When it comes to foods that lower cancer risk, color may count.
Researchers report in the Journal of the National Cancer Institute that women loading up carotenoids, the micronutrients found in red, yellow and deeply colored fruits and vegetables such as carrots, sweet potatoes spinach and kale, showed lower rates of breast cancer than those who didn’t eat as many of these foods.
Previous studies looking at the link between carotenoid levels and breast cancer had varying results, with some reporting high levels associated with a reduced cancer risk and others finding no such link. Dr. Heather Eliassen, assistant professor of medicine at Harvard Medical School and her colleagues analyzed the data from eight cohort studies that cover over 80% of currently published research on carotenoids in the blood and breast cancer rates.
The researchers took the data, which covered over 3,000 participants and nearly 4,000 controls, and standardized the carotenoid levels measured in the blood by re-analyzing the participants’ blood samples at the Harvard School of Public Health.
Women with carotenoid levels in the the top 20% of measured ranges had a 15-20% reduced risk of breast cancer compared to those with carotenoid levels in the lowest category. “It looks like it is a linear relationship,” says Eliassen. “The higher you go, the [lower] your risk is. There is some benefit at a moderate level of carotenoids and there is even more benefit at a higher level.”
There is also encouraging news for women with a type of breast cancer that is notoriously difficult to treat—those that are missing receptors for estrogen, so-called estrogen-receptor negative (ER-) cancer. The lower risk was especially strong among women with these types of tumors, suggesting carotenoids are an adjustable risk factor for these cases. “I think this is an interesting finding given that the common risk factors we know about are a lot more profoundly associated with the ER + tumors, like having children, breast feeding, the age you go through menopause and weight gain and older women. We don’t know a lot about what factors contribute to ER- breast cancers and what could be effective,” says Eliassen.
Exactly why carotenoids have a anti-carcinogenic effect isn’t clear, and the authors acknowledge there could be other agents and hormones at play. However, earlier studies suggested that carotenoids may indirectly reduce cancer risk by metabolizing into retinol, which regulates cell growth and gene expression and may curb tumor growth. Another possible explanation holds that carotenoids may improve cell communication and enhance immune system function and the body’s ability to suppress abnormally growing cells.
But to add to the confusion, there is also evidence that carotenoids, in the form of beta-carotene supplements, are linked to an increased risk for lung cancer, which is why Eliassen says she and her team are cautious about interpreting their breast cancer results. “We are not at a point to recommend supplements,” she says. “We know from other studies that certain supplements can increase the risk of lung cancer among smokers. We are not going to go in that direction clearly, but increasing fruit and vegetable intake clearly can provide lots of health benefits and may also reduce the risk of breast cancer.”
Dr. Stephanie Bernik, chief of surgical oncology at Lenox Hill Hospital in New York says more research is needed, but it paves the way for some new preventative recommendations. “This is more evidence leading us in the direction of how to attack cancer from multiple angles,” says Bernik. “We know what to do when someone has cancer, but this could be a way of preventing it from even developing. We want to cure cancer, but ideally you could prevent it all together.” And if that’s as simple as filling your plate with more colorful fare, it might be worth a try.