Evaluation of the Efficacy of Flaxseed Meal and Flaxseed Extract in Reducing Menopausal Symptoms

Abstract

The objective of this study was to evaluate the efficacy of flaxseed meal and flaxseed extract in reducing climacteric symptoms of menopausal women. Ninety menopausal women were randomly distributed into three study groups: group I received 1 g per day of flaxseed extract containing at least 100 mg of secoisolariciresinol diglucoside (SDG), group II received 90 g per day of flaxseed meal containing at least 270 mg of SDG, and group III received 1 g per day of collagen (placebo group). Subjects were assessed for menopausal symptoms by the Kupperman index at the beginning and at the end of the 6 months of treatment. Subjects were also assessed for endometrial thickness and vaginal cytology. The Kupperman index values at the beginning and end of the treatments were analyzed using the paired t-test. Both the flaxseed extract (P=.007) and the flaxseed meal (P=.005) were effective in reducing the menopausal symptoms when compared with the placebo control (P=.082). Alternatively, the changes in Kupperman index were also computed and submitted to analysis of variance. In this case, no significant differences were found (P=.084) although the data indicate a decreasing tendency for the Kupperman index by both the flaxseed extract and the flaxseed meal groups. Neither the flaxseed extract nor the flaxseed meal exerted clinically important estrogenic effects on the vaginal epithelium or endometrium as revealed by the absence of changes in the blood levels of follicle stimulating hormone and estradiol, as well as in the endometrial thickness, and vaginal epithelial maturation value. No serious adverse events related to the treatments were reported. Although the results of the present study do not allow an unequivocal conclusion about the action of flaxseed on the menopausal symptoms, they suggest that it could be premature to conclude that no such action exists. Clearly the matter still deserves further experimental attention.

Introduction

W ith the increase in life expectancy, many women live more than one-third of their lifespan in a postmenopausal state.¹ Many of them experience vasomotor disturbances, dyslipidemia, vaginal atrophy, and osteoporosis that can negatively affect the quality of life. ^2,3 The synthetic hormone replacement therapy (HT) is used during menopause to prevent symptoms and diseases related to menopause.³ This type of therapy, however, is directly linked to risks, such as increased incidence of breast and endometrium cancer, thromboembolic complications, and strokes in hypertensive women.^4
–6 These concerns have limited the use of the HTs and greatly encouraged the search for alternative treatments for symptoms and diseases present during menopause.

Several alternative therapies, including the use of phytoestrogens, have been studied for those patients suffering with menopausal symptoms for whom HT is contraindicated.^3,7

–12 Phytoestrogens are compounds with similar structure and functionality of the natural female estrogens and can bind to the same receptor and mimic their action.⁸ Phytoestrogens exert their effects primarily through binding to estrogen receptors, presenting a weak estrogenic effect.¹³ However, their estrogenic activity is much weaker than that of endogenous estrogens, and they may actually block or antagonize the effects of estrogens in some tissues.¹⁴ In addition to interaction with estrogen receptors, phytoestrogens may also modulate the concentration of endogenous estrogens by binding or inactivating some enzymes, such as sulfatase, 17β hydroxysteroid dehydrogenase, aromatase, and sulfotransferase.¹⁵ Further, phytoestrogens may also affect the bioavailability of sex hormones by binding or stimulating the synthesis of sex hormone binding globuline.¹⁵

More than 300 plants have been evaluated as having estrogenic activity.⁹ Several concentrations and formulations are available on the market to facilitate their consumption. These alternative treatments have been used by women, not only for their beneficial effects in the treatment of the menopausal symptoms, but also for their alleged anticancer properties.^7

