Lignans may protect against prostate cancer
26 per cent, says a new study from Sweden, news that has been
welcomed by a leading lignan manufacturer.
Over half a million men worldwide are diagnosed with prostate cancer every year, with over 200,000 deaths from the disease. The lowest incidence of the cancer is in Asia and the Far East, in particular India, Japan and China.
Previous studies have already linked phytoestrogens, such as lignans from sesame and rye, and isoflavones from soy, to reduced risks of the cancer.
The Swedish study, led by Maria Hedelin from the Karolinska Institute, Stockholm, evaluated the dietary intake of lignans for 1499 men with prostate cancer (cases), and 1130 healthy men (controls) using a food frequency questionnaire.
Subgroups of 221 controls and 218 cases had blood samples taken in order to measure levels of serum enterolactone, a metabolite of plant lignans.
"High intake of food items rich in phytoestrogens (flaxseed, sunflower seeds, berries, peanuts, beans and soy) was associated with a monotonically decreasing overall risk [26 per cent] of prostate cancer," wrote Hedelin.
Interestingly, no direct link was made between total lignan intake and prostate cancer risk, a result that is explained by the researchers as an inability of the questionnaire to cover all sources of lignan, an incomplete database of lignans/enterolactone precursors, and differences in individual metabolism of lignans.
There did appear to be a relationship between blood levels of the lignan metabolite and reduced risk of prostate cancer.
"High serum levels of enterolactone were associated with a decreased risk of prostate cancer. However the trend was non-linear, with the strongest inverse association of intermediate levels of enterolactone - 15.3 to 23.9 nanomoles per liter," reported Hedelin.
Experimental design could not identify the mechanism of protection. The researchers proposed however that the decreased risk of prostate cancer due to phytoestrogens could be due to regulation of sex and/or growth hormones, antioxidant properties, apoptosis (programmed cell death) of prostate cancer cells, or inhibition of metastasis (the spread of cancer cells).
"If this association is indeed causal, then a substantial reduction in prostate cancer incidence would be achievable through moderate increases in phytoestrogens intake," concluded the researchers.
The study has been welcomed by Swiss company Linnea, manufacturer of HMRlignanT (hydroxymatairesinol), a highly bioavailable and efficient precursor of enterolactone derived from the Norway Spruce (Picea abioes).
Robin Ward, vice president of marketing for Linnea said: "An increasing body of research evidence supports the health benefits of enterolactone, [which] appears to have direct inhibitory effects associated with cancer cell growth and signaling."
"Research has shown that enterolactone competes with E2 for the type II estrogen receptor, induces sex hormone binding globulin (SHBG) and influences steroid metabolism and synthesis, thus potentially reducing proliferation of hormone dependent prostate," said Ward.
It should be stressed that lignan and isoflavone intakes for the Swedish population was different from those of a typical American diet.
Average intake of lignans in the US diet is estimated to be less than one milligram a day due to over-processing of foods and low intakes of fruit, fiber and unrefined grains.
The US specialist retail market for lignans was believed to worth $50m in 2004.
