Abstract
Background
Abnormal sperm quality, particularly high sperm DNA fragmentation levels, is associated with infertility and a higher risk of pregnancy loss. While short abstinence periods may improve semen quality, the specific role of ejaculation frequency (EF) remains unclear. EF refers to the number of times an individual ejaculates within a given period, which is distinct from the abstinence period, defined as the time interval between ejaculations. This study investigates the association between EF and semen quality, including sperm DNA fragmentation.
Methods
This cross-sectional study included 1,349 men who underwent semen analysis at a reproductive center between November 2023 and July 2024. The subjects were categorized into three groups based on their self-reported EF over the past four weeks: EF1: <1/week, EF2: ≥1 and <2/week, and EF3: ≥2/week.
Results
As EF increased, significant decreases were observed in sperm DNA fragmentation index (DFI) (P < 0.001), semen volume (P = 0.012), sperm concentration (P < 0.001), and total sperm count (P < 0.001). Sperm vitality showed a positive association with EF (P < 0.001), while no association was found between sperm progressive motility and EF. Lower risks of elevated sperm DFI and necrozoospermia were observed in EF2 and EF3 compared to EF1. However, there was no increased risk of oligozoospermia or asthenozoospermia with increased EF.
Conclusions
Higher ejaculation frequency is associated with improved sperm vitality and lower DFI without negatively impacting motility. EF should be considered alongside abstinence in male fertility assessments.
Trial registration
The study was registered on ClinicalTrials.gov (identifier NCT06127875).
Date of registration
November 11th, 2023. Date of enrollment of the first subject: November 11th, 2023.
Keywords: Ejaculation frequency, Semen parameter, DNA fragmentation index, Abstinence period
Introduction
Conceiving a healthy baby is not an easy endeavor. Infertility remains a global public health concern, affecting approximately 8–12% of couples of reproductive age [1]. According to a population-based register study, 13.5% of pregnancies intended to be carried to term ended with fetal loss [2]. The European Society of Human Reproduction and Embryology (ESHRE) indicated miscarriage rates ranging from 10–15% [3]. When addressing infertility or miscarriage, it is crucial to evaluate not only female factors, but also male factors such as paternal age, sperm quality, occupational exposures, and lifestyle factors (smoking, alcohol consumption, and obesity) [4–6].
Conventional and functional sperm parameters, including sperm concentration, motility, morphology, and DNA fragmentation index (DFI), continue to serve as significant predictors of fertility outcomes. Nonetheless, it is crucial to recognize the inherent variability of semen parameters, both within and among different individuals. This variability may be influenced by several self-controllable factors, including the duration since the last sexual activity and the ejaculation frequency (EF). With regards to the ejaculatory abstinence time, the World Health Organization (WHO) laboratory manuals for the examination and processing of human semen published since 1980 and the most recently released in 2021 recommend that semen be collected after a minimum of 2 days and a maximum of 7 days of ejaculatory abstinence [7]. However, ESHRE recommended an abstinence period of only 3–4 days [8]. Prolonging the ejaculation abstinence period may increase semen volume and sperm count but could compromise sperm motility and sperm DFI [9]. A recent meta-analysis indicated that, compared with longer abstinence periods, a short ejaculatory abstinence was likely to improve pregnancy and live birth rates and decrease the level of DNA fragmentation in semen [10]. Another meta-analysis found that obtaining semen from a subsequent ejaculation with a very short abstinence period (1 day or a few hours) may result in improved sperm parameters, particularly beneficial for assisted reproductive technologies (ART), which can rapidly improve sperm DFI and increase pregnancy success rates [11]. However, the sperm in the cauda epididymis of humans will be emptied after two to three ejaculations [12]. It is uncertain whether the highest quality sperm can be obtained only by relying on the abstinence period of the last time.
Despite the importance of EF, studies on this aspect remain limited. The National Institute for Health and Care Excellence (NICE) in the UK recommended having intercourse every 2 to 3 days to optimize fertility for couples attempting to conceive, although this recommendation lacks robust literature support [13]. Mayorga-Torres et al. reported that frequent daily ejaculation for two weeks has no major negative effect on both conventional and functional parameters [14]. However, this regimen may not be feasible for couples pursuing natural conception due to the challenges of sustaining daily ejaculations or multiple ejaculations within a day over several months or even years before achieving pregnancy. Therefore, for couples seeking fertility, determining the optimal timing and frequency of sexual intercourse to achieve a healthy baby is of utmost concern. Moreover, it remains uncertain whether assessing semen parameters solely based on WHO’s abstinence standards, without considering recent EF, contributes to parameter variability.
Clearly, further investigation is necessary to elucidate the relationship between EF and semen quality. Thus, this study aims to compare the impact of varied ejaculation frequencies on male semen parameters.
