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Andrology. 2021;00:1–10.
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1wileyonlinelibrary.com/journal/andr
Received: 16 November 2020
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Revised: 28 December 2020
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Accepted: 15 January 2021
DOI: 10.1111/andr.12978
ORIGINAL ARTICLE
Data from 14,597 penile measurements of vietnamese men
Bac Nguyen Hoai1,2 | Quan Pham Minh2 | Thang Nguyen Cao2 |
Andrea Sansone3 | Elena Colonnello3 | Emmanuele A. Jannini3
© 2021 American Society of Andrology and European Academy of Androlog y
1Hanoi Medical University, Hanoi,
Vietnam
2Depar tment of Andrology and Sexual
Medicine, Hanoi Medical University’s
Hospital, Hanoi, Vietnam
3Chair of Endocrinology and Sexual
Medicine (ENDOSEX, Department of
Systems Medicine, Univer sity of Rome Tor
Vergata, Rome, Italy
Correspondence
Bac Nguyen Hoai, Department of
Andrology and Sexual Medicine, Hanoi
Medical University ’s Hospit al, Hanoi
Medical University, No.1 Ton That Tung
street, Dong Da district, Hanoi, Vietnam.
Email: nguyenhoaibac@hmu.edu.vn
Funding information
EAJ was partially suppor ted by the MIUR
grant 2017S9K TNE_002.
Abstract
Background: Penis size is a highly sensitive topic, which has often raised concerns
associated with human masculinity and male sexual health. Although data regarding
penile dimensions have been published worldwide, little is known about these meas-
urements in South- East Asian countries.
Objective: This study aimed to provide the reference range in penile length, circum-
ference, and diameter of Vietnamese men and their variations among men with erec-
tile dysfunction and other diseases.
Materials and Methods: Information about flaccid length, stretched length, mid- shaft
circumference, and glans diameter from the health records of 14,597 men attend-
ing the Andrology Consultation was collected. These men were classified into three
groups being regular reproductive health screening group, sexual dysfunction group,
and other disease groups.
Results: We found that penile dimensions follow a non- parametric distribution, as
tested by Kolmogorov- Smirnov test. The median values are 9.03 cm for flaccid length,
14.67 cm for stretched length, 8.39 cm for mid- shaft circumference, and 2.86 cm for
unaroused glans diameter. Length and girth of the penis also changed among the dif-
ferent groups, especially in flaccid state; specifically, men with erectile dysfunction
had a greater value in all penile dimensions except for change ratio compared with
other groups. Circumcision, which rarely occurs in Vietnam, was associated with a
2 mm reduced penis length.
Discussion: Findings on correlations between penile dimensions and somatometric
parameters from previous studies are questionable and some measurements, such as
glans dimension, have not been thoroughly investigated so far. Nevertheless, penile
dimensions provide useful insight concerning conditions affecting sexual develop-
ment and might be a valuable parameter in the assessment of erectile dysfunction.
Conclusion: Results of this study provide informative materials for the assessment of
penile size, including reference values drawn from a large sample of Vietnamese men
that can be useful in clinical practice and sexual health education.
KEYWORDS
penis size, penile measurements, penile length, glans circumference, erectile dysfunction,
men's health
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NGUYEN H OAI Et Al .
1 | INTRODUCTION
“Is that big enough?” This is a common, yet sensitive question fre-
quently asked by men requesting andrological consultation during
external genital examination. In fact, a preoccupation with penis size
has existed during the history of human development. Through the
ages, from the artistry work to pornography, the penis has featured
as a symbol of masculinity, virility, fertility, power, and strength.1,2
Starting from 1899, for a century, studies about penile length have
been captivating scientists.3 A lar ge bod y of pa per s con cerning peni s
sizes was published; however, because of differences in methodol-
ogy and patient selection, the results were not consistent and thus
incomparable.
Male genital satisfaction is an important aspect of psychologi-
cal and sexual health, both being possibly affected by either mor-
phological abnormalities or normal penis.4 According to a study on
more than 25,0 00 heterosexual men in the US, at least 45% of men
would like to have a larger penis size and an increased satisfaction
of the partner.2 Concerns over penile size are based on belief in in-
adequately stereotypical ideals leading some men to seek surgical
penile lengthening procedures.5,6 Thus, because the burden of penis
enlargement services was uncontrollable, the definition of a normal
penile size has been created and should be used as educational ma-
terial for patients to correct their choice.
