AMERICAN JOURNAL OF HUMAN BIOLOGY 26:99–102 (2014)
Short Report
Testosterone Concentrations in Young Healthy US Versus Chinese Men L. XU,1 S.L. AU YEUNG,1 S. KAVIKONDALA,1 G.M. LEUNG,1 AND C.M. SCHOOLING1,2* 1 School of Public Health, Li Ka Shing Faculty of Medicine, The University of Hong Kong, Hong Kong SAR, China 2 CUNY School of Public Health and Hunter College, New York, USA
ABSTRACT: Background: Previous small studies examining differences in testosterone concentrations by ethnicity found mixed results for Caucasians and Chinese men, which might be confounded by age differences and living standards. The aim of the present study is to examine the differences in total, free, and bioavailable testosterone concentrations between healthy young men from the United States (US) and from the most economically developed part of China, i.e., Hong Kong (HK). Methods: Cross-sectional analysis based on 365 young men from the Third National Health and Nutrition examination Survey (NHANES III) in the US and 299 Chinese men recruited from university students. All participants were aged from 18 to 29 years. Main outcome measures were total testosterone (TT) and calculated bioavailable testosterone (Bio T) and free testosterone (FT). Results: In both US and Chinese men, TT, FT, and Bio T concentration peaked at 20–24 years of age, at 23.19, 0.49, and 12.23 nmol/l in US men, and 20.72, 0.48 and 12.59 nmol/l in Chinese men, respectively. Among those aged 18–24 years, after adjusting for age, US men had higher TT (mean, 95% confidence interval: 21.64, 21.31–21.99 versus 20.20, 20.12–20.28 nmol/l), but not FT (0.47, 0.47–0.48 versus 0.47, 0.47–0.47 nmol/l) or Bio T (11.90, 11.83–11.97 versus 12.39, 12.35–12.42 nmol/l) than Chinese men. Conclusions: TT, but not FT or Bio T concentrations are lower in young healthy Chinese men than US men. These differences apparent in young men may be important in understanding different patterns of diseases between Western C 2013 Wiley Periodicals, Inc. V and Asian populations. Am. J. Hum. Biol. 26:99–102, 2014. INTRODUCTION Previous studies found lower androgen related parameters, such as spermatid volume, testicular weight (Johnson et al., 1998), and prostate volume (Jin et al., 1999) in Chinese men compared with Caucasians. However, few studies have directly compared serum testosterone. One study comparing 10 Caucasian American men (age 22–27 years) and 10 Hong Kong Chinese men (age 24–39 years) showed higher testosterone in Caucasians (Santner et al., 1998), another comparing 57 Chinese (age 18–47 years) and 53 Caucasian men (age 21–35 years) found no difference (Lookingbill et al., 1991), whilst older Chinese men from Hong Kong (mean age 72 years) had higher testosterone than US white men (mean age 74 years) (Orwoll et al., 2010). Other studies in US or Chinese men suggest higher testosterone in US men than Chinese (Alvarado, 2010; Bhasin et al., 2011; Chu et al., 2008; Qin et al., 2012). However, different studies using different samples of varying age ranges may not be appropriate for direct comparison because testosterone falls with aging and illhealth. Given the small samples with different age ranges, further research is necessary to clarify the issue, specifically a younger sample which would be better suited to detect between population variation. Greater exposure to testosterone is positively associated with prostate cancer (Shaneyfelt et al., 2000). Western men have higher incidence of prostate cancer than men from China, which could be due to population differences in testosterone (Alvarado, 2013). Experimental evidence suggests that testosterone improves strength and muscle mass (Bhasin et al., 1996), and the reby glucose metabolism (Jones et al., 2011). Chinese people have a higher prevalence of diabetes at a lower level of body mass index than US men (Yoon et al., 2006). One possible explanation is differences in testosterone between Chinese and C 2013 Wiley Periodicals, Inc. V
American populations. Population level differences in testosterone levels are more pronounced in young men (Alvarado, 2013). We compared total (TT), calculated free (FT), and bioavailable testosterone (Bio T) in young healthy men from the Third National Health and Nutrition examination Survey (NHANES III) in the United States (US) and from a region of China with a similar living standard to the US, i.e., Hong Kong. METHODS Hong Kong young adult survey Two hundred and ninety-nine Chinese men students aged 18–29 years were recruited from the University of Hong Kong from February to December 2011. The participants were restricted to (1) those whose parents and at least three grandparents were born in Hong Kong or Guangdong province; and (2) those who were not taking medication which affects sex steroid concentrations. Selfadministered questionnaires were used to collect other relevant information such as socioeconomic position and health status. The Institutional Review Board of the University of Hong Kong and the Hospital Authority Hong Kong West Cluster approved the study. All participants gave written, informed consent before participation.