Methods
Ethical approval
This cross-sectional study was conducted with the approval of the medical ethics committee of the First Hospital of Jilin University (approval number: 23K227-001). The study was registered on ClinicalTrials.gov (identifier: NCT06172504). Written informed consent was obtained from all participating patients and the study was performed in accordance with the Declaration of Helsinki.
Patients
A total of 1,697 men who underwent semen analysis at the Reproductive Center of the First Hospital of Jilin University between November 2023 and July 2024 were included in this study. The study population included healthy men, infertile men, and men whose partners had a history of pregnancy loss (men with PL). Infertile men were defined as those whose partners did not conceive within one year of unprotected sexual intercourse, while healthy men included those seeking fertility assessment with their partners and aiming to conceive within less than a year. All male participants were aged between 22 and 45 years old. The exclusion criteria were extremely severe oligospermia (sperm density < 1*106), azoospermia, urogenital infections (epididymitis, orchitis), genital surgery (testicular cancer, cryptorchidism, and testicular torsion), moderate to severe varicocele, and occupational exposure (high temperature, chemicals, and radiation). Furthermore, we recorded the abstinence periods of the last two ejaculations, and male participants were excluded from the study if these abstinence periods did not meet the criteria for their respective groups. Ultimately, 1,349 men were enrolled in this study (Fig. 1).
Fig. 1.
Flow diagram for the selection of the eligible study population
Questionnaires
Questionnaires collected demographic characteristics (age, height, weight, educational level, occupation, and place of residence), lifestyle habits (alcohol consumption, smoking), and medical history (urogenital infections and genital surgery), pregnancy and delivery history of the female partner. Body mass index (BMI) was calculated as weight in kilograms divided by height in meters squared. Due to the variable nature of EF among males, we categorized it using interval ranges. In this study, participants were classified into three groups based on their self-reported EF over the past four weeks: EF1: <1/week, EF2: ≥1 and < 2/week, and EF3: ≥2/week. Specifically, these groups were defined as follows: EF1: Participants who had 0 or 1 ejaculation in each of the past four weeks. This includes those who had a mix of weeks with 1 ejaculation and weeks with no ejaculation. EF2: Participants who had 1 or 2 ejaculations in each of the past four weeks. This includes those who ejaculated exactly 1 time per week in all four weeks and those who had a mix of weeks with 1 ejaculation and weeks with 2 ejaculations, but not consistently 2 times per week. EF3: Participants who had 2 or more ejaculations in each of the past four weeks. To minimize the potential for bias, we provided participants with a detailed questionnaire that included specific prompts and examples, clarifying the definition of EF and its classification. We also invited the wives to assist their husbands in recalling the information, confirming it week by week to ensure accuracy. Additionally, we recorded the abstinence periods of the last two ejaculations. Only participants who met the selected grouping criteria were eligible for inclusion in the study. Questionnaires were completed before the semen test results were reported.
Semen collection
The semen samples were collected by masturbation into a pre-weighted disposable clean container, abstinence for 2–7 days accordingly. The degree of liquefaction was observed every 10 min. The container containing the sample was weighed. Then the weight of the container was subtracted and the volume was calculated from the sample weight. The semen volume (ml) = weight (g)/density (g/ml).
Semen analysis
The procedure of semen analysis has been described in our previous article [15]. The samples were incubated at 37 °C until completely liquefied. Conventional semen analysis was then conducted. Semen samples were analyzed for sperm concentration, motility and viability. We extracted 5-ml semen samples from well-mixed semen and examined sperm concentration, motility and viability through the computer-automated semen analysis system (CASA) (BEION S3, Beion Medical Technology Co. LTD, Shanghai, China). Total sperm count = Sperm concentration (106/ml) × volume (ml). Total progressive motility sperm count = total sperm count (106/ejaculate) × progressive motility %. Semen parameters were classified according to the guidelines of the WHO Laboratory Manual [7].
Sperm DFI was assessed by adding liquid A (20× phosphate-buffered saline (PBS)) to the semen sample, and the concentration was adjusted to 5–10 × 106/ml using liquid A. A volume of 100 µl of the adjusted semen sample was taken into a flow cytometer detection tube (MindRay, Shenzhen, China), then 200 µl of B solution (Anke Biotechnology, Anhui, China) was added, mixed, and incubated for 30 s. Subsequently, 600 µl of C solution (Anke Biotechnology, Anhui, China) was added, mixed, and the sample was then loaded into the flow cytometer (MindRay, Shenzhen, China) for analysis. At least 5,000 sperm cells per sample were counted, recorded, and subjected to statistical analysis.
