Adlercreutz et al.7 first showed in 1982, in a small number of subjects, that postmenopausal Finnish women with breast cancer (n = 7) had a lower urinary mammalian lignan excretion compared to healthy controls (n = 20), suggesting that the lignans are associated with a reduced risk of breast cancer. More studies, detailed in Table 19.1, have since been conducted, utilizing larger sample sizes and either urinary or serum lignans levels, or lignan intake as biomarkers, to determine if the lignans are associated with breast cancer risk. From 1997-2002, three case-control studies11-13 showed negative association between urinary lignans or lignan intake and breast cancer risk, while a case-control study14 showed no association between lignan intake and breast cancer risk in pre- and postmenopausal women. In another case-control study, when both pre- and postmenopausal women were combined, there was a significant negative association between serum lignans and breast cancer risk.15 A prospective study16 showed no association between urinary lignans and breast cancer risk in a group of postmenopausal women, while in another prospective study17 utilizing three separate cohorts in Sweden, two of the cohorts showed a weak positive association between serum lignans and breast cancer risk, while the other showed a negative association between serum lignans and breast cancer risk. However, the authors17 stated that their results should be viewed with caution due to the small sample sizes in each cohort.
The above six studies gave contradictory results regarding the association between lignans and breast cancer risk. Therefore, more epidemiological studies, further described in greater detail below, were conducted in recent years using newer methods of estimating lignan exposure (i.e., intake and serum levels), in hopes to clarify the lignan and breast cancer association.
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