Associations between Self-Reported Anatomical Characteristics of the Penis, Age and Sexual Dysfunction in Men

doi:10.21203/rs.3.rs-3042385/v1

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Associations between Self-Reported Anatomical Characteristics of the Penis, Age and Sexual Dysfunction in Men

https://doi.org/10.21203/rs.3.rs-3042385/v1

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Premature ejaculation and erectile dysfunction are common male sexual dysfunctions worldwide, causing substantial distress in men as well as their partners and decrease the quality and stability of romantic relationships. We investigated the associations between self-reported anatomical characteristics of the penis and sexual dysfunctions in an urban sample of Chinese men. We recruited 1085 Chinese urban men aged 18 to 50 (M = 31.37, SD = 5.52) to fill out an online questionnaire regarding anatomical characteristics of the penis as well as early ejaculation and erectile problems via two Chinese online survey platforms. Participants reported their age, height, weight, penile length, penile circumference, circumcision status, and foreskin characteristics as well as answered the International Index of Erectile Function-5 and Checklist for Early Ejaculation Symptoms. Both increasing penile length (M = 14.49, SD = 2.22) and girth (M =15.46, SD = 4.36) were associated with fewer early ejaculation problems, but only increasing penile length was associated with fewer erectile problems. Less foreskin covering the glans penis was associated with fewer early ejaculation and erectile problems. Age was found to have a non-linear relationship with early ejaculation and erectile problems in this cross-sectional study. Specifically, early ejaculation problems increased up to a certain age (31) and then decreased with further increases in age. In conclusion, the relationship between the anatomical characteristics of the penis and sexual function was complex. Also, the results suggest that there is a curvilinear non-monotonic relationship between age and sexual dysfunction.

Biological sciences/Psychology/Human behaviour

Health sciences/Signs and symptoms

Premature Ejaculation

Erectile Dysfunction

Penis Size

Foreskin

Age

Premature ejaculation (PE) and erectile dysfunction (ED), which cause negative outcomes in men and their partners, are common sexual dysfunctions worldwide (1). Little research has focused on the association between the anatomical characteristics of the penis and sexual dysfunction. In the present study, we investigated the associations between self-reported anatomical characteristics of the penis and PE and ED. Given that age has been previously found to be associated with sexual dysfunction (2, 3) as well as there being the reason to believe that age could be associated with how men relate to their sexual anatomy, we also included age in our analyses.

PE and ED

Premature ejaculation (PE) is characterized by a lack of control over the timing of ejaculation, a short intravaginal ejaculation latency time (i.e., the time between the start of vaginal penetration to ejaculation), and subsequent sexual distress (4, 5). On the one hand, men with PE experience lower self-confidence and self-esteem (6, 7), higher anxiety and depression (8), and interpersonal difficulties (9, 10). On the other hand, PE is associated with lower relationship and sexual satisfaction and an increased prevalence of sexual dysfunctions for female partners (2). In a related vein, one in five women reported that they had broken up or divorced men because of early ejaculation problems in a large sample (11).

Erectile dysfunction (ED) is defined as the inability to attain or maintain an erection sufficient to obtain satisfaction from sexual intercourse (12). Also, ED is associated with lower self-esteem and sexual satisfaction (13). Several studies have also found that ED is associated with an increased risk of PE (14, 15).

Penis Size and Sexual Dysfunction

Penis size is a specific concern related to body image among men as part of men’s appearance self-esteem (16). In a sample of 25,594 heterosexual men, 45% suffered from dissatisfaction and anxiety with their penis size including men with an objectively normal size penis (17). Excessive worry and shame concerning penis size may meet the criteria of body dysmorphic disorder with men being preoccupied with a perceived defect with their penis that may not be observable to others or may only appear slight (18). Such concerns have been found to be negatively associated with erectile and orgasmic function and sexual intercourse satisfaction (19). Prior studies have demonstrated that a generally negative body image is linked to decreased sexual satisfaction and sexual function (20, 21). Satisfaction with penis size has also been found to be associated with fewer early ejaculation and erectile problems (22, 23). We suggest that a possible mechanism is excessive anxiety, worry, and shame concerning penis size during sex triggering an overactive sympathetic nervous system response (24–26) which in turn would disturb both normal erectile function as well as ejaculation control (27, 28).

