Adequate blood carotenoid levels may reduce breast cancer risk

Blood concentrations of beta-carotene, lutein and total carotenoids seem to be associated with reductions in breast cancer risk, suggests a new UK review.

The meta-analysis included 24 prospective studies and aimed to investigate a potential association between dietary intake and blood concentrations of carotenoids and breast cancer risk (1). The analysis found no association between dietary intake of carotenoids and breast cancer risk, except for a weak reduction in risk with dietary beta-carotene. However, blood concentrations of total carotenoids, beta-carotene, alpha-carotene, and lutein were more strongly associated with reductions in breast cancer risk.

The researchers commented that errors resulting from the food-frequency questionnaire measuring dietary intake of fruit and vegetables may have weakened associations with breast cancer risk and might explain the weak associations observed in epidemiological studies. It could not be excluded that the association found for blood concentrations may have been biased, as people with higher exposure to carotenoids may be more physically active, less overweight and also have a lower alcohol and dietary fat intake. However, most of the studies included in this meta-analysis adjusted for these and other potential confounders. The scientists concluded that the use of certain biomarkers may help to clarify the inconsistent and weak results of studies examining associations between dietary intake and breast cancer risk.

It has been hypothesized that intake of fruit and vegetables may reduce the risk of breast cancer. However, prospective studies examining dietary intake of fruit and vegetables and breast cancer risk have been inconsistent and have generally found weak and non-significant associations. It is not clear whether these associations reflect true weak associations or rather weakened risk estimates because of measurement errors in the assessment of dietary intake. Several (2,3), but not all (4,5), studies reported a stronger association between increased plasma or serum concentrations of carotenoids and decreased breast cancer risk, although they were not always statistically significant (6).

Several mechanisms might explain the protective effect of carotenoids against breast cancer. Carotenoids may act as antioxidants by scavenging free radicals and protecting against DNA damage. Multiple antioxi-dants may act synergistically to reduce breast cancer risk. Beta-carotene may reduce cell proliferation and induce apoptosis (7,8) and may interfere with estrogen signaling in breast cancer cells (9).

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8. Cui Y. et al. beta-Carotene induces apoptosis and up-regulates peroxisome proliferator-activated receptor gamma expression and reactive oxygen species production in MCF-7 cancer cells. Eur J Cancer. 2007; 43:2590–2601.
   
   
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