Contract grant sponsor: Research Grant Council General Research Fund; Contract grant number: 769710; Contract grant sponsor: Research Grant Council of Hong Kong, Hong Kong SAR, People’s Republic of China. *Correspondence to: C.M. Schooling, Units 624-627, Level 6, Core F, Cyberport 3, 100 Cyberport Road, Hong Kong. E-mail: [email protected] Received 16 September 2013; Revision received 24 October 2013; Accepted 26 October 2013 DOI: 10.1002/ajhb.22482 Published online 19 November 2013 in Wiley Online Library (wileyonlinelibrary.com).
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TABLE 1. Age adjusted mean and 95% confidence intervals (CI) for total, free, and bioavailable testosterone by age group among 299 men from
Hong Kong Young Adult Survey, 2011, and 344 US men from the Third National Health and Nutrition Examination Survey, 1988–1994 NHANES III
Age, years Sex hormone binding globulin (nmol/l) Albumin (g/l) Total testosterone (nmol/l) 18–19 20–24 25–29 18–24 Free testosterone (nmol/l) 18–19 20–24 25–29 18–24 Bioavailable testosterone (nmol/l) 18–19 20–24 25–29 18–24
Numbers
Means (95% CI)
Numbers
Means (95% CI)
365 365 365
24.1 (23.8–24.5) 28.7 (27.5–30.1) 45.7 (44.6–46.8)
299 299 299
21.0 (20.8–21.2) 23.1 (22.1–24.1) 48.4 (48.1–48.8)
45 148 172 193
18.60 (17.67–19.57) 23.19 (22.99–23.40) 20.94 (20.72–21.15) 21.64 (21.31–21.99)
103 187 9 290
19.29 (19.16–19.42) 20.72 (20.69–20.74) 18.07 (15.86–20.60) 20.20 (20.12–20.28)
45 148 172 193
0.44 (0.44–0.46) 0.49 (0.49–0.49) 0.45 (0.44–0.45) 0.47 (0.47–0.48)
103 187 9 290
0.46 (0.45–0.46) 0.48 (0.48–0.48) 0.43 (0.38–0.49) 0.47 (0.47–0.47)
45 148 172 193
11.32 (11.07–11.58) 12.23 (12.20–12.26) 10.94 (10.82–11.07) 11.90 (11.83–11.97)
103 187 9 290
12.02 (11.91–12.13) 12.59 (12.58–12.60) 10.99 (9.72–12.43) 12.39 (12.35–12.42)
Blood was drawn after an overnight fast in the morning between 0800 and 1100 hours for sex steroid assessment. All assays were performed in the Department of Pathology & Clinical Biochemistry, Queen Mary Hospital, Hong Kong, which has been accredited by the Hong Kong Accreditation Service for the Accreditation of Laboratories. Testosterone was assessed by radioimmunoassay. Sex hormone binding globulin (SHBG) was measured by two-site chemiluminescent immunometric assay (IMMULITE; Siemens Diagnostics). Measured albumin and SHBG were used to calculate FT and Bio T (Vermeulen et al., 1999). NHANES III NHANES III is a cross-sectional study conducted in the US by the National Center for Health Statistics between 1988 and 1994. The protocols for the conduct of NHANES III were approved by the institutional review board of the National Center for Health Statistics, Centers for Disease Control and Prevention. Informed consent was obtained from all participants. The assay of stored serum specimens for the Hormone Demonstration Program was approved by the Institutional Review Boards at the Johns Hopkins Bloomberg School of Public Health and the National Center for Health Statistics, Centers for Disease Control and Prevention. Blood was drawn after an overnight fast in the morning for 1,529 men who were randomly selected from the overall men for the morning examination session to reduce extraneous variation due to diurnal production of hormones. Sex steroid hormones and SHBG have been reported to be stable when exposed to multiple freeze– thaw cycles (Comstock et al., 2008). Competitive electrochemiluminescence immunoassays on the 2010 Elecsys autoanalyzer (Roche Diagnostics, Indianapolis, IN) were used for serum testosterone and SHBG at the Children’s Hospital Boston, MA. The samples were randomly ordered for testing, and the laboratory technicians were blinded to the men’s identities and ages. Quality control specimens with known hormone concentrations spanning higher and lower concentrations were used to determine reliability. FT and Bio T was estimated from measured American Journal of Human Biology
HKYAS
testosterone, SHBG, and albumin (Vermeulen et al., 1999). To minimize any confounding by age and to establish whether testosterone levels differ by ethnicity in young men, we only included men aged from 18 to 29 years and we also excluded those whose ethnicity was classified as “others.” Thus 365 men with measured sex steroids in the NHANES III were included in the current study. Statistical analysis Linear regression was used to calculate age adjusted means of TT, FT, and Bio T; 95% confidence intervals were used to compare age adjusted differences between samples. Data analysis was performed using STATA to weight the US sample back to the US population and take account of the complex survey design. RESULTS Among the 365 US men, 151 (41%) were MexicanAmerican, 101 (28%) were non-Hispanic white, and 113 (31%) were non-Hispanic black. TT, FT, and Bio T concentrations peaked at 20–24 years of age, at 23.19, 0.49, and 12.23 nmol/l in US men, and 20.72, 0.48, and 12.59 nmol/l in Chinese men, respectively. US men had higher SHBG and age but lower albumin than Chinese men. Only nine Chinese men were aged 25–29 years, so we also compared TT, FT, and Bio T at 18–24 years. After adjusting for age, US men had higher TT, with comparable FT and lower Bio T than Chinese men (Table 1). Figure 1 shows that US men had higher TT and FT at ages 18–24 years, but slightly lower Bio T after the age of 22 years than HK men. Stratified by ethnicity in the US sample, we also found higher TT in Mexican-American, non-Hispanic Black, and non-Hispanic White men than Hong Kong men (data not shown). DISCUSSION To our knowledge, this is the first study on two comparative samples of young healthy men aged 18–29 years showing that US men have higher TT but not FT and Bio
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TESTOSTERONE IN CHINESE MEN AND US MEN
Fig. 1. Total (a), free (b), and bioavailable testosterone (c) for men aged 18–24 years in HK (dash dot) compared with US (solid).
