Thyroid hormones and male sexual function

Transcription

1 international journal of andrology ISSN ORIGINAL ARTICLE Thyroid hormones and male sexual function G. Corona, 1,2 F. C. W. Wu, 3 G. Forti, 4 D. M. Lee, 5 D. B. O Connor, 6 T. W. O Neill, 5 N. Pendleton, 7 G. Bartfai, 8 S. Boonen, 9 F. F. Casanueva, 10 J. D. Finn, 5 A. Giwercman, 11 T. S. Han, 12 I. T. Huhtaniemi, 13 K. Kula, 14 M. E. J. Lean, 15 M. Punab, 16 D. Vanderschueren, 17 E. A. Jannini, 18 E. Mannucci, 19 M. Maggi 1 and the EMAS Study Group* 1 Department of Clinical Physiopathology, Sexual Medicine and Andrology Unit, University of Florence, Florence, Italy, 2 Medical Department, Endocrinology Unit, Azienda Usl Bologna Maggiore-Bellaria Hospital, Bologna, Italy, 3 Department of Endocrinology, Manchester Royal Infirmary, The University of Manchester, Manchester, UK, 4 Department of Clinical Physiopathology, Endocrinology Unit, University of Florence, Florence, Italy, 5 ARC Epidemiology Unit, The University of Manchester, Manchester, UK, 6 Institute of Psychological Sciences, University of Leeds, Leeds, UK, 7 Clinical Gerontology, Hope Hospital, The University of Manchester, Salford, UK, 8 Gynaecology and Andrology, Albert Szent-Gyorgy Medical University, Szeged, Hungary, 9 Department of Experimental Medicine, Division of Gerontology and Geriatrics & Centre for Musculoskeletal Research, Katholieke Universiteit Leuven, Leuven, Belgium, 10 Department of Medicine, Santiago de Compostela University, Complejo Hospitalario Universitario de Santiago (CHUS); CIBER de Fisiopatología Obesidad y Nutricion (CB06 03), Instituto Salud Carlos III; Santiago de Compostela, Spain, 11 Reproductive Medicine Centre, Malmö University Hospital, University of Lund, Sweden, 12 Department of Endocrinology, Royal Free Hospital, Royal Free and University College Hospital Medical School, Hampstead, UK, 13 Department of Reproductive Biology, Imperial College London, Hammersmith Campus, London, UK, 14 Department of Andrology and Reproductive Endocrinology, Medical University of Lodz, Lodz, Poland, 15 Department of Human Nutrition, University of Glasgow, Glasgow, UK, 16 Andrology Unit, United Laboratories of Tartu University Clinics, Tartu, Estonia, 17 Department of Andrology and Endocrinology, Katholieke Universiteit Leuven, Leuven, Belgium, 18 Department of Experimental Medicine, School of Sexology, University of L Aquila, L Aquila, Italy and 19 Department of Critical Care, Diabetes Section Geriatric Unit, University of Florence, Florence, Italy Summary Keywords: erectile dysfunction, hypoactive sexual desire, testosterone, thyroid hormones Correspondence: Prof. Mario Maggi, Department of Clinical Physiopathology, Sexual Medicine and Andrology Unit, Viale Pieraccini 6, Florence, Italy. m.maggi@dfc.unifi.it *The members of the European Male Ageing Study (EMAS) group are listed in the Appendix S1. Received 22 October 2011; revised 7 February 2012; accepted 16 February 2012 doi: /j x The role of thyroid hormones in the control of erectile functioning has been only superficially investigated. The aim of the present study was to investigate the association between thyroid and erectile function in two different cohorts of subjects. The first one derives from the European Male Ageing Study (EMAS study), a multicentre survey performed on a sample of 3369 community-dwelling men aged years (mean 60 ± 11 years). The second cohort is a consecutive series of 3203 heterosexual male patients (mean age 51.8 ± 13.0 years) attending our Andrology and Sexual Medicine Outpatient Clinic for sexual dysfunction at the University of Florence (UNIFI study). In the EMAS study all subjects were tested for thyroid-stimulating hormone (TSH) and free thyroxine (FT4). Similarly, TSH levels were checked in all patients in the UNIFI study, while FT4 only when TSH resulted outside the reference range. Overt primary hyperthyroidism (reduced TSH and elevated FT4, according to the reference range) was found in 0.3 and 0.2% of EMAS and UNIFI study respectively. In both study cohorts, suppressed TSH levels were associated with erectile dysfunction (ED). Overt hyperthyroidism was associated with an increased risk of severe erectile dysfunction (ED, hazard ratio = 14 and 16 in the EMAS and UNIFI study, respectively; both p < 0.05), after adjusting for confounding factors. These associations were confirmed in nested case-control analyses, comparing subjects with overt hyperthyroidism to age, BMI, smoking status and testosterone-matched controls. Conversely, no association between primary hypothyroidism and ED was observed. In conclusion, erectile function should be evaluated in all individuals with hyperthyroidism. Conversely, assessment of thyroid function cannot be recommended as routine practice in all ED patients. International Journal of Andrology, 2012, 35, ª 2012 The Authors 668 International Journal of Andrology ª 2012 European Academy of Andrology

2 G. Corona et al. Thyroid and male sexual function Introduction Erectile dysfunction (ED) is a very common multidimensional disorder that significantly hampers the patient s and partner s quality of life, with a detrimental effect on sexual and reproductive activity. Gonadal, pituitary (e.g. oxytocin and prolactin) and thyroid hormones are involved in the control of sexual function (Jannini et al., 1995; Buvat, 2003; Carani et al., 2005; Corona et al., 2007, 2009; Krassas et al., 2008, 2010; Buvat et al., 2010; Corona & Maggi, 2010). Only few evidence-based reports, however, have investigated the relationship between thyroid dysfunction and ED (Carani et al., 2005; Davies & Larsen, 2008; Krassas et al., 2008). Anecdotal data indicate that ED is frequent (up to 70%) in men with hyperthyroidism (Meikle, 2004). Small studies in Italian (n = 48; Carani et al., 2005) and Greek (n = 56; Krassas et al., 2008) patients with thyroid dysfunctions have demonstrated that both hypothyroidism and hyperthyroidism are commonly associated with ED (as detected by validated questionnaires), and that the correction of the underlying conditions restores erectile function. In particular, in the Krassas s study (2008), 63 and 70% of the hypo- and hyperthyroid subjects were found to have some form of ED compared with 34% of the control group. While the prevalence of ED in hypothyroidism was similar in Carani s study (64%; Carani et al., 2005) the reported number of hyperthyroid subjects showing a pathological score (erectile function domain <26) of International Index of Erectile Function (IIEF) was remarkably lower (15%). So far, no information on the prevalence of thyroid dysfunction in ED men is available either for the general population or for men seeking medical care for sexual problems. The aim