So far, little research into the connections between penis size and male sexual function has been conducted. Recently, men have started to seek surgical penile augmentation to increase penile length or circumference (29, 30). The increases in penile length and circumference after penile augmentation (e.g., the use of allografts, specifically an acellular inert dermal matrix derived from donated human skin tissue, to enhance the circumference of the penis) have been found to improve the participants’ sexual self-esteem, satisfaction with the penis (29). Further, increased penile circumference after penile augmentation has been associated with longer ejaculation latency times and better erectile function probably due to the reduction of penile sensation compared to baseline data before the surgery (30). Although suggestive of a causal effect of penile length on sexual function, these findings may not be generalizable given that men seeking surgery may be different from other men. A study of 1027 Egyptian men found that men with ED had shorter fully stretched penis lengths than men without ED, but no connection between the penile circumference and ED was found (31). However, a study of 689 Brazilian men did not find any association between penile length and erectile function (23).

So far, no studies have directly investigated the link between penis size and sexual function in a non-clinical Asian sample. Based on the available evidence, we expected men with longer penises to have fewer early ejaculation and erectile problems while only conducting analyses regarding girth in an exploratory manner.

Penile Circumcision and Sexual Dysfunction

Circumcision of the penis is one of the most common surgical procedures worldwide. The procedure involves the surgical removal of part or all the foreskin from the penis for, among others, religious, cultural, and medical reasons. Approximately one in three men has been circumcised worldwide (32). The foreskin is the double layer of skin that covers the glans penis. Possible roles of the foreskin may include keeping the glans moist (33), protecting the developing penis in the womb (34), and enhancing sexual pleasure due to the presence of nerve receptors (35). Tight foreskin (i.e., phimosis) may cause erectile problems and even pain during sexual intercourse (36) which is a common medical reason for circumcision.

The effect of penile circumcision on sexual function has been investigated for a long time but remains controversial. Recent reviews indicate that penile circumcision may not have a robust effect on sexual function (37, 38), penile sensitivity (37, 38), or sexual pleasure (37, 38). Bronselaer et al. (39) found that male circumcision decreased men’s sexual pleasure and orgasm intensity. However, some recent studies have found that circumcised men reported better erectile function and less penile pain at rest and during sex which might be the reason for observed improvements of erectile function (36), higher intravaginal ejaculatory latency times and better control over ejaculation and more satisfaction with sexual intercourse compared to themselves before circumcision (40).

Bossio et al. (41) found that uncircumcised men’s foreskin sensitivity to tactile stimulation was higher than that of other penile sites (glans penis, proximal to midline shaft of the penis, midline shaft). Further, penile sensitivity was not different between circumcised and uncircumcised men among the latter penile sites (41). In conclusion, the foreskin of the penis may be one of the most important sites for tactile stimulation during sex. One possibility is that the reason that circumcision can improve ejaculation control is reduced penile sensitivity via removing part of the foreskin. In addition, a previous study also found circumcised men to report less sexual pleasure and lower orgasm intensity (39). In conclusion, we assumed that male circumcision improves erectile function (due to unknown reasons) and ejaculation control (due to reduced sensitivity).

We also looked at differences between men who naturally had different degrees of foreskin covering the glans penis while the penis had or did not have a full erection. In the flaccid state, the glans penis with a lower degree of foreskin coverage is more likely to come into contact with undergarments, resulting in friction between the glans penis and the clothes leading to thicker skin and thereby decreased sensitivity of the penis to stimulation which in turn would lead to a higher threshold to ejaculation. Assuming a correlation between foreskin coverage in flaccid and erect states, we expected erect state coverage to have the same effect. Also, considering the difficulty with erection if the penis has an excessively tight foreskin (36, 41), we expected men with less degree of foreskin covering glans when the penis was erect to have a less tight foreskin that would have less impact on the erection, resulting in fewer erectile problems.