Statistical analyses
Qualitative variables are reported as frequencies, and quantitative variables are reported as the mean ± standard deviation (s.d.). For comparisons between the two groups, Student’s t-test and the Mann-Whitney U test were used for parametric and nonparametric data, respectively, and Pearson’s Chisquared test was used when needed. For comparison of more than two groups, analysis of variance (ANOVA) was used for quantitative variables with a normal distribution, the Kruskal–Wallis test was employed for nonparametric comparisons, and Pearson’s Chi-squared test was used for categorical variables. According to the 2021 version of World Health Organization (WHO) guidelines, the lower reference limits for the semen parameters are as follows: total sperm count < 39 × 106/ml (oligozoospermia), progressive sperm motility < 32% (asthenozoospermia), and vitality sperm < 58% (necrozoospermia) [7].
Data were analyzed using different EF groups in multiple linear regression model analyses for each semen parameter outcome separately. Covariates initially included factors possibly associated with semen parameters, including multiple linear regression model analyses adjusted for age, BMI, smoking, alcohol consume, education level, abstinence time, duration of cohabitation, number of pregnancy losses. All tests were two-sided, and P < 0.05 was considered to indicate statistical significance. Statistical analyses were processed using the statistical package R (The R Foundation; http://www.r-project.org; version 4.2.3) and EmpowerStats software (www.empowerstats.net; X&Y solutions, Inc. Boston, Massachusetts).
Results
Clinical characteristics of the participants
The clinical characteristics and semen parameters of the participants were shown in Table 1. The mean age of the study subjects (mean ± s.d.) was 32.3 ± 4.0 years, and the BMI (mean ± s.d.) was 26.2 ± 4.1 kg/m2. The fraction of men who consumed alcohol more than 2 times per week accounts for 7%. Moreover, nearly 40% of men were smokers (n = 528, 39.1%). The majority of men have achieved an undergraduate education level (n = 898, 66.4%). The mean cohabitation duration (mean ± s.d.) for couples was 4.2 ± 3.3 years. The cohabitation duration in the group of healthy men was shorter than that in the infertility and PL groups (P < 0.001). The average abstinence time was 4.2 ± 1.2 days. Healthy men had a significantly lower age (P < 0.001), cohabitation duration (P < 0.001) and a significantly higher education level (P < 0.001). In addition, men with PL had a significantly higher sperm concentration (P = 0.032), total sperm count (P = 0.016), progressive motility (P = 0.012), sperm vitality (P = 0.011) and total progressive motility sperm count (P = 0.003).
Table 1.
Characteristics and descriptive statistics of the whole cohort
| Clinical characteristic | Total (n = 1,349) | Healthy men (n = 567) | Infertile men (n = 342) | Men with PL (n = 440) | P |
|---|---|---|---|---|---|
| Age (year), mean ± s.d. | 32.3 ± 4.0 | 31.2 ± 3.7 | 33.2 ± 4.2 | 33.1 ± 4.0 | < 0.001** |
| BMI (kg/m2), mean ± s.d. | 26.2 ± 4.1 | 26.3 ± 4.3 | 26.2 ± 3.9 | 26.0 ± 3.9 | 0.416 |
| Smokers, n (%) | 528 (39.1) | 203 (35.8) | 152 (44.4) | 173 (39.3) | 0.035* |
| Alcohol consumer, n (%) (> 2 times/week), | 95 (7.0) | 31 (5.5) | 33 (9.7) | 31 (7.1) | 0.058 |
| Education level, n (%) | < 0.001** | ||||
| No higher than university | 316 (23.4) | 86 (15.2) | 110 (32.2) | 120 (27.3) | |
| University | 896 (66.4) | 399 (70.4) | 214 (62.6) | 283 (64.3) | |
| University above | 137 (10.2) | 82 (14.5) | 18 (5.3) | 37 (8.4) | |
| Duration of cohabitation (year), mean ± s.d | 4.2 ± 3.3 | 3.2 ± 2.7 | 4.4 ± 3.3 | 5.4 ± 3.7 | < 0.001** |
