Premenopausal plasma carotenoids, fluorescent oxidation products, and subsequent breast cancer risk in the nurses' health studies.

High levels of circulating carotenoids are hypothesized to reduce breast cancer risk, potentially due to their antioxidant properties. However, little is known about the relationship between carotenoid exposure earlier in life and risk. We examined associations of premenopausal plasma carotenoids and markers of oxidative stress and risk of breast cancer among 1179 case-control pairs in the Nurses' Health Study (NHS) and NHSII. Levels of α- and β-carotene, β-cryptoxanthin, lycopene, and lutein/zeaxanthin were quantified by high-performance liquid chromatography. Three fluorescent oxidation products (FlOP_360, FlOP_320, FlOP_400) were measured in a subset of participants by spectrofluoroscopy. Multivariate conditional logistic regression was used to estimate odds ratios and 95 % confidence intervals for breast cancer by quartile, as well as P values for tests of linear trend. We additionally examined whether 45 single-nucleotide polymorphisms (SNPs) in five genes involved in oxidative and antioxidative processes or carotenoid availability were associated with risk. Carotenoid measures were not inversely associated with breast cancer risk. No differences by estrogen receptor status were observed, though some inverse associations were observed among women postmenopausal at diagnosis. Plasma FlOP levels were not positively associated with risk, and suggestive inverse associations with FlOP_320 and FlOP_360 were observed. Several SNPs were associated with carotenoid levels, and a small number were suggestively associated with breast cancer risk. We observed evidence of interactions between some SNPs and carotenoid levels on risk. We did not observe consistent associations between circulating levels of premenopausal carotenoids or FlOP levels and breast cancer risk.