T than Chinese men, probably because of higher albumin in the Chinese men. As serum sex steroid concentrations decrease with age and ill-health, measurement of testosterone at older ages might not reflect lifelong endogenous exposure. Earlier studies comparing TT, FT, or Bio T between young to middle-aged Chinese and Caucasian American men were inconclusive, probably because of small sample sizes and different age ranges (Lookingbill et al., 1991; Santner et al., 1998). Age-specific testosterone reference ranges are higher for Caucasian (Bhasin et al., 2011) than Chinese men (Chu et al., 2008; Qin et al., 2012). Several factors may account for the discrepancies. The studies differed in the age range of the participants, the method of recruitment, and the methods of measurement. The US men were selected from NHANES III, a nationally representative study in the US. In contrast, we chose a sample of student volunteers from the University of Hong Kong that in theory could not be representative of the general population of young adults; however in the US young men testosterone was not associated with education after adjustment for age (data not shown). All students were in self-reported good health and matched on age with the US
men from NHANES III, to minimize any effects of age or underlying illness on testosterone. Several algorithms have been developed to calculate FT and Bio T which are not all well-validated and may have high variance for FT and Bio T (de Ronde et al., 2006). However, we used the same formula as in NHANES III (Vermeulen et al., 1999) to calculate FT and Bio T, which has high validation and reliability and is widely used (Rinaldi et al., 2002). Furthermore, immunoassay rather than the gold-standard mass spectrometry (MS)-based method was used to measure testosterone; however the same technique was used in both samples, which facilitates comparison. Although the MS-based method provides more accurate measurements, immunoassay is generally valid (Khosla et al., 2008), useful, and widely used in clinical practice, especially for large population-based research. Further studies using MS-based methods are warranted to make more accurate comparison between these two populations. Finally, testosterone is only one measure of androgens, representing largely production from the gonads rather than overall androgen production throughout the body. As about 25% of dihydrotestosterone is left in the prostate after castration (Nishiyama et al., 2004), suggesting that American Journal of Human Biology
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androgens can be also produced outside the gonads, reliable measures of all sources of androgens of testicular and peripheral origin would be useful. In conclusion, we have shown lower total, but not bioavailable or free testosterone among young healthy Chinese men compared to US men. Including two strictly age-matched samples, our findings could be an important initial step in understanding different patterns of diseases between Western and Asian populations, such as low incidence of prostate cancer and high prevalence of diabetes in China. Further large-scale studies are needed in other populations to confirm or refute our findings including measurement of other androgen metabolites to make an accurate assessment and comparison of androgen status between different populations. LITERATURE CITED Alvarado LC. 2010. Population differences in the testosterone levels of young men are associated with prostate cancer disparities in older men. Am J Hum Biol 22:449–455. Alvarado LC. 2013. Do evolutionary life-history trade-offs influence prostate cancer risk? A review of population variation in testosterone levels and prostate cancer disparities. Evol Appl 6:117–133. Bhasin S, Pencina M, Jasuja GK, Travison TG, Coviello A, Orwoll E, Wang PY, Nielson C, Wu F, Tajar A, Labrie F, Vesper H, Zhang A, Ulloor J, Singh R, D’Agostino R, Vasan RS. 2011. Reference ranges for testosterone in men generated using liquid chromatography tandem mass spectrometry in a community-based sample of healthy nonobese young men in the Framingham Heart Study and applied to three geographically distinct cohorts. J Clin Endocrinol Metab 96:2430–2439. Bhasin S, Storer TW, Berman N, Callegari C, Clevenger B, Phillips J, Bunnell TJ, Tricker R, Shirazi A, Casaburi R. 1996. The effects of supraphysiologic doses of testosterone on muscle size and strength in normal men. N Engl J Med 335:1–7. Chu LW, Tam S, Kung AW, Lo S, Fan S, Wong RL, Morley JE, Lam KS. 2008. Serum total and bioavailable testosterone levels, central obesity, and muscle strength changes with aging in healthy Chinese men. J Am Geriatr Soc 56:1286–1291. Comstock GW, Burke AE, Norkus EP, Gordon GB, Hoffman SC, Helzlsouer KJ. 2008. Effects of repeated freeze-thaw cycles on concentrations of cholesterol, micronutrients, and hormones in human plasma and serum. Am J Epidemiol 168:827–830. de Ronde W, van der Schouw YT, Pols HA, Gooren LJ, Muller M, Grobbee DE, de Jong FH. 2006. Calculation of bioavailable and free testosterone in men: a comparison of 5 published algorithms. Clin Chem 52: 1777–1784.