–12 One of the most known class of phytoestrogens are the lignans.^1,7
–9 The flaxseed grain (Linun usitatissimum) has considerable quantities of the lignans secoisolariciresinol and matairesinol.¹⁶ These molecules are released after the ingestion of flaxseeds and are converted to biologically active mammalian lignans, enterodiol and enterolactone.¹⁷ These metabolites are then recognized and bind to estrogen receptors after hepatic metabolization and are eventually eliminated by the kidneys.^18,19 The efficacy of this process is dependent on the type of formulation that is ingested—powder, oil, or whole flaxseed.²⁰ It is also dependent on the ingested amount, hormonal stage, individual conditions of intestinal absorption, and on the use of certain antibiotics.^21
–23

So far the few studies evaluating the effectiveness of flaxseed in reducing menopausal symptoms have led to contradictory results, which indicate the need of new studies to assess the effectiveness of flaxseed and its lignans as alternative forms of treatment for menopausal symptoms.^1,24

–28 Thus, the purpose of this study was to evaluate the effect of flaxseed (concentrated extract and whole meal) on the cell maturation index measured by vaginal cytology, on the endometrial hypertrophy signals assessed by transvaginal ultrasound, and on the subjective clinical symptoms evaluated by the Kuperman index in menopausal women. The hot flashes symptom was also evaluated separately because it is the most frequent menopausal symptom and the primary reason for which women seek medical treatment.

Materials and Methods

Study design and sample selection

This study was a randomized placebo-controlled clinical trial. The population group included 90 Brazilian women, selected in a gynecology service in the municipality of Maringá, Paraná, Brazil, between October 2009 and March 2010. The samples consisted of women aged between 46 and 68 years, with an average of 55.2 years, showing levels of the follicle stimulating hormone (FSH) above 40 mIU/mL and estradiol under 30 pg/mL, with amenorrhea for >12 months, and climacteric symptoms. The following exclusion criteria were adopted: (1) one or more contraindications to the use of synthetic HT, for example, a past history of thrombosis or thrombophlebitis, undiagnosed vaginal bleeding, family history of breast and/or endometrium cancer, and suspicious mammogram (over BI-RADS–Breast Imaging Reporting and Data System-3); (2) use of any synthetic hormone medication in the past 6 months; (3) use of antibiotics in the past 6 months; and (4) signs of gastrointestinal malabsorption syndrome. The patients were made aware that the study would not include hormone replacement and agreed not to make use of the conventional therapy even after clarification of its risks and benefits. All the participating women signed a term of consent for the study that was approved by the ethics committee of the State University of Maringá.

Methodology

The initial evaluation included a clinical history assessment, gynecological examination, body weight measurement, vaginal cytology, mammography, endovaginal ultrasound, and collection of blood samples for the assay of FSH and estradiol. The patients were randomly distributed into three groups of 30 women per group. The patients received a 30-day supply of product once every month and were advised not to discontinue the treatment without notice during the entire trial period of 6 months and not to add or withdraw any habitual medication without communicating with the research team. The patients from group I were directed to take two 500 mg capsules of flaxseed extract per day supplied by the Medicinal Compounding Pharmacy under the brand name of Biogalênica. Each capsule contained 50 mg of standardized lignan (as secoisolariciresinol diglucoside [SDG]). The patients from group II were directed to take two tablespoons (45 g) of ground whole flaxseed by the same supplier. The consumption of 90 g of flaxseed provided at least 270 mg of lignan as SDG.²⁹ These amounts were determined based on previous studies.^{1,21

–28} The patients from group III (placebo group) were directed to take two 500 mg of capsules of collagen per day prepared by the same pharmacy. All patients were directed to take the products in the morning before the first meal and in the case of group II the ground flaxseeds should be mixed with milk, yogurt, or juice.

Study protocol

Each patient was followed for 6 months and was submitted to initial and final examinations. The patients answered a questionnaire about their symptoms each month and the Kupperman index was used to evaluate menopausal symptoms (Table 1). The Kupperman index is a numerical conversion system that classifies 11 symptoms that compose the climacteric syndrome, such as hot flashes, insomnia, paresthesia, nervousness, melancholy, vertigo, arthralgia/myalgia, weakness, headache, palpitation, and buzz. These symptoms receive numeric values according to their intensity (light=1, moderate=2, and severe=3), which when multiplied by the conversion values recommended by Kupperman represent the importance of symptoms during the climacteric syndrome. The effect of treatments on the hot flashes score was evaluated separately because it is the most frequent symptom.³⁰

Table 1.