To date, there are only some studies on this topic that have
used population- based sampling method.7 - 9 Moreover, except for
erectile dysfunction,1 , 1 0 - 1 2 differences in penile dimensions be-
cause of different concomitant diseases remain largely unknown.
Therefore, we conducted this study to evaluate reference range
of normal penis size and its alteration among different disease
groups.
2 | MATERIALS AND METHODS
The Andrology Consultation of Hanoi Medical University's
Hospital is a recognized outpatient clinic for diagnosis and treat-
ment of men's health problems. Patients presenting for various
reasons were firstly evaluated by several experienced androlo-
gists following a systematized protocol including medical and sex-
ual history, physical examination, evaluation of external genitalia
abnormalities, and penile measurements. Further investigations
(such as blood sample, semen analysis, diagnostic imaging) were
used for sp ecific sit uatio ns. Finall y, an andro logic al ex per t took re-
sponsibility for counseling and diagnosing based on International
Statistical Classification of Diseases and Related Health Problems
10th Revision.13 Patient's information used to assess treatment
progression was safely protected in the hospital's record storage
system.
To establish the reference size of penis for Vietnamese men,
approximately 30,000 patients who visited our clinic from January
2014 to December 2019 were screened for this study. Among them,
19,910 men had their penis size measured. To minimize the selection
bias in this study, we excluded young men under 17 years old, men
without the measurement of hormonal concentration, particularly
with testosterone, and testicular ultrasound. Men detected with
genital abnormalities such as penile curvature, hypospadias, phi-
mosis, or pre- pubertal hypogonadism were also excluded. A total of
14,597 men aged 17– 84 years old who met the inclusion criteria and
had complete penile measurements and serum testosterone concen-
tration assay were selected for data analysis (Figure 1). They were
subsequently classified into 3 groups including regular reproductive
health screening group, sexual dysfunction group, and other disease
groups. Subjects within sexual dysfunction group were further di-
vi d e d into 2 su b- gro ups : men dia gno s e d with er ect ile dy s f unctio n ac-
cording to EAU guidelines14 and men wi th ot her sexua l dys func tio ns.
Because the data about the condition of the foreskin (circumcised or
uncircumcised) was recently upgraded in the hospital's record stor-
age system after 2018, a subgroup of 3938 men among participants
having this information was further investigated. The study was ap-
proved by the ethics council of Hanoi Medical University's Hospital.
Penile dimensions were taken once by 5 well- trained androlo-
gists following a consistent measurement protocol immediately after
penile exposure to minimize temperature effects.15 Penile parame-
ters were measured by a rigid ruler for lengths and a steel caliper
for diameters in the standing position with the penis held parallel
to floor. Penile length was the linear distance from the pubo- penile
junction to the tip of glans along dorsal side by pushing pre- pubic fat
pad to the bone in flaccid and fully stretched state without erection.
Penile diameters were defined as the line between two points on
the circumference of penile shaft's middle point, and corona of glans
that concludes their center. Mid- shaft circumference was calculated
by the formula for perimeter of a circle (Mid- shaft diameter × π).
Change ratio, defined as stretched penile length divided by flaccid
penile length, was also reported. Also, the age, height, and weight
were recorded then body mass index (BMI) was calculated for each
participant.
2.1 | Statistical analysis
Data analysis was performed by using R version 3.6.1 for Windows.
Penile dimensions were not normally distributed as result of
Kolmogorov- Smirnov test. All variables were presented in mean,
standard deviation, median, and range. Correlations of differ-
ence factors were computed by Spearman test. The Kruskal- Wallis
test followed by Dunn multiple comparison post hoc tests with
Bonferroni adjustment was performed to detect the differences be-
tween groups of reason for referral. The Wilcoxon signed rank test
was used to compare penile parameters between erectile dysfunc-
tion group and the others. The level of significance was chosen as
p = 0.05. Multivariate linear regression analyses were performed to
detect the effect of anthropometric indicators, testosterone, erec-
tile function, and circumcision history on penile parameters among
the total study population (n = 14,597) and a subgroup of 3938 men
with data about the condition of the foreskin.