American Journal of Human Biology
Jin B, Turner L, Zhou Z, Zhou EL, Handelsman DJ. 1999. Ethnicity and migration as determinants of human prostate size. J Clin Endocrinol Metab 84:3613–3619. Johnson L, Barnard JJ, Rodriguez L, Smith EC, Swerdloff RS, Wang XH, Wang C. 1998. Ethnic differences in testicular structure and spermatogenic potential may predispose testes of Asian men to a heightened sensitivity to steroidal contraceptives. J Androl 19:348–357. Jones TH, Arver S, Behre HM, Buvat J, Meuleman E, Moncada I, Morales AM, Volterrani M, Yellowlees A, Howell JD, Channer KS, Times Investigators. 2011. Testosterone replacement in hypogonadal men with type 2 diabetes and/or metabolic syndrome (the TIMES2 study). Diabetes Care 344):828–837. Khosla S, Amin S, Singh RJ, Atkinson EJ, Melton LJ III, Riggs BL. 2008. Comparison of sex steroid measurements in men by immunoassay versus mass spectroscopy and relationships with cortical and trabecular volumetric bone mineral density. Osteoporos Int 19:1465–1471. Lookingbill DP, Demers LM, Wang C, Leung A, Rittmaster RS, Santen RJ. 1991. Clinical and biochemical parameters of androgen action in normal healthy Caucasian versus Chinese subjects. J Clin Endocrinol Metab 72: 1242–1248. Nishiyama T, Hashimoto Y, Takahashi K. 2004. The influence of androgen deprivation therapy on dihydrotestosterone levels in the prostatic tissue of patients with prostate cancer. Clin Cancer Research 10:7121–7126. Orwoll ES, Nielson CM, Labrie F, Barrett-Connor E, Cauley JA, Cummings SR, Ensrud K, Karlsson M, Lau E, Leung PC, Lunggren O, Mellstrom D, Patrick AL, Stefanick ML, Nakamura K, Yoshimura N, Zmuda J, Vandenput L, Ohlsson C, Osteoporotic Fractures in Men Research Group. 2010. Evidence for geographical and racial variation in serum sex steroid levels in older men. J Clin Endocrinol Metab 95: E151–E160. Qin X, Lv H, Mo Z, Chen Z, Lin L, Peng T, Zhang H, Yang X, Gao Y, Tan A, Huang S, Li H, Wu H, Deng Y, Li S. 2012. Reference intervals for serum sex hormones in Han Chinese adult men from the Fangchenggang Area Male Health and Examination Survey. Clin Lab 58:281–290. Rinaldi S, Geay A, Dechaud H, Biessy C, Zeleniuch-Jacquotte A, Akhmedkhanov A, Shore RE, Riboli E, Toniolo P, Kaaks R. 2002. Validity of free testosterone and free estradiol determinations in serum samples from postmenopausal women by theoretical calculations. Cancer Epidemiol Biomarkers Prev 11(10 Part 1):1065–1071. Santner SJ, Albertson B, Zhang GY, Zhang GH, Santulli M, Wang C, Demers LM, Shackleton C, Santen RJ. 1998. Comparative rates of androgen production and metabolism in Caucasian and Chinese subjects. J Clin Endocrinol Metab 83:2104–2109. Shaneyfelt T, Husein R, Bubley G, Mantzoros CS. 2000. Hormonal predictors of prostate cancer: a meta-analysis. J Clin Oncol 18:847–853. Vermeulen A, Verdonck L, Kaufman JM. 1999. A critical evaluation of simple methods for the estimation of free testosterone in serum. J Clin Endocrinol Metab 84:3666–3672. Yoon KH, Lee JH, Kim JW, Cho JH, Choi YH, Ko SH, Zimmet P, Son HY. 2006. Epidemic obesity and type 2 diabetes in Asia. Lancet 368: 1681–1688.