Age and Sexual Dysfunction

The association between age and sexual function is still not fully understood. Although some previous research has found that older men have longer self-reported ejaculation latency times (2), age has not always been found to be associated with PE (42, 43). However, previous studies have relatively consistently found that higher age is associated with a higher risk of ED (15, 44), particularly in men aged over 40 (3). Also, on one hand, the higher risk of ED with increased age might also drive an increased risk of PE as PE and ED are positively associated (14, 45, 46). On the other hand, more sexual experience as a function of increased age may lead to less sexual performance anxiety (especially within long-term relationships) which in turn might decrease the risk of PE and ED (47).

Interestingly, both cross-sectional and longitudinal studies have shown that testosterone levels decline gradually as men age from their 30s to their 90s (48–50). Testosterone plays a role in every step of the male sexual response (51) with previous research showing that lower testosterone levels are associated with reduced sexual desire (52) and a higher risk of ED (52, 53). In addition, testosterone replacement treatment can improve the latency times of men with acquired PE (PE appearing only after a man’s first sexual experience) (54). However, a recent review has indicated that the effectiveness of testosterone replacement treatment in improving sexual function is modest and inconsistent, comparable to that of lifestyle interventions (53). In a similar vein, another contributing factor is cardiovascular disease contributing to ED with age (55). Based on the above, we supposed that the association between age and sexual dysfunction may not simply be linear. Instead, the effects of age on sexual function could be positive among younger men (due to the psychological effects of increased sexual experience) and negative among older men (due to biological changes caused by aging). Therefore, we investigated the association between age and sexual function among adult men while considering age itself also as a potential moderating factor.

Hypotheses

Previous research has indicated that a longer penile length is associated with fewer erectile problems (30, 56, 57) and longer ejaculation latency times (30), but penile circumference has not been found to have this effect. Therefore, we hypothesized that men with longer penises would experience fewer early ejaculation and erectile problems and only conducted analyses regarding girth in an exploratory manner (Hypothesis 1).

Previous research has suggested penile circumcision has a positive effect on ejaculation control and erectile function (36, 40, 58). Therefore, we hypothesized that circumcised men would experience fewer early ejaculation and erectile problems (Hypothesis 2). Based on the reduced sensitivity to friction stimulation due to friction between the glans penis with the less coverage of the foreskin and underclothes in the flaccid state, the highest sensitivity to tactile stimulation of the foreskin in the erection state, and the difficulty with erection if the penis has an excessively tight foreskin (36, 41), we expected that men with less degree of foreskin covering glans while the penis during full erection would experience fewer early ejaculation and erectile problems (Hypothesis 3).

The association between age and sexual function is still controversial (2, 42, 43). Testosterone levels in adult men, which are positively associated with better sexual function (51–53) begin to decline after age 30 (48–50). In contrast, as young men gain more sexual experience with increasing age, they may be less likely to experience sexual performance anxiety, particularly in long-term relationships, which could lower the risk of both PE and ED (47). Therefore, we expected that the association between age and sexual function is positive among younger men and negative among older men via the increasing sexual experience (Hypothesis 4).

Participants

Adult men who lived in Shanghai, China, were recruited to participate in the survey. Finally, 1085 participants who were aged from 18 to 50 (M = 31.37, SD = 5.52) reported that their biological sex at birth was male, that they were only sexually attracted to women, that their sexual identity was straight, that they had a stable sexual partner were included, and reported their penile length. We wanted to initially focus on straight men with female partners in order to be able to investigate PE and ED without confounding related to the sexual dysfunction of same-sex attracted men who were in relationships with women, a relatively common occurrence in China (59). In this sample, the majority of participants, 66.5% (722), reported having an undergraduate level of education. A smaller proportion, 22% (239), reported having a postgraduate level of education, while 7.8% (85) reported having a junior college level of education. Additionally, 1.7% (18) of participants reported having a technical secondary school education, 1.4% (15) reported having a senior high school education, and 0.5% (5) reported having a junior high school education. Only one participant (0.1%) reported only having a primary school education. The majority of participants, 713 (65.7%), reported being married.

Measures

Demographic Information

Participants were first asked to answer questions regarding their age, height, weight, assigned sex at birth, sexual identity, whether they had a stable sexual partner or not, and education level. The response options for sexual identity were straight, gay, bisexual, asexual, and uncertain. They also answered a question about the sex of the persons they were attracted to with response options men, women, both, neither, and uncertain. The response options for education level were primary school, junior high school, technical secondary school, senior high school, junior college, undergraduate, and postgraduate.