Baseline Characteristics of the Study Participants

Variables	Group I Flaxseed extract (n=28)	Group II Flaxseed meal (n=22)	Group III (n=25) Placebo
Age (years)	53.57±4.60	54.16±4.50	56.57±6.10
Body weight (kg)	67.60±12.80	67.42±12.71	63.00±7.60
Kupperman index	9.89±5.30	10.23±4.38	11.64±5.19
Baseline hot flashes	6.08±2.78	4.54±3.14	6.96±2.67
Vaginal epithelial maturation value (%)	39.80±15.10	41.6±10.90	35.7±12.90
Endometrium (mm)	1.94±1.11	1.77±1.10	2.15±1.30
FSH (mIU/mL)	81.14±26.07	64.24±18.32	68.88±19.80
Estradiol (pg/mL)	23.25±7.35	22.8±7.40	29.57±6.14

Values are means±standard deviations.

FSH, follicle stimulating hormone.

The endovaginal ultrasound was performed for the evaluation of endometrial thickness at the beginning and after 6 months of treatment using a Toshiba Power Vision 600 instrument equipped with a transvaginal 7.5 MHz transducer. The endometrial measurement is considered the point with the highest thickness involving the two endometrium leaflets in sagittal view and expressed in millimeters. This measurement was considered normal for the menopause phase when <4 mm.

The samples for the vaginal cytology were collected at the beginning and after 6 months of the study to evaluate the response of the cervical cytology to the treatments. These samples were collected during a vaginal examination through a speculum, using a spatula on the entire surface of the cervix and a brush to collect cells from the wall of the uterus endocervix. All vaginal cytology samples were evaluated by the same gynecologic pathologist. The vaginal epithelial maturation (VEM) value for each vaginal sample was calculated as follows: 100 cells were examined and classified as parabasal, intermediate, or superficial cells. Parabasal cells were given a score of 0, intermediate cells 0.5, and superficial cells 1.0.³¹

Mammography was performed at the beginning of the study, with the only purpose of exclusion of patients suspected or with alterations in the breast. Blood samples of each patient were collected at baseline and after 6 months by venipuncture after a 12-h fast for measuring FSH and estradiol. These hormones were analyzed by means of commercial immunoassay kits (Immulite; Siemens). The body weight of each patient was measured at the beginning and end of the study using a digital scale (Toledo).

Statistical analysis

Statistical differences between values at the beginning and at the end of the treatments were analyzed by means of the paired-sample t-test. The differences in Kupperman index and hot flashes intensity between before and after treatments were submitted to analysis of variance (ANOVA) analysis. The Graph Pad Prism 3.00 for Windows (Graph Pad Software) was used for the statistical analysis and a P value <.05 was considered significant.

Results

The patients were enquired monthly about their compliance with the treatments and possible side effects. Of the 90 randomized women, 75 completed the 6-month study: 28 in the flaxseed extract group, 22 in the flaxseed meal group, and 25 in the placebo group. The treatment with both flaxseed extract and flaxseed meal was well-tolerated without a serious adverse event being reported. However, gastrointestinal complaints, especially flatulence and abdominal distension, were the main causes of withdrawal from the use of flaxseed meal. There were no statistically significant differences in baseline parameters among the treatment groups (P>.05) (Table 1).

To evaluate menopausal symptoms, the Kupperman index questionnaire was applied. At baseline, symptoms were similar in the placebo, flaxseed extract, and flaxseed meal groups. After the 6-month treatment period, the menopausal symptoms of the participants using flaxseed extract and flaxseed meal were significantly reduced (P=.007 and P=.005, respectively), while no significant difference was found in the placebo group (P=.082) (Table 2). The intensity of hot flashes, as an isolated aspect, was also evaluated at the baseline and after 6 months of treatment. There was a significant reduction in the intensity of the hot flashes in the flaxseed extract group (P=.001) and in the flaxseed meal group (P=.035). Again, in the placebo group, the reduction of the intensity of hot flashes was not significant (P=.231) (Table 2).

