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 new retrospective study, published in the June issue of Cancer Epidemiology Biomarkers and Prevention (Vol. 15, pp. 1132-1136), indicates it is the first to report that the metabolites of lignans may also be beneficial for people with colorectal adenomas, growths in the colon and rectum that are considered by some scientists to be precursors for colorectal cancer.
The researchers, based in Wageningen University and the RIKILT - Institute of Food Safety in the Netherlands, enrolled 532 cases (at least one histologically confirmed colorectal adenoma, average age 59.6, 47 per cent female) and 503 healthy controls (average age 52.8, 62 per cent female). Plasma enterodiol and enterolactone levels were measured.
While plasma levels of enterodiol and enterolactone did not differ significantly between the cases and controls, the researchers did find that risk associated with incident cases was significantly reduced when plasma levels of enterodiol and enterolactone were high.
The benefits of lignans appeared to be dose-dependent, meaning that a higher plasma level of the metabolites enterodiol and enterolactone was associated with a greater benefit.
After adjusting for possible confounders such as age, sex and antibiotic use, a plasma level of enterodiol of more than 3.1 nanomoles per litre was associated with a reduction in the risk of colorectal adenomas of 52 per cent, compared with people with intakes of less than 0.7 nanomoles per litre.
A plasma level of enterolactone of more than 26.3 nanomoles per litre was associated with a reduction in the risk of colorectal adenomas of 37 per cent, compared with people with intakes of less than 4.6 nanomoles per litre.
No such associations were observed for prevalent cases.
"Enterodiol was similarly associated with colorectal adenomas as enterolactone in this study, although concentrations of enterodiol were five to ten-fold lower. This suggests that in the human body, enterodiol might be more active than enterolactone," wrote lead author Anneleen Kuijsten.
The authors indicate that this is the first time that such an association between plant lignan intake and colorectal cancer has been published, although they do concede that studies have reported that a higher intake of lignan-containing foods such as cereals, fruits, nuts and grains have been linked to lower risks of colorectal cancer.
"To further investigate the role of enterolignans on the development of colorectal cancer, more prospective studies or recurrence trials are needed," concluded the researchers.
Such studies are underway, with the same researchers currently involved in another on-going prospective study, and are considering other short-term epidemiological studies.
Researcher Peter Hollman, Associate Professor Nutrition and Health, Wageningen University, told NutraIngredients.com that no intervention trials were planned and that such studies were too far away at the moment.
"We are interested in investigating the mechanisms before starting on any long-term or intervention studies," said Dr Hollman.
The results were welcomed by Marian Verbruggen Ph.D., Director R&D/QA with Acatris, producer of LinumLife - secoisolariciresinol diglucoside (SDG) from flaxseed.
Dr. Verbruggen told NutraIngredients.com most of the research to date has focused on the health effects of flax lignans, related to their antioxidant and modest (anti-)oestrogenic properties.
"This study indicates that the health benefits of lignans might not be limited to these mechanisms, but that we should keep an eye open for more. Hopefully the results will be confirmed in prospective studies in future," she said.
There are 363,000 new cases of colorectal cancer every year in Europe, with an estimated 945,000 globally. There are about 492,000 deaths from the cancer each year. Only about five per cent of colorectal adenomas are thought to become malignant, and this process could take between five and ten years.