| Abstinence time (day) | 4.2 ± 1.2 | 4.3 ± 1.2 | 4.3 ± 1.2 | 4.2 ± 1.2 | 0.386 |
| DFI, (%), mean ± s.d. | 15.3 ± 9.4 | 15.0 ± 9.1 | 16.0 ± 9.8 | 15.0 ± 9.5 | 0.099 |
| Semen volume (ml), mean ± s.d. | 3.8 ± 1.5 | 3.8 ± 1.5 | 3.7 ± 1.5 | 3.7 ± 1.4 | 0.211 |
| Sperm concentration (millions/ml), mean ± s.d. | 66.0 ± 40.0 | 64.7 ± 41.0 | 63.5 ± 37.8 | 69.6 ± 40.3 | 0.032* |
| Progressive motility, (%), mean ± s.d. | 32.4 ± 15.7 | 32.0 ± 15.6 | 31.2 ± 16.0 | 33.9 ± 15.4 | 0.043* |
| Sperm vitality, (%), mean ± s.d. | 74.1 ± 10.5 | 74.3 ± 10.4 | 72 0.4 ± 11.8 | 75.2 ± 9.4 | 0.011* |
| Total progressive motility sperm count (millions), mean ± s.d. | 77.6 ± 62.6 | 75.8 ± 59.5 | 71.6 ± 64.1 | 84.7 ± 64.8 | 0.003* |
| Total sperm count (millions), mean ± s.d. | 234.2 ± 149.0 | 232.9 ± 148.8 | 220.6 ± 146.8 | 246.6 ± 150.2 | 0.016* |
*P < 0.05; **P < 0.001; PL: pregnancy loss; BMI: body mass index; DFI: DNA fragmentation index; s.d.:standard deviation
Comparison of clinical characteristics in different ejaculation frequency
Table 2 presents the participants categorized into three groups based on their weekly EF. The EF in infertile men and men with PL groups was lower than in the healthy men group (P < 0.001). Age (P < 0.001), duration of cohabitation (P < 0.001), the number of pregnancies (P = 0.018) and the number of pregnancy losses(P = 0.007) showed a negative correlation with EF. No statistically significant association was observed between BMI, smokers, alcohol consumer, and abstinence time. Sperm DFI will decrease with the increase of the EF (P < 0.001). Semen volume (P = 0.012), sperm concentration (P < 0.001), total sperm count (P < 0.001) and total progressive motility sperm count (P < 0.001) decreased as the EF increased. However, sperm vitality had a positive association with EF (P < 0.001). No association was found between sperm progressive motility and EF.
Table 2.
Comparison of clinical characteristics in different ejaculation frequency
| Clinical characteristics | Total, n | EF1 (n = 444) |
EF2 (n = 700) |
EF3 (n = 205) |
P |
|---|---|---|---|---|---|
| Participants, n (%) | 1349 | < 0.001** | |||
| Healthy men | 567 | 148 (33.3) | 314 (44.9) | 105 (51.2) | |
| Infertile men | 342 | 127 (28.6) | 167 (23.9) | 48 (23.4) | |
| Men with PL | 440 | 169 (38.1) | 219 (31.3) | 52 (25.4) | |
| Age (year), mean ± s.d. | 1349 | 32.9 ± 4.1 | 32.2 ± 3.9 | 31.6 ± 4.0 | < 0.001** |
| BMI (kg/m2), mean ± s.d | 1349 | 26.4 ± 4.0 | 26.0 ± 4.1 | 26.4 ± 4.0 | 0.092 |
| Smokers, n (%) | 1349 | 171 (38.5) | 272 (38.9) | 85 (41.5) | 0.755 |
| Alcohol consumer (> 2 times/week), n (%) | 1349 | 30 (6.8) | 51 (7.3) | 14 (6.8) | 0.936 |
| Duration of cohabitation (year), mean ± s.d. | 1349 | 4.8 ± 3.7 | 4.0 ± 3.2 | 3.7 ± 2.9 | < 0.001** |
| Abstinence time (day) | 1349 | 4.3 ± 1.2 | 4.2 ± 1.2 | 4.2 ± 1.1 | 0.583 |
| Pregnancies (n), mean ± s.d | 1349 | 0.7 ± 0.9 | 0.6 ± 0.9 | 0.5 ± 0.8 | 0.018* |
| Pregnancy losses(n), mean ± s.d | 1349 | 0.5 ± 0.8 | 0.5 ± 0.8 | 0.4 ± 0.8 | 0.007* |
| DFI, (%), mean ± s.d. | 1349 | 18.1 ± 11.8 | 14.3 ± 7.7 | 12.3 ± 7.0 | < 0.001** |
| Semen volume (ml), mean ± s.d. | 1349 | 3.9 ± 1.6 | 3.7 ± 1.4 | 3.5 ± 1.3 | 0.012* |
| Sperm concentration (millions/ml), mean ± s.d. | 1349 | 70.2 ± 41.1 | 66.4 ± 39.9 | 55.6 ± 36.4 | < 0.001** |
| Progressive motility, (%), mean ± s.d. | 1349 | 32.6 ± 15.4 | 33.0 ± 15.9 | 32.3 ± 15.2 | 0.317 |
| Sperm vitality, (%), mean ± s.d. | 1349 | 72.2 ± 0.11.7 | 74.8 ± 10.0 | 75.6 ± 8.7 | < 0.001** |
| Total progressive motility sperm count (millions), mean ± s.d. | 1349 | 81.8 ± 64.4 | 79.2 ± 61.5 | 63.0 ± 60.6 | < 0.001** |
