A study has reported that, among supplement users, women who frequently take vitamin C or vitamin E after being diagnosed with breast cancer are somewhat more likely to survive than those who do not. On the other hand, those who take combination multiple carotenoids (vitamin A or beta-carotene, lycopene, alpha-carotene, beta-cryptoxanthin, lutein, zeaxanthin) are twice as likely to die. The study was designed to investigate the association between antioxidant supplement use and breast cancer outcome. There is concern that antioxidant supplement use may interfere with the pro-oxidant effects of chemotherapy and radiotherapy, however the effects on recurrence and survival have not been established.

The study included participants in the Life After Cancer Epidemiology (LACE) Study. The 2,264-member LACE cohort consists primarily of women in the Kaiser Permanente Northern California Cancer Registry who were diagnosed with early stage primary breast cancer between 1997 and 2000 and who were enrolled approximately two years after diagnosis. The women completed a mailed questionnaire at baseline which collected data concerning the frequency of antioxidant supplement use since diagnosis (multivitamins with or without minerals, vitamin C, vitamin E, beta-carotene, lycopene, combination multiple carotenoids, selenium, zinc, coenzyme Q10, and soy), as well as known or suspected breast cancer risk factors. Breast cancer outcomes were determined yearly using mailed questionnaires and confirmed by medical chart review. Antioxidant supplement use after diagnosis was reported by 81% of the study participants - 71% used multivitamins, 40% used vitamin C, 48% used vitamin E, and 7% used combination carotenoids.

Among antioxidant supplement users, frequent use of vitamin C and vitamin E were found to be associated with 27% (vitamin C) and 23% (vitamin E) lower risk of breast cancer recurrence, however these results barely reached statistical significance. Vitamin E was also associated with 24% decreased risk of death from any cause, again the result was weak. On the other hand, frequent use of combination multiple carotenoids was associated with twice the risk of death from breast cancer and 1.8 times the risk death from any cause among supplement users and this result was statistically significant. However, no such relationship was seen with beta-carotene alone or lycopene alone. The authors conclude that frequent use of vitamin C and vitamin E in the period following breast cancer diagnosis is associated with decreased likelihood of recurrence. Frequent use of combination multiple carotenoids during the same period was associated with decreased survival. The effects of antioxidant supplement use after diagnosis likely differ by type of antioxidant.

Comments regarding the study

We would treat the study results with caution. Previous studies have also reported possible breast cancer-related risks of carotenoid supplements. However, the results for vitamin C and vitamin E have been mixed. There is some evidence that taking vitamin E or vitamin C supplements increases the risk of breast cancer for women who are not deficient and may interfere with breast cancer treatment. For example, vitamin E supplements have been reported to reduce the therapeutic effects of tamoxifen. Based on the available evidence, breast cancer patients should avoid taking supplements during radiation or chemotherapy. While various antioxidants found in fruits, vegetables and other foods have been shown to help protect against breast cancer development and metastasis, some of the same micronutrients might enable breast cancer cells to survive breast cancer treatment, especially if taken in concentrated form. Please see our article on vitamin C and breast cancer.