Effects of Soya Consumption for One Month on Steroid Hormones in Premenopausal Women: Implications for Breast Cancer Risk Reduction’

Home , Daidzein, Genistein, Isoflavonoid

Vol. 5. 63-70, JWZI4(U%’ 1996 Cancer Epidemiology, Biomarkers & Prevention 63

Lee-Jane W. Lu,2 Karl E. Anderson, James J. Grady, Introduction and Manubai Nagamani Ovarian hormones and other reproductive factors (e.g. , ages of Departments of Preventive Medicine and Community Health [L-J. W. L.. menarche, menopause, and parity) have important influences K. E. A.. J. J. G.j and Obstetrics and Gynecology [M. NI. University of on breast cancer development ( I ). Increased levels of estrogens Texas Medical Branch. Galveston. Texas 77555 in blood and urine are markers for high risk for breast cancer (2-5). For example, in a large prospective, case-control study, Toniolo et a!. (5) reported a significant relationship between Abstract serum estrogen levels and the risk for breast cancer in women Soybean consumption is associated with reduced rates of in New York. Goldin et a!. (6) reported 44% lower blood levels breast, prostate, and colon cancer, which is possibly of estrogens and androgens in oriental women who emigrated to related to the presence of isoflavones that are weakly the United States from areas of low breast cancer risk, when estrogenic and anticarcinogenic. We examined the effects compared to Caucasian Americans, who have a higher risk for of soya consumption on circulating steroid hormones in breast cancer. Women in rural China have a low risk for breast six healthy females 22-29 years of age. Starting within cancer and 36% lower plasma estrogen levels when compared 6 days after the onset of menses, the subjects ingested a to women in Britain where breast cancer is more common (7). 12-oz portion of soymilk with each of three meals daily Similarly, postmenopausal women in Japan have lower blood for 1 month on a metabolic unit. Daily isoflavone intakes estrogen levels and a lower risk for breast cancer than do white were 100 mg of daidzein (mostly as daidzin) and -100 women in the United States (8). Earlier studies (9) are in mg of genistein (mostly as genistin). Serum 17fi-estradiol agreement with these recent observations. levels on cycle days 5-7, 12-14, and 20-22 decreased by Dietary factors, such as legumes, may account at least in 31% (P = 0.09), 81% (P = 0.03), and 49% (P 0.02), part for these differences in hormone levels and breast cancer respectively, during soya feeding. Decreases persisted for risk. Consumption of legumes is greater in countries such as two to three menstrual cycles after withdrawal from soya China, Japan, and Thailand, where breast and prostate cancers feeding. The luteal phase progesterone levels decreased are less common than in Western countries (10-13). Legumes by 35% during soya feeding (P 0.002). are the major source of protein for vegetarians, another group Dehydroepiandrosterone sulfate levels decreased that is at low risk for many cancers (14, 15). A cross-sectional progressively during soya feeding by 14-30% (P 0.03). study in Australia found that legume consumption was associ- Menstrual cycle length was 28.3 ± 1.9 days before ated with lower risk for colon cancer ( I 5). Consumption of rice soymilk feeding, increased to 31.8 ± 5.1 days during the and tofu (a soy product) was inversely related to prostate cancer month of soymilk feeding (P = 0.06), remained increased risk among men of Japanese ancestry in Hawaii ( 10). Among at 32.7 ± 8.4 days (P 0.1 1) at one cycle after premenopausal women in Singapore, breast cancer risk was termination of soymilk feeding, and returned to pre-soya inversely related to soy protein intake (16. 17). These epide- diet levels five to six cycles later. These results suggest miological observations are supported by results of animal that consumption of soya diets containing phytoestrogens studies in which soya feeding was protective against experi- may reduce circulating ovarian steroids and adrenal mentally induced mammary and other organ cancers ( 13, 18). androgens and increase menstrual cycle length. Such Possible mechanisms for the cancer protective effects of effects may account at least in part for the decreased risk soya in humans are not established. However. soya contains of breast cancer that has been associated with legume significant amounts of the isoflavones daidzein and genistein consumption. ( 19). These isoflavones are weak estrogens with uterotropic potencies about I X l0 that ofdiethylstilbestrol and binding affinities for mammalian estrogen receptors, including those from MCF-7 cells (20), about 0.1-2 X lO_2 that of 17f3- Received 5/23/95: revised 9/25/95: accepted 9/27/95. estradiol (2 1 ). These isoflavones may act as anti-estrogens by The costs of publication of this article were defrayed in part by the payment of competing with endogenous estrogens for receptor binding, and page charges. This article must therefore be hereby marked ad,’ertise,nent in this may reduce estrogen-induced stimulation of breast cell accordance with 18 U.S.C. Section 1734 solely to indicate this fact. proliferation (20) and breast tumor formation. Alternatively. I This study was supported by USPHS Grants CA56273 and CA45181, and NIH National Center for Research Resources General Clinical Research Center Grant they may reduce breast cancer risk by decreasing endogenous MOI RROO()73. ovarian steroid levels. For example, genistein stimulates pro- 2 To whom requests for reprints should be addressed. at Department of Preventive gesterone synthesis by isolated bovine granulosa cells at a Medicine and Community Health, University of Texas Medical Branch. 2. I 02 Ewing Hall. Rt. I I 10. Galveston. TX 77555-I I 10. Phone: (409) 772-1730: Fax: concentration <0.2 ,.LM but inhibits progesterone synthesis at a (409 ) 772-9 108; E-mail: [email protected]. concentration >2 .LM (22) and antagonizes TGF-a-induced

