But according to findings published in the American Journal of Clinical Nutrition, however, there was no overall beneficial effect when women of all ages were considered, suggesting the benefit may be limited to postmenopausal women.
The meta-analysis, which used data from 21 published studies, adds to the overall body of science supporting the link between increased dietary lignan intake, and/or increased levels of enterolactone and/or enterodiol and protection/reduced risk of a wide range of conditions. Breast cancer, prostate cancer, and reduced hair loss were cited as the most notable of these.
Plant lignans, from sources such as flax seed, whole grain cereals, berries, vegetables and fruits, are metabolised in the colon by microflora into enterodiol and enterolactone. Previous research has focussed on plant lignans as reducing the risk of prostate cancer, and in improving menopause health.
The main lignan from flaxseed is secoisolariciresinol diglucoside (SDG), which is metabolised to give enterodiol and enterolactone. These two metabolites are then absorbed from the gut and transported to the liver where they undergo further reactions before entering circulation.
SDG-containing products are well-represented on the market, including Frutarom’s LinumLife.
Other lignan sources also have market representation, including the 7-hydroxymatairesinol (HMR) from Norwegian spruce. The lignan, commercialised by Swiss company, Linnea, is metabolised differently in the body, forming mostly enterolactone (ENL) and some 7-hydroxyenterolactone (HENL), but no enterodiol.
The new meta-analysis, performed by scientists from the German Cancer Research Center, included 11 prospective cohort and 10 case-control studies.
The highest lignin intakes were associated with a 14 per cent reduction in the risk of breast cancer amongst post-menopausal women, while breast cancer risk was also associated with enterolignan consumption, said the German researchers.
On the other hand, no link between breast cancer risk and enterolactone levels was observed.
“High lignan exposure may be associated with a reduced breast cancer risk in postmenopausal women,” wrote the scientists in the AJCN. “Additional work is warranted to clarify the association between lignan exposure and breast cancer risk.”
The meta-analysis was supported by the Deutsche Forschungsgemeinschaft.
The new meta-analysis follows hot on the heels of a review published in Comprehensive Reviews in Food Science and Food Safety that found that flaxseed lignans might offer protection against breast, prostate, colon, and skin cancers, while the soluble fibre they contain could help maintain steady blood sugar levels.
Researchers from Canada, England and China called for further research to be undertaken to assess any potential adverse effects from over consumption of the seed: “More in vivo studies are needed to ascertain the propitious effects of lignans secoisolariciresinol and to see if there are any dangers in possible overdoses.”
Source: American Journal of Clinical Nutrition
Published online ahead of print, doi: 10.3945/ajcn.2009.28573
"Meta-analyses of lignans and enterolignans in relation to breast cancer risk"
Authors: Katharina Buck, Aida Karina Zaineddin, Alina Vrieling, Jakob Linseisen, and Jenny Chang-Claude