Lignans and breast cancer risk in pre- and post-menopausal women: meta-analyses of observational studies

Abstract

Phyto-oestrogens are plant compounds structurally similar to oestradiol, which have been proposed to have protective effects against breast cancer. The main class of phyto-oestrogens in the Western diet is lignans. Literature reports on the effect of lignans in breast cancer risk have been conflicting. We performed three separate meta-analyses to examine the relationships between (i) plant lignan intake, (ii) enterolignan exposure and (iii) blood enterolactone levels and breast cancer risk. Medline, BIOSIS and EMBASE databases were searched for publications up to 30 September 2008, and 23 studies were included in the random effects meta-analyses. Overall, there was little association between high plant lignan intake and breast cancer risk (11 studies, combined odds ratio (OR): 0.93, 95% confidence interval (95% CI): 0.83 -1.03, P ¼ 0.15), but this association was subjected to marked heterogeneity (I 2 ¼ 44%). Restricting the analysis to post-menopausal women, high levels of plant lignan intake were associated with reduced breast cancer risk (7 studies, combined OR: 0.85, 95% CI: 0.78, 0.93, Po0.001) and heterogeneity was markedly reduced (I 2 ¼ 0%). High enterolignan exposure was also associated with breast cancer (5 studies, combined OR: 0.73, 95% CI: 0.57, 0.92, P ¼ 0.009) but, again, there was marked heterogeneity (I 2 ¼ 63%). No association was found with blood enterolactone levels (combined OR: 0.82, 95% CI: 0.59 -1.14, P ¼ 0.24). In conclusion, plant lignans may be associated with a small reduction in post-menopausal breast cancer risk, but further studies are required to confirm these results. (Beral, 2003) have both been associated with increased breast cancer risk. Isoflavones and lignans are plant compounds structurally similar to 17b-oestrodiol known as phyto-oestrogens, capable of oestrogen receptor binding (Kuiper et al, 1998;Mueller et al, 2004). Isoflavones are mostly found in soybean products, which are a staple of the Asian diet, whereas lignans are the principal group of phyto-oestrogens in Western diets. Lignans are more widespread in foods than isoflavones and are present in grain cereals, vegetables, seeds, tea and coffee (Mazur, 1998a;Mazur et al, 1998b). Microflora in the colon (Setchell et al, 1981) convert plant lignans into enterolignans, which are detectable in blood and urine. Their levels have been correlated with the amount of plant lignans ingested (Nesbitt et al, 1999).In a recent meta-analysis, an inverse dose-response relationship was shown between breast cancer risk and soy-food intake in Asian, but not in Western women (Wu et al, 2008). Lignans have been shown to exhibit anti-carcinogenic properties (Wang et al, 1994;Prasad 2000;Bergman Jungeström et al, 2007), and it is hypothesised that exposure to high levels may be associated with a reduction in breast cancer risk. However, results from a number of studies in Western populations have been variable. The aim of our systematic review was to establish whether an association exists between lignan exposure and breast cancer ris...

Enterolignan-Producing Phenotypes Are Associated with Increased Gut Microbial Diversity and Altered Composition in Premenopausal Women in the United States

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