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NGUYEN H OAI Et Al .
3 | RESULTS
General characteristics of 14,597 subjects involved in this study
including age, weight, height, and BMI were described in Table 1.
Distribution of age was similar with respect to the general popula-
tion. Most males came to andrology consultation because of rea-
sons related to reproductive and sexual health (22.6% and 25.6%,
respectively).
The result of descriptive statistics was shown in Table 2. The
median values of penile dimensions were: flaccid length 9.03 cm
(ranged from 5.10 to 13.20 cm), stretched length 14.67 cm (ranged
from 8.30 cm to 19.90 cm), mid- shaft circumference 8.39 cm (ranged
from 5.34 to 11.3 cm), and glans diameter 2.86 cm (ranged from 1.80
to 4.10 cm). Differences between stretched and flaccid length were
also reported with mean change ratio of 1.63 (ranged from 1.04 to
2.38). All penile dimensions were not normally distributed accord-
ing to Kolmogorov- Smirnov test <0.01. However, these distributions
were approximately symmetric with Skewness between – 0.5 and
0.5 as illustrated in Figure 2.
The penile dimensions and age of different groups were pre-
sented in Table 3. Kruskal- Wallis test showed the significant dif-
ferences of age and penile parameters between the three groups
(p < 0.001). Patients with sexual dysfunction had the mean age of
38.5 years (compared with 28.6 years in patients who came for reg-
ular reproductive health screening and 32.4 years in patients with
other diseases). Regarding the penile dimensions, subjects in sexual
dysfunction group presented with greater penile length in both flac-
cid state and stretched state. These men also had increased glans
diameter of 2.91 cm compared with regular reproductive health
screening and other disease groups.
To further investigate the effect of sexual dysfunctions to penile
dimensions, we divided group 2 into men with ED and other sexual
dysfunctions. Our results indicated that patients with ED possessed
bigger penis in all dimensions except for the change ratio compared
with non- ED patients including men in regular reproductive health
screening group, other sexual dysfunction group, and other disease
groups, the differences being statistically significant with p < 0.05
(Table 4). However, the same results were not observed between
other sexual dysfunction group and the remaining groups except for
the difference in stretched length.
Correlation analysis showed that: (1) flaccid length was mod-
erately correlated with stretched length (Spearman's rho = 0.676),
mid- shaft circumference (Spearman's rho = 0.385), glans diame-
ter (Spearman's rho = 0.443), and change ratio (Spearman's rho =
- 0.556); (2) another moderate correlations were found between
stretched length/mid- shaft circumference (Spearman's rho = 0.388),
stretched length/glans diameter (Spearman's rho =0.418), mid- shaft
circumference/glans diameter (Spearman's rho = 0.658). The correla-
tions between penile parameters and age, height, weight, BMI were
significant but relatively weak. No correlations were found between
mid- shaft circumference/age (Table 5).
As results from multivariate linear regression analysis shown in
Tabl e 6, despite st at istic signific ances of all models (p < 0.0 01), the
adjusted R2 was insufficient, ranging between 0.0243 and 0.0713.
Without consideration about circumcision history, increases in
age, height, weight, and total testosterone positively related to
all penile parameters, except for the negative relation between
weight and stretched length and the lack of effects between age
and mid- shaft circumference. Erectile dysfunction was associated
with larger penis size, especially with longer stretched length and
wider glans diameter. Concerning the foreskin, circumcised men
had shorter penile length in both flaccid and stretched states,
whereas mid- shaft circumference and glans diameter were larger
than uncircumcised men.
FIGURE 1 Flow chart of the study.
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NGUYEN H OAI Et Al .
4 | DISCUSSION
Reference values for penile dimensions of 14,597 Vietnamese men
were initially established by one of the largest cohor ts to our best
knowledge. Indeed, most of previous repor ts on penis size col-
lected data among Caucasian (Europeans, South Asiansn and North
Africans), while studies in Mongoloids (East Asians, especially South
and South- East Asians) were limited.16,17 Moreover, being penile
lengths and girths affected by methodology, these values were dif-
ferent among studies,15,17 and it was difficult to have an appropriate
range of measurements. This information was essential for adequate
interventions in case of micro- penis, small penis anxiety, or Body
Dysmorphic Disorder that can be treated properly by sex education
and psychosexual counseling.18,19 Thus, results of this present study
could be useful in clinical practice, education purposes, or counsel
for patient with concerns related to penile dimensions.
