Objectives: The role of estrogens among men has rarely been explicitly considered. We examined differences in total, free, and bioavailable estradiol (Bio E) between young men from the United States (US) and the most economically developed part of China, that is, Hong Kong (HK).
Methods: Cross-sectional analysis was conducted based on 365 young men from the Third National Health and Nutrition Examination Survey in the US and 299 young Chinese men. All participants were aged from 18 to 29 years. Main outcome measures were total estradiol (E2) and calculated Bio E and free estradiol (FE).
Results: In both young US and Chinese men, E2 concentrations peaked at ages 25-29 years, at 43.3 pg/ml [95% confidence interval (CI) 41.9-44.8] in US men and 29.0 pg/ml (95% CI 26.2-32.0) in Chinese men. After adjustment for age and ethnicity, in all participants, US men had higher average concentrations of E2 [39.0 (95% CI 38.6-39.4) versus 28.3 (95% CI 28.3-28.4) pg/ml], FE [72.9 (95% CI 72.7-73.7) versus 56.8 (95% CI 56.6-56.9) ng/dl], and Bio E [17.9 (95% CI 17.7-18.1) versus 14.9 (95% CI 14.8-14.9) pg/ml] than HK men. Further adjustment for height or body mass index did not change the results.
Conclusions: Estradiol, and free and Bio E concentrations are much lower in young healthy Chinese men than US men. However, these findings based on comparison between the two assays in the two different locations need further confirmation.
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