Soja tijdens de jeugd verlaagt de kans op
borstkanker flink.*
Vrouwen die al tijdens hun jeugd vaker soja producten zoals miso en tofu
gegeten hebben verlagen daarmee de kans op het krijgen van borstkanker. Dit
blijkt een Amerikaanse studie onder 1.600 vrouwen. De meeste reductie van de
kans op borstkanker werd gevonden bij vrouwen die tussen hun 5e en 11e
jaar regelmatig soja producten gegeten hadden, zij hadden tot wel 60% minder
kans. Zij die als tiener of volwassenen vaker sojaproducten eten verlagen de
kans met 25%. De wetenschappers veronderstellen dat dit effect komt door de
aanwezigheid in soja van veel bepaalde bioactieve stoffen zoals de isoflavonen
of fyto-oestrogenen.
Childhood soy intake and breast
cancer risk in Asian-American women
In
a novel study of Asian-American women, a team of researchers led by National
Cancer Institute (NCI) investigators has found that consuming soy during
childhood, adolescence and adult life were each associated with a decreased risk
of breast cancer, but that the strongest and most consistent effect was seen for
childhood intake.
They
found that women who ate the most soy-based foods (such as tofu, miso, natto)
during ages 5-11 reduced their risk of developing breast cancer by 58 percent,
compared to women who ate the least amount. The corresponding reductions for
adolescent and adult intake were about 25 percent.
"Childhood
soy intake was significantly associated with reduced breast cancer risk in our
study, suggesting that the timing of soy intake may be especially critical,"
said the study's lead investigator, Larissa Korde, M.D., MPH, a staff clinician
at the NCI's Clinical Genetics Branch, in the Division of Cancer Epidemiology
and Prevention. Korde worked in collaboration with epidemiologists at the
University of Hawaii, the Northern California Cancer Center, and the University
of Southern California.
The
underlying mechanism is not known. However, Korde said that one hypothesis for
the decreased risk associated with childhood intake is that soy isoflavones have
estrogenic effects that cause changes in breast tissue, leading to decreased
sensitivity to carcinogens. A similar protective effect has been found in
studies of overweight girls, perhaps because fat tissue also secretes estrogens,
she added.
"Hormonal
exposures in adulthood, such as use of estrogen and progesterone replacement
therapy, are established breast cancer risk factors. However, a growing body of
evidence suggests that hormonally related exposures early in life may also
modify susceptibility to breast cancer," Korde said.
Studies
investigating adult soy intake and breast cancer risk have had mixed results,
but the two studies that looked at adolescent consumption found that the risks
of developing breast cancer later in life were cut in half. This study is the
first to address the relationship between soy consumption during childhood and
future risk of breast cancer.
As
provocative as the findings are, the senior investigator on the study, Regina
Ziegler, Ph.D, MPH, cautioned that it would be premature to recommend changes in
childhood diet. "This is the first study to evaluate childhood soy intake
and subsequent breast cancer risk, and this one result is not enough for a
public health recommendation," she said. "The findings need to be
replicated through additional research."
The
researchers conducted a case-control study of women of Chinese, Japanese and
Filipino descent who were living in the San Francisco Bay area, Los Angeles, or
Oahu, Hawaii. Included were 597 Asian-American women with breast cancer and 966
women without the disease, who answered questions about their adult and
adolescent diet and lifestyle. In addition, for a subset of 255 participants
whose mothers were alive and living in the US, the mothers were asked about
their daughter's early childhood exposures.
Soy intake was then divided into thirds, based on frequency of consumption, and by comparing the highest category to the lowest, the researchers found an inverse association between the risk of developing breast cancer and the amount of soy consumed. The childhood relationship held in all three races and all three study sites, and in women with and without a family history of breast cancer. Since the effects of childhood soy could not be explained by other measures of Asian lifestyle during childhood or adult life, researchers concluded that early soy intake might itself be protective.
(Nov. 2006)