In the online edition of Molecular Nutrition and Food Research, Ruth Chan and collaborators provided a review on prostate cancer (CaP) and vegetable consumption.
There is data that suggests a diet high in vegetable intake can reduce the risk of CaP. The primary mechanism of this protective vegetable effect is antioxidant protection against DNA and cell damage.
Available literature was identified for this review. Of the available studies, 29 were cohort studies, 69 case-control studies, and 4 randomized clinical trials. Highlights of this extensive review are presented herein. Tomatoes and their byproducts contain the carotenoid antioxidant lycopene. Two cohort studies reported tomatoes decreased CaP risk and 3 cohort studies reported a non-significant association. For case-control studies, 2 showed significant decreased risk and 5 showed a non-significant association. One study suggested that the potential benefit was greater in advanced as compared to localized CaP. Overall, studies for tomatoes and lycopenes show inconsistent results on decreasing CaP risk, but lycopene based foods are probably protective.
Yellow orange vegetables contain the antioxidant beta-carotene. Data on beta-carotene and CaP risk from cohort and case-control studies were inconclusive for a protective effect. Supplemental use of beta-carotene was not shown to be protective. Flavonoids are a carbon structure compound ubiquitously present in plant foods and have anti-oxidative and anti-inflammatory properties. They may suppress angiogenesis, induction of apoptosis and down-regulation of hormone receptors expression. Overall there is some evidence suggesting that consumption of legumes, including soy and soy products, is protective against CaP.
Regarding vitamins, vitamin C has had limited study, but with the data available there is no evidence of a protective effect. Vitamin E is a naturally occurring fat-soluble vitamin found predominantly in plant foods and some animal foods. In a supplementation trial, there was suggestion that vitamin E was of benefit, but all the participants were smokers. Two other publications failed to show a benefit, and a preliminary report from the selenium and vitamin E trial does not suggest a benefit. As for allium vegetables which include garlic, onions, leeks, chives, scallions and shallots, while in vitro data suggest a protective benefit, population based studies are limited and a protective effect remains to be determined. Finally, cruciferous vegetables include broccoli, cauliflower Brussels sprouts, cabbage, bok choy, collard greens and kale. These are rich in sulforaphane and indole-3 carbinol, which have anticarcinogenic properties. To date, population-based studies are limited and a positive protective benefit remains to be determined.