Penile Characteristics

Next, participants were asked to report their penis length and circumference. There was a picture showing the length and circumference of the penis and instructions for participants regarding how to measure the length and circumference of the penis (see Fig. 1; (60). Questions were “Do you know your penis length (cm) when you have a full erection?” and “Do you know your penis girth or circumference (cm) when you have a full erection?”. The options are “Yes, I know (When this option is selected, a fill-in-the-blank number for length or circumference appears).” and “No, I do not know”. The instruction to measure penile length after erection is “1. You should keep standing and the penis must be parallel to the ground; 2. Try to reduce the impact of pre-public symphysis fat where public hair grows by starting the measurement as close to the base of the penis as possible; 3. Measure along the upper side of the penis from the base and extend to the top.” A corresponding instruction was given for measuring the circumference of the penis. Based on the result of previous studies (61–63), for penile length, we removed values lower than 4 cm and higher than 20 cm. For penile circumference, we assumed that values lower than 8.5 cm must be diameters and changed them to circumference using geometry, and removed values higher than 30 cm.

Then, participants were asked “Has your penis been circumcised?” If they chose “No”, they were asked to answer two questions regarding the degree of the foreskin covering the glans of the penis when they do not have an erection and when they have a full erection. Questions were “To what degree does your foreskin cover your glans penis (the tip of your penis) when you do not have an erection?” and “To what degree does your foreskin cover your glans penis (the tip of your penis) when you have a full erection?”. Figure 1 shows the options indicating the different degrees of the foreskin covering the glans penis (100%, 75%, 50%, 25%, and 0%). Participants were asked to choose one of the five options. Higher values mean less degree of the foreskin covering the glans of the penis (64) in a forward direction from the start of the glans of the penis to where the foreskin meets the shaft. In addition, we re-coded the degree of the foreskin covering the glans penis of participants who reported that their penises were circumcised as 0%.

[Figure 1 near here]

Note

Upper is the Measurement of the Length and Circumference of the Penis. Below is the option indicating the different degrees of the foreskin covering the glans of the penis in a forward direction from the start of the glans of the penis to where the foreskin meets the shaft.

International Index of Erectile Function-5 (IIEF-5)

The International Index of Erectile Function-5 (IIEF-5), which was developed from the 15-item version (65), was used to measure erectile dysfunction (ED) (66). An example item is: “How do you rate your confidence that you could get and keep an erection?”. The sum of the five items was computed so that each item was evaluated on a 5-point Likert scale ranging from 1 to 5 for each participant. In a previous Chinese study, the internal consistency assessed with Cronbach’s α was .790 (67). The electronic version of IIEF-5 has been found to have excellent internal consistency, excellent test-retest reliability, and convergent validity in Western samples (68). Cronbach’s α was .784 for these items in the present study. Higher values indicated that better erectile function.

Checklist for Early Ejaculation Symptoms (CHEES)

The 5-item diagnostic tool Checklist for Early Ejaculation Symptoms (CHEES), which was developed from three earlier ejaculation diagnostic tools and has improved validity (69), was used to measure the ejaculation control of the participants. This measure has been proven to perform well in differentiating men with and without PE in a Western population sample (AUC = 0.98) (69) and to have good internal reliability of .760 (70). It has not previously been used with Chinese samples. Therefore, we first translated the scale into a Chinese version using translation software. This version was then modified by native Chinese-speaking sex researchers with Ph.D. students. An example item is: “Over the past six months, was your control over ejaculation during sexual intercourse?” The sum of the five items was computed in which each item was evaluated on a 5-point Likert scale ranging from 1 to 5. In the present study, Cronbach’s α was .776. Higher values indicated more early ejaculation symptoms.

Procedure

The questionnaire was created on two Chinese survey platforms: WJX (https://www.wjx.cn) and CREDAMO (https://www.credamo.com).