Short Report
Testosterone Concentrations in Young Healthy US Versus Chinese Men L. XU,1 S.L. AU YEUNG,1 S. KAVIKONDALA,1 G.M. LEUNG,1 AND C.M. SCHOOLING1,2* 1 School of Public Health, Li Ka Shing Faculty of Medicine, The University of Hong Kong, Hong Kong SAR, China 2 CUNY School of Public Health and Hunter College, New York, USA
ABSTRACT: Background: Previous small studies examining differences in testosterone concentrations by ethnicity found mixed results for Caucasians and Chinese men, which might be confounded by age differences and living standards. The aim of the present study is to examine the differences in total, free, and bioavailable testosterone concentrations between healthy young men from the United States (US) and from the most economically developed part of China, i.e., Hong Kong (HK). Methods: Cross-sectional analysis based on 365 young men from the Third National Health and Nutrition examination Survey (NHANES III) in the US and 299 Chinese men recruited from university students. All participants were aged from 18 to 29 years. Main outcome measures were total testosterone (TT) and calculated bioavailable testosterone (Bio T) and free testosterone (FT). Results: In both US and Chinese men, TT, FT, and Bio T concentration peaked at 20–24 years of age, at 23.19, 0.49, and 12.23 nmol/l in US men, and 20.72, 0.48 and 12.59 nmol/l in Chinese men, respectively. Among those aged 18–24 years, after adjusting for age, US men had higher TT (mean, 95% confidence interval: 21.64, 21.31–21.99 versus 20.20, 20.12–20.28 nmol/l), but not FT (0.47, 0.47–0.48 versus 0.47, 0.47–0.47 nmol/l) or Bio T (11.90, 11.83–11.97 versus 12.39, 12.35–12.42 nmol/l) than Chinese men. Conclusions: TT, but not FT or Bio T concentrations are lower in young healthy Chinese men than US men. These differences apparent in young men may be important in understanding different patterns of diseases between Western C 2013 Wiley Periodicals, Inc. V and Asian populations. Am. J. Hum. Biol. 26:99–102, 2014. INTRODUCTION Previous studies found lower androgen related parameters, such as spermatid volume, testicular weight (Johnson et al., 1998), and prostate volume (Jin et al., 1999) in Chinese men compared with Caucasians. However, few studies have directly compared serum testosterone. One study comparing 10 Caucasian American men (age 22–27 years) and 10 Hong Kong Chinese men (age 24–39 years) showed higher testosterone in Caucasians (Santner et al., 1998), another comparing 57 Chinese (age 18–47 years) and 53 Caucasian men (age 21–35 years) found no difference (Lookingbill et al., 1991), whilst older Chinese men from Hong Kong (mean age 72 years) had higher testosterone than US white men (mean age 74 years) (Orwoll et al., 2010). Other studies in US or Chinese men suggest higher testosterone in US men than Chinese (Alvarado, 2010; Bhasin et al., 2011; Chu et al., 2008; Qin et al., 2012). However, different studies using different samples of varying age ranges may not be appropriate for direct comparison because testosterone falls with aging and illhealth. Given the small samples with different age ranges, further research is necessary to clarify the issue, specifically a younger sample which would be better suited to detect between population variation. Greater exposure to testosterone is positively associated with prostate cancer (Shaneyfelt et al., 2000). Western men have higher incidence of prostate cancer than men from China, which could be due to population differences in testosterone (Alvarado, 2013). Experimental evidence suggests that testosterone improves strength and muscle mass (Bhasin et al., 1996), and the reby glucose metabolism (Jones et al., 2011). Chinese people have a higher prevalence of diabetes at a lower level of body mass index than US men (Yoon et al., 2006). One possible explanation is differences in testosterone between Chinese and C 2013 Wiley Periodicals, Inc. V
American populations. Population level differences in testosterone levels are more pronounced in young men (Alvarado, 2013). We compared total (TT), calculated free (FT), and bioavailable testosterone (Bio T) in young healthy men from the Third National Health and Nutrition examination Survey (NHANES III) in the United States (US) and from a region of China with a similar living standard to the US, i.e., Hong Kong. METHODS Hong Kong young adult survey Two hundred and ninety-nine Chinese men students aged 18–29 years were recruited from the University of Hong Kong from February to December 2011. The participants were restricted to (1) those whose parents and at least three grandparents were born in Hong Kong or Guangdong province; and (2) those who were not taking medication which affects sex steroid concentrations. Selfadministered questionnaires were used to collect other relevant information such as socioeconomic position and health status. The Institutional Review Board of the University of Hong Kong and the Hospital Authority Hong Kong West Cluster approved the study. All participants gave written, informed consent before participation.
