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Purpose: Many studies have examined the association of isoflavone intake with type 2 diabetes (T2D), and produced inconsistent results. Few studies, however, explored the association using objective biomarkers (particular for daidzein metabolite-equol) of isoflavones. We aimed to explore the association of urinary equol, daidzein and genistein concentrations with T2D and examine the mediating roles of high-sensitivity C-reactive protein (hsCRP) and retinol binding protein 4 (RBP4)., Methods: This prospective study included 2818 subjects. Urinary concentrations of equol, daidzein and genistein were measured by high-performance liquid chromatography-tandem mass spectrometry. The associations between urinary isoflavones and T2D incidence were evaluated by cox proportional hazards model., Results: After adjustment for covariates, urinary equol except daidzein and genistein was inversely associated with T2D incidence. In comparison with the first tertile, multivariable adjusted hazard ratios (HRs) and 95% confidence intervals (95% CIs) for T2D incidence in the second and third tertile of equol concentration were 0.52 (0.37, 0.73) and 0.72 (0.53, 0.97), respectively. In stratified analyses by sex, the HR (95% CI) of men in the second vs. first tertile of equol was 0.29 (0.14, 0.58). Equivalent estimation in women was 0.67 (0.45, 1.01). Neither women nor men in the third tertile showed significant difference of T2D incidence compared with the first tertile. In path analyses, there was no evidence of mediating effects of hsCRP and RBP4 on the "equol-T2D" relationship., Conclusions: Urinary equol was favorably associated with a decreased T2D incidence in Chinese adults. The equol-T2D relationship might not be mediated by hsCRP and RBP4., Trial Registration: This study has been registered at http://www.clinicaltrials.gov as NCT03179657.

Soy and its isoflavones have been suggested to suppress thyroperoxidase (TPO), induce goiter, inhibit deiodinase, and modulate immune functions. This study initially investigated the effects of dietary soy consumption on maternal thyroid functions and anti-TPO antibody (TPOAb) production during early pregnancy. Data were collected through questionnaire from 505 women enrolled during early pregnancy by random sampling in Shenyang, China. Based on soy intake frequency, the subjects were divided into three groups (frequent [three or more times per week], conventional [more than twice per month but less than three times per week], and occasional [two or fewer times per month]). Serum thyrotropin (TSH), free thyroxine (FT(4)), and TPOAb were measured by chemiluminescence immunoassay. Additionally, the concentrations of two primary isoflavones (daidzein and genistein) and creatinine were assessed in the spot urine samples from representative subjects (about 20%) randomly selected from the three groups. The percentages of frequent, conventional, and occasional consumers were 18.6%, 62.6%, and 18.8%, respectively. No difference was found in age, medical records, family history of thyroid diseases, serum FT(4), TSH, and TPOAb levels, TPOAb-positive percentages, or prevalence of thyroid dysfunctions among the groups. Both urinary daidzein and genistein levels were significantly higher in the frequent consumers compared with the other two groups. No correlations were found between urinary isoflavone levels and serum FT(4) or TSH. Urinary isoflavone levels were not significantly different between TPOAb-positive and -negative women among the randomly selected representative subjects. On the whole, our findings suggest dietary soy consumption during early pregnancy is not associated with the development of thyroid dysfunction or autoimmunity.

Objectives: The aims of this study were to estimate the dietary intake of phytoestrogens and to measure urinary phytoestrogen excretion in postmenopausal Chinese women., Methods: Postmenopausal Chinese women were recruited from the hormone replacement clinic of the Prince of Wales Hospital. Dietary intake of phytoestrogen-rich foods was estimated using a food frequency questionnaire. Urinary output of the isoflavonoids daidzein and genistein and the metabolite of daidzein, equol, was measured using high-performance liquid chromatography., Results: The mean daily excretion of daidzein, genistein and equol was 3.24 (+/- 3.63), 1.47 (+/- 1.75) and 0.64 (+/- 1.53) mumol, respectively. The total mean daily isoflavonoid excretion was 5.36 (+/- 5.27) mumol., Conclusions: Urinary excretion of isoflavonoid phytoestrogens in this Chinese population was lower than that reported in Japanese subjects. This may be due to the higher consumption of legumes, especially soy products, in the Japanese compared to the Chinese diet. The intake of green vegetables was higher in the Chinese subjects, and this food group may be the main contributor to their total phytoestrogen intake.

Isoflavones are present in soybeans and its products in concentrations up to 300 mg/100 g, have estrogenic and antiestrogenic properties, and may be protective against hormone-related cancers. The purpose of this cross-sectional study was to investigate the association between urinary isoflavone excretion and self-reported soy intake. A total of 102 women of Caucasian, Native Hawaiian, Chinese, Japanese, and Filipino ancestry completed a dietary questionnaire for soy products consumed during the last year and during the 24-h period before urine collection. Overnight urine samples were analyzed for coumestrol and the soy isoflavones genistein, daidzein, and glycitein and their main human metabolites by reverse-phase high-pressure liquid chromatography. Soy protein and isoflavone intake (predominantly from tofu) were estimated using published nutritional databases. Wilcoxon's rank-sum test scores and Spearman rank correlation coefficients were computed. Japanese women excreted more daidzein, genistein, and glycitein than did Caucasian women, whereas Caucasian women excreted slightly more coumestrol. Soy intake differed significantly among ethnic groups. Dietary soy protein and isoflavone intakes during the previous 24 h were positively related to urinary isoflavone excretion [rs = 0.61 (P < 0.0001) and 0.62 (P < 0.0001), respectively]. Urinary excretion of isoflavones was also related to annual dietary soy protein and isoflavone intake [rs = 0.32 (P < 0.0012) and 0.31 (P < 0.0016), respectively]. The strong correlation between urinary isoflavone excretion and self-reported soy intake validates the dietary history questionnaire that is now used in a study exploring dietary risk factors for breast cancer.