Doctors consider carotenoids, as measured by a blood test, to be an indicator of the amount of fruits and vegetables in a person’s diet. As the amounts of fruits and vegetables in the diet increase, blood carotenoid levels are assumed to rise as well.

A group of researchers led by Paolo Toniolo, MD, director for the New York University-National Institutes of Environmental Health Sciences Center’s epidemiology and biostatistics program, followed 540 women enrolled in the New York University Women’s Health Study. Half of the women had breast cancer and the other half were free of breast cancer. The amount of six different carotenoids (lutein, zeaxanthin, b -cryptoxanthin, lycopene, a -carotene, and b -carotene) were measured in the women’s blood.

The investigators found that the amount of carotenoids in the blood for four of the six carotenoids (lutein, b -cryptoxanthin, a -carotene, b -carotene) predicted breast cancer risk.

Women with relatively low levels of the four influencing carotenoids were 1.6 to 2.2 times more likely to develop breast cancer when compared with women with the highest concentrations. Those with the lowest levels of total carotenoids faced almost a two-and-one-half time greater risk of breast cancer.

Despite the results obtained by Toniolo and his colleagues, the beneficial effects of carotenoids on breast cancer risk remain in question. Other studies have demonstrated no relationship between the two, while some even indicate breast cancer risk increases with higher blood carotenoid levels.

"What this could be indicating is that, as a marker for fruit and vegetable intake, [carotenoids] could be protective, although a lot of the dietary studies have been a little bit conflicting about that," says Carolyn Jonas, PhD, RD, an epidemiologist for the American Cancer Society (ACS). "Carotenoids can reflect healthy lifestyle behaviors in general, and it’s often difficult in studies to sort that out."

In a commentary that follows Toniolo’s article, Thomas E. Rohan, MD, PhD, chairman of the department of epidemiology and social medicine at the Albert Einstein College of Medicine, casts a skeptical eye on the study’s outcome. Toniolo says it is difficult to determine the effect of one group of substances out of a diet containing thousands of chemicals (some of which may be potentially carcinogenic), lifestyle factors other than diet, and the amount of carotenoids that actually enter breast tissue.

Toniolo acknowledges the possible confounding factors in a response to Rohan’s commentary, but holds on to his conclusion in the original article.

"These observations offer evidence that a low intake of carotenoids, through a poor diet and/or lack of vitamin supplementation, may be associated with increased risk of breast cancer and may have public health relevance for people with markedly low intakes," Toniolo writes.

Jonas points out that although evidence supporting the protective nature of carotenoids may not be compelling for women at risk of developing breast cancer, a diet high in fruits and vegetables has many other health benefits.

"The study does still indicate such dietary patterns may be beneficial and are certainly in line with the ACS guidelines for increasing intake of fruits and vegetables which contain a lot of other components beyond carotenoids that may be protective against cancer," says Jonas.

The ACS Guidelines on Diet, Nutrition, and Cancer Prevention advocate that you "choose most of the foods you eat from plant sources" by having at least five servings of fruits and vegetables each day. Nutrition During and After Cancer Treatment suggests, "In the absence of clinical trials, it is reasonable for cancer survivors to adopt the general dietary recommendations issued by many different agencies, namely, to eat at least five servings of fruits and vegetables—fresh, canned, frozen, or juiced—each day."

The Healthy Eating Cookbook, available in the ACS bookstore, contains hundreds of delicious recipes that comply with the ACS Nutrition Guidelines.