As part of the andrological evaluation, measurements of penis
in flaccid state could provide accessible informative materials for
both clinicians and patients. Flaccid penis size is an important com-
ponent of male perceptions about masculinity2 and exerts a signifi-
cant influence on male attractiveness.20 In one recent online sur vey,
men reported highest dissatisfaction with the size of their flaccid
penis (27%), followed by length of erect penis (19%) and girth of
erect penis (15%).4 In comparison with results from previous stud-
ies, Vietnamese men have medium flaccid length which was compa-
rable with those from Western Asians (8.96 ± 1.13 cm)3 , 1 1 , 2 1 - 2 3 and
USA (9.01 ± 2.15 cm),24 ,25 whereas mid- shaft penile circumference
was not different with other Asians and smaller than Caucasians
(10.00 ± 0.75 cm of Italians and 9.52 ± 0.52 cm of US Americans)
(Table 7). However, it should be noted that the penile circumference
was here calculated from mid- shaft diameter with assumption sug-
gested by Spyropoulos et al26 that may need fur ther studies to be
confirmed. Despite methodological variations, differences in size
of penis might not adhere to ordinary evolution principle suggested
by Rushton's theory that Mongoloids had smallest penis compared
with other populations.17 Further multicenter studies with standard
penile measurement technique are needed to discover racial effects
and related factors that change the penis size as it is for many other
body parameters.
Glans dimensions were usually underrated and ignored in studies
about penis size. As part of the phallus, glans penis acts protectively,
TABLE 1 General characteristics of 14,597 subjects.
Participant distribution
n (%) Mean (SD)
Age (years) 33.1 (10.7)
1 7 – 2 9 6735 (46.1%)
3 0 – 4 4 5741 (39.3%)
4 5 – 5 9 1670 (11.4%)
≥60 451 (3.1%)
Height (cm) 167.8 (5.52)
Weight (kg) 63.1 (8.57)
BMI (kg/m2) 22.4 (2.60)
BMI <18.5 847 (5.8%)
18.5 ≤ BMI <23 7937 (54.4%)
23 ≤ BMI <25 3578 (24.5%)
25 ≤ BMI <27.5 1790 (12.3%)
27.5 ≤ BMI <30 354 (2.4%)
BMI ≥30 91 (0.6%)
Serum total testosterone
concentration (nmol/L)
16.9 (6.00)
<12 nmol/L 2932 (20.1%)
≥12 nmol/L 11,665 (79.9%)
Foreskina
Circumcised 221 (5.6%)
Uncircumcised 3717 (94.4%)
Smokingb
Yes 3098 (22.4%)
No 10,756 (77.6%)
Marriage statusc
Single 4808 (33.1%)
Married 9717 (66.9%)
Reason for referral
Regular reproductive
health screening
3302 (22.6%)
Sexual dysfunction 3732 (25.6%)
Other 7563 (51.8%)
Abbreviations: SD, standard deviation.
aFor 3938 individuals.
bFor 13,854 individuals.
cFor 14,525 individuals.
TABLE 2 Descriptive statistics for penile parameters.
Mean −2SD +2SD Min Max Median
5th
percentile
95th
percentile Skew Kurtosis
Flaccid length (cm) 9.0 3 7. 0 1 11. 05 5.10 13.20 8.90 7. 5 0 10.70 0.27 0.42
Stretched length (cm) 14.67 11.99 1 7. 35 8.30 19.90 14.70 12.50 16.70 − 0.17 0.28
Mid- shaft circumference
(cm)
8.39 6.55 10.23 5.34 11.3 8.16 6.91 10.05 0.18 0.27
Glans diameter (cm) 2.86 2.22 3.50 1.80 4.10 2.80 2.40 3.40 0.28 0 .12
Change ratio 1.63 1.37 1.89 1.04 2.38 1.63 1.42 1.86 0.27 0. 55
Abbreviations: SD, standard deviation.
