Lots of epidemiological factors, including age, gender, ethnicity, genetic factors, family history, lifestyle, region and diet, have been considered to be associated with the development of PCa . For example, Asian populations are generally at lower PCa risk compared with the Western populations . Moreover, the average annual incidence rate of PCa between 1988 and 1992 among Chinese men in the United States was 15 times higher than that of their counterparts living in Shanghai and Tianjin , specially, the change of diet and lifestyle inevitably resulted in the increased prevalence of obesity in East Asia , which might be responsible for increasing trend of PCa in East Asia—all of which suggest that variations in lifestyle and diet may play a crucial role in PCa. Among a large number of components of foods, carotenoids, especially its main active ingredients—carotene and lycopene, have received special attention due to its promising antioxidative properties [8–10].
Carotenoids, which include α-carotene, β-carotene, lycopene, β-cryptoxanthin, lutein, and zeaxanthin that represent the major carotenoids in the human diet , provide the yellow, orange and red pigments in fruits and vegetables . Carotenoids have distinct antioxidative properties, including protecting DNA and other important biomolecules from free radicals . In 1981, Peto et al. hypothesized that dietary β-carotene from fruit and vegetables may reduce human cancer incidence rates , since then a flurry of epidemiologic studies had addressed this topic [14–17]. Carotenes(including α-carotene and β-carotene) have been investigated for many years now, but whether carotenes are related to the PCa are still mostly inconsistent. Lycopene is one of the most effective oxygen radical quenching agents among the carotenoids , which is found in relatively high concentrations in the prostate gland . The results of epidemiological studies have generally supported a protective effect on cancer of carotenoid-rich foods. According to the latest Continuous Update Project(CUP) report summarized by the World Cancer Research Fund(WCRF) in November 2014, there is limited evidence for the effect of lycopene on PCa risk . In contrast, substantial intake of β-carotene is unlikely to have any effect on the PCa risk. These inconsistencies could be mainly due to confounding by nutritional as well as non-nutritional factors and lack of validity of carotenoids estimates due to inaccurate dietary or blood concentration assessment.
Based on these inconsistencies, we conducted this meta-analysis on all published epidemiologic studies to date to reevaluate and quantify the relation between dietary intake or blood concentrations of α-carotene, β-carotene, lycopene and risk of PCa.