of this study was to investigate the association between thyroid and erectile function in a general population sample (European Male Ageing study, EMAS study) and in patients seeking medical care for sexual dysfunction (University of Florence Study, UNIFI study). Materials and methods Study design This is a cross-sectional study involving two different cohorts of subjects. EMAS study (general population) Study population. Present analyses are based on cross-sectional data from EMAS, a prospective, non-interventional cohort study of male ageing in Europe (EMAS study). Details regarding recruitment, response rates and assessments have been described elsewhere (Lee et al., 2009; Corona et al., 2010). Briefly, non-institutionalized men aged years were recruited from municipal or population registers in eight centres: Florence (Italy); Leuven (Belgium); Łódź (Poland); Malmö (Sweden); Manchester (UK); Santiago de Compostela (Spain); Szeged (Hungary); Tartu (Estonia). For the baseline survey, stratified random sampling was used with the aim of recruiting equal numbers of men into each of four age bands (40 49, 50 59, and years). Participants were invited by letter to complete a short postal questionnaire and to attend for screening at a local clinic. Overall, the mean response rate for full participation in the study was 41%. The study was funded by the European Union and ethical approval was obtained in accordance with local institutional requirements in each centre. The sociodemographical and clinical characteristics of the sample are reported in Table 1. Evaluation. Participants completed a postal questionnaire at baseline that included information about self-reported health, employment, education, smoking and alcohol consumption and the presence of concomitant morbidities (Lee et al., 2009; Corona et al., 2010). The participants also attended a research clinic to complete an interviewer-assisted questionnaire and undergo clinical assessments. The questionnaires included Beck s Depression Inventory (BDI), the Short Form 36 health survey (SF- 36) (Lee et al., 2009; Corona et al., 2010). Subjects then completed the EMAS sexual function questionnaire (EMAS-SFQ; O Connor et al., 2008) in private. Single item scores were used for ED: You are (Always able Usually able Sometimes able Never able ) to get and keep an erection which would be good enough for sexual intercourse. Development and validation of the EMAS-SFQ have been described previously (O Connor et al., 2008). All patients underwent a measurement of blood pressure (mean of three measurements 5 min apart, in sitting position, with a standard sphygmomanometer), height and weight from which body mass index (BMI) was calculated (kg m 2 ) (Lee et al., 2009; Corona et al., 2010). A single fasting morning (before 10:00 h) venous blood sample was obtained and processed serum stored at )80 C. Measurement of prolactin (PRL) and thyroidstimulating hormone (TSH), free thyroxin (FT4) and sex hormone binding globulin (SHBG) was performed using a chemiluminescence immunoassays (IA). The lower limits were 6.3 mu L, 0.01 mu L, 1.3 pmol L and 0.02 nmol L for PRL, TSH, FT4 and SHBG respectively. The coefficients of variation (CV) were 5.3, 3.44, 1.95 and 5.3% within runs and 2.5, 2.44, 3.31 and 6.6% between runs for PRL, TSH, FT4 and SHBG respectively. A validated gas ª 2012 The Authors International Journal of Andrology, 2012, 35, International Journal of Andrology ª 2012 European Academy of Andrology 669

3 Thyroid and male sexual function G. Corona et al. Table 1 Characteristics of the sample UNIFI study EMAS study Age (years) 51.8 ± ± 11.0 Morbidities (%) Current smoker Hypertension Diabetes mellitus Clinical and laboratory parameters BMI (Kg m 2 ) 26.5 ± ± 4.1 SBP (mmhg) 135 [ ] 144 [ ] DBP (mmhg) 80 [80 0] 86 [79 95] Glycaemia (mg dl) 5.3 [ ] 5.3 [ ] Total cholesterol (nmol L) 5.3 ± ± 1.3 HDL cholesterol 1.3 ± ± 0.4 Triglycerides (mg dl) 1.3 [ ] 1.3 [ ] TSH (mu L) 3.8 [ ] 1.5 [ ] FT4 (pmol L) 14.3 [ ] 15.9 [ ] Total testosterone (nmol L) 16.1 ± ± 6.0 Calculated free ± ± 89.2 testosterone (pmol L) DHT (nmol L) 1.3 ± 0.6 Total estradiol (pmol L) 73.7 ± 25.4 Calculated free estradiol (pmol L) 1.3 ± 0.5 Psychological parameters P MHQ score 32.1 ± 11.9 SF-36 mental componet 51.6 ± 9.3 score SF-36 physical componet 50.0 ± 8.2 score BDI score 6.9 ± 6.5 Sexual parameters (%) Erectile dysfunction Severe erectile dysfunction 7.5 Data are expressed as mean ± SD when normally distributed, median [quartiles] when not normally distributed and as percentages when categorical. BMI, body mass index; SBP, systolic blood pressure; DBP, diastolic blood pressure; HDL, high-density lipoprotein; TSH, thyroid-stimulating hormone; FT4, free thyroxin; DHT, dyidrotestosterone; MHQ, Middlesex Hospital Questionnaire; SF-36, Short Form 36 health survey questionnaire; BDI, Beck s Depression Inventory. chromatography-mass spectrometry (GC-MS) system (Labrie et al., 2006) was used to analyse total testosterone (T) (lower limit of quantification (LLOQ), 0.17 nmol L; intra-assay coefficient of variation (CV), 2.9%; interassay CV 3.4%), estradiol (E2) (LLOQ, 7.3 pmol L; intra-assay CV, 3.5%; interassay CV 3.7%) and dihydrotestosterone (DHT) (LLOQ, 0.07 nmol L; intra-assay CV, 3.1%; interassay CV 4.1%). All GC-MS analyses were performed in the Laboratory of Molecular Endocrinology, Laval University, Quebec. Calculated free T and E2 were derived using Vermeulen formula as previously described (Vermeulen et al., 1999). Calculated free T and E2 are calculated measures, based on total T and total E2 and SHBG: hence, their reproducibility can be assessed as the sum of variances of each variable plus the covariance of the two variables. According to Bland-Altman statistic, in our population the mean IA GC-MS difference (negative bias) for total T was a low and non-significant )0.036 (CI )0.113 to 0.040) nmol L. Taking >20% as a clinically significant deviation, 9% of the T levels by IA were more than 20% higher than the GC-MS levels, and 3% were over 20% lower. There was no significant trend in the relationship between the percentage bias and the average T concentration of the two methods (Huhtaniemi et al., 2012). Analyses for total cholesterol, high-density lipoprotein (HDL) cholesterol and triglycerides were performed locally in all centres using commercially available enzymatic methods. Fasting glucose was measured using standard hexokinase enzymatic assays. UNIFI study (patients with sexual dysfunction) Study population. An unselected consecutive series of male patients attending our Andrology and Sexual Medicine Outpatient Clinic for the first time with sexual dysfunction were retrospectively studied at the University of Florence (UNIFI study). A previous large study (Bancroft et al., 2005) including a convenience sample of gay men (n = 1379) and an age-matched sample of heterosexual men (n = 1558) has demonstrated that ED was more frequently reported by gay men and premature ejaculation more frequently by heterosexual men. In addition, important differences in the type of relationship (exclusive or non-exclusive) as well in measures of depression and anxiety were also reported. Hence, only heterosexual patients were included in this study, to make the results more comparable. The socio-demographical and clinical characteristics of the sample are reported in Table 1. All patients enrolled underwent the usual diagnostic protocol applied to newly referred subjects at the Andrology Outpatient clinic. All the data provided were collected as part of the routine clinical procedure. All patients provided informed consent to take part in the study. Patients were interviewed prior to the beginning of any treatment, and before any specific diagnostic procedures, using the SIEDY Structured Interview (Petrone et al., 2003; Corona et al., 2006). This is a 13-item interview made up of three scales, which identify and quantify components concurring with sexual dysfunctions. Patient s hypoactive sexual desire (HSD) was evaluated using question no.14 of SIEDY ( Did you have more or less desire to make love in the last three months? ) (Petrone et al., 2003). The characteristics of ED were assessed using SIEDY Appendix S1 as previously described (Petrone et al., 2003). In particular, severe ED was defined International Journal of Andrology, 2012, 35, ª 2012 The Authors 670 International Journal of Andrology ª 2012 European Academy of Andrology

4 G. Corona et al. Thyroid and male sexual function when patients reported an erection absent in more than 75% of occasions as previously reported (Petrone et al., 2003). Patients were also asked to complete the Middlesex Hospital Questionnaire, modified (MHQ) (Crown & Crisp, 1966), a brief self-reported questionnaire for the screening of mental disorders in a non-psychiatric setting. Patients were asked to report any kind of current drugs used. Chronic Diseases Score (CDS), an index of concomitant morbidities, was calculated as previously described (McGregor et al., 2005). Evaluation. All patients underwent a complete physical examination as in EMAS study. Blood samples were drawn in the morning, after an overnight fast, for determination of blood glucose (by glucose oxidase method), total cholesterol, HDL cholesterol and triglycerides (by automated enzymatic colorimetric method), total T, PRL and TSH, (by electrochemiluminescent method). FT4 was measured only when TSH values were outside the reference ranges ( mu L). The lower limits were 0.5 nmol L, 3.4 mu L, mu L and 1.67 pmol L for total T, PRL, TSH and FT4 respectively. The CV were 5.1, 2.3, 5.1 and 3.0% within runs and 7.2, 7.9, 6.4 and 3.6% between runs for PRL, TSH and FT4 respectively. SHBG (evaluated by electrochemiluminescence immunoassay; lower limit 0.02 nmol L, CV = 5.3% within runs and 6.6% between) was available for a subset of 1490 patients who were studied between September 2006 and September In this subset of our sample, calculated free T was derived using Vermeulen formula (Vermeulen et al., 1999). Calculated free T is a calculated measure, based on total T and SHBG: hence, its reproducibility can be assessed as the sum of variances of each variable plus the covariance of the two variables. Samples Identification of case patients and controls. To assess the effects of hyperthyroidism on sexual function, cases of overt hyperthyroidism according to the study method reference range for TSH (<0.35 and 0.4 for EMAS and UNIFI respectively) and FT4 (>23 and 21 pmol L for EMAS and UNIFI study respectively) were compared with controls, selected from the same cohort with a 1 : 5 ratio. For each case, the first five following patients within the same series with the same age (±4 years), body mass index (±2 kg m 2 ), smoking status (current former never smoker) and T levels (±4 nmol L), were taken as controls. In addition, in the EMAS study the same analysis was performed also considering only the Florence centre by comparing subjects with over hyperthyroidism with controls with 1 : 10 ratio. Statistical analysis All patients underwent the same diagnostic procedures; the data were adjusted for confounders. Differences were evaluated by one-way anova or Kruskal Wallis test, according to normal or not normal distribution. Correlations were assessed using Spearman s or Pearson s method for not normally or normally distributed data respectively. Unpaired two-tailed Student s t-tests were used for comparison of means of normally distributed parameters. In all other cases (i.e. not normally distributed variables), Mann Whitney U test was used for comparisons between groups. Stepwise multiple linear or logistic regression was applied for multivariate analysis, for continuous or categorical dependent variably respectively. All statistical analyses were performed using spss (Statistical Package for the Social Sciences, Chicago, IL, USA) for Windows Results General population (EMAS study) Among a total of 3369 men, TSH and FT4 levels were available in 3337 and 3351 subjects respectively. Low TSH levels (<0.35 mu L) were detected in 108 (3.3%) subjects. Among these, high FT4 levels (>23 pmol L) were observed in nine individuals (0.3% of the whole sample), of whom two were detected in the Florence centre (0.5% of the sample centre). Primary biochemical hypothyroidism (TSH > 5.5 mu L) was detected in 38 men (1.1%), seven (0.2% of the whole sample) of whom showed overt biochemical hypothyroidism (TSH > 10 mu L and FT4 < 11.5 pmol L). At univariate analysis, logarithmically transformed TSH was significantly related to age (r = )0.058; p < 0.001), and to logarithmically transformed PRL (r = 0.164; p < ). In addition, significant differences among eight EMAS centres were observed (p < at anova). Hence, all the following analyses were adjusted for age, logarithmically transformed PRL and EMAS centres. No significant association was found between BMI and TSH levels (not shown). However, subjects with lower TSH levels showed lower total cholesterol and triglycerides, when compared with the rest of the sample (Adjusted r = 0,046, p = and 0.040, p = for total cholesterol and triglycerides respectively). In addition, SHBG and total T but not free T levels were inversely related to TSH, (Fig. 1, panel A C). Similarly, SHBG was higher in subjects with higher logarithmically transformed FT4 levels (Fig. 1, panel D). Accordingly, total T levels were positively related to FT4, even after adjusting for age, PRL and study centres (Fig. 1, panel E), while calculated free T resulted unchanged (Fig. 1, panel F). In addition, DHT levels (mass ª 2012 The Authors International Journal of Andrology, 2012, 35, International Journal of Andrology ª 2012 European Academy of Andrology 671

