Study questions lignans for colorectal cancer protection
in the blood, may not be associated with colorectal cancer risk,
says a new study that challenges previous findings.
Over 35,000 participants aged between 20 and 59 were followed for 7.5 years, and no relationship found between plasma enterodiol and enterolactone levels, states the study in the American Journal of Epidemiology. "These findings do not support the hypothesis that high plasma enterodiol or enterolactone concentrations are associated with reduced risk of colorectal cancer," wrote lead author Anneleen Kuijsten from the Dutch National Institute for Public Health and the Environment, RIKILT-Institute of Food Safety (Wageningen), and Wageningen University. 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 results are at odds with research from the same university published in 2006 in Cancer Epidemiology Biomarkers and Prevention (Vol. 15, pp. 1132-1136). The earlier study indicated it was 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. Indeed, the earlier study reported that a dietary intake of plant lignans could reduce the risk of colorectal cancer by half. The new study challenges this view and reports no link between blood levels of enterodiol and enterolactone and the risk of colorectal cancer. During the 7.5 years of follow-up, the researchers documented 160 incident cases of colorectal cancer. The cancer cases were then frequency-matched to 387 healthy by age, sex, and study centre. Blood samples were taken, and Kuijsten and co-workers report that plasma levels of enterolactone were not associated with the risk of colorectal. Moreover, an increase in the risk was observed when they considered the results in terms of body mass index and sex, with women linked to a rise in risk. The researchers also report that: "The association between plasma enterodiol and colorectal cancer risk was modified by smoking status; risk was increased among current smokers." With conflicting results being reported on the subject, the need for further research is clear, with more epidemiological studies needed. It should also be noted that other 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. 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. Source: American Journal of Epidemiology Published on-line ahead of print 12 January 2008, doi:10.1093/aje/kwm349 "Plasma Enterolignan Concentrations and Colorectal Cancer Risk in a Nested Case-Control Study" Authors: A. Kuijsten, P.C.H. Hollman, H.C. Boshuizen, M.N.C.P. Buijsman, P. van 't Veer, F.J. Kok, I.C.W. Arts, H.B. Bueno-de-Mesquita