Table 2.

Variation in the Kupperman Index and Intensity of Hot Flashes in the Experimental Groups at Baseline and After 6 Months of Treatment

Parameters	Baseline	Posttreatment (6 months)	P values (paired t-test)
Flaxseed extract group (n=28)
Kupperman index	9.89±5.30	7.39±3.30	.007
Intensity of hot flashes	6.08±2.78	4.48±2.95	.001
Flaxseed meal group (n=22)
Kupperman index	10.23±4.38	7.18±3.30	.005
Intensity of hot flashes	4.54±3.14	3.50±2.06	.035
Placebo group (n=25)
Kupperman index	11.64±5.19	10.36±4.55	.082
Intensity of hot flashes	6.96±2.67	6.75±2.79	.231

Values are means±standard deviations.

The decreases in the hot flashes score for the three groups are shown in Figure 1A. Standard deviations are high because the individual responses varied considerably. The decreases were 1.59±2.84 points for the flaxseed extract group, 1.04±1.99 points for the flaxseed meal group, and 0.21±1.49 points for the placebo group. No significant difference was detected by ANOVA (P=.084). Similarly, the decreases in the Kupperman index were 2.50±5.06 points for the flaxseed extract group, 3.50±4.10 points for the flaxseed meal group, and 1.28±4.10 points for the placebo group (Fig. 1B). Also, in this case no significant differences were revealed by ANOVA (P=.242). To evaluate the effects of flaxseed meal and flaxseed extract on endogenous hormones and estrogen target tissues, this study also evaluated the blood levels of FSH and estradiol, as well as the endometrial thickness, VEM, and body weight of the three groups at baseline and after 6 months of treatment (Table 3). For all these parameters no changes were observed (P≥.05, paired t-test).

FIG. 1.

Decreases in the hot flashes and Kupperman index of the experimental groups. The differences between before and after treatment in the hot flashes score (A) and Kupperman index (B) were computed. Values are presented as means±standard deviations. No significant differences were revealed by analysis of variance. In (A) P=.084; in (B) P=.242.

Table 3.

Variation in the Vaginal Epithelial Maturation Value, Endometrial Thickness, Hormonal Profile, and Body Weight in the Experimental Groups at Baseline and After 6 Months of Treatment

Parameters	Baseline	After 6 months
Vaginal epithelial maturation value (%)
Flaxseed extract group	39.8±15.1	32.4±18.3
Flaxseed meal group	41.6±10.9	36.9±16.0
Placebo group	35.7±12.9	32.0±19.0
Endometrial thickness (mm)
Flaxseed extract group	1.99±1.11	1.79±1.12
Flaxseed meal group	1.77±1.10	1.79±1.21
Placebo group	2.15±1.30	2.12±1.29
Estradiol (pg/mL)
Flaxseed extract group	23.25±7.35	23.29±7.53
Flaxseed meal group	22.80±7.40	24.68±8.08
Placebo group	29.57±6.14	25.54±7.82
FSH (mIU/mL)
Flaxseed extract group	81.14±26.07	77.89±24.87
Flaxseed meal group	64.24±18.32	61.72±23.93
Placebo group	68.88±19.88	72.65±24.96
Body weight (kg)
Flaxseed extract group	67.60±12.8	66.82±12.3
Flaxseed meal group	67.42±12.71	67.56±12.6
Placebo group	63.00±7.60	63.75±11.6

Values are means±standard deviations. P≥.05, paired t-test.

