- Christos S Mantzoros,
- Emmanuel I Georgiadis, head, Endocrine Unita,
- Dimitrios Trichopoulos, professor and chiefb
- a 401 Military Hospital, Athens, Greece Christos Mantzoros, resident in medicine
- b Department of Epidemiology, Harvard School of Public Health, Boston, Massachusetts 02215, USA
- Correspondence to: Dr Mantzouros, Department of Endocrinology, RN 324, Beth Israel Hospital, Harvard Medical School, 330 Brookline Avenue, Boston, Massachusetts 02115, USA.
- Accepted 21 March 1995
Objective: To document the relative importance of endogenous sex steroids in modulating the frequency of orgasms, the dominant aspect of sexual behaviour in healthy eugonadal men.
Design: Measurement of adrenal and testicular sex steroids in a sample of army recruits and study of their relation to frequency of orgasms ascertained by questionnaire after potential confounding variables were controlled for.
Setting: Military campus and military hospital laboratories in Athens, Greece.
Subjects: 92 consecutively enrolled healthy male recruits aged 18-22 years.
Main outcome measures: Weekly number of orgasms. Serum concentrations of testosterone, dehydroepiandrosterone sulphate, dihydrotestosterone, oestradiol, oestrone, δ-4-androstenedione, and sex hormone binding globulin.
Results: Serum dihydrotestosterone concentration was the only independent hormonal predictor of the frequency of orgasms; an increase in concentration of 1.36 nmol/l (about 2 SD) corresponded to an average increase of one orgasm a week.
Conclusions: Differences in concentrations of circulating dihydrotestosterone within the normal range may represent a major predictor of sexual activity in healthy young men.
The hormone that determines sexual behavior has not yet been conclusively identified in healthy adults
This study shows that dihydrotestosterone is the dominant hormonal determinant of the frequency of orgasms in young healthy adults
The frequency of orgasms depends not only on psychosocial factors but on variation of dihydrotestosterone concentrations within the normal range
Male sexual function is at least partially dependent on androgens in most species.1 Evidence from non-human primates suggests that testosterone and its major metabolite dihydrotestosterone are essential for male sexuality.1 Studies in humans indicate that subnormal libido and sexual function because of induced or spontaneous hypogonadism improve with testosterone treatment.1 2 It remains unclear, however, whether the beneficial effect is because of testosterone itself or dihydrotestosterone. We have studied recruits to the Greek army to explore whether testosterone, dihydrotestosterone, or other sex steroid hormones are important determinants of sexual function as reflected in the frequency of orgasms.
Subjects and methods
Participants in the present study were 100 consecutively enrolled male army recruits aged 18-22 who consented to having a single blood sample drawn between 900 and 1100 am during their first day in the army. Subjects were healthy and were taking no medication.
The participants responded to a questionnaire administered by an interviewer that covered basic demographic and lifestyle variables. Specifically, the participants were asked to indicate their age in completed years, height in centimetres, weight in kilograms, and educational level in years of schooling. Quetelet's index (body mass index) was calculated as weight/height.2 In addition, subjects were asked to indicate whether they were smokers and if so the daily number of cigarettes smoked. Information was also provided on the amount of coffee drunk in cups a day and usual alcohol intake in glasses a day. Greek (Turkish) coffee was the type consumed by nearly all subjects, whereas alcohol consumed in the standard measures of most drinks is about the same for wine, beer, and spirits. Voluntary physical activity was recorded in hours a day, but no attempt was made to weight it according to intensity. Finally, the participants were asked to indicate the average number of orgasms a week over the past month. Recalled number of orgasms a week has been previously shown to represent a major and reliable expression of male sexual behaviour.3 It was made clear to the study participants collectively as well as individually that the object of the study was to assess the total number of events rather than the mode of their initiation in the context of sexual intercourse, masturbation, or spontaneous nocturnal orgasms. This approach was adopted to optimise the validity of the response since young men could be tempted to overreport orgasms during intercourse and underreport ones during masturbation.
Blood samples for the hormone determinations were centrifuged immediately, and serum was frozen at −34°C until determination. Serum hormone concentrations were determined by commercially available RIA kits (Coat-a-Count, DPC, Los Angeles, for testosterone and dehydroepiandrosterone sulphate; Amersham International for dihydrotestosterone; EIRRIA, Switzerland, for oestradiol and oestrone; Buhlman Lab, Italy, for δ-4-androstenedione; and Biodata Spa, Switzerland, for sex hormone binding globulin). The sensitivity of the assays was as follows: testosterone 0.14 nmol/l, oestrone 30.0 pmol/l, oestradiol 22.8 pmol/l, δ-4-androstenedione 0.07 nmol/l, dihydrotestosterone 17.34 pmol/l and dehydroepiandrosterone sulphate 0.06 μmol/l. The coefficients of variation in the range of values measured were 5.2% for dihydrotestosterone, 4.5-5.5% for dehydroepiandrosterone sulphate, 5.8% for testosterone, 5-8% for δ-4-androstenedione, 5-6% for oestradiol and oestrone, and 2.8-6.9% for sex hormone binding globulin.