estrogen biosynthesis in granulosa and theca cells (23). 33.49 ± 14.48 mg (mean ± SD; n = 1 1) of daidzin plus Genistein inhibits the enzyme activity ofestrogen-specific 17f3- daidzein, and 38.39 ± 14.62 mg of genistin plus genistein/ hydroxysteroid oxidoreductase type I, an enzyme that converts l2-oz lot, mostly as daidzin and genistin, but 15-19% of the estrone to l7-estradiol (24). Unlike some other flavonoids, total isoflavones were the aglycones daidzein and genistein. isoflavones are in general weak inhibitors for aromatase (25) Thus, the subjects ingested - 100 mg daidzin plus daidzein and

and inefficient inducers of monooxygenase and transferase - 100 mg genistin plus genistein/day. Soymilk ingestion began activities (26). Soya isoflavones may also decrease cancer in- 4.7 ± 1 .0 days (range, 3-6 days) after onset of menses. At cidence by mechanisms that do not involve alteration of steroid biweekly intervals and for 1-2 days, the subjects ingested all levels. For example, genistein is a specific inhibitor of tyrosine three l2-oz portions of soymilk within 30 mm for determination kinase (Ref. 27: an important enzyme in transmembrane signal of isoflavone absorption and disposition.4 Blood samples for transduction) induces cell differentiation (28), inhibits the ac- hormone determinations were obtained before and 1 day after tivity of topoisomerase II (29), and inhibits angiogenesis (30). starting soymilk and, thereafter, at weekly intervals during soya l7f3-Estradiol stimulates breast cell proliferation and may feeding. promote breast tumor growth (3 1 ). Progesterone antagonizes Hormone levels in normal women during a 28-30-day the proliferative effect of l73-estradiol on the endometrium but menstrual cycle are well described (38). 1 7/3-Estradiol levels its role in l7-estradiol-induced breast cell proliferation is not are the lowest (<50 pg/ml) during the early follicular phase clear. Human breast epithelial cells proliferate two to three (days 1-7), peak during days 12-14 (> 200 pg/ml), decrease times more rapidly during the luteal phase when progesterone precipitously after the LH surge (to < 100 pg/ml), peak again levels are also high (32). This suggests that proliferation of during days 20-24 (100-200 pg/ml), and then decrease to breast cells induced by I 7-estradiol may be further enhanced earlier follicular levels before the onset of menses. Progester- by high levels of progesterone (3 1). DHEA3 is an adrenal one levels are all <0. 1 ng/ml during the follicular phase, began androgen, an intermediate in the biosynthesis of l7-estradiol to rise after the LH surge (near day 14), and peak during the (33) and has a biphasic dose effect on breast cell proliferation midluteal phase (5-12 ng/ml; days 20-24; Ref. 38). Therefore, in vitro (34). The role of DHEA as an influence on human blood samples were obtained from our subjects on days 5-7, breast cancer development is still controversial (35). However, 12-14, and 20-22 of each menstrual cycle. This was accom- a DHEA sulfate-supplemented diet reduced the incidence of plished for one cycle before soya feeding in three subjects (only mammary tumors in mice (36). Therefore, l73-estradiol, pro- on day 5 for one subject), and for the month of soya feeding and gesterone, and DHEA sulfate may be useful biomarkers for for at least 3 cycles within the first 6 months after termination breast cancer risk. The purpose of the present study was to of soya feeding in all subjects. We were able to follow four of determine if consumption of soya containing isoflavones can the six subjects as outpatients for up to 10 months by frequent alter these three circulating steroid levels in premenopausal phone contacts; the lengths of their menstrual cycles were women and, thereby, protect them from developing breast recorded, and blood samples were obtained for hormone cancer. analysis. Hormone Analysis. 