Numerous studies have reported that carotenoid consumption is linked to reduced risk of breast cancer, although some studies have reported no association. Carotenoids consist of a group of yellow, orange and red plant pigments found in a variety of vegetables and fruits. Included are alpha-carotene, beta-carotene, lycopene, beta-cryptoxanthin, lutein, and zeaxanthin, as well as some less well known carotenoids such as crocetin (found in saffron) and fucoxanthin (seaweed). Beta-cryptoxanthin, a red pigment, is closely related to beta-carotene. Multiple carotenoids are typically found together in the same plant. Now a new prospective study has reported that while circulating beta-cryptoxanthin is associated with reduced risk of breast cancer, lycopene is associated with increased risk.
Lycopene and breast cancer
Lycopene is a red pigmented carotenoid present in fruits and vegetables such as grapefruit, watermelon and tomatoes. Lycopene is an angiogenesis inhibitor, reducing the growth of new blood vessels (without which tumors cannot grow beyond a tiny size). Lycopene has been shown to inhibit proliferation in hormone receptor positive (ER+/PR+) breast cancer cells. Lycopene has also been shown to induce apoptosis (programmed cell death) in triple negative (ER-/PR-/HER2-) breast cancer cells resistant to chemotherapy.
Population studies have reported conflicting findings regarding lycopene and breast cancer risk. There is some evidence that lycopene might reduce breast cancer risk for women with high breast density. However, several studies have reported that high lycopene levels are associated with increased risk. This finding appear to be unexpected in some cases, since the authors express surprise or doubt about the results. Nevertheless, these scattered findings raise the possibility that supplementation with lycopene could be detrimental for breast cancer survivors.
Sources of lycopene
Tomatoes constitute the major U.S. dietary source of lycopene. However, it is also found in a variety of other red or orange fruits and vegetables. Below are good sources of lycopene that have also been associated with reduced risk of breast cancer:
Latest research finds opposite results for β-cryptoxanthin and lycopene
The prospective nested case-control study referenced at the beginning of this news story was designed to examine the associations between circulating levels of vitamin A and major carotenoids and risk of breast cancer. The study included 159 breast cancer cases newly diagnosed in the SU.VI.MAX cohort between 1994 and 2002, as well a 159 matched cancer-free controls. The SU.VI.MAX study was a randomized, double-blind, placebo-controlled trial in which participants received a combination of low-dose antioxidants or a placebo from 1994 to 2002. Baseline dietary data were assessed by repeated dietary records in 1994-1995. Plasma concentrations of carotenoids and retinol were measured at baseline.
Plasma beta-cryptoxanthin concentrations were found to be associated with modestly reduced breast cancer risk. However, plasma lycopene concentrations were found to be associated with modestly increased breast cancer risk, an association that was statistically significant when cancer cases diagnosed during the first year of the study were excluded. The authors conclude that there might be an inverse association between circulating beta-cryptoxanthin and breast cancer risk. The association between lycopene and cancer risk deserves further investigation, according to the authors.