On both platforms, an invitation link to the questionnaire was sent to the potential participants who were adult men 18–50 years old and currently living in Shanghai. (https://www.wjx.cn/vj/reLdx3e.aspx; https://www.credamo.com/survey.html#/share/a3a55918c4d245b5b1486dd24cc23db0). The potential participants who were interested in participating could click the survey link. After the potential participants clicked the link, they would read the consent form online, and then decide whether they wanted to participate in the study or not and click the "Yes, I agree to participate (and confirm that I am eligible for this study)." in case they did. Only participants who were over 18 years of age, male, Chinese, and had a regular sexual partner were asked to participate. The present study was reviewed and approved by the Institutional Review Board. Each participant responding on WJX was paid from 4 to 7 RMB for their participation while each participant responding on CREDAMO was paid 12.5 RMB for their participation in line with the internal processes of the two platforms for a questionnaire of this length. The payment procedure was as follows: We paid the data collection service fee to the WJX and CREDAMO platforms. After the participants completed the survey, both platforms would transfer the payment to each participant. The internal processes of the WJX and CREDAMO platforms can prevent multiple submissions from the same IP address that may have been motivated by monetary incentives. Finally, there are 1055 responses from WJX and 996 responses from CREDAMO.

Participants from CREDAMO had higher age (t(1974) = 6.394, p < .001) than participants from WJX. We also investigated the stability of the associations between the sexual dysfunction variables and the other variables between the two platforms. The confidence intervals of correlations between the correlation between age and the CHEES, the correlation between age and penile circumference, the correlation between CHEES and penile length, the correlation between CHEES and penile circumference, the correlation between penile length and circumference did not overlap. All the other correlations’ confidence intervals overlapped between the two platforms.

Statistical analyses

The data analyses were conducted using SPSS 27. and R 4.2.2(71) and RStudio(72).

First, we conducted a missing value analysis in SPSS to impute the missing values of penis girth for participants who had reported penile length. This was done using quantitative variables of age, height, weight, penis length, and girth using the expectation maximization procedure. In total, 445 missing values were imputed.

Then, we conducted linear regression analyses to investigate whether age, penile length, penile circumference, and the degree of foreskin covering the glans when the penis has a full erection or not were associated with early ejaculation and erectile problems using the interactions package(73).

Next, we conducted moderation model analyses for age as both an independent variable and a moderator in the relationship between age and early ejaculation and erectile problems using the interactions package(73) .

Then, we created an age group variable by splitting the data into a younger group (aged 31 or younger than 31; n = 583) and an older group (older than 31; n = 502) to illustrate the moderation effect. The age of 31 was the median. Finally, we investigated the moderation effect of age groups on the relationship between age and early ejaculation and erectile problems using the interactions package(73) .

Table 1 displays the descriptive statistics and the results of correlation analyses between age, penile length, penile circumference, early ejaculation and erectile problems. Longer penis length and great penis girth were found to be associated with fewer early ejaculation problems while only a longer penis was associated with fewer erectile problems.

Table 1

*Descriptive Statistics and Correlations between Age, BMI, Penile Length, Penile Circumference, and Early Ejaculation and Erectile Problems.*
	n	M	SD	CHEES	IIEF-5	Age	Penile Length
CHEES (Early Ejaculation)	1085	9.63	2.85
IIEF-5 (Erectile Function)	1085	21.71	2.55	− .544**
Age	1085	31.37	5.52	− .094**	.045
Penile Length	1085	14.49	2.22	− .201**	.117**	.008
Penile Girth	1085	15.46	4.36	− .194**	.053	.276**	.289**
Note. Higher values of CHEES suggest more early ejaculatory problems. Higher values of IIEF-5 suggest fewer erectile problems which also suggests better erectile function. Penile length means the penile length when the penis has a full erection. Penile girth means the penile circumference when the penis has a full erection. p < .05, *p < .01.

