Increased
intake of soy isoflavones significantly reduced the risk of prostate
cancer amongst Japanese men by as much as 50 per cent, says a new study.
«To our knowledge, this is the first prospective study to report an
inverse association between isoflavone and localized prostate cancer in
Japanese, whose intake of soy food is high,» wrote lead author Norie
Kurahashi from Japan’s National Cancer Center. Over half a million news
cases of prostate cancer are diagnosed every year world wide, and the
cancer is the direct cause of over 200,000 deaths. More worryingly, the
incidence of the disease is increasing with a rise of 1.7 per cent over
15 years. «The incidence of prostate cancer is much lower in Asian than
Western populations? Although isoflavones have been suggested to show a
preventive effect against prostate cancer in animal experiments, the
results of epidemiologic studies are inconsistent,» stated the
researchers in the journal Cancer Epidemiology Biomarkers &
Prevention. The study recruited 43,509 Japanese men (average age 57)
with a generally high soy isoflavone intake. Dietary assessment was
performed using a validated 147-item food frequency questionnaire.
During the five years of follow-up, 307 men were newly diagnosed with
prostate cancer (74 cases were advanced), and 220 cases were organ
localized. While no relationship between total prostate cancer risk and
dietary intakes of genistein, daidzein, miso soup, and soy food was
observed, all four food items were associated with significant risk
reduction for localised prostate cancer. The highest intake of soy
isoflavones (at least 32.8 milligrams of genistein per day) had a 40 per
cent reduced risk compared to those with the lowest intake (less than
13.2 mg/d), the researchers found. The mechanism behind the benefits was
linked to the weak oestrogenic activity of soy isoflavones, which may
act to reduce testosterone levels and inhibit 5?-reductase – an enzyme
involved in the metabolism of testosterone.
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Source: NutraIngredients