Given the debate about the effects of taking antioxidant supplements during conventional breast cancer treatment, the primary aims of this dissertation are (1) to describe factors associated with antioxidant supplement use before and after breast cancer diagnosis among women with breast cancer, including during conventional breast cancer treatment, and (2) to analyze the association of antioxidant supplement intake with oxidative stress, as measured by plasma protein carbonyl, and the joint effects of antioxidants and plasma protein carbonyl on breast cancer risk. We analyzed data from the Long Island Breast Cancer Study Project Follow-up of breast cancer patients for aim 1, and data from the original Long Island Breast Cancer Study Project case-control study of women with breast cancer and age-matched controls for aim 2.

Among the women with breast cancer in the follow-up study, antioxidant supplement use was common before (72.6%) and after (85.1%) diagnosis as well as during breast cancer treatment; 38.7% of women reported use during chemotherapy, 42.2% during radiation therapy, and 61.9% during tamoxifen therapy. Though use of antioxidants diminished during treatment, many women who used during treatment used doses that exceeded the recommended daily intake. Women who used antioxidant supplements also engaged in other health-oriented behaviors, including high levels of physical activity, having a low BMI, using other over-the-counter healthcare products, following special diets, and seeking care from CAM practitioners.

Our analyses suggest that high doses of antioxidant supplements are associated with increased plasma protein carbonyl concentrations, and that chemotherapy modifies this measure of oxidative stress among women with low-dose antioxidant intake and low intake of fruits and vegetables. Our data also suggested that antioxidant intake may have slight additive interaction with high plasma protein carbonyl concentrations to increase breast cancer risk.

We conclude that clinical trials and observational studies should be conducted to determine the effects of taking antioxidant supplements of various kinds, at various doses, and in various combinations, during conventional breast cancer treatment on toxicities, tumor response, recurrence and survival.