Statistical analysis was by modelling weekly number of orgasms as a function of demographic, lifestyle, and endocrine variables. Weekly number of orgasms was approximately normally distributed with a mean (SD) of 3.9 (1.9). For eight subjects one or more values were missing and these subjects were excluded from the analysis.
Table I shows representative values of the demographic and lifestyle variables. The mean (SD) weekly number of orgasms was 3.9 (1.9), the median and the mode 3.5, the range 0 to 11, and the first and third quintiles 2.2 and 5.5, respectively. Table I also shows simple regression coefficients and those derived from multiple regression of the weekly number of orgasms, regressed on these variables. Only age was a significant predictor of the frequency of orgasms. Table I also gives representative values of the endocrine variables as well as regression coefficients of weekly number of orgasms regressed on these hormones. Only dihydrotestosterone and perhaps δ-4-androstenedione seemed to be independent predictors of the weekly number of orgasms. By contrast, testosterone was unrelated to the frequency of the orgasms. There were no problems of colinearity in the statistical analysis. The highest value of the Pearson correlation coefficient between any two of the hormones studied was 0.27 for dihydrotestosterone with δ-4-androstenedione.
In table II the weekly frequency of orgasms is regressed on age, dihydrotestosterone, and δ-4-androstenedione—that is, the variables that seemed to be the important predictors of the frequency of orgasms on the basis of the models presented in tables I and II. Age and dihydrotestosterone remained significant and independent predictors of the frequency of orgasms, whereas the partial regression coefficient for δ-4-androstenedione was reduced from 0.184 to 0.147 and the corresponding significance weakened from 0.063 to 0.105. The values of the pearson correlation coefficients between the weekly frequency of orgasms on the one hand and dihydrotestosterone and age on the other were 0.28 and 0.30, respectively. Regressing the frequency of orgasms on free hormone indices (calculated as the ratio of testosterone, oestradiol, or oestrone over sex hormone binding globulin) generated essentially identical results; age (P=0.001) and dihydrotestosterone (P=0.006) remained the only significant predictors of the weekly frequency of orgasms.
Among androgens, testosterone and dihydrotestosterone have been found to be important determinants of sexual function in rodents and non-human primates.1 The effect of sex steroids other than testosterone has not been adequately studied in humans.1 2 4 Men with hypogonadism because of pituitary or testicular failure have decreased libido and sexual activity that can be restored with testosterone replacement treatment.4 It is not known whether supplementation with testosterone improves sexual activity by increasing concentrations of circulating testosterone or through conversion to the much more potent dihydrotestosterone.4 In normal men, pronounced testosterone reduction because of spontaneous or induced hypogonadism by administration of luteinising hormone releasing hormone agonist2 has been associated with impaired sexual behaviour, which was restored with testosterone treatment.2 Concentrations of testosterone and any testosterone metabolite were not measured in these studies, making it difficult to identify the active androgenic compound.2 In most cross sectional studies in eugonadal adult men no correlation has been found between sexual activity and circulating concentrations of testosterone,4 although weak positive5 and negative6 correlations have also been reported in small studies. Therefore, at the time of our study there was equivocal evidence for the role of testosterone in determining sexual activity of healthy adults and virtually no evidence concerning the possible role of dihydrotestosterone.
Our results strongly support the hypothesis that dihydrotestosterone is the active hormone for male sexual function as reflected in the frequency of orgasms. An increase of dihydrotestosterone by about 2 SD (1.36 nmol/l) was associated with an increase of the weekly number of orgasms by at least one and conceivably more depending on the extent of biologically generated variation and consequent misclassification. Additionally, within the age range studied, a difference of three years corresponded to an increase of the weekly number of orgasms by about two; this increase is likely to reflect socially conditioned enhancement of opportunities with increasing age (possibly including marital status which was not ascertained in this study).
Only orgasms were evaluated in this investigation, and no attempt was made to ascertain other aspects of male sexual behaviour.7 Previous studies, however, have found that self reported frequency of orgasms in men is a highly reliable method for the evaluation of the effects of androgens on sexual activity that tends to remain stable over time.3 8 There is undoubtedly misclassification in the reporting of the frequency of orgasms as well as in the laboratory determinations of dihydrotestosterone and the other hormones. The corresponding errors, however, are clearly uncorrelated since laboratory tests were blindly performed and the staff concerned had no knowledge of the identity of the subjects or their questionnaire data. Non-differential misclassification can bias the regression coefficients towards the null values, but the extent of this misclassification was no smaller for dihydrotestosterone than for other hormones.
It seems that in normal young adults the potent testosterone metabolite dihydrotestosterone, which binds much more avidly with the androgen receptor,9 is the most important and perhaps the only important androgen in determining male sexual behaviour as reflected in the frequency of orgasms, whereas physiological concentrations of serum oestrogen and adrenal steroids do not seem to play an independent part of comparable importance.
This study was supported by a grant from the medical services of the Greek Army and by a grant to Harvard University by George S Livanos, Switzerland.