[Table 1 near here]

Table 2 displays the result of linear regression analyses between age, penile length, penile circumference, and early ejaculation (R² = .102, F(5, 1079) = 25.52, p < .001) or erectile problems (R² = .037, F(5, 1079) = 9.276, p < .001). Longer penile length (Min = 5 cm, Max = 20 cm) was found to be associated with fewer early ejaculation and erectile problems. Greater penile circumference (Min = 4.7 cm, Max = 30 cm) was only associated with fewer early ejaculation problems. Less foreskin covering the glans penis was associated with fewer early ejaculation and erectile problems both when the penis has no erection or has a full erection. Separate regression analyses also indicated that circumcision was associated with fewer early ejaculation (R² = .037, F(5, 1079) = 9.276, p < .001; B = -1.267, SE = .171, t = -7.405, p = < .001) and erectile problems (R² = .006, F(1, 1083) = 7.421, p = .007, B = .426, SE = .157, t = 2.724, p = .007).

Table 2

Linear Regression Analyses of Associations between Age, Penile Length, Penile Girth, Degrees of Foreskin Covering the Glans Without an Erection and With a Full Erection and Early Ejaculation and Erectile Problems.
Dependent	Independent	B	SE	t	p
CHEES
	Age	− .023	− .016	-1.474	.141
	Penile Length	− .191	− .038	-4.935	< .001
	Penile Girth	− .071	− .021	-3.450	< .001
	Foreskin Coverage When Penis No Erect	− .351	− .071	-4.912	< .001
	Foreskin Coverage When Penis Full Erect	− .324	− .015	-2.183	.029
IIEF-5
	Age	.015	.014	1.022	.307
	Penile Length	.118	.036	3.279	.001
	Penile Girth	− .003	.019	− .145	.885
	Foreskin Coverage When Penis No Erect	.140	.066	2.109	.035
	Foreskin Coverage When Penis Full Erect	.456	.137	3.316	< .001
Note. Higher values of CHEES suggest more early ejaculation problems. Higher values of IIEF-5 suggest fewer erectile problems. Penile length means the penile length when the penis has a full erection. Penile girth means the penile circumference when the penis has a full erection. Higher values mean less degree of the foreskin covering the glans of the penis.

[Table 2 near here]

Table 3 displays the moderation effect of age and age groups on the relationship between age and early ejaculation and erectile problems.

Table 3

*Moderation Effect of Age and Age Groups on the Associations Between Age and early ejaculation and erectile problems.*
	Group	B	SE	t	p
CHEES	Age	-0.466	0.129	-3.614	< .001
	Age: Age	0.006	0.002	3.264	.001
CHEES	Age	-0.200	0.089	-2.251	.024
	Age Group	-4.432	1.661	-2.668	.007
	Age: Age Group	0.124	0.053	2.323	.020
IIEF-5	Age	0.267	0.116	2.297	.022
	Age: Age	-0.003	0.001	-2.132	.030
IIEF-5	Age	0.101	0.080	1.261	.207
	Age Group	2.265	1.497	1.512	.131
	Age: Age Group	-0.068	0.048	-1.331	.184
Note. Higher values of CHEES suggest more early ejaculation problems. Higher values of IIEF-5 suggest fewer erectile problems. The younger and older groups were split by the median age of 31. Participants aged 31 or younger were defined as younger. Participants older than 31 were defined as older.

Analyses for age as both an independent and moderating variable in the relationship between age and early ejaculation problems (R² = .017, F(2,1082) = 10.16, p < .001) or erectile problems (R² = .004, F(2,1082) = 3.394, p = .034) showed that higher age was overall associated with fewer early ejaculation and erectile problems but that age also had a significant moderating effect on these relationships.

Analyses using age group as a moderation variable in the association between age and early ejaculation problems showed that age group had a significant moderating effect on the relationship (R² = .010, F(3,1081) = 6.618, p < .001) but not for the relationship between age and erectile problems (R² = .027, F(3,1081) = 1.788, p = .148). A higher age group was also associated with fewer early ejaculation problems.

[Table 3 near here]

Table 4 displays the simple slopes analyses for the relationship between age and early ejaculation and erectile problems in different age groups. Figure 2 shows the interaction effect between age and age groups on the relationship between age and early ejaculation problems. In the younger group, increasing age was associated with fewer early ejaculation problems while the relationship was reversed in the older group.

