A new French prospective study has concluded that intakes of carotenoids such as beta-carotene, as well as tocopherols (vitamin E) and retinol (vitamin A), do not influence the risk of breast cancer. Vitamin A is produced in the body by converting sources of provitamin A such as beta-carotene. The study included women in the E3N Study, the French portion of the European Prospective Investigation into Cancer and Nutrition (EPIC). The women completed a dietary questionnaire and provided blood samples at baseline (1995-1998) and were followed for an average of seven years. During this time, 366 new cases of invasive breast cancer were diagnosed (84 premenopausal and 282 postmenopausal). To perform the analysis, a group of controls (also in the E3N Study) was matched based on age, menopausal status at blood collection, fasting status at blood collection, date, and geographic location (collection center). Serum carotenoids, tocopherols and retinol levels were measured using high pressure liquid chromatography. No statistically significant reductions in breast cancer risk and blood levels of carotenoids, tocopherols, and retinol were found. The authors conclude that the findings did not support the hypothesis that fat soluble antioxidant micronutrients found in fruits and vegetables protect against breast cancer, at least in postmenopausal women.
Other studies have reported more nuanced results
It is fairly well established that increasing dietary vitamin E intake is not associated with reduced risk of breast cancer in Western populations, which are unlikely to suffer from vitamin E deficiencies. However, dietary sources of vitamin A and various carotenoids (alpha-carotene, beta-carotene, beta-cryptoxanthin, lutein, lycopene, and zeaxanthin) have been found to be associated with lower risks of breast cancer in some women. Below, we summarize some of the results of relevant studies that were published during 2009:
- A recent study which included 604 breast cancer cases in the Nurses' Health Study found that total circulating carotenoid levels were inversely associated with overall breast cancer risk for women with high breast density (considered a high risk group)
- Another recent study found that dietary beta-carotene intake was associated with reduced risk of breast cancer in postmenopausal women using hormone replacement treatment (HRT) or who had relatively high alcohol consumption
- Another, longer-term study using repeated measurements of serum carotenoids, retinol, and tocopherols in postmenopausal women found that risk of invasive breast cancer was inversely associated with serum alpha-carotene and beta-carotene concentrations. However, the study also found that the risk of breast cancer was positively associated with lycopene and γ-tocopherol (which accounts for 70 to 80% of dietary vitamin E) intake
- A laboratory study found that beta-carotene significantly reduced the percentage of proliferating hormone receptor positive breast cancer cells. In addition, retinol and lycopene administered together with paclitaxel (Taxol) and tamoxifen significantly reduced the percentage of proliferating cells, compared with paclitaxel group alone
- A study which included 5,707 U.S. women with invasive breast cancer found that high consumption of carotenoids may reduce the risk of premenopausal, but not postmenopausal breast cancer, particularly among smokers
- A study which included 3,043 women who had been diagnosed with early stage breast cancer and followed for approximately seven years concluded that higher carotenoid intake was associated with greater likelihood of breast cancer-free survival
- A Chinese population study found an inverse association with breast cancer risk for intakes of vitamin A, carotene, vitamin C, vitamin E, and fiber. Consumption of carotenoid-rich foods such as watermelon, papaya, cantaloupe, carrots, and tomatoes were each associated with lower breast cancer risk
- A study of postmenopausal early stage breast cancer survivors who were followed for at least 12 years found that low plasma retinol strongly predicted poorer prognosis.
Carotenoids should be obtained by consuming foods. Supplementation with vitamin A or with beta-carotene will not provide the same beneficial effects as consuming high-carotenoid foods such as carrots. In fact, these supplements have been associated with increased risk of certain cancers (e.g., lung cancer).