5 Thyroid and male sexual function G. Corona et al. spectrometry) were inversely related to TSH and directly associated with FT4, even after adjusting for confounding factors (Adjusted r = )0.076 and for TSH and FT4 respectively; both p < ). Conversely, no relationship was found between TSH or FT4 and total (Adjusted r = )0.009, p = and 0.002, p = for TSH and FT4 respectively) or calculated free E2 levels (Adjusted r = 0.030, p = 0 and )0.029, p = for TSH and FT4 respectively) after adjustment for age (mass spectrometry). Accordingly, no difference in total or calculated free T E2 ratio was observed comparing subjects with or without overt biochemical hyperthyroidism (268.1 ± 74.2 vs ± 88.9, p = and ± 78.3 vs ± 82.0, p = 0.623; respectively for total and calculated T E2 ratio in subjects with or without overt biochemical hyperthyroidism). When quality of life (QoL) assessed by the Short Form 36 Questionnaire (SF-36) was evaluated, after adjusting for age, TSH was directly related to both physical and mental impairments of QoL, (adjusted r = 0.59, p = and 0.45, p = respectively). Subjects with overt biochemical hyperthyroidism have lower SF-36 physical and mental scores than euthyroid subjects (40.2 ± 12.3 vs ± 8.1, p = and 43.9 ± 15.2 vs ± 9.3, p = respectively). The association between biochemical hyperthyroidism and SF-36 physical and mental components remained significant even after adjustments for age, EMAS centres and PRL levels (p = and respectively). In contrast to the above observations of biochemical hyperthyroidism and its significant associations with QoL, no associations between overt biochemical hypothyroidism and SF-36 mental and physical components were found (not shown). Moreover, no difference in BDI score was found in patient with overt biochemical hyperthyroidism or hypothyroidism after adjustment for confounders (data not shown). When sexual parameters were investigated, no difference between TSH levels and sexual desire was observed (data not shown). Conversely, logarithmically transformed TSH was inversely related to ED prevalence (Fig. 2, panel A 0.20 B 0.20 C Adj r = 0.068; p = Adj r = 0.076; p = I II III IV I II III IV I II III IV SHBG quartiles Total testosterone quartiles Calculated free testosterone quartiles r = 0.004; p = D Log 10 [FT4] pmol/l 0.09 Adj r = 2; p = E Log 10 [FT4] pmol/l 0.09 Adj r = 0.044; p = F Log 10 [FT4] pmol/l 0.09 r = 0.001; p = I II III IV SHBG quartiles I II III IV Total testosterone quartiles I II III IV Calculated free testosterone G Adj r = 0.061; p = 0.05 H Adj r = 0.047; p = I Adj r = 0.004; p = I II III IV SHBG quartiles I II III IV Total testosterone quartiles I II III IV Calculated free testosterone quartiles Figure 1 Relationship between sex hormone binding globulin (SHBG), total testosterone (T) and calculated free T (expressed as quartiles) and thyroid-stimulating hormone (TSH) levels (logarithmically transformed) in the European Male Ageing Study (EMAS; panels A C) and University of Florence Study (UNIFI study; panels G I). Panels D F: relationship between SHBG total testosterone and calculated free T (expressed as quartiles) and free thyroxin (FT4) levels (logarithmically transformed) in the EMAS study. The insets indicate the adjusted relationship. International Journal of Andrology, 2012, 35, ª 2012 The Authors 672 International Journal of Andrology ª 2012 European Academy of Andrology

6 G. Corona et al. Thyroid and male sexual function A) and subjects reporting to never have erections showed higher FT4 levels (Fig. 2, panel B). These associations were confirmed in a multivariate analysis, when the number of self-reported morbidities, BMI, BDI score, SF36 score (physical component), use of antidepressants, smoking habit and T levels were entered as confounders (adjusted r = )0.060; p = and 0.050; p = for TSH and FT4 respectively). Among subjects with subclinical and overt biochemical hyperthyroidism, a significantly higher proportion reported no erections, when compared with the euthyroid men, whereas no difference was observed in subjects with subclinical and overt biochemical hypothyroidism (Fig. 2, panel C). The association between biochemical hyperthyroidism and impairment of erectile function was confirmed in a logistic multivariate analysis after adjustment for BMI, SF36 (mental and physical component) score, BDI score, use of antidepressants, smoking habit and T levels (Hazard ratio, HR = 2.31, p = and 14.18, p = 0.019; for subclinical and overt hyperthyroidism respectively). The effects of thyroid hormones on sexual function parameters were also assessed by comparing subjects with overt biochemical hyperthyroidism with age, BMI, smoking habit, T and PRL-matched controls. The prevalence of absence of erections was significantly higher in men with overt biochemical hyperthyroidism (Table 2). Similar results were observed when only Florence centre was considered (Table 3). Population with ED (UNIFI study) Among a consecutive series of 3203 men, 108 (3.4%) had low TSH levels (<0.4 mu L). Further biochemical and instrumental analyses (including thyroid releasing hormone stimulation test and magnetic resonance imaging of the hypothalamus-pituitary region) showed the presence of central hypothyroidism in five of 108 patients, who were excluded from the following analyses. Among the remaining 103 patients, seven (0.2% of the whole sample) showed overt hyperthyroidism (TSH < 0.4 mu L and FT4 > 21 pmol L: four cases of Graves disease, one of multinodular toxic goitre, one of uninodular toxic goitre and one of drug-induced hyperthyroidism; see also Table 4) while in the remaining 96 patients a diagnosis of subclinical hyperthyroidism was provided. Hypothyroidism (TSH > 4.5 mu L) was detected in 79 cases (2.5%). Among them nine (11.4%) showed overt hypothyroidism (TSH > 10 mu L and FT4 < 11.5 pmol L): five cases of Hashimoto s thyroiditis, three cases of post-surgical hypothyroidism and one case of iatrogenic hypothyroidism. A Adj r = 0.066; p = B Log 10 [FT4] pg/ml Adj r = 0.055; p = Always/Usually Sometimes Normal Erection Never Always/Usually Sometimes Normal Erection Never C 70 p < % of subjects reporting no erections p < Overt Subclinical Overt Subclinical Hyperthyroidism Euthyroidism Hypothyroidism Figure 2 Relationship between erectile function, thyroid-stimulating hormone (TSH) levels (logarithmically transformed; Panel A) and free thyroxin (FT4) (logarithmically transformed; Panel B) in the European Male Ageing Study (EMAS). Panel C shows the prevalence of subjects reporting no erections (never able to get and keep an erection good enough for sexual intercourse) for patients with overt hyperthyroidism (TSH < 0.35 mu L and FT4 > 23 pmol L), subclinical hyperthyroidism (TSH < 0.35 mu L and FT4 23 pmol L), euthyroidism (TSH mu and FT pmol L), subclinical hypothyroidism (TSH mu L) or overt hypothyroidism (TSH > 10 mu L and FT4 < 11.5 pmol L). Panel A B, the insets indicate the adjusted relationship. ª 2012 The Authors International Journal of Andrology, 2012, 35, International Journal of Andrology ª 2012 European Academy of Andrology 673