Discussion

It is estimated that 75% of women have some symptoms related to estrogenic deficiency, mainly hot flashes, night sweats, vaginal dryness, and sleep disturbances.³² These symptoms can have a negative impact on their daily activities and compromise their quality of life.^33,34 Hormone therapy is the main form of treatment for menopausal symptoms. However, in 2002, the WHI (Women's Health Initiative) study presented results that alarmed the population demonstrating increased risk in the development of invasive breast cancer and cardiovascular complications with the use of synthetic HT over 5 years.³⁵ Since then, the number of studies seeking improved efficacy and safety of alternative treatments that would reduce the symptoms of menopause has increased.

Up to now a few number of studies with flaxseed have been published using postmenopausal women as research subjects and their results can be compared with those of the present study. In two studies,^24,25 the daily dose of flaxseed meal was 25 g, while in the other two studies it was 40 g.^1,26 The duration of the treatments ranged from 3 to 12 months. In one of these studies the flaxseed supplementation improved lipid profiles in postmenopausal women.²⁶ In the other three studies the consumption of flaxseed was not more effective than the placebo for the control of lipid profiles and menopausal symptoms.^1,24,25 In another recent study, 188 postmenopausal women with or without breast cancer were randomly assigned to a flaxseed bar (providing 410 mg of lignans) for 6 weeks versus a placebo bar.²⁸ The mean hot flashes score was reduced by 4.9 points in the flaxseed group and 3.5 points in the placebo group (P=.29). The authors conclude that the results obtained in this study do not support the use of 410 mg of lignans for the reduction of hot flashes. When our data were analyzed in the same way, that is, in terms of the difference between before and after treatment, they also failed to reveal a statistically significant modification in spite of indicating a much stronger tendency toward improvement than that reported by Pruthi et al. ²⁸ However, when analyzing in terms of the absolute values of both the Kupperman index and the hot flashes intensities a different picture emerged. In this case both the flaxseed extract and the flaxseed meal were effective in reducing the clinical symptoms of menopause. This effectiveness was revealed by the statistical analysis using the paired t-test, which is appropriate for analyzing such before and after scenarios.

Our data show that flaxseed did not exert clinically important estrogenic effects on vaginal epithelium or endometrium. The phytoestrogens in general have antiproliferative action on hormone-responsive cancers, such as endometrium and prostate cancers; hence, its use is considered safe for the endometrium.⁴ In agreement with previous studies using phytoestrogens,^36

–39 no significant increase in the circulating level of estradiol was observed. In this respect, thus, the use of flaxseed (meal and extract) can be considered as safe.

Although gastrointestinal complaints have been reported in this work, the number of adverse events occurring during treatment with flaxseed was low, comparable to that of the placebo. Treatment with phytoestrogens is in general associated with a low incidence of adverse events and good adherence to treatment.

Conclusions

Although the results of the present study do not allow an unequivocal conclusion about a positive action of flaxseed on the menopausal symptoms, they at least suggest that it could be premature to conclude that no such action exists. Clearly the matter still deserves further experimental attention to completely understand the action of flaxseed as a possible option for reducing the menopausal symptoms. Considering that the bioactivity of flaxseed lignans depends on their transformation by gut bacteria, future studies should center on the possible individual differences in the intestinal bacteria, and on the absorption and metabolism of lignans. Measurement of plasma levels of mammalian lignans would also be especially important within this context.

Footnotes

Acknowledgment

This work was supported by grant from the Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq).

Author Disclosure Statement

No competing financial interests exist.

References

Simbalista

, Sauerbronn

, Aldrighi

, Arêas

JAG

. Consumption of a flaxseed-rich food is not more effective than a placebo in alleviating the climacteric symptoms of postmenopausal women. J Nutr, 2010; 140:293–297.

Palacios

, Borrego

, Forteza

. The importance of preventive health care in post-menopausal women. Maturitas, 2005; 52:53–60.

Borrelli

, Ernst

. Alternative and complementary therapies for the menopause. Maturitas, 2010; 66:333–343.

