Carotenoids, alpha-tocopherols, and retinol in plasma and breast cancer risk in northern Sweden

Objective: Using a nested case-referent design we evaluated the relationshi p between plasma levels of six carotenoids, alpha-tocopherol, and retinol, sampled before diagnosis, and later breast cancer risk. Methods: In total, 201 cases and 290 referents were selected from three pop ulation-based cohorts in northern Sweden, where all subjects donated blood samples at enrolment. All blood samples were stored at -80 degreesC. Cases and referents were matched for age, age of blood sample, and sampling centr e. Breast cancer cases were identified through the regional and national ca ncer registries. Results: Plasma concentrations of carotenoids were positively intercorrelat ed. In analysis of three cohorts as a group none of the carotenoids was fou nd to be significantly related to the risk of developing breast cancer. Sim ilarly, no significant associations between breast cancer risk and plasma l evels of alpha -tocopherol or retinol were found. However, in postmenopausa l women from a mammography cohort with a high number of prevalent cases, ly copene was significantly associated with a decreased risk of breast cancer. A significant trend of an inverse association between lutein and breast ca ncer risk was seen in premenopausal women from two combined population-base d cohorts with only incident cases. A non-significant reduced risk with hig her plasma alpha -carotene was apparent throughout all the sub-analyses. Conclusion: In conclusion, no significant associations were found between p lasma levels of carotenoids, alpha -tocopherol or retinol and breast cancer risk in analysis of three combined cohorts. However, results from stratifi ed analysis by cohort membership and menopausal status suggest that lycopen e and other plasma-carotenoids may reduce the risk of developing breast can cer and that menopausal status has an impact on the mechanisms involved.