Soy has attracted
a great deal of attention for its use in alleviating menopausal
symptoms because of its use in other cultures. For example,
the Japanese have no word for “hot flash”;
the same is true for other far eastern cultures. The women
in these cultures have a very low incidence of hot flashes
and other menopausal symptoms. Researchers have studied
the reason for the low incidence of menopausal symptoms
in these cultures and determined that dietary differences
appear to be a major factor. Eastern women consume significantly
more vegetables, grains, and beans and far less animal
protein. A major component in their diet is soy. Soy contains
isoflavones, which aid in reducing menopausal symptoms,
specifically hot flashes.
are not estrogens as commonly defined by medical professionals;
however, they do have estrogen-like effects. Isoflavones
bind to estrogen receptors and through an adaptogenic
process work to restore homoeostasis of estrogen levels.
Isoflavones have a very low level of estrogen-like activity.
It is not possible to arrive at a single estimate of potency,
as potency varies by tissue. However, potency has been
estimated at approximately 2% or less of endogenous estrogen.
What is well established is that serum isoflavone levels
in response to even modest soy food consumption can reach
the low micromolar range, about 100 to 1,000 times that
of estrogen. This suggests, even assuming very weak potency,
that isoflavones have the potential to exert biological
effects. That they do so has been reported in several
trials, which are discussed later in this section.
Over 25 clinical
studies have been conducted on the efficacy of soy isoflavones
in alleviating the discomfort of hot flashes. Two major
analytical reviews were recently published. A review of
the data by Krebs et al. (2004) concluded that soy isoflavones
were not effective in menopause relief in comparison to
a placebo treatment. A regression analysis conducted by
Messina and Hughes (2003) looked at 19 studies (13 using
a parallel design) involving more than 17,000 women. The
trials exposed women to intakes of 34 to 100 mg isoflavones
per day (in most cases equal to or greater than 70 mg/day).
Of the 13 studies used in the final analysis only 4 showed
negative results while 9 reported positive results. The
final results revealed a statistically significant relationship
(P = 0.01) between initial hot flash frequency and treatment
efficacy. The results of this regression analysis suggest
that patients with frequent hot flashes might want to
consider soy foods or soy supplements for the alleviation
of the menopausal symptoms.
to the published review and regression-analysis several
other studies have recently been published that suggest
soy isoflavones, while not a replacement for HRT, are
a viable option for women who do not wish to take hormone
Han et al.
(2002) conducted a double blind, placebo-controlled study
in which 80 women were randomly assigned to isoflavone
(100 mg aglycone) and placebo treatments (n=40 per group)
for 4 months of treatment. The data demonstrated that
isoflavone treatments resulted in a significant decrease
in menopausal symptoms compared to baseline (P < 0.01)
and compared to the placebo treatment (P < 0.01). In
this study, isoflavone treatment also significantly reduced
total cholesterol and LDL cholesterol. This study suggests
that a 100-mg isoflavone aglycone treatment may be a safe
and effective alternative therapy for menopausal symptoms,
while offering cardiovascular benefits. This is an important
finding since heart disease is the number one killer of
Nahas et al.
(2004) conducted a prospective, double blind, placebo-controlled,
randomized study of 50 postmenopausal women. In this study
(60 mg per day, capsules) the isoflavone treatment was
significantly more effective than placebo (P < 0.05)
in regards to the percentage of women who became asymptomatic
for hot flashes (44% versus 10% for the isoflavone and
placebo treatments, respectively) and in regards to percent
change in hot flashes from baseline (-57% vs. -19% for
the isoflavone and placebo treatments, respectively).
Isoflavone treatment also resulted in a reduction of LDL
by 11.8% and an increase in HDL by 27.3% (P < 0.05)
suggesting a beneficial effect on the cardiovascular system.
A study by
Crisafulli et al. (2004) measured the effects of hot flashes
in 90 early postmenopausal women in a randomized, double
blind, placebo-controlled, positively controlled trial
in which the women were treated for one year with 54 mg
genistein per day. Compared to the placebo treatment,
the percent change in daily hot flashes was reduced significantly
(P < 0.01) by a mean of 22% after 3 months, 29% after
6 months, and by a mean of 24% after 12 months of genistein
treatment. Additionally, genistein administration did
not induce any changes in endometrial thickness. It was
concluded that genistein administration might have beneficial
effects by reducing hot flashes without causing adverse
effects on the endometrium. The overall results suggest
that genistein may be a viable natural option in the management
of postmenopausal symptoms.
Most of the
attention to soy isoflavones is directed towards menopause
and soy’s ability to reduce the discomfort of menopause.
However, soy isoflavones may also have a positive role
in reducing PMS. Soy has been shown to lower premenopausal
estrogen levels (Lu et al., 2000; Wu et al., 2000) and
increase sex hormone binding globulin (Wu et al., 2000),
which is important because high estrogen levels cause
more severe PMS symptoms and soy can decrease luteal phase
length (high estrogen levels during luteal phase produces
severe PMS symptoms). Preliminary evidence from two ongoing
clinical trials suggest that soy isoflavones significantly
improve PMS symptoms (Bryant et al., 2003; Ishiwata et
numerous studies have shown that soy isoflavones can have
a positive effect (reduced number and intensity) on menopausal
hot flashes and that these beneficial effects may be related
to initial hot flash frequency and intensity. Also, soy
isoflavones have the potential to help premenopausal women
with PMS. Therefore, soy can serve a positive role in
the overall health of women.
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for treatment of menopausal symptoms: a systematic review.
Obstet Gynecol 2004; 104:824-836
2. Messina M, Hughes C. Efficacy of soy foods and soybean
isoflavone supplements for alleviating menopausal symptoms
is positively related to initial hot flash frequency.
J Med Food 2003; 6:1-11
3. Han KK, Soares Jr JM, Haidar MA, de Lima GR, Baracat
EC. Benefits of soy isoflavone therapeutic regimen on
menopausal symptoms. Obstet Gynecol 2002; 99:389-394
4. Nahas EP, Neto JN, De Luca L, Traiman P, Pontes A,
Dalben I. Benefits of soy germ isoflavones in postmenopausal
women with contraindication for conventional hormone replacement
therapy. Maturitas 2004; 48:372-380.
5. Crisafulli A, Marini H, Bitto A, Altavilla D, Squadrito
G, Romeo A, Adamo EB, Marini R, D'Anna R, Corrado F, Batolone
S, Frisina N, Squadrito F. Effects of genistein on hot
flushes in early postmenopausal women: a randomized, double-blind,
EPT- and placebo-controlled study. Menopause 2004; 11:400-404.
6. Lu LJ, Anderson KE, Grady JJ, Kolhen F, Nagamani M.
Decreased ovarian hormones during a soya diet: implications
for breast cancer prevention. Cancer Res 2000; 60:4112-4121
7. Wu AH, Stanczyk FZ, Hendrich S, Murphy PA, Zhang C,
Wan P, Pike MC. Effects of soy foods on ovarian function
in premenopausal women. Br J Cancer 2000; 82:1879-1886
8. Bryant M, Dye L, Hill C, Powell J, Talbot D, Cassidy
A. Role of Phytoestrogens on Menstrual Cycle Symptoms.
UK 5th International Symposium on the Role of Soy in Preventing
and Treating Chronic Disease, Sept. 21-24th, 2003 Orlando,
9. Ishiwata N, Uesugi S, Uehara M, Watanabe S. Effects
of Soy Isoflavones on Premenstrual Syndrome, 5th International
Symposium on the Role of Soy in Preventing and Treating
Chronic Disease, Sept 21-24th, 2003 Orlando, FL.
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