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NGUYEN H OAI Et Al .
absorbing forces during coitus27 and def ines the unique shape of the
penis. In our knowledge, there were several studies reporting flaccid
glans length,8,15, 26 but only one interesting Chinese study that pre-
sented an average flaccid glans diameter of 2.6 ± 0.3 cm, similar with
our findings.15 These results were essential for the achievement of
knowledge for penile plastic surgeries or augmentations for which
construction of glans with adequate size would be required.
Stretched length could be used effectively to predict penile size
during erection without intra- cavernous injection,23, 24 which is not
suitable for every individual in usual clinical setting.2 3,24 Chen et al.
FIGURE 2 Distribution of penile
parameters.
TAB LE 3 Mean and standard deviation of penile parameters from three main disease groups.
NAge (years)
Flaccid length
(cm)
Stretched
length (cm)
Mid- shaft
circumference (cm)
Glans diameter
(cm) Change ratio
Group 1 3302 28.6 (6.4 4) 8.99 (1.01)A14.6 (1.39) 8.42 (0.95)A2.84 (0.31)A1.63 (0.13) A
Group 2 3732 38.5 (12.3) 9.09 (1.01) 14.8 (1.30) 8.43 (0.94)A2.91 (0.33) 1.63 (0.14) AB
Group 3 7563 32.4 (10.1) 9.02 (1.01)A14.7 (1.32) 8.36 (0.90) 2.85 (0.31)A1.6 4 (0.14) B
Note: No significant differences were found between groups shared the same letter.
Group 1: regular reproductive health screening (RRHS); Group 2: sexual dysfunctions; Group 3: other diseases (OD).
TABLE 4 Comparisons between penile parameters of erectile dysfunction and the other groups.
NAge (years)
Flaccid length
(cm)
Stretched
length (cm)
Mid- shaft
circumference (cm)
Glans diameter
(cm)
Change
ratio
ED 1897 44.0 (12.9) 9.19 (1.03) 14.9 (1.25) 8.48 (0.94) 2.96 (0.33) 1.63 (0.14)
N o n - E D 12700 31.5 (9.25)# 9.01 (1.00)# 14.6 (1.34)# 8.38 (0.92)# 2.85 (0.31)# 1.63 (0.13)
OSD 1835 32.9 (8.71)# 8.99 (0.98)# 14.6 (1.33)# 8.37 (0.94)# 2.86 (0.32)# 1.63 (0.13)
RRHS 3302 28.6 (6.4 4) # 8.99 (1.01)# 14.6 (1.39)# 8.42 (0.95)*2.84 (0.31)# 1.63 (0.13)
OD 7563 32.4 (10.1)# 9.02 (1.01)# 14.7 (1.32) # 8.36 (0.90)# 2.85 (0.31)# 1.64 (0.14)
Abbreviations: ED, erectile dysfunction; RRHS, regular reproductive health screening; OSD, other sexual dysfunction (without erectile dysfunction),
OD, other diseases.
#p < 0.001— Compare with ED.
*p < 0.05— Compare with ED.
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NGUYEN H OAI Et Al .
Flaccid
length
Stretched
length
Mid- shaft
circumference
Glans
diameter
Change
ratio
Age 0.090*0.021# 0.012 0.160*−0.093*
Weight 0.084*0.051*0.202*0.191*−0.054*
Height 0.095*0.144*0.14 4*0.108*0.037*
BMI 0.046*−0.022# 0.156*0.16 3*−0.087*
Flaccid length 1.000
Stretched length 0.676*1.000
Mid- shaft circumference 0.385*0.388*1.000
Glans diameter 0.443*0. 418*0.658*1.000
Change ratio −0.556*0.174*−0.095*−0.134*1.000
#p < 0.01.
*p < 0.001.
TABLE 5 Spearman's rho for
correlation between variables.
TAB LE 6 Multivariate linear regression analysis for predict the change of each penile parameter with and without the effect of
circumcision.