7 Thyroid and male sexual function G. Corona et al. Table 2 Comparison between subjects with overt hyperthyroidism and age-bmi-smoking habit- PRL-testosterone-matched controls in the European Male Ageing Study (EMAS) Case patients Controls p Age (years) 67.2 ± ± BMI (Kg m 2 ) 25.2 ± ± Total testosterone 16.6 ± ± (nmol L) PRL (mu L) 154.0[ ] 139.5[ ] Current smoker (%) Subjects reporting no erections (%) Data were expressed as mean ± SD when normally distributed, as median [quartiles] when non-parametric and as percentages when categorical. BMI, body mass index; PRL, prolactin; ED, erectile dysfunction. Table 3 Comparison between subjects with overt hyperthyroidism and age-bmi-smoking habit- PRL-testosterone-matched controls in the Florence centre of the European Male Ageing Study (EMAS) Case patients Controls p Age (years) 65.4 ± ± BMI (Kg m 2 ) 22.3 ± ± Total testosterone 16.3 ± ± (nmol L) PRL (mu L) 146.3[ ] 158.3[ ] Current smoker (%) Subjects reporting no erections (%) Data were expressed as mean ± SD when normally distributed, as median [quartiles] when non-parametric and as percentages when categorical. BMI, body mass index; PRL, prolactin; ED, erectile dysfunction. At univariate analysis, logarithmically transformed TSH was negatively related to age (r = )0.099; p < ), and positively to logarithmically transformed PRL (r = 0.199; p < ). Hence, all the following analyses were significantly adjusted for the aforementioned factors. Subjects with lower TSH levels were leaner and had a more favourable lipid profile, when compared with the rest of the sample (Adjusted r = 0,063, p = 0.003; 0.051, p = and 0,063, p = for BMI, total cholesterol and triglycerides respectively). When the association between thyroid hormones and sex steroid levels was investigated, SHBG levels were inversely related to TSH (Fig. 1, panel G). Accordingly, total T levels were higher in patients with lower TSH levels (Fig. 1, panel H), whereas calculated free T resulted unchanged (Fig. 1, panel I). No association between TSH levels and MHQ parameters was observed. In addition, MHQ score was not different in subjects with or without overt hypo- or hyperthyroidism (data not shown). When sexual parameters were analysed, subjects reporting moderate or severe hypoactive sexual desire showed higher TSH levels, when compared with the rest of the sample [HR = 1.51( ) vs. 1.43( ) mu L; p = 0.03]. However, this association was not confirmed by multivariate analysis when T, indeces of comorbidities (chronic disease score, CDS) and of general psychopathology ( P -MHQ) were introduced in the model as confounders (data not shown). At univariate analysis, TSH levels were negatively associated with the ability to have an erection sufficient for intercourse, as assessed by question 1A of SIEDY Appendix S1 (Fig. 3; panel A). This association was confirmed by multivariate analysis, after adjusting for age, smoking habit, T levels and CDS (Adjusted r = )0.044; p = 0.035). Subjects with overt hyper- and hypo-thyroidism were more frequently reported severe ED - as assessed by question 1D of SIEDY Appendix S1 when compared with euthyroid individuals (Fig. 3; panel B). Milder forms of ED were not associated with thyroid dysfunctions (not shown). The Table 4 Clinical and biochemical characteristics of patients with overt hyperthyroidism in UNIFI study Thyroid hormones Blood pressure (mmhg) Heart rate (bpm) Weight (Kg) Graefe Moebius (yes no) Tremors Patient # Age (years) Aetiology TSH (mu L) FT4 (pmol L) BT AT BT AT BT AT BT AT BT AT 1 63 Graves-Basedow disease No No No No 2 39 Graves-Basedow disease No No Mild No 3 67 Drug-induced No No 4 51 Graves-Basedow disease No No Moderate No 5 62 Graves-Basedow disease No No Moderate No 6 71 Toxic uninodular goitre No No 7 68 Toxic multinodular goitre No No BT, before medical therapy; AT, after medical therapy-induced normalization of thyroid hormones. International Journal of Andrology, 2012, 35, ª 2012 The Authors 674 International Journal of Andrology ª 2012 European Academy of Andrology

8 G. Corona et al. Thyroid and male sexual function association between severe ED and overt hyperthyroidism, but not overt hypothyroidism, was confirmed after adjusting for age, smoking habit, T, PRL levels and CDS (HR = 11.67; p = 0.023). Similar results were observed when the presence of premature ejaculation was introduced in the model, as a possible confounding factor (HR = 16.02; p = 0.016). The effects of thyroid hormones on sexual function were also assessed by comparing subjects with overt hyperthyroidism with age, BMI, smoking habit, T and PRL-matched controls. No significant difference was detected between cases and controls in the prevalence of hypoactive sexual desire, while the prevalence of severe ED was significantly higher in patient with over hyperthyroidism (Table 5). Medical therapy-induced normalization of thyroid hormone (Table 4) was able to significantly improve hyperthyroidism-related symptoms, including mean systolic blood pressure (131.4 ± 6.3 vs ± 10.2 mmhg; p = 0.008), mean heart rate (75.4 ± 3.9 vs ± 9.7 beats per minute; p = 0.035), mean body weight (77.9 ± 7.7 vs ± 8.9 Kg; p = ), prevalence of any degree of tremors (0% vs. 28.6%) and decrease the prevalence of severe ED (0% vs. 28.6%). Discussion This study evaluated the association between thyroid hormones and erectile function in two independent European populations, one including healthy men (EMAS study), and the other composed of patients seeking treatment for ED (UNIFI study). In both cohorts, we found that TSH levels were inversely related to ED, suggesting an association between hyperthyroidism and poor erectile functioning. In line with this finding, in the EMAS cohort the prevalence of ED increased as a function of FT4 levels. Consistently, overt biochemical hyperthyroidism was associated with an increased risk of absence of erections in a nested case-control analysis of the EMAS study. Similarly, patients with overt hyperthyroidism in the UNIFI study showed a significantly higher prevalence of severe