Hopert

, Beyer

, Frank

, Strunck

, Wünsche

, Vollmer

. Characterization of estrogenicity of phytoestrogens in an endometrial-derived experimental model. Environ Health Perspect, 1998; 106:581–586.

Rossouw

, Anderson

, Prentice

, LaCroix

, Kooperberg

, Stefanick

, Jackson

, Beresford

, Howard

, Johnson

, Kotchen

, Ockene

. Risks and benefits of estrogen plus progestin in healthy postmenopausal women. JAMA, 2002; 288:321–333.

Simon

, Snabes

. Post-menopausal hormone therapy improving the risky benefit ratio with ultra-low doses of estrogens. US Endocrinol Dis, 2007; 1:77–79.

Panay

, Rees

. Alternatives to hormone replacement therapy for management of menopause symptoms. Curr Obstet Gynaecol, 2005; 15:259–266.

Prestwood

. The search for alternative therapies for menopausal women: estrogenic effects of herbs. J Clin Endocrinol Metab, 2003; 88:4075–4076.

Patisaul

, Jefferson

. The pros and cons of phytoestrogens. Front Neuroendocrinol, 2010; 31:400–419.

10.

Warren

, Shortle

. Use of alternative therapies in menopause. Best Pract Res Clin Obstet Gynaecol, 2002; 16:411–448.

11.

Rees

. Alternative treatments for the menopause. Best Pract Res Clin Obstet Gynaecol, 2009; 23:151–161.

12.

Cremoux

, This

, Leeclerq

, Jacquot

. Controversies concerning the use of phytoestrogens in menopause management, bioavailability and metabolism. Maturitas, 2010; 65:334–339.

13.

Turner

, Agatonovic-Kustrin

, Glass

. Molecular aspects of phytoestrogen selective binding at estrogen receptors. J Pharm Sci, 2007; 96:1879–1885.

14.

Mense

, Hei

, Ganju

, Bhat

. Phytoestrogens and breast cancer prevention: possible mechanisms of action. Env Health Persp, 2008; 116:426–433.

15.

Johnston

. Phytochemical, Functional Foods. CRC Press, Inc., 2003; 66–68.

16.

Thompson

, Robb

, Serraino

, Cheung

. Mammalian lignan production from various foods. Nutr Cancer, 1991; 16:43–52.

17.

Clavel

, Doré

, Blau

. Bioavailability of lignans in human subjects. Nutr Res Rev, 2006; 19:187–196.

18.

Mazur

, Uehara

, Wähälä

, Adlercreutz

. Phyto-oestrogen content of berries, and plasma concentrations and urinary excretion of enterolactone after a single strawberry-meal in human subjects. Br J Nutr, 2000; 83:381–387.

19.

Gelfand

, Moreau

, Ayotte

, Hilditch

, Wong

, Lau

. Clinical assessment and quality of life of postmenopausal women treated with a new intermittent progestogen combination hormone replacement therapy: a placebo-controlled study. Menopause, 2003; 10:29–36.

20.

Kuijsten

, Arts

ICW

, van't Veer

, Hollman

PCH

. The relative bioavailability of enterolignans in humans is enhanced by milling and crushing of flaxseed. J Nutr, 2005; 135:2812–2816.

21.

Thompson

, Chen

, Li

, Strasser-Weippl

, Goss

. Dietary flaxseed alters tumor biological markers in postmenopausal breast cancer. Clin Cancer Res, 2005; 11:3828–3835.

22.

Peterson

, Dwyer

, Adlercreutz

, Scalbert

, Jacques

, McCullough

. Dietary lignans: physiology and potential for cardiovascular disease risk reduction. Nutr Rev, 2010; 68:571–603.

23.

Webb

, McCullough

. Dietary lignans: potential role in cancer prevention. Nutr Cancer, 2005; 51:117–131.

24.