Variables
Total study population (n = 14,597) Subgroup (n = 3938)
Flaccid
length (cm)
Stretched
length
(cm)
Mid- shaft
circumference
(cm)
Glans
diameter
(cm)
Flaccid length
(cm)
Stretched
length (cm)
Mid- shaft
circumference
(cm)
Glans
diameter
(cm)
β coefficient β coefficient
Age (year) 0.0109*0.0057*−0.0004 0.0142*0.0085*0.0035 0.0030 0.0158*
Weight (kg) 0.0036# −0.0071*0.0210*0.0182*0.0040 −0.00660 0.0239*0.0193*
Height (cm) 0.0196*0.0459*0.0087*0.0130*0.0210*0.0470*0.0114*0.0113*
TT (nmol/L) 0.0090*0.0092*0.0095*0.0072*0.0103*0.0104# 0.0125*0.0088#
ED (vs. non- ED) 0.06400 0.2659*0.0887*0.1508*−0.10340 −0.0208 0.0109 0.0278
Circumcised (vs.
uncircumcised)
−0.2209# −0.2091# 0.1710# 0.2416*
Intercept 4.99 7. 0 4 5.44 5.05 4.88 7. 3 1 4.85 5.39
Adjusted R20.0267 0.0343 0.0506 0.0681 0.0243 0.0423 0.0666 0.0713
Abbreviations: TT, total testosterone; ED, erectile dysfunction.
0p < 0.05.
#p < 0.01.
*p < 0.001.
TABLE 7 Published reports for penile dimensions (pooled data from different countries).
Region Race
Flaccid length (cm) Stretched length (cm)
Mid- shaft
circumference (cm) Glans diameter (cm)
Mean (SD) Study Mean (SD) Study Mean (SD) Study Mean (SD) Study
Western Asia Caucasian 8.96 (1.13) 3 , 1 1 , 2 1 - 2 3 13.21 (1.53) 3,8,11,21- 23,46 8.81 (0.96) 3,8,11 NA
South Asia Caucasian 8.21 (1.44) 47 10.88 (1.42) 47 9.14 (1.02) 47 NA
Europe Caucasian 9.26 (1.77) 7,12,26,48- 5 0 13.51 (2.35) 7, 12 , 26 , 50 10.0 (0.75) 7NA
North America Mixed race 9.01 (2.15) 24, 25 15.52 (2.64) 24,25 9.52 (1.52) 24, 25 NA
East Asia Mongoloid 6.54 (0.73) 15,45,51 12.79 (1.21) 15,45,51 8.01 (0.81) 15 ,51 2.6 (0.3) 15
Vietnam (South-
East Asian)
Mongoloid 9.03 (1.01) 14.67 (1.34) 8.39 (0.92) 2.86 (0.32)
Abbreviations: SD, standard deviation; NA , not available.
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NGUYEN H OAI Et Al .
reported that, in order to obtain a ratio of erected length to stretched
length that equals to 1, a critical stretching force value of approxi-
mately 450 gram should be applied. 23 However, tension forces while
stretching and measuring penis are usually not stable and are con-
ducted in supine position, which challenges clinicians to perform op-
timal force vector compared with standing position. Consequently,
differences in stretched length among studies could be explained
insufficiently. Although systematic training with consistent proto-
col could reduce the variability of measures, erect penis size should
be studied in the future for indicating the underestimated rate of
stretched length and measuring inter- rater concordance.