ED in comparison with matched controls The association between low TSH and poor erectile functioning was retained in both cohorts even after adjusting for possible confounders, including other hormones (testosterone and PRL) and hyperthyroidism-induced impairment of quality of life (SF-36); this suggests a direct effect of thyroid hormones on erectile function. In contrast, elevated TSH and overt hypothyroidism were not independently associated with erectile problems. Although, an association between hypothyroidism and ED was found in the UNIFI, it was not confirmed in the EMAS cohort, and it did not persist in a multivariate model, after adjusting for possible confounders. Hence, hyperthyroidism only, and not hypothyroidism, as previously suggested (Carani et al., 2005; Krassas et al., 2008), is significantly and independently associated with ED. Hyperthyroidism is a common endocrine disease with a prevalence of 0 2% in men (Dasgupta & Savage, 2005; Fumarola et al., 2010). Our data are essentially in line with this figure: about 3% of subjects in both cohorts showed any form of hyperthyroidism, while an overt disease was found in only a minority of cases ( %). The prevalence of hyperthyroidism was not different between the two populations, suggesting that hyperthyroidism is not a frequent cause for ED consultation. Accordingly, the prevalence of overt hyperthyroidism was not different when EMAS subjects enrolled in the Florence centre when compared with UNIFI patients. It should be considered that the series of patients with ED A p = at ANOVA Always/Usually Sometimes Never Erection sufficient for penetrations B Prevalence of severe ED % p = p = Overt Subclinical Overt Subclinical Hyperthyroidism Euthyroidism Hypothyroidism Figure 3 Relationship between erectile dysfunction severity (as derived from question 1A of SIEDY Appendix S1) and thyroid-stimulating hormone (TSH) levels (logarithmically transformed; Panel A) in patients with erectile dysfunction (ED). Panel B shows the prevalence of severe ED (erection absent >75% of cases, as derived from question 1 D of SIEDY Appendix S1) for patients with overt hyperthyroidism (TSH < 0.4 mu L and free thyroxin, FT4 > 21 pmol L), subclinical hyperthyroidism (TSH < 0.4 mu L and FT4 21 pmol L), euthyroidism (TSH mu and FT pmol L), subclinical hypothyroidism (TSH mu L) or overt hypothyroidism (TSH > 10 mu L and FT4 < 11.5 pmol L). The inset indicates the unadjusted relationship. ª 2012 The Authors International Journal of Andrology, 2012, 35, International Journal of Andrology ª 2012 European Academy of Andrology 675

9 Thyroid and male sexual function G. Corona et al. Table 5 Comparison between subjects with overt hyperthyroidism and age-bmi-smoking habit- testosterone- matched controls in University of Florence (UNIFI) study Case patients Controls p Age (years) 60.1 ± ± BMI (Kg m 2 ) 24.9 ± ± Total testosterone 20.5 ± ± (nmol L) PRL (mu L) 116.5[ ] 123.5[ ] 0.58 Current smoker (%) Severe ED (%) Data were expressed as mean ± SD when normally distributed, as median [quartiles] when non-parametric and as percentages when categorical. Severe ED was quantified by question 1D, SIEDY, Appendix S1 (erection absent >75% of cases). BMI, body mass index; PRL, prolactin; ED, erectile dysfunction. enrolled at Andrology Clinic are, by no means, representative of patients with ED in the general population. Referral bias could have produced relevant distortions, for example patient with overt hypo- or hyperthyroidism could have been referred to Endocrinology Clinics not primarily involved in treatment of sexual dysfunction, potentially reducing the estimates of the prevalence of those disturbances in the clinical sample of patients with ED. However, it should be recognized that EMAS is a representative sample of community-dwelling ageing male. Hence, our data suggest that, in subjects with hyperthyroidism, other symptoms, rather that ED, would be more important for medical consultation. The specific mechanisms through which thyroid hormones might affect erectile function are unclear. Hyperthyroidism is associated with fatigue, myalgia and mood disturbances such as irritability and depression, which can contribute to sexual dysfunction. In our sample we could not confirm any association between hyperthyroidism and psychiatric symptoms, despite the finding that TSH levels were negatively related to QoL, as assessed by SF36. Hyperthyroidism was associated with ED even after adjusting for QoL and psychological symptoms, suggesting that this association is not primarily mediated by hyperthyroidism-induced mood disturbances. Thyroid hormones could be involved in the regulation of male sexual desire. An impairment of sexual desire has been reported in a small sample of hypothyroid patients (Carani et al., 2005). However, thyroid dysfunction did not appear to have any major, independent effect on sexual desire in the two cohorts enrolled in the present study. Hyperthyroidism has been associated with premature ejaculation (PE, 3), even in previous UNIFI studies (Corona et al., 2004, 2011). Although an association between ED and PE has been suggested (Jannini et al., 2005), the introduction of PE as a further covariate in a multiple regression model did not affect the relationship between hyperthyroidism and severe ED. Thyroid hormones are known to alter the reproductive axis in men (Krassas et al., 2010), which in turn might contribute to ED (Vela zquez & Bellabarba Arata, 1997, Zähringer et al., 2000; Krassas & Pontikides, 2004). In line with previous observations (Vermeulen et al., 1969; Olivo et al., 1970; Ruder et al., 1971; Ridgway et al., 1975; Rosner et al., 1984; Sarne et al., 1988; Abalovich et al., 1999), we found a thyroid hormone-dependent increase of both SHBG and total T levels, without modification of calculated free testosterone. As free T is the biologically relevant hormone, it is unlikely that hyperthyroidismassociated ED is owing to hypogonadism. In addition, the conversion rate of testosterone to dihydrotestosterone (assessed by mass spectrometry only in the EMAS study) was found to be increased, and not decreased, in hyperthyroidism, confirming previous results (Tagawa et al., 2001).Hyperthyroidism-induced increase of SHBG, which binds androgens with higher affinity than estrogens, might lead to a relative hyperestrogenism (Ridgway et al., 1982). However, E2 levels (assessed by mass spectrometry only in the EMAS study) in our cohort of subjects were not different between those with or without hyperthyroidism. Overall, hyperthyroidism appears to increase the conversion of T into its active metabolite, DHT, without modifications of free T or E2 or T E2 ratio. Hence, it is unlikely that the