Table 4

*Simple Slopes Results of Relationship Between Age and Early Ejaculation and Erectile Problems in Different Age Groups.*
	Group	B	SE	t	p
CHEES	Younger	-0.077	0.041	-1.869	.062
	Older	0.046	0.033	1.384	.167
IIEF-5	Younger	0.038	0.037	1.010	.313
	Older	-0.026	0.030	-0.868	.386
Note. Higher values of CHEES suggest more early ejaculation problems. Higher values of IIEF-5 suggest fewer erectile problems. The younger and older groups were split by the median age of 31. Participants aged 31 or younger were defined as younger. Participants older than 31 were older.

[Table 4 near here]

[Figure 2 near here]

The present study investigated the associations between age, penile length and circumference, foreskin characteristics, early ejaculation and erectile problems. Results indicated that the greater length and girth of the penis were associated with fewer early ejaculation problems while only a longer penile length was associated with better erectile function. In addition, a complex relationship between age and early ejaculation problems was found.

The average self-reported erect penis was 14.49cm long. This is slightly shorter than the 16.8cm reported for a European sample (62), but similar to what has been reported for a US sample (14.2cm) (61) and other Asian samples (13.0cm) (63). The mean erect circumference was 15.46cm which is higher than in the above-mentioned Western samples (61,62) and Asian samples (63) which suggested that the mean erect circumference was approximately 11.5cm. However, the measurement method, social desirability on the part of the reporting man, and the presence of fat tissue can impact the accuracy of the outcomes of penile size measurement (74). For example, the instruction of the present study instructed reduced the participants to keep standing and keep the penis parallel with the ground while other studies have not done so. Having a longer penis was associated with also having a penis with greater circumference, which has also been found in previous research (31,75). However, the correlation between length and circumference was not very strong. A previous study found the longer penile length pubis to distal glans (bone to tip) was associated with greater penile circumference (r = .55, p < .001) but not for penile length from the suprapubic skin to distal glans (skin to tip). (75) Therefore, in the present study, we considered that the weak correlation observed may be attributed to bias resulting from variations in the measurement of penile length. Specifically, some participants may have measured the penile length from the bone to the tip, while others may have measured it from the skin to the tip.

Men with a shorter penis reported more ejaculatory and erectile problems in the study. It has previously been reported that men with a shorter penis would suffer from more dissatisfaction and anxiety about their penis size (76). In addition, insufficient erect penile also may trigger more dissatisfaction with their penis performance. The dissatisfaction and anxiety about penis size can trigger worry and shame regarding body image and sexual performance during sex (19), even body dysmorphic disorder (19). The balance and timing of the sympathetic and parasympathetic nervous systems are crucial for a well-functioning male sexual response (27). Excess anxiety about the body and performance during sex can trigger sympathetic overactivity which might inhibit erection and facilitate ejaculation. This may result in insufficient erection and early ejaculation (19,22,23). Men with longer erect penises were associated with less erectile problems in this study. However, erect penile circumference seems to not have an association with erection which was consistent with previous research (23,31).

For younger men (younger than or aged 31 years), increasing age had an association between better ejaculation control and erectile function. For older men (older than 31 years), increasing age had a negative association with ejaculation control. We assumed that the underlying mechanism may be that in men aged 31 years or younger, psychological factors (i.e., less sexual performance anxiety with increased sexual experience) positively affect sexual function with increased age. However, in men over 31, biological factors (i.e., cardiovascular disease, sex hormone level decline) would start having a negative impact on at least erectile function overwhelming the benefits from sexual experience. It is less clear why men in the older group would have more early ejaculation problems when getting older. We assumed the underlying mechanism may be that in men over 31, the physical condition would decrease because the cardiovascular disease risk arises and sex hormone level decline. Sexual intercourse is most physically demanding for lumbar flexion in men (77). They would experience more physical problems during sexual intercourse (i.e., exhaustion and musculoskeletal pain) because of poor physical condition compared with younger men (78). Exhaustion and musculoskeletal pain might lead to an early and more sympathetic activity which could lower their ejaculation threshold and early activate the ejaculatory reflex.

