Phyto-oestrogen intake and breast cancer risk in South Asian women in England: findings from a population-based case-control study

Objective: This study investigates whether intake of phyto-oestrogens is associated with breast cancer risk in South Asian women from the Indian subcontinent, whose diet is rich in pulses and vegetables but poor in soyfoods. Methods: A total of 240 South Asian breast cancer cases living in England and 477 age-matched population-based controls were recruited into the study. Dietary intake was measured using a validated food frequency questionnaire. Conditional logistic regression models were used to estimate the effect of phyto-oestrogen intake on breast cancer risk. Results: After adjustment for known breast cancer risk factors and total energy intake, there was moderate evidence of a dose-effect response in the odds of breast cancer with isoflavone intake (p-value for trend 0.08), with women in the top quartile having approximately half the odds of breast cancer of those in the bottom one ( odds ratio ( OR) 0.58, 95% confidence interval (CI) 0.33, 1.00) but with no reductions in the odds for women in the second and third quartiles. The ORs for second, third and highest quartiles of total lignan intake compared to the lowest were 0.78 ( 95% CI 0.48, 1.26), 0.74 (0.46, 1.19) and 0.66 (0.41, 1.07), respectively, again with moderate evidence of a linear dose-effect response (p-value for trend 0.09). Further adjustment for non-startch polysaccharides (NSP) intake slightly weakened the phyto-oestrogens-breast cancer associations. Conclusions: These findings are consistent with the possibility that high phyto-oestrogen intake may protect against breast cancer, but further research is required to confirm this hypothesis.