Contract grant sponsor: Research Grant Council General Research Fund; Contract grant number: 769710; Contract grant sponsor: Research Grant Council of Hong Kong, Hong Kong SAR, People’s Republic of China. *Correspondence to: C.M. Schooling, Units 624-627, Level 6, Core F, Cyberport 3, 100 Cyberport Road, Hong Kong. E-mail: [email protected] Received 16 September 2013; Revision received 24 October 2013; Accepted 26 October 2013 DOI: 10.1002/ajhb.22482 Published online 19 November 2013 in Wiley Online Library (wileyonlinelibrary.com).
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TABLE 1. Age adjusted mean and 95% confidence intervals (CI) for total, free, and bioavailable testosterone by age group among 299 men from
Hong Kong Young Adult Survey, 2011, and 344 US men from the Third National Health and Nutrition Examination Survey, 1988–1994 NHANES III
Age, years Sex hormone binding globulin (nmol/l) Albumin (g/l) Total testosterone (nmol/l) 18–19 20–24 25–29 18–24 Free testosterone (nmol/l) 18–19 20–24 25–29 18–24 Bioavailable testosterone (nmol/l) 18–19 20–24 25–29 18–24
Numbers
Means (95% CI)
Numbers
Means (95% CI)
365 365 365
24.1 (23.8–24.5) 28.7 (27.5–30.1) 45.7 (44.6–46.8)
299 299 299
21.0 (20.8–21.2) 23.1 (22.1–24.1) 48.4 (48.1–48.8)
45 148 172 193
18.60 (17.67–19.57) 23.19 (22.99–23.40) 20.94 (20.72–21.15) 21.64 (21.31–21.99)
103 187 9 290
19.29 (19.16–19.42) 20.72 (20.69–20.74) 18.07 (15.86–20.60) 20.20 (20.12–20.28)
45 148 172 193
0.44 (0.44–0.46) 0.49 (0.49–0.49) 0.45 (0.44–0.45) 0.47 (0.47–0.48)
103 187 9 290
0.46 (0.45–0.46) 0.48 (0.48–0.48) 0.43 (0.38–0.49) 0.47 (0.47–0.47)
45 148 172 193
11.32 (11.07–11.58) 12.23 (12.20–12.26) 10.94 (10.82–11.07) 11.90 (11.83–11.97)
103 187 9 290
12.02 (11.91–12.13) 12.59 (12.58–12.60) 10.99 (9.72–12.43) 12.39 (12.35–12.42)
Blood was drawn after an overnight fast in the morning between 0800 and 1100 hours for sex steroid assessment. All assays were performed in the Department of Pathology & Clinical Biochemistry, Queen Mary Hospital, Hong Kong, which has been accredited by the Hong Kong Accreditation Service for the Accreditation of Laboratories. Testosterone was assessed by radioimmunoassay. Sex hormone binding globulin (SHBG) was measured by two-site chemiluminescent immunometric assay (IMMULITE; Siemens Diagnostics). Measured albumin and SHBG were used to calculate FT and Bio T (Vermeulen et al., 1999). NHANES III NHANES III is a cross-sectional study conducted in the US by the National Center for Health Statistics between 1988 and 1994. The protocols for the conduct of NHANES III were approved by the institutional review board of the National Center for Health Statistics, Centers for Disease Control and Prevention. Informed consent was obtained from all participants. The assay of stored serum specimens for the Hormone Demonstration Program was approved by the Institutional Review Boards at the Johns Hopkins Bloomberg School of Public Health and the National Center for Health Statistics, Centers for Disease Control and Prevention. Blood was drawn after an overnight fast in the morning for 1,529 men who were randomly selected from the overall men for the morning examination session to reduce extraneous variation due to diurnal production of hormones. Sex steroid hormones and SHBG have been reported to be stable when exposed to multiple freeze– thaw cycles (Comstock et al., 2008). Competitive electrochemiluminescence immunoassays on the 2010 Elecsys autoanalyzer (Roche Diagnostics, Indianapolis, IN) were used for serum testosterone and SHBG at the Children’s Hospital Boston, MA. The samples were randomly ordered for testing, and the laboratory technicians were blinded to the men’s identities and ages. Quality control specimens with known hormone concentrations spanning higher and lower concentrations were used to determine reliability. FT and Bio T was estimated from measured American Journal of Human Biology
HKYAS
testosterone, SHBG, and albumin (Vermeulen et al., 1999). To minimize any confounding by age and to establish whether testosterone levels differ by ethnicity in young men, we only included men aged from 18 to 29 years and we also excluded those whose ethnicity was classified as “others.” Thus 365 men with measured sex steroids in the NHANES III were included in the current study. Statistical analysis Linear regression was used to calculate age adjusted means of TT, FT, and Bio T; 95% confidence intervals were used to compare age adjusted differences between samples. Data analysis was performed using STATA to weight the US sample back to the US population and take account of the complex survey design. RESULTS Among the 365 US men, 151 (41%) were MexicanAmerican, 101 (28%) were non-Hispanic white, and 113 (31%) were non-Hispanic black. TT, FT, and Bio T concentrations peaked at 20–24 years of age, at 23.19, 0.49, and 12.23 nmol/l in US men, and 20.72, 0.48, and 12.59 nmol/l in Chinese men, respectively. US men had higher SHBG and age but lower albumin than Chinese men. Only nine Chinese men were aged 25–29 years, so we also compared TT, FT, and Bio T at 18–24 years. After adjusting for age, US men had higher TT, with comparable FT and lower Bio T than Chinese men (Table 1). Figure 1 shows that US men had higher TT and FT at ages 18–24 years, but slightly lower Bio T after the age of 22 years than HK men. Stratified by ethnicity in the US sample, we also found higher TT in Mexican-American, non-Hispanic Black, and non-Hispanic White men than Hong Kong men (data not shown). DISCUSSION To our knowledge, this is the first study on two comparative samples of young healthy men aged 18–29 years showing that US men have higher TT but not FT and Bio
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TESTOSTERONE IN CHINESE MEN AND US MEN
Fig. 1. Total (a), free (b), and bioavailable testosterone (c) for men aged 18–24 years in HK (dash dot) compared with US (solid).