detrimental effects of increased thyroid hormones on sexual functioning are owing to sex steroid derangements. Both alpha and beta nuclear thyroid hormone receptors have been described in rat and human corpora cavernosa (CC) endothelial and smooth muscle cells (Owen et al., 2007; Carosa et al., 2010). Studies in animal models of hyperthyroidism indicate an impairment of nitric oxidedependent relaxation of corpora cavernosa (Ozdemirci et al., 2001; Hu et al., 2009). In rabbit CC strips, both acetylcholine- and electrical field stimulation-induced relaxation were impaired, whereas sensitivity to the nitric oxide (NO) donor, sodium nitroprusside, was unchanged (Ozdemirci et al., 2001). These data suggest that thyroid hormones have an effect on penile NO formation which is supported by studies using a rat model (Hu et al., 2009). It is therefore possible that hyperthyroidism-associated ED could be owing to a direct effect of thyroid hormones on their cognate receptors. Only prospective, intervention studies might clarify this point. However, in line with two other previous small European intervention studies (Carani et al., 2005; Krassas et al., 2008), we now report that treating hyperthyroidism restored erectile functioning. Several limitations of the present investigation should be recognized. The two different populations were International Journal of Andrology, 2012, 35, ª 2012 The Authors 676 International Journal of Andrology ª 2012 European Academy of Andrology

10 G. Corona et al. Thyroid and male sexual function evaluated through different methods and structured inventories, making the results not totally comparable. Although ED was quantified with validated inventories in both studies (Petrone et al., 2003; O Connor et al., 2008), the self-reported questionnaire used in the EMAS study (O Connor et al., 2008) was totally different from the structured interview (SIEDY, Petrone et al., 2003) used in UNIFI study. However, the fact that the allocation between overt hyperthyroidism and the most severe forms was observed in both samples, despite differences in assessment methods, strengthens the results. In the UNIFI cohort, which consists of subjects complaining of sexual dysfunction, the association between hyperthyroidism and ED was confirmed, in multivariate analysis, only in those referred with a severe degree of ED. Information on follow-up, and in particular on sexual function outcome, was available only in UNIFI study. UNIFI study was restricted on only heterosexual patients. Data derived from patients attending our Andrology Clinic for sexual dysfunction could have different characteristics from those individuals with ED who are consulting general practitioners, or who are not seeking medical care or without sexual dysfunction. The overall response rate for participation in the study was 41%. Those individuals who participated may have differed to those who did not participate with respect to levels of thyroid hormones and erectile dysfunction and some caution therefore is needed in interpreting our data (Lee et al., 2009; O Connor et al., 2011). EMAS routine clinical examination did include thyroid palpation or eliciting clinical features of hypo hyperthyroidism for all participants. Total testosterone was measured using different assays in the EMAS (gas chromatography-mass spectrometry) and UNIFI (electrochemiluminescent method) study, which have been reported poor correlation. Finally, we recognize that the use of calculated hormones such as free T is controversial and that recent studies have demonstrated that empirical formulae (such as the Vermeulen method) overestimate free T relative to laboratory measurement by equilibrium dialysis (e.g. Sartorius et al., 2009; Ly et al., 2010). In conclusion, our study shows that ED is a symptom frequently observed in patients with overt hyperthyroidism (more than 60%), although the latter is an infrequent (<1%) clinical condition in patients seeking medical care for ED. These observations suggest that erectile function should be evaluated in all men with hyperthyroidism. Conversely, assessment of thyroid function should not be recommended as routine practice for all ED patients, and probably investigated only in those reporting a severe form of ED. Hypothyroidism, either subclinical or overt, does not appear to be directly associated with poor erectile functioning. Conflicting interests and financial disclosure Nothing to declare. Acknowledgments The EMAS is funded by the Commission of the European Communities Fifth Framework Program Quality of Life and Management of Living Resources Grant QLK6-CT Additional support was also provided by the Arthritis Research Campaign (United Kingdom). The authors wish to thank the men who participated in the eight countries, the research nursing staff in the eight centers: C. Pott (Manchester), E. Wouters (Leuven), M. Nilsson (Malmö), M. del Mar Fernandez (Santiago de Compostela), M. Jedrzejowska (Lodz), H.-M. Tabo (Tartu), and A. Heredi (Szeged) for their data collection, and C. Moseley (Manchester) for data entry and project coordination. References Abalovich M, Levalle O, Hermes R, Scaglia H, Aranda C, Zylbersztein C, Oneto A, Aquilano D & Gutierrez S. (1999) Hypothalamic-pituitary-testicular axis and seminal parameters in hyperthyroid males. Thyroid 9, Bancroft J, Carnes L, Janssen E, Goodrich D & Long JS. (2005) Erectile and ejaculatory problems in gay and heterosexual men. Arch Sex Behav 34, Buvat J. (2003) Hyperprolactinemia and sexual function in men: a short review. Int J Impot Res 15, Buvat J, Maggi M, Gooren L, Guay AT, Kaufman J, Morgentaler A et al. (2010) Endocrine aspects of male sexual dysfunctions. J Sex Med 7, Carani C, Isidori AM, Granata A, Carosa E, Maggi M, Lenzi A & Jannini EA. (2005) Multicenter study on the prevalence of sexual symptoms in male hypo- and hyperthyroid patients. J Clin Endocrinol Metab 90, Carosa E, Di Sante S, Rossi S, Castri A, D Adamo F, Gravina GL et al. (2010) Ontogenetic profile of the expression of thyroid hormone receptors in rat and human corpora cavernosa of the penis. J Sex Med 7, Corona G & Maggi M. (2010) The role of testosterone in erectile dysfunction. Nat Rev Urol 7, Corona G, Petrone L, Mannucci E, Jannini EA, Mansani R, Magini A, Giommi R, Forti G & Maggi M. (2004) Psycho-biological correlates of rapid ejaculation in patients attending an andrologic unit for sexual dysfunctions. Eur Urol 46, Corona G, Jannini EA & Maggi M. (2006) Inventories for male and female sexual dysfunctions. Int J Impot Res 18, Corona G, Mannucci E, Fisher AD, Lotti F, Ricca V, Balercia G, Petrone L, Forti G & Maggi M. (2007) Effect of hyperprolactinemia in male patients consulting for sexual dysfunction. J Sex Med 4, Corona G, Mannucci E, Jannini EA, Lotti F, Ricca V, Monami M et al. (2009) Hypoprolactinemia: a new clinical syndrome in patients with sexual dysfunction. J Sex Med 6, Corona G, Lee DM, Forti G, O Connor DB, Maggi M, O Neill TW et al. (2010) Age-related changes in general and sexual health in middle-aged and older men: results from the European Male Ageing Study (EMAS). J Sex Med 7, ª 2012 The Authors International Journal of Andrology, 2012, 35, International Journal of Andrology ª 2012 European Academy of Andrology 677