Penis grows before birth and during the development of male
body until the end of puberty. Penile development is influenced
by circulating testosterone levels and hormonal activity of the
hypothalamic- pituitary axis.2 8 - 3 0 Therefore, hormonal defects could
be identified as the main cause in a majority of cases of micro-
penis.29 In fact , a general ass essment of endocr ine leve ls is also valu-
able with patient concerned about penis size because of misleading
sexual conception, even when their phallus is normal in length.18 ,19
Micro- penis is widely defined as flaccid length lower than 4.0 cm
and stretched length lower than 7.5 cm.24 In this present study,
any man was diagnosed as having true micro- penis because of pre-
pubertal hypogonadism or developmental abnormalities having
been excluded by previous laboratory tests and physical examina-
tion. However, the size of a penis is not consistent even after full
growth. During adulthood, testosterone still plays a critical role in
the preservation of penile trabecular smooth muscle structure, then
by its turn, maintaining the length and width of the penis.31,32 The
previous experimental studies in castrated animals and observation
in patients with androgen deprivation therapy after prostate cancer
treatments (surgery or radiation) rationally showed reduced penile
length, possibly because of the degeneration of trabecular smooth
muscle content and the change in the structure of extracellular
connective tissue.31- 33 Although this effect could rapidly reverse
after 4 weeks of androgen replacement therapy in sexually mature
adult rats regardless of the androgen deprivation time, the recovery
of penis length in humans after this kind of treatment is not well-
known.33 Even after 6 to 12 months of testosterone therapy to treat
men with late- onset hypogonadism, the stretched penis length was
not significantly changed.34 Moreover, the total testosterone levels
reached during androgen deprivation therapy (<1.7 nmol/L) were
only found in 2 individuals among our 14,597 men.35 Because the
actual influence of testosterone on adult penis size was still contro-
versial, our multivariate linear regression models showed the posi-
tive relations between total testosterone and all penis parameters,
but with no more than 0.2 mm change for every 2 nmol/L increases
in total testosterone. Despite the statistical significance, these
changes were not enough to create a visible difference in the clini-
cal view. Therefore, except for apparent evidence of the continuous
androgen interruption shortening the penile length, the actual role
of testosterone deficiency in penis parameters still needs further
investigation. Radical prostatectomy is another potential factor re-
ported to shorten the adult penile length: however, this is a topic that
is still only partially understood, and complete recovery has been
described after 48 months.36 This could be also because of differ-
ent measurement methods, as starting at the pubo- penile skin angle
might yield different results than starting at the pubic bone.25,36,37
In our protocol, because penile parameters were measured at the
first time of attending before the initial intervention, the effect of
treatments on patients’ penis size was minimized. Furthermore, the
number of patients with a history of radical prostatectomy was min-
imal (34/14,597 men). Thus, our results could be considered as the
reference for normal penis size of Vietnamese men.
While assuming that scar formation after circumcision could
reduce the elasticity of penile skin, especially in the fully stretched
state, the penis shortening complication of circumcision is still not
well- known. However, an observational study in adult men 18 to
28 years old, who had already been circumcised, showed that cir-
cumcision at an earlier age was associated with shorter penile
erected length.38 The flaccid length of the newborn male circum-
cision (NMC) group is even smaller than the non- NMC group. The
present study showed that circumcised men had a significantly re-
duced penis length compared with uncircumcised men; the differ-
ence was only 2 mm, which was possibly not clinically meaningful.
Moreover, differing from the other countries in which circumcision
is obligatory or common for religious and non- religious reasons,
this intervention has not been performed routinely in Vietnam, but
mostly for personal or medical purposes, and with a small prevalence
(5.6% in our study).39
In several papers, correlations between penile dimensions
and somatometric parameters have been investigated; however,
these findings remained questionable. Results from a systematic
rev iew with up to 15,521 mal es in 20 studies showe d that all these
correlations were either inconsistent or weak and the most con-
sistent and strongest significant correlation was between flaccid
stretched length and height.16 Again, our study replicated the
results of relationships found in other studies and demonstrated
weak correlations between penile dimensions and weight, height,
or BMI (with Spearman rho ≤0.200). Furthermore, the size of our
study population could also give greater opportunity to detect
statistical significance even with minor correlations. Interestingly,
BMI was almost non- correlated with penile length (w ith Spearman
rho = 0.046, p < 0.001 for flaccid length and Spearman rho =
−0.022, p < 0.01 for stretched length) when pre- pubic fat pad in-
fluence was eliminated. An increase in fat pad depth might reduce
the visible pendulous length of the penis,24 whi le fun ctio nal le ngth
was not defected. It should be noted that there was a bidirectional
relationship between testosterone levels and obesity40 resulting
in testosterone deficiency, which in its turn might affect the de-
velopment of penis. However, having here a lack of information
regarding the effects of body fat mass during the critical frame
of testosterone action on the penis size, that is, puberty, and the
decrease of penile potential length is a limitation that should be
analyzed by further studies.