17-Estradiol and progesterone concen- Materials and Methods trations in the serum were measured by specific RIA after fractionation by microcelite column chromatography as de- Study Design. Six healthy, nonvegetarian women with regular scribed previously (39, 40). Briefly, 1 ml of serum was ex- menstrual cycles (26-3 1 days) were admitted for 33 days to the tracted twice with 3 volumes of ether after adding 3H tracers of General Clinical Research Center at The University of Texas 17j3-estradiol and progesterone for assessment of recovery. The Medical Branch. Four subjects were Caucasian, 1 African- American, and 1 Hispanic. Their age range was 22-29 years, extracts were dried under nitrogen and chromatographed on microcelite columns with ethylene and propylene glycol as the height 1.6-1.7 m, weight 53.8-70.5 kg, and body mass index stationary phase. This chromatographic separation is effective 18.9-26.2 kg/m2. Five subjects had never taken birth control pills and one had taken an oral contraceptive until 2 months in removing steroids that can interfere with the assay because of cross-reactivity. The fractions containing progesterone and before the study. History, physical examination, blood cell l7/3-estradiol were collected and dried, and the residue was counts, blood chemistry profiles, and serum ferritin were normal. The study was approved by the Institutional Review Board dissolved in the assay buffer. Two aliquots of different volumes of this solution were used in the assay, and 0. 1 ml was used for of the University of Texas Medical Branch and written in- recovery calculations. Blank and control sera were run with formed consent was obtained from each subject. Subjects consumed a standard hospital diet and three each assay. The antibody used in I 7-estradiol assay was 12-oz portions of soymilk (one with each meal) daily for 1 highly specific with <0. 1% cross-reactivity with estrone and month under the supervision of the dietary staff. Soymilk used estriol. Levels of DHEA sulfate were measured by direct RIA (41). The intra-assay coefficient ofvariation was 4-8% and the for this study was an homogenized, pasteurized preparation interassay variation was 5-9%. Steroid assays began only after containing no preservatives (Banyan Foods Co., Houston, TX). Isoflavone content in soymilk was analyzed as described (37). the collection of samples from all six subjects was completed. Briefly, an 80% methanolic extract was prepared from soymilk, All of the samples from each subject were analyzed in a single assay. dried and redissolved in water. Portions of the aqueous solution with or without f3-glucosidase digestion were purified by Statistical Analysis. To determine if the duration of soymilk ChemElut chromatography. The dried eluates after silylation ingestion had an effect on steroid hormone levels, Friedman’s were analyzed by gas chromatography equipped with a flame two-way ANOVA of the ranked data was used. If Friedman’s ionization detector. Selected lots used in the study contained test showed that the duration of treatment significantly affected

:‘ The abbreviations used are: DHEA. dehydroepiandrosterone: LH. luteinizing 4 L-J. W., Lu, S. N. Lin, J. J. Grady. M. Nagamani, and K. E. Anderson, hormone. manuscript in preparation.

(I) >1

. 4 a) C C) . .2 4O 0 Fig. I. Individual (symbols) and mean menstrual cy- >i dc length during soya injestion and I and 2-3 months C.) (Mon) after soya ingestion in six women who ingested CC three I 2-oz portions of soymilk daily for I month. I- Cl) 3O C) =OO6.

