1. ¹Department of Surgery, Breast Cancer Research Group, University College London, Charles Bell House, 67-73 Riding House St, London W1W 7EJ, UK
2. ²Cancer Epidemiology and Prevention Research Group, Centre for Public Health, Queen's University Belfast, Mulhouse Building, Grosvenor Road, Belfast BT12 6BJ, UK
3. ³Department of Surgery, Royal Free Hospital, Pond St, London NW3 2QG, UK
4. ⁴Nutrition and Metabolism Group; Centre for Public Health, Queen's University Belfast, Mulhouse Building, Grosvenor Road, Belfast BT12 6BJ, UK

Correspondence: Dr LS Velentzis, E-mail: l.velentzis@ucl.ac.uk

Received 22 January 2009; Revised 5 March 2009; Accepted 5 March 2009; Published online 31 March 2009.

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=0.15), but this association was subjected to marked heterogeneity (I²=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, P<0.001) and heterogeneity was markedly reduced (I²=0%). High enterolignan exposure was also associated with breast cancer (5 studies, combined OR: 0.73, 95% CI: 0.57, 0.92, P=0.009) but, again, there was marked heterogeneity (I²=63%). No association was found with blood enterolactone levels (combined OR: 0.82, 95% CI: 0.59–1.14, P=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.