Carotenoids are oil-soluble plant pigments that the body can convert to vitamin A. They are responsible for the bright colors of produce. The best known carotenoid is beta-carotene. Beta carotene also has the most vitamin A activity of all of the carotenoids. Other carotenoids include alpha carotene, lycopene, lutein, astaxanthin, beta crpytoxanthin, and zeaxanthin.
A study appearing in Cancer Research (2009; 69(24): 9323-9) compared 602 breast cancer patients to 626 controls. It found that 
the amount of carotenoids circulating in the blood was inversely related to the risk for breast cancer. Women with high mammographic density enjoyed as much as a 50% reduction in breast cancer risk when they had high levels of carotenoids. The relationship did not exist in women with low mammographic density.