The results indicated that being circumcised might be associated with improved sexual function. Specifically, compared to uncircumcised men, circumcised men had better ejaculation control and erection. These results were consistent with a previous study conducted in China (40) and inconsistent with recent reviews (37,38) . We suggest that the underlying mechanism of the positive effect of male circumference on sexual function may be that the part of the foreskin, which was the most sensitive site of the penis to tactile stimulation during sex (41), was removed. In addition, because of the exposure of the skin of the glans penis to the air and friction with the underpants could further reduce the sensitivity of the glans penis after circumcision. Therefore, circumcised men would have better ejaculation control because of reduced penile sensitivity. Surprisingly, we also found that circumcised men had less erectile problems. The main reason why men in China get circumcised is due to medical reasons (i.e., phimosis) (40). We assumed that the reason might be the tight foreskin of the penis glans (i.e., phimosis) would disturb the erection which in turn leads to an insufficient erection in some cases. Circumcision that overall or partial removal of the foreskin glans would reduce the effect and consequently reduce the erectile problems.

Men with more erectile problems also had more early ejaculation problems which was in line with the prior study (14,15,46). Men with erectile problems have less self-confidence in having a sufficient erection allowing penetration. Then, this lower self-confidence will lead to excessive worry and anxiety regarding the penis size while erection as well as sexual performance (47,79). This excessive anxiety will disturb the parasympathetic activity to facilitate erection and earlier results in an overactive sympathetic nervous system (24–26) triggering a worse imbalance of autonomic nervous activity which may also be a cause of poorer ejaculatory function in men. In this way, ED symptoms can have a positive association with PE symptoms. However, further studies are needed to understand the details of this process.

The result indicated men of an older age would have a thicker erect penis which was in line with a prior study (80). However, a prior study found a weekly negative correlation between age and flaccid circumference (81). In addition, some studies indicated age was not correlated with penile length and circumference (82,83). It is possible that the reason for this could be fat tissue accumulating in the penis with increasing age. However, there is little research to investigate the relationship between age and the fat tissues of the penis.

Limitations and Future Directions

There were some limitations to the study. First, the penis size was measured by self-reported. The potential limitation of such self-reports is that some participants may make estimations for the penis size. Future studies should measure the penis size by experimenters who have the related training using the device. Second, we only measured the circumcision status of the men but not the age at which circumcision had been performed. A new review indicated that circumcision performed in infancy, childhood, and adulthood has different psychological effects on men (84). Future studies should also measure the age of circumcision. Last but not least, the present study omitted questions that ask men to rate their penis size in comparison with the norm for their population or comparison group, as well as their satisfaction with their penis size. Future studies should have these questions to measure participants’ satisfaction and potential anxiety with their penis size to future investigate the underlying mechanism of the association between penis size and sexual dysfunction.

Data Availability Statement

The datasets generated during and/or analysed during the current study are available in the OSF repository, [PERSISTENT WEB LINK TO DATASETS].

Author Contribution Statement

Caoyuan Niu: Investigation, Data Collection, Data curation, Methodology, Formal analysis, Writing-original draft, Visualization

Daniel Ventus: Writing-Review & Editing, Visualization

Patrick Jern: Writing-Review & Editing, Visualization.

Pekka Santtila: Conceptualization, Supervision, Writing-Review & Editing

Funding

The original data collections were funded by an internal NYU Shanghai grant to the last author.

Ethical Approval

This study had approved by the NYU Shanghai IRB. Informed consent will be obtained from subjects, but no signed consent form will be used. The potential participants will read the consent form online, and then decide whether they will participate in the study or not and click the "yes, I agree to participate (and confirm that I am eligible for this study). " They need not answer any information that identifies them personally.

Competing Interests

The authors declare no competing interests.

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There is NO conflict of interest to disclose.

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Associations between Self-Reported Anatomical Characteristics of the Penis, Age and Sexual Dysfunction in Men

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Abstract

Figures

Introduction

PE and ED

Penis Size and Sexual Dysfunction

Penile Circumcision and Sexual Dysfunction

Age and Sexual Dysfunction

Hypotheses

Material and Methods

Participants

Measures

Demographic Information

Penile Characteristics

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International Index of Erectile Function-5 (IIEF-5)

Checklist for Early Ejaculation Symptoms (CHEES)

Procedure

Statistical analyses

Results

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[Table 2 near here]

[Table 3 near here]

[Table 4 near here]

[Figure 2 near here]

Discussion

Declarations

References

Additional Declarations

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