-mean 20 ---- Baseline During I Mon 2-3 Mon Soya Post Post Soya Soya

hormone levels, multiple comparisons of the various treatments soymilk feeding on individual and mean 17f3-estradiol levels, were made using paired t tests on the unranked data. Subjects when these were averaged over a cycle (Fig. 14 ) and analyzed with missing data at a particular time point were not included separately on specific cycle days (Fig. 2, B-D). One month of in the post hoc analysis by paired t tests for only that specific soya feeding reduced 17/3-estradiol levels either when all mea- time point, but their data from other time points were included surements were averaged during a cycle (Fig. 2A: P = 0.00 15, in the ANOVA and the calculation of the means shown in the Friedman’s test) or when they were analyzed on cycle days 5-7 figures. (Fig. 2B; P = 0.16), 12-14 (Fig. 2C; P = 0.0001), and 20-22 (Fig. 2D; P = 0.08). Fig. 14 shows that compared to the Results baseline, the mean cycle levels of 17j3-estradiol decreased by 62% during soymilk feeding (P = 0.03, paired t test), by 58% Fig. 1 shows the effect of I-month soymilk ingestion on mdi- during the first post-soymilk cycle (P = 0.05), and by 46% vidual and mean menstrual cycle lengths. The mean (± SD) during the second to the third cycles after soya (P = 0. 1 1). Fig. cycle length for this group of six women was 28.3 (± 1.9) days 2B shows that 17-estradiol levels in the early follicular phase before soya feeding; it increased slightly to 31.8 (± 5.1) days (days 5-7) decreased by 31% during chronic soymilk feeding during the month of soymilk feeding (P = 0.06, paired t test) compared to control periods (P = 0.09). Fig. 2C shows that and to 32.7 (± 8.4) days one cycle after termination of soymilk compared to the baseline, l7f3-estradiol levels during the late feeding (P = 0. 1 1 ). Five women experienced increase in cycle length of 1-12 days during soymilk feeding, whereas one follicular phases (days 12-14) decreased by 81% during soya woman had a 2-day decrease. The subject who was taking an feeding (n = 5; P = 0.03), by 72% during the first cycle oral contraceptive 2 months before the study had a 3-day post-soya (n = 5, P = 0.056), and by 68% during the second increase in cycle length, which was similar to other subjects. to third cycles after soya feeding (n = 5; P = 0.045). The late All women returned to their pre-soymilk cycle lengths five follicular phase l7-estradiol levels during soya feeding were cycles after termination of soymilk feeding (results not shown); also 41% lower than those during the second to third cycles this included a subject who had a cycle length of42 days during after soymilk feeding (P = 0.003). Fig. 2D shows that com- soymilk feeding and 49 days during the first cycle after soymilk pared to the baseline, 17f3-estradiol levels during the luteal feeding. This subject consumed soymilk for 4 extra days and phases (days 20-22) decreased by 49% during soya feeding also provided one blood sample after the last soymilk dose for (n 5; P = 0.02), by 68% during the first cycle post-soya hormone measurements. (n 4; P = 0.04), and by 29% during the second and third With only one exception, our subjects had baseline hor- cycles post-soya (n = 4; P = 0.24). Thus, chronic soya inges- mone levels within expected normal ranges (see “Materials and tion decreased l7-estradiol levels that persisted for two cycles Methods;” Ref. 38). Hormone levels from one cycle before and after soya ingestion. During the soymilk feeding, only one for five to ten cycles after termination of soymilk feeding from woman (who was previously on an oral contraceptive) had a our study subjects were similar and, therefore, were averaged small l7-estradiol peak (57 pg/ml) on day 14. During the and regarded as baseline values for each subject. The results of month of soymilk feeding, higher levels of l7f3-estradiol in all the second and third cycle after soymilk feeding were combined six subjects were detected on cycle days 22-37 (range, 60-135 because there were no detectable differences in hormone levels pg/ml) compared with those on cycle days 12-14 (range, 22-57 between these two cycles. pg/ml), and this was in contrast to the profiles observed during Fig. 2 shows the effect and persistence of 1 month of baseline periods. If the highest levels (e.g., independent of