T than Chinese men, probably because of higher albumin in the Chinese men. As serum sex steroid concentrations decrease with age and ill-health, measurement of testosterone at older ages might not reflect lifelong endogenous exposure. Earlier studies comparing TT, FT, or Bio T between young to middle-aged Chinese and Caucasian American men were inconclusive, probably because of small sample sizes and different age ranges (Lookingbill et al., 1991; Santner et al., 1998). Age-specific testosterone reference ranges are higher for Caucasian (Bhasin et al., 2011) than Chinese men (Chu et al., 2008; Qin et al., 2012). Several factors may account for the discrepancies. The studies differed in the age range of the participants, the method of recruitment, and the methods of measurement. The US men were selected from NHANES III, a nationally representative study in the US. In contrast, we chose a sample of student volunteers from the University of Hong Kong that in theory could not be representative of the general population of young adults; however in the US young men testosterone was not associated with education after adjustment for age (data not shown). All students were in self-reported good health and matched on age with the US
men from NHANES III, to minimize any effects of age or underlying illness on testosterone. Several algorithms have been developed to calculate FT and Bio T which are not all well-validated and may have high variance for FT and Bio T (de Ronde et al., 2006). However, we used the same formula as in NHANES III (Vermeulen et al., 1999) to calculate FT and Bio T, which has high validation and reliability and is widely used (Rinaldi et al., 2002). Furthermore, immunoassay rather than the gold-standard mass spectrometry (MS)-based method was used to measure testosterone; however the same technique was used in both samples, which facilitates comparison. Although the MS-based method provides more accurate measurements, immunoassay is generally valid (Khosla et al., 2008), useful, and widely used in clinical practice, especially for large population-based research. Further studies using MS-based methods are warranted to make more accurate comparison between these two populations. Finally, testosterone is only one measure of androgens, representing largely production from the gonads rather than overall androgen production throughout the body. As about 25% of dihydrotestosterone is left in the prostate after castration (Nishiyama et al., 2004), suggesting that American Journal of Human Biology
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androgens can be also produced outside the gonads, reliable measures of all sources of androgens of testicular and peripheral origin would be useful. In conclusion, we have shown lower total, but not bioavailable or free testosterone among young healthy Chinese men compared to US men. Including two strictly age-matched samples, our findings could be an important initial step in understanding different patterns of diseases between Western and Asian populations, such as low incidence of prostate cancer and high prevalence of diabetes in China. Further large-scale studies are needed in other populations to confirm or refute our findings including measurement of other androgen metabolites to make an accurate assessment and comparison of androgen status between different populations. LITERATURE CITED Alvarado LC. 2010. Population differences in the testosterone levels of young men are associated with prostate cancer disparities in older men. Am J Hum Biol 22:449–455. Alvarado LC. 2013. Do evolutionary life-history trade-offs influence prostate cancer risk? A review of population variation in testosterone levels and prostate cancer disparities. Evol Appl 6:117–133. Bhasin S, Pencina M, Jasuja GK, Travison TG, Coviello A, Orwoll E, Wang PY, Nielson C, Wu F, Tajar A, Labrie F, Vesper H, Zhang A, Ulloor J, Singh R, D’Agostino R, Vasan RS. 2011. Reference ranges for testosterone in men generated using liquid chromatography tandem mass spectrometry in a community-based sample of healthy nonobese young men in the Framingham Heart Study and applied to three geographically distinct cohorts. J Clin Endocrinol Metab 96:2430–2439. Bhasin S, Storer TW, Berman N, Callegari C, Clevenger B, Phillips J, Bunnell TJ, Tricker R, Shirazi A, Casaburi R. 1996. The effects of supraphysiologic doses of testosterone on muscle size and strength in normal men. N Engl J Med 335:1–7. Chu LW, Tam S, Kung AW, Lo S, Fan S, Wong RL, Morley JE, Lam KS. 2008. Serum total and bioavailable testosterone levels, central obesity, and muscle strength changes with aging in healthy Chinese men. J Am Geriatr Soc 56:1286–1291. Comstock GW, Burke AE, Norkus EP, Gordon GB, Hoffman SC, Helzlsouer KJ. 2008. Effects of repeated freeze-thaw cycles on concentrations of cholesterol, micronutrients, and hormones in human plasma and serum. Am J Epidemiol 168:827–830. de Ronde W, van der Schouw YT, Pols HA, Gooren LJ, Muller M, Grobbee DE, de Jong FH. 2006. Calculation of bioavailable and free testosterone in men: a comparison of 5 published algorithms. Clin Chem 52: 1777–1784.
