A Few Soy Studies

Effect of soymilk consumption on serum estrogen and androgen concentrations in Japanese men.

Nagata C, Takatsuka N, Shimizu H, Hayashi H, Akamatsu T, Murase K.
Department of Public Health, Gifu University School of Medicine, Japan.

Soy consumption has been associated with a reduced risk of prostate cancer. The mechanism for this association may involve the effect of soy on the endocrine system. We conducted a randomized dietary intervention study to determine the effects of soy consumption on serum levels of steroid hormones in men. Thirty-five men were randomly assigned to either a soymilk-supplemented group or a control group. The men in the soy-supplemented group were asked to consume 400 ml of soymilk daily for 8 weeks. The men in the control group maintained their usual diet. Blood samples were obtained just before the initiation of the dietary period and thereafter every two weeks for 12 weeks. Changes in hormone concentrations were analyzed and compared between the two groups using the mixed linear regression model against weeks from the start of the dietary period. The mean (SD) soymilk intake estimated from dietary records during the dietary study period was 342.9 (SD, 74.2) ml in the soymilk-supplemented group. There was a significant difference between the two groups in terms of changes in serum estrone concentrations, which tended to decrease in the soy-supplemented group and increase in the control group over time. None of the other hormones measured (estradiol, total and free-testosterone, or sex hormone-binding globulin) showed any statistical difference between the two groups in terms of patterns of change. The results of the study indicate that soymilk consumption may modify circulating estrone concentrations in men.

PMID: 11303585 [PubMed - indexed for MEDLINE]

Soy milk intake in relation to serum sex hormone levels in British men.
Allen NE, Appleby PN, Davey GK, Key TJ.

Cancer Research UK Epidemiology Unit, University of Oxford, Oxford OX2 6HE, UK.

Soy beans contain high levels of the isoflavones genistein and daidzein and their glycosides and have been implicated in the prevention of prostate cancer, possibly via their effects on sex hormone metabolism. The aim of this study was to assess the relation between dietary soy intake and sex hormone levels in a cross-sectional analysis of 696 men with a wide range of soy intakes. Soy milk intake was measured using a validated semiquantitative food frequency questionnaire, and serum hormone concentrations were measured by immunoassay. Multiple regression was used to investigate the association between soy milk intake, an index of isoflavone intake, and hormone levels after adjustment for pertinent confounders. Soy milk intake was not associated with serum concentrations of testosterone, free testosterone, androstanediol glucuronide, sex hormone-binding globulin, or luteinizing hormone. These results suggest that soy milk intake, as a marker of isoflavone intake, is not associated with serum sex hormone concentrations among free-living Western men.

PMID: 12094627 [PubMed - indexed for MEDLINE]


Soy milk intake and plasma sex hormones: a cross-sectional study in pre- and postmenopausal women.

Verkasalo PK, Appleby PN, Davey GK, Key TJ. Imperial Cancer Research Fund Cancer Epidemiology Unit, University of Oxford, Oxford

Soy beans contain high levels of the isoflavones genistein and daidzein and their glucosides. We investigated the relationship between soy milk intake and plasma concentrations of estradiol, sex hormone-binding globulin, and, in premenopausal women, follicle-stimulating hormone, luteinizing hormone, and progesterone in a cross-sectional study of 636 premenopausal and 456 postmenopausal British women. Sixty-five percent of the women were vegetarians or vegans. Data on soy milk intake and other factors were obtained from a validated food frequency questionnaire, hormone concentrations were measured by immunoassays, and variations in geometric means were compared using analysis of covariance. We observed no statistically significant trends or meaningful associations between soy milk intake and circulating sex hormones. Adjusting for factors possibly affecting circulating hormone concentrations did not materially alter the results. We conclude that soy milk intake does not change plasma concentrations of sex hormones in pre- or postmenopausal British women who consume soy milk as a part of their regular diet.

PMID: 11962259 [PubMed - indexed for MEDLINE]