Researchers who zeroed in on specific carotenoids—natural pigments that give some fruits and vegetables their yellow, orange, and red hues—found that lycopene had a more pronounced effect than several others they studied in reducing women’s risk of developing breast cancer.
The findings, reported in the Journal of the National Cancer Institute, are particularly promising for women with difficult-to-treat estrogen receptor (ER)–negative tumors. Carotenoids’ risk-reduction capabilities were greater for ER-negative cancers than for the more common ER-positive tumors that have more treatment options.
The investigators said risk reduction among ER-negative tumors highlights carotenoids as “one of the first modifiable risk factors for this poor prognosis tumor type.”
Nearly 2 dozen researchers in the United States, China, and Sweden collaborated on the analysis, which included data from 8 prospective studies aimed at examining the links between the amount of carotenoids circulating in women’s blood and their breast cancer risk.
The data collection included 3055 women with breast cancer and 3956 matched controls, representing more than 80% of the world’s published prospective studies on circulating blood levels of carotenoids and breast cancer risk. The researchers adjusted carotenoid values in participants’ plasma and serum samples to account for variations among laboratory analyses and populations in the original studies.
Women in the study were divided into 4 groups based on their carotenoid levels. Breast cancer risk was 19% lower in women with the highest levels of total carotenoids compared with women having the lowest levels.
Women with the highest levels of lycopene had a 22% decreased breast cancer risk; those having the highest beta-carotene levels had a 17% decreased risk; women with the highest levels of lutein and zeaxanthin (levels were read together) had a 16% reduced risk; and those with the highest levels of alpha-carotene had a 13% reduced risk compared with women having the lowest levels. All differences in risk were statistically significant. The only carotenoid that didn’t reduce risk significantly was beta-cryptoxanthin.
Previous studies have linked at least 1 of the 20 carotenoids that are measureable in the body with reduced breast cancer risk, the researchers said. But not all the studies have shown similar results for specific carotenoids.
The researchers said carotenoids may have several avenues available to reduce breast cancer risk. They are metabolized to retinol, which in turn regulates cell growth and differentiation and programmed cell death. Carotenoids also may enhance immune system functioning or help mop up oxygen-reactive species that cause cell damage.
Carotenoids are plentiful in carrots (alpha-carotene), sweet potatoes and leafy greens (beta-carotene), tomatoes (lycopene), and citrus fruits (beta-cryptoxanthin).