American Journal of Human Biology
Jin B, Turner L, Zhou Z, Zhou EL, Handelsman DJ. 1999. Ethnicity and migration as determinants of human prostate size. J Clin Endocrinol Metab 84:3613–3619. Johnson L, Barnard JJ, Rodriguez L, Smith EC, Swerdloff RS, Wang XH, Wang C. 1998. Ethnic differences in testicular structure and spermatogenic potential may predispose testes of Asian men to a heightened sensitivity to steroidal contraceptives. J Androl 19:348–357. Jones TH, Arver S, Behre HM, Buvat J, Meuleman E, Moncada I, Morales AM, Volterrani M, Yellowlees A, Howell JD, Channer KS, Times Investigators. 2011. Testosterone replacement in hypogonadal men with type 2 diabetes and/or metabolic syndrome (the TIMES2 study). Diabetes Care 344):828–837. Khosla S, Amin S, Singh RJ, Atkinson EJ, Melton LJ III, Riggs BL. 2008. Comparison of sex steroid measurements in men by immunoassay versus mass spectroscopy and relationships with cortical and trabecular volumetric bone mineral density. Osteoporos Int 19:1465–1471. Lookingbill DP, Demers LM, Wang C, Leung A, Rittmaster RS, Santen RJ. 1991. Clinical and biochemical parameters of androgen action in normal healthy Caucasian versus Chinese subjects. J Clin Endocrinol Metab 72: 1242–1248. Nishiyama T, Hashimoto Y, Takahashi K. 2004. The influence of androgen deprivation therapy on dihydrotestosterone levels in the prostatic tissue of patients with prostate cancer. Clin Cancer Research 10:7121–7126. Orwoll ES, Nielson CM, Labrie F, Barrett-Connor E, Cauley JA, Cummings SR, Ensrud K, Karlsson M, Lau E, Leung PC, Lunggren O, Mellstrom D, Patrick AL, Stefanick ML, Nakamura K, Yoshimura N, Zmuda J, Vandenput L, Ohlsson C, Osteoporotic Fractures in Men Research Group. 2010. Evidence for geographical and racial variation in serum sex steroid levels in older men. J Clin Endocrinol Metab 95: E151–E160. Qin X, Lv H, Mo Z, Chen Z, Lin L, Peng T, Zhang H, Yang X, Gao Y, Tan A, Huang S, Li H, Wu H, Deng Y, Li S. 2012. Reference intervals for serum sex hormones in Han Chinese adult men from the Fangchenggang Area Male Health and Examination Survey. Clin Lab 58:281–290. Rinaldi S, Geay A, Dechaud H, Biessy C, Zeleniuch-Jacquotte A, Akhmedkhanov A, Shore RE, Riboli E, Toniolo P, Kaaks R. 2002. Validity of free testosterone and free estradiol determinations in serum samples from postmenopausal women by theoretical calculations. Cancer Epidemiol Biomarkers Prev 11(10 Part 1):1065–1071. Santner SJ, Albertson B, Zhang GY, Zhang GH, Santulli M, Wang C, Demers LM, Shackleton C, Santen RJ. 1998. Comparative rates of androgen production and metabolism in Caucasian and Chinese subjects. J Clin Endocrinol Metab 83:2104–2109. Shaneyfelt T, Husein R, Bubley G, Mantzoros CS. 2000. Hormonal predictors of prostate cancer: a meta-analysis. J Clin Oncol 18:847–853. Vermeulen A, Verdonck L, Kaufman JM. 1999. A critical evaluation of simple methods for the estimation of free testosterone in serum. J Clin Endocrinol Metab 84:3666–3672. Yoon KH, Lee JH, Kim JW, Cho JH, Choi YH, Ko SH, Zimmet P, Son HY. 2006. Epidemic obesity and type 2 diabetes in Asia. Lancet 368: 1681–1688.
