"High dietary intakes of plant lignans and high exposure to enterolignans were associated with reduced risks of ER- and PR-positive postmenopausal breast cancer in a Western population that does not consume a diet rich in soy," wrote lead researcher Marina Touillaud from France's Institut National de la Santé et de la Recherche Médicale.
Plant lignans, found widely in plants and seeds, such as flax seed, whole grain cereals, berries, vegetables and fruits, are metabolised in the colon by microflora into enterodiol and enterolactone.
Lignans are well-known phytoestrogens - active substances derived from plants that have a weak oestrogen-like action, and have been linked before to breast health, as well as offering benefits for postmenopausal women.
The new prospective study, published in the Journal of the National Cancer Institute , investigated the effects of dietary intakes of four plant lignans (pinoresinol, lariciresinol, secoisolariciresinol, and matairesinol) and estimated exposure to two enterolignans (enterodiol and enterolactone) on the incidence of invasive breast cancer in 58 049 postmenopausal French women not taking soy isoflavone supplements.
Over one million women worldwide are diagnosed with breast cancer every year, with the highest incidences in the US and the Netherlands.
China has the lowest incidence and mortality rate of the disease.
Hormone-sensitive oestrogen-receptor (ER) positive and progesterone-receptor (PR) positive tumours are said to be the most common type diagnosed among breast cancer patients in the US.
Dietary intakes were assessed using a self-administered diet history questionnaire.
After an average of 7.7 years of follow-up, the researchers documented 1469 breast cancer cases.
After adjusting for potential confounding factors, the researchers report that a daily intake greater than 1395 micrograms was associated with a 17 per cent reduction in breast cancer risk, compared to the lowest daily intake.
The inverse associations were limited to ER- and PR-positive breast cancer, said the researchers, with the highest intake of total lignans associated with a 28 per cent reduction of these cancers, and a 23 per cent reduction for highest intake versus the lowest intake of total enterolignans.
Further research is needed to support these results, but if the association is found to be causal, a potential preventive approach for reducing the incidence of breast cancer could be to increase lignan intake.
The study does have several notable limitations, including being based on a selected population, which limits the ability of the researchers to generalise.
Last year a study published in the European Journal of Cancer Prevention (Vol. 15, pp.
225-232), reported that women with high plasma levels of enterolactone (above 12.96 nanomoles per litre), linked to high lignan intake, was associated with a 58 per cent reduction of breast cancer risk.
Source: Journal of the National Cancer Institute 21 March 2007, Volume 99, Number 6, Pages 475-486; doi:10.1093/jnci/djk "Dietary Lignan Intake and Postmenopausal Breast Cancer Risk by Estrogen and Progesterone Receptor Status" Authors : M.S. Touillaud, A.C.M. Thiébaut, A. Fournier, M. Niravong, M.-C. Boutron-Ruault, F. Clavel-Chapelon