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Fig. 2. The effect of I month (Moo) of soymilk ingestion on individual and mean serum levels of l7-estradiol in six women. Comparisons are for average levels of a cycle (A) and for cycle days 5-7 (B). days 12-14 (C). and days 20-22 (D). Baseline values are averages from one menstrual cycle before and/or five to six menstrual cycles after termination of soymilk ingestion. P values (paired I test) refer to comparisons with baseline values.

cycle day) were compared, those during soymilk feeding (84.7 3.0 ng/ml; range, 3.2-12.5 ng/ml) were all lower than their ± 21 .6 pg/ml; range, 60-135 pg/ml) were also lower than respective maximal values during baseline periods (9.5 ± 2.9

during baseline study periods (186.9 ± 99.3 pg/ml; range, ng/ml; range, 4-17.5 ng/ml; P - 0.06). Fig. 3 shows the effect 50-402.5 pg/ml; P = 0.04). The subject who was on an oral of 1 month of soymilk feeding on individual and mean proges- contraceptive previously had a similar but smaller decrease in terone levels measured on cycle days 20-22. The progesterone I 7f3-estradiol levels compared with other subjects. levels during the soymilk ingestion cycle were 35% lower than Follicular phase progesterone levels before, during, and baseline (P = 0.002) and 28-38% lower than the first three after soymilk feeding were all <0. 1 ng/ml, as expected (results cycles after termination of soya feeding (0. 10 < P < 0.03). The not shown). Luteal phase progesterone levels during baseline subject who used birth control pills before entering the study periods in five subjects were 4-18 ng/ml on cycle days 20-22, did not provide a blood sample on cycle days 20-22 during the which is within the expected range ofwomen with a 28-30 day baseline period; therefore, her data was not included in the post cycle (3 1). Luteal phase samples could not be obtained in the hoc analysis by paired t test. sixth subject during baseline periods. During soymilk feeding, DHEA sulfate levels were measured at least three times! four subjects had higher progesterone levels on cycle days cycle. Because DHEA sulfate levels do not undergo cyclic 20-24 than on other cycle days as for baseline periods. Two changes, all measurements in a cycle were averaged for each subjects who experienced 5- and 12-day increases in cycle subject. Thus, the values during the soymilk feeding repre- length had progesterone levels <0. 1 ng/ml on cycle days 20- sented means from varying lengths of soymilk ingestion. Base- 24, and these levels were lower than those on cycle days 27 and line intra-individual variability in DHEA sulfate levels within a 37 (9 and 3 ng/ml, respectively). The highest progesterone cycle were -15%, and inter-individual variability was -40%. levels detected for all subjects during soymilk feeding (7.1 ± One month of soymilk feeding reduced DHEA sulfate levels

a x 15 . . . . p=0.002 w S 0 C) 10 ‘I) Fig. 3. The effect in six women of I month (Mon) of C) soymilk ingestion on individual and mean serum levels of progesterone on cycle days 20-22. P value (paired 0 t test) refers to comparisons with baseline values. a-

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Baseline During I Mon 2-3 Mon soya Post Post Soya Soya

