Carotenoids and cervical, breast, ovarian, and colorectal cancer. Epidemiology and clinical trials
Recent observational studies and clinical trials that have investigated the relationship between carotenoids (or diets rich in these compounds) and cervical, breast, ovarian, and colorectal cancer have increased knowledge in this area. Although epidemiological studies suggest a protective association, five randomized controlled trials testing the effect of beta-carotene supplementation on regression of cervical dysplasia, a preneoplastic lesion, did not find an effect on rate of regression. In the Women's Healthy Eating and Living (WHEL) Study, the effects of a high-vegetable carotenoid-rich diet on disease-free survival following treatment for breast cancer is being examined in a randomized multicenter diet intervention trial. Few epidemiological studies of dietary factors and risk for ovarian cancer have been conducted, with mixed results. Early case-control and cohort studies of colorectal cancer have generally suggested a protective effect of vegetable consumption, although a recent large cohort study did not confirm this relationship. In two randomized trials, beta-carotene supplementation was not observed to reduce risk of adenoma recurrence. The Polyp Prevention Trial (PPT), which tested the effect of prescribing increased fruit, vegetable, and fiber intake, and reduced dietary fat, revealed no effect of these efforts on adenoma recurrence in the intent to treat analysis. However, serum carotenoid concentrations were associated with decreased risk of recurrence in that study. To move this area of study forward, more research on mechanisms, surrogate biomarkers, and dietgene interactions is needed.