Soy Isoflavone Genistein Associated with Abnormal Ovary and Egg
Development in Mice, Says NIH Study
Independent
article
Date
Posted: 3/10/2006
Source:
Soyatech.com 12/03/06
Newswise --
A substance found in soy-based infant formula and over-the-counter
dietary supplements affects the development of ovaries and eggs in
female infant mice, according to a study conducted by researchers at
the National Institutes of Health (NIH) and Syracuse University. The
study, "Neonatal Genistein Treatment Alters Ovarian Differentiation in
the Mouse: Inhibition of Oocyte Nest Breakdown and Increased Oocyte
Survival," was published in a recent issue of the journal Biology of
Reproduction. Melissa Pepling, assistant professor of biology in The
College of Arts and Sciences at Syracuse University, was an
investigator on the study.
Genistein,
a phytoestrogen, is the primary naturally occurring estrogen in plants,
which can mimic the effects of estrogen in the body. Previous research
showed that female mice given genistein immediately after birth had
irregular menstrual cycles, problems with ovulation, and problems with
fertility in their adulthood. Researchers undertook this study to
determine when this damage occurs.
Newborn
female mice were given different doses of genistein during their first
five days of life. The genistein was comparable to what human infants
might receive in a soy-based formula (6-9 mg/kg per day). All of the
mice that were treated were affected by genistein in some way. The mice
that received low levels of genistein were subfertile, meaning they had
fewer pups in each litter and fewer pregnancies. The mice that received
the high dose were infertile, and the mice with the highest dose were
infertile and had a high percentage of eggs that remained in clusters
and did not develop normally. In order for an egg to be able to be
fertilized, it must break down from clusters into individual eggs
(oocytes). The researchers believe that genistein inhibits this
process.
The largest
difference between the treated and untreated mice occurred at six days
of age, when untreated mice had 57 percent single or unclustered egg
cells, compared to only 36 percent found in genistein-treated mice.
"It is not
yet clear how genistein works and how it causes these effects," says
Pepling. "This will be the focus of future studies." Although human
testing has not yet been conducted, Pepling points out that pregnant or
nursing mothers should be cautious when considering using soy-based
products. Experiments on pregnant mice do not show effects of genistein
on the ovary, but do show other developmental abnormalities.
Pepling has
been working on mouse oogenesis (how eggs develop) since 1995. She
became involved in the study about three and a half years ago, when she
met the study's lead researcher, Wendy Jefferson of the National
Institute of Environmental Health Sciences.
During the
study, Jefferson injected the mice with genistein and harvested the
ovaries. Pepling labeled the ovaries with markers for the oocytes,
examined them using microscopy, and performed the quantitative
analysis.
The
research yielded mixed results, suggesting some beneficial effects as
well adverse effects of genistein, depending on the timing of exposure,
dose level and endpoint examined. Some studies show that exposure to
genistein early in life prevents carcinogen-induced mammary gland
cancer, while others show increased mammary gland cancer occurs
following treatment during specific developmental windows. Others have
shown improved cholesterol synthesis rates of human infants consuming
soy-based formulas.
However,
vegetarian diets usually contain high levels of soy, and recent
epidemiology reports have shown an association of a vegetarian diet
during pregnancy with an increased incidence of hypospadias (a
urological birth defect) in male offspring and an increase in
autoimmune disease and the use of allergy medicines in children fed
soy-based infant formulas.
|
HOME