averaged over a cycle (P = 0.0006. Friedman’s test; Fig. 4A), luteal phase than during the follicular phase (32), an increase in and this change increased with the duration soya ingestion (P = cycle length, as observed in our subjects with soya feeding. may 0.06; Fig. 4B). Levels of DHEA sulfate averaged over the cycle shorten the duration of exposure of breast tissues to progester- were lowest during soya feeding and were 23% lower than one in the luteal phase. If this occurs repeatedly over a long before soya (P 0.03; Fig. 4A), 20% lower than during the period of time of soya ingestion, the relative amount of time first cycle after soya (P = 0.01), and 27% lower than during the during which breast tissue is stimulated to proliferate may second to third cycles after soya feeding (P = 0.006). DHEA decrease accordingly, and this may decrease the overall risk of sulfate levels at two to three cycles post-soya were slightly breast cancer development. Indeed, Henderson et a!. (43) sug- greater than pre-soya levels (P 0.08). Fig. 4B shows that gested that menstrual cycle length may modulate breast cancer during soymilk ingestion, DHEA sulfate levels decreased pro- risk. Differences in cycle lengths between breast cancer cases gressively as the number of days of soymilk ingestion in- and controls (44) and between populations of women in coun- creased. Compared with baseline, the decrease was significant tries with different breast cancer risks are consistent with this after >8 days (P values are shown in Fig. 4B). suggestion (45). During baseline cycles, our subjects had plasma levels of Discussion 17/3-estradiol and progesterone that were similar to those re- Steroid hormones such as 17-estradiol, progesterone, and ported by others in normal women (38). Their levels of l7- DHEA sulfate can modulate the proliferative rates of mammary estradiol were highest on cycle days 12-14, intermediate on epithelial cells. A change in menstrual cycle length alters the cycle days 20-22, and the lowest on cycle days 5-7. 17j3- relative duration of mammary epithelial cells in the luteal phase Estradiol levels were considerably lower during soymilk feed- of a cycle during which time the breast cells are more prolif- ing, when averaged over each cycle (Fig. 14 ), when compared erative. Thus, levels of these steroid hormones and menstrual during certain days of the cycle (Figs. 2, B-D), or when the cycle length are recognized risk factors for breast cancer (re- highest levels detected were compared. Moreover, during viewed in Refs. 31, 35). In this study. the effects of consuming soymilk feeding in all women, peak levels of 17f3-estradiol a soya diet rich in isoflavones (-200 mg/day) on these risk were observed only after cycle day 20. Soya feeding reduced factors were studied in six healthy, premenopausal women. We 17-estradiol levels in all six women, including one who had a found that 1 month of soymilk ingestion effectively reduced 2-day decrease in cycle length. These observations suggest that levels of l7-estradiol, progesterone, and DHEA sulfate and total 17f3-estradiol production was decreased during the month increased menstrual cycle length. of soymilk ingestion. Progesterone production may also be One month of soya feeding increased menstrual cycle reduced by soymilk feeding. All six women had lower luteal length in five of the six subjects. The increase was most progesterone levels during soya consumption than during base- pronounced in the two subjects who during soymilk feeding had line cycles. DHEA sulfate levels, which unlike 17-estradiol very low levels (<0. 1 ng/ml) of progesterone on cycle days and progesterone do not exhibit cyclicity, were also reduced 20-24 (Fig. 3), suggesting that there were delays in ovulation. during soymilk feeding (Fig. 4). DHEA sulfate levels in this In general, when cycle length increases, the length of follicular study decreased in a time-dependent manner with longer dura- phase increases more than the luteal phase (42). Because breast tion of soymilk feeding (Fig. 4B). Thus, the effect of soya cells proliferate two to three times more rapidly during the feeding on DHEA sulfate levels may result from the inhibition

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of the synthesis of DHEA. which is an intermediate in the length had progesterone levels > 1 ng!ml and peak l7-estra- biosynthesis of 1 7-estradiol. Reduction of 17j3-estradiol, pro- diol levels on cycle days 27 and 37, reduced levels of ovarian gesterone, and DHEA sulfate levels during soya feeding may steroids during soymilk feeding may be at least in part a reduce the extent of breast cell proliferation (3 1 ) and, thus, consequence of delays in peak and ovulation. The delays in breast cancer risk. ovulation during soya feeding would also account for the in- Reduced 17f3-estradiol and progesterone (but not DHEA crease in menstrual cycle lengths in our subjects. This will sulfate) levels during soymilk ingestion may in part result from decrease the duration of breast cells in the luteal phase and in delayed peak formation and subsequently delayed ovulation proliferation and, thus, lower breast cancer risk, as already because cycle length increased in five of six women during discussed. soya ingestion. All six subjects had higher levels of l7- The effectiveness of soya feeding in reducing circulating estradiol during the luteal phase of the cycle when soymilk was ovarian steroid levels in premenopausal women may explain ingested in contrast to higher levels on days 12-14 during epidemiological observations that legume consumption is pro- baseline periods (compare Figs. 2, C and D). Because the two tective against breast cancer development ( 16, 17), and that women who experienced >5-day increases in menstrual cycle Chinese and Japanese women from low risk areas have lower