11 Thyroid and male sexual function G. Corona et al. Corona G, Jannini EA, Lotti F, Boddi V, De Vita G, Forti G, Lenzi A, Mannucci E & Maggi M. (2011) Premature and delayed ejaculation: two ends of a single continuum influenced by hormonal milieu. Int J Androl 34, Crown S & Crisp AH. (1966) A short clinical diagnostic self-rating scale for psychoneurotic patients. The Middlesex Hospital Questionnaire (M.H.Q.). B J Psych 112, Dasgupta S & Savage MW. (2005) Evaluation of management of Graves disease in District General Hospital: achievement of consensus guidelines. Int J Clin Pract 59, Davies TF & Larsen PR. (2008) Thyrotoxicosis. In: Williams Textbook of Endocrinology, 11 th edn (eds HM Kronenberg, S Melmed, KS Polonsky & PR Larsen), pp Saunders Elsevier, Philadelphia. Fumarola A, Di Fiore A, Dainelli M, Grani G & Calvanese A. (2010) Medical treatment of hyperthyroidism: state of the art. Exp Clin Endocrinol Diab 118, Hu CL, Wu YD, Liu HT, Qin WB & Wang GZ. (2009) Effect of thyroid hormone on the contents of NOS and CO in the penile corpus cavernosum of rats. Zhonghua Nan Ke Xue 15, Huhtaniemi IT, Tajar A, O Neill TW, Finn JD, Bartfai G, Boonen S et al. (2012) Comparison of serum testosterone and estradiol levels in 3174 European men as measured by a platform immunoassay and mass spectrometry; relevance for the diagnostics in aging men. Eur J Endocrinol. 2012; 166, Jannini EA, Ulisse S & D Armiento M. (1995) Thyroid hormone and male gonadal function. End Rev 16, Jannini EA, Lombardo F & Lenzi A. (2005) Correlation between ejaculatory and erectile dysfunction. Int J Androl 28(Suppl. 2), Krassas GE & Pontikides N. (2004) Male reproductive function in thyroid alterations. Best Pract Res Clin Endocrinol Metab 18, Krassas GE, Tziomalos K, Papadopoulou F, Pontikides N & Perros P. (2008) Erectile dysfunction in patients with hyper- and hypothyroidism: how common and should we treat? J Clin Endocrinol Metab 93, Krassas GE, Poppe K & Glinoer D. (2010) Thyroid function and human reproductive health. End Rev 31, Labrie F, Bélanger A, Bélanger P, Bérubé R, Martel C, Cusan L et al. (2006) Androgen glucuronides, instead of testosterone, as the new markers of androgenic activity in women. J Steroid Biochem Mol Biol 99, Lee DM, O Neill TW, Pye SR, Silman AJ, Finn JD, Pendleton N et al. (2009) The European Male Ageing Study: design, methods and recruitment. Int J Androl 32, Ly LP, Sartorius G, Hull L, Leung A, Swerdloff RS, Wang C & Handelsman DJ. (2010) Accuracy of calculated free testosterone formulae in men. Clin Endocrinol (Oxf) 73, McGregor JC, Kim PW, Perencevich EN, Bradham DD, Furuno JP, Kaye KS, Fink JC, Langenberg P, Roghmann MC & Harris AD. (2005) Utility of the chronic disease score and charlson comorbidity index as comorbidity measures for use in epidemiologic studies of antibioticresistant organisms. Am J Epidemiol 161, Meikle AW. (2004) The interrelationships between thyroid dysfunction and hypogonadism in men and boys. Thyroid 14(Suppl. 1), S17 S25. O Connor DB, Corona G, Forti G, Tajar A, Lee DM, Finn JD et al. (2008) Assessment of sexual health in Ageing Men in Europe: development and validation of the European Male Ageing Study (EMAS) sexual function questionnaire (EMAS-SFQ). J Sex Med 5, O Connor DB, Lee DM, Corona G, Forti G, Tajar A, O Neill TW et al. (2011) The relationships between sex hormones and sexual function in middle-aged and elderly European men. J Clin Endocrinol Metab 96, e1577 e1587. Olivo J, Southren AL, Gordon GG & Tochimoto S. (1970) Studies of the protein binding of testosterone in plasma in disorders of thyroid function: effect of therapy. J Clin Endocrinol Metab 31, Owen PJ, Sabit R & Lazarus JH (2007) Thyroid disease and vascular function. Thyroid 17, Ozdemirci S, Yildiz F, Utkan T, Ulak G, Cetinaslan B, Erden F & Gacar N. (2001) Impaired neurogenic and endothelium-dependent relaxant responses of corpus cavernosum smooth muscle from hyperthyroid rabbits. Eur J Pharmacol 428, Petrone L, Mannucci E, Corona G, Bartolini M, Forti G, Giommi R & Maggi M. (2003) Structured interview on erectile dysfunction (SIEDYª): a new, multi-dimensional instrument for quantification of pathogenetic issues on erectile dysfunction. Int J Impot Res 15, Ridgway EC, Longcope C & Maloof F. (1975) Metabolic clearance and blood production rates of estradiol in hyperthyroidism. J Clin Endocrinol Metab 41, Ridgway EC, Maloof F & Longcope C. (1982) Androgen and oestrogen dynamics in hyperthyroidism. J Endocrinol 95, Rosner W, Aden DP & Khan MS. (1984) Hormonal influences on the secretion of steroid-binding proteins by a human hepatoma-derived cell line. J Clin Endocrinol Metab 59, Ruder H, Corvol P, Mahoudeau JA, Ross GT & Lipsett MB. (1971) Effects of induced hyperthyroidism on steroid metabolism in man. J Clin Endocrinol Metab 33, Sarne DH, Refetoff S, Rosenfield RL & Farriaux JP. (1988) Sex hormone-binding globulin in the diagnosis of peripheral tissue resistance to thyroid hormone: the value of changes after short term triiodothyronine administration. J Clin Endocrinol Metab 66, Sartorius G, Ly LP, Sikaris K, McLachlan R & Handelsman DJ. (2009) Predictive accuracy and sources of variability in calculated free testosterone estimates. Ann Clin Biochem 46, Tagawa N, Takano T, Fukata S, Kuma K, Tada H, Izumi Y, Kobayashi Y & Amino N. (2001) Serum concentration of androstenediol and androstenediol sulfate in patients with hyperthyroidism and hypothyroidism. Endoc J 48, Vela zquez EM & Bellabarba Arata G. (1997) Effects of thyroid status on pituitary gonadotropin and testicular reserve in men. Arch Androl 38, Vermeulen A, Verdonck L, Van der Straeten M & Orie N. (1969) Capacity of the testosterone-binding globulin in human plasma and influence of specific binding of testosterone on its metabolic clearance rate. J Clin Endocrinol Metab 29, 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, Zähringer S, Tomova A, von Werder K, Brabant G, Kumanov P & Schopohl J (2000) The influence of hyperthyroidism on the hypothalamic-pituitary-gonadal axis. Exp Clin Endocrinol Diab 108, International Journal of Andrology, 2012, 35, ª 2012 The Authors 678 International Journal of Andrology ª 2012 European Academy of Andrology