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

OBJECTIVE: Using a nested case-referent design we evaluated the relationship 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 population-based cohorts in northern Sweden, where all subjects donated blood samples at enrolment. All blood samples were stored at -80 degrees C. Cases and referents were matched for age, age of blood sample, and sampling centre. Breast cancer cases were identified through the regional and national cancer registries.
RESULTS: Plasma concentrations of carotenoids were positively intercorrelated. In analysis of three cohorts as a group none of the carotenoids was found to be significantly related to the risk of developing breast cancer. Similarly, no significant associations between breast cancer risk and plasma levels of alpha-tocopherol or retinol were found. However, in postmenopausal women from a mammography cohort with a high number of prevalent cases, lycopene was significantly associated with a decreased risk of breast cancer. A significant trend of an inverse association between lutein and breast cancer risk was seen in premenopausal women from two combined population-based cohorts with only incident cases. A non-significant reduced risk with higher plasma alpha-carotene was apparent throughout all the sub-analyses.
CONCLUSION: In conclusion, no significant associations were found between plasma levels of carotenoids, alpha-tocopherol or retinol and breast cancer risk in analysis of three combined cohorts. However, results from stratified analysis by cohort membership and menopausal status suggest that lycopene and other plasma-carotenoids may reduce the risk of developing breast cancer and that menopausal status has an impact on the mechanisms involved.