Dodin

, Lemay

, Jacques

, Legare

, Forest

J-C

, Masse

. The effects of flaxseed dietary supplement on lipid profile, bone mineral density, and symptoms in menopausal women: a randomized, double-blind, wheat germ placebo-controlled clinical trial. J Clin Endocrinol Metab, 2005; 90:1390–1397.

25.

Lewis

, Nickell

, Thompson

, Szalai

, Kiss

, Hilditch

. A randomized controlled trial of the effect of dietary soy and flaxseed muffins on quality of life and hot flashes during menopause. Menopause, 2006; 13:631–642.

26.

Lucas

, Wild

, Hammond

, Khalil

, Juma

, Daggy

, Stoecker

, Arjmandi

. Flaxseed improves lipid profile without altering biomarkers of bone metabolism in postmenopausal women. J Clin Endocrinol Metab, 2002; 87:1527–1532.

27.

Franco

, Burger

, Lebrun

CEI

, Peeters

PHM

, Lamberts

SWJ

, Grobbee

, van Der Schouw

. Higher dietary intake of lignans is associated with better cognitive performance in postmenopausal women. J Nutr, 2005; 135:1190–1195.

28.

Pruthi

, Qin

, Terstreip

, Liu

HMS

, Loprinzi

, Shah

TRC

, Tucker

, Dakhil

, Bury

, Carolla

, Steen

, Vuky

, Barton

. A phase III, randomized, placebo-controlled, double-blind trial of flaxseed for the treatment of hot flashes: North Central Cancer Treatment Group N08C7. Menopause, 2012; 19:48–53.

29.

Milder

, Arts

, van de Putte

, Venema

, Hollman

. Lignan contents of Dutch plant foods: a database including lariciresinol, pinoresinol, secoisolariciresinol and matairesinol. Br J Nutr, 2005; 93:393–402.

30.

Milder

, Feskens

, Arts

, Bueno de Mesquita

, Hollman Howes

, Howes

, Knight

. Isoflavone therapy for menopausal flushes: a systematic review and meta-analysis. Maturitas, 2006; 55:203–211.

31.

Ducan

, Underhill

KEW

, Xu

, LaValleur

, Phipps

, Kurzer

. Modest hormonal effects of soy isoflavones in postmenopausal women. JCEM, 1999; 84:3479–3484.

32.

Dennerstein

, Lehert

, Guthrie

. The effects of the menopausal transition and biopsychosocial factors on well-being. Arch Womens Ment Health, 2002; 5:15–22.

33.

Kurzer

. Phytoestrogen supplement use by women. J Nutr, 2003; 133:1983S–1986S.

34.

Kok

, Kreijkamp-Kaspers

, Grobbee

, Lampe

, van der Schouw

. A randomized, placebo-controlled trial on the effects of soy protein containing isoflavones on quality of life in postmenopausal women. Menopause, 2005; 12:56–62.

35.

WHI. Risks and benefits of estrogen plus progestin in healthy postmenopausal women (writing group for the women's health initiative investigators) JAMA, 2002; 288:321–333.

36.

Verhoeven

, van der Mooren

, van de Weijer

PHM

, Verdegem

PJE

, van der Burgt

LMJ

, Kenemans

. Effect of a combination of isoflavones and Actaea racemosa Linnaeus on climacteric symptoms in healthy symptomatic perimenopausal women: a 12-week randomized, placebo-controlled, double-blind study. Menopause, 2005; 12:412–420.

37.

Wilcox

, Wahlquist

, Burger

, Medley

. Oestrogenic effects of plant foods in postmenopausal women. Br Med J, 1990; 301:905–906.

38.

Le Donne

, Caruso

, Mancuso

, Costa

, Iemmo

, Pizzimenli

, Cavallari

. The effect of vaginally administered genistein in comparison with hyaluronic acid on atrophic epithelium in postmenopause. Arch Gynecol Obstet, 2010; 283:1319–1323.

39.

Scheiber

, Rebar

. Isoflavones and postmenopausal bone health: a viable alternative to estrogen therapy? Menopause, 1999; 6:233–241.