To our knowledge, this was one of the first studies that il-
lustrated discrepancies in penile dimensions between men with
8
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NGUYEN H OAI Et Al .
different conditions; however, these variances were inconsider-
able. In addition, because of the nature and limitations of non-
parametric test itself, differences in mean between groups might
be misleading. Exceptionally, flaccid length of erectile dysfunction
males was significantly longer than others, especially in cases of
regular reproductive health screening. These results contrasted
with prior studies in which patients with erectile dysfunction have
been found to have significantly shorter penises compared with
normal potent men,10,11 but their data might be limited by the ef-
fect of selective participation that was minimized by our methodol-
ogy. In fact, besides corpus cavernosa and corpus spongiosum, the
role of the tunica albuginea should be taken into consideration in
flaccid penile shape. Tunica albuginea is almost entirely composed
of undulating collagenous bundles connected by elastic fibers.41 It s
branches penetrate the tissue of the corpora cavernosa and act as
an inextensible fibrous frame to support intra- cavernous compo-
nents.42 Patients affected by impotence of all causes showed an
almost complete absence of elastic fibers in tunica albuginea that
produced a stretching of collagen fiber waves.42 Consequently,
these changes slightly lengthened penis in flaccid state in erectile
dysfunction. Treatments are an additional factor possibly affecting
the penile length in patients with erectile dysfunction. Previous
studies have demonstrated that vacuum device can extend length
of th e penis slightly. 43,44 How eve r, in ou r st u d y, all subjec t s ha d their
penis measured at the first time they visited our clinic. Therefore,
patients with erectile dysfunction were either untreated or pre-
scribed with oral pharmacotherapy only because other therapies
such as intra- cavernous injection and vacuum devices had not been
officially approved in Vietnam. Because of minor differences be-
tween each disease groups that could not be clearly interpreted
with current consciousness, further investigation should be per-
formed to confirm these findings.
The present study re- emphasized that penile dimensions did not
follow normal distribution regarding a large sample of men without
factors that could affect penile growth. This hypothesis was men-
tioned in a study of 3,300 young healthy Italian men.7 Ponchietti et al.
suggested that penile length and circumference were characterized
by a high degree of individual variability. Although penile character-
istics were bona fide considered related to paternal impact, the trans-
missions of these phenotypes were still unexplored. In fact, as week
8th of gestation, penis formation and its capacity to grow had been
regulated by fetal androgen action.45 Testosterone action in this state
could be indirectly indicated by digit ratio of right hand correlated
with Homeobox genes (Hox a and d) and androgen receptor (AR) gene
polymorphism.45 However, these findings were not enough to define
penile shape as qualitative phenotypes that basically fell into different
categories with discrete distribution. While waiting for further discov-
ery, normal reference of penile dimensions could be taken impossibly
in either population- based or clinical enrollment with carefully into ac-
count for “normality conditions”.
To date, this was the largest prospective, single center study in
the world for this type of study. However, some limitations should
be mentioned. Although penile measurements were performed as a
part of our physical examination, the participants were not drawn
directly from the population, and as such results of this study might
not represent the general population. Another limitation came from
the number of investigators who directly measured patient's penis,
which was of 5 clinicians. However, experienced andrologists in this
clinic were training under careful observation by the same supervi-
sor with a fixed protocol that might reduce rater errors.
This was the first study establishing reference of penile dimen-
sions for Vietnamese men. These results were valuable for the clini-
cian in practice and might be referred as “normal range” that greatly
assisted in counseling patient. Despite inconsiderable differences
in length and girth of penis between disease groups, these varia-
tions made scientists more aware of micro- changes in penile inner
structure during specific illness, especially with the case of erectile
dysfunction. Finally, because the distributions of penile dimensions
are not normal in nature, sample size might be the main factor that
influenced results of studies on penis size.
AUTHOR CONTRIBUTIONS
Conceptualization: BNH; Data collection: BNH, QPM, TNC; Formal
analysis: AS, EC; Drafting the Article: BNH, AS, EC; Critical revision
and super vision: BNH, EAJ.
ORCID
Bac Nguyen Hoai https://orcid.org/0000-0003-1608-8812
Quan Pham Minh https://orcid.org/0000-0002-2067-741X
Thang Nguyen Cao https://orcid.org/0000-0003-3497-3356
Andrea Sansone https://orcid.org/0000-0002-1210-2843
Emmanuele A. Jannini https://orcid.org/0000-0002-5874-039X
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How to cite this article: Nguyen Hoai B, Pham Minh Q,
Nguyen Cao T, Sansone A, Colonnello E, Jannini EA . Data
from 14,597 penile measurements of vietnamese men.
Andrology. 2021;00:1–10. https://doi.o rg /10.1111/
andr.12978