plasma estrogen levels than do women from regions with high DHEA sulfate and increase cycle length in premenopausal risk (6-8). Among the many chemopreventive components of women. These endocrine factors are known to influence breast soya (reviewed in Refs. 12, 18, 46-49), only the isoflavones cell proliferation and breast cancer risk (2-5, 43, 44). There- and their metabolites have been detected in urine and blood of fore, these effects of soya on ovarian steroid levels may provide humans from populations with low breast and prostate cancer a biological basis for epidemiological observations that legume risks (37, 50-53). Thus, the soya isoflavones may play an consumption is associated with reduced estrogen levels in important role in protecting women from developing breast blood and urine (6-8) and reduced risk for breast cancer (16, cancer. However, other potentially chemopreventive compo- 17). We also showed that the effects of soya feeding on l73- nents of soya. such as Bowman-Birk protease inhibitor, phyt- estradiol levels persisted after termination of soya diets, sug- osterols, saponins, and inositols may also contribute to the gesting that soya consumption may be oncoprotective without effects observed ( 18. 54). daily consumption. However, the persistence of this effect in An anti-estrogenic effect may be one of the mechanisms relationship to endocrine function also requires more studies. by which the soya phytoestrogens reduce proliferation of breast epithelial cells and thus breast cancer risk. However, soya Acknowledgments phytoestrogens may also modify breast cell proliferation by We are grateful to the nursing, dietary, and administrative staff of the General decreasing circulating ovarian steroid levels. Our observation Clinical Research Center at the University of Texas Medical Branch for their that the levels of three different steroids, l7f3-estradiol, pro- skillful assistance. We thank Ann Livengood. RD., for diet preparation and gesterone, and DHEA sulfate, were reduced suggests that the supervision of the subjects and Dr. Lyle D. l3roemeling for statistical advice. synthesis of these steroids were inhibited during soya diets. Moreover, the effects on I 7-estradiol levels persisted for two References cycles after termination of soymilk feeding, during which time I. Marshall, E. Search for a killer: focus shifts from fat to hormones in special soya isoflavones were no longer detected in blood and urine report on breast cancer. Science (Washington DC), 259: 618 - 621 , 1993. (53). In in vitro assays, genistein inhibits the biosynthesis of 2. MacMahon. B., Cole, P., and Lin, T. M. Age at first birth and breast cancer progesterone by bovine granulosa cells (22), antagonizes trans- risk. Bull. WHO. 43: 209-221, 1970. forming growth factor a-induced synthesis of estrogen in gran- 3. Key. T. J. A., and Pike. M. C. The role of oestrogens and progestogens in the ulosa and theca cells (23) and inhibits the enzyme activity of epidemiology and prevention of breast cancer. Eur. J. Cancer & Clin. Oncol., 24: 17j3-hydroxysteroid oxidoreductase type I (24), an enzyme that 29-43. 1988. converts estrone to 17/3-estradiol. The effect of genistein on the 4. Bernstein, L., Yuan. J. M., Ross, R. K., Pike. M. C., Hanisch, R., Lobo, R., Stanczyk. F.. Gao. Y. T.. and Henderson. B. E. Serum hormone levels in synthesis of these three steroids may result from its effect on pre-menopausal Chinese women in Shanghai and white women in Los Angles: transmembrane signal transduction, a mechanism that may ex- results from two breast cancer case-control studies. Cancer Causes & Control, 1: plain the persistence of soya-induced effect on 17j3-estradiol 51-58, 1990. levels. Phytoestrogens are weak estrogens but at high doses 5. Toniolo. P. G., Levitz, M., Zeleniuch-Jacquotte, A.. Banerjee. S., Koenig. K. may have sufficient estrogenic activity to down-regulate the L.. Shore. R. E.. Strax, P., and Pasternack. B. S. A prospective study of endogenous estrogens and breast cancer in postmenopausal women. J. NatI. Cancer hypothalamus and pituitary and, thereby, reduce the ovarian Inst., 87: 190-197, 1995. synthesis of estrogens. However, in vitro studies have shown 6. Goldin, B. R.. Adlercreutz, H., Gorbach, S. L., Woods, M. N., Dwyer. J. T.. that some of biological effects of the genistein are independent Conlon. T.. Bohn. E.. and Gershoff, S. N. The relationship between estrogen of estrogen receptor status (55). levels and diets of Caucasian American and Oriental immigrant women. Am. J. Cassidy et a!. (56) reported that daily consumption of a Clin. 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L J Lu, K E Anderson, J J Grady, et al.

Cancer Epidemiol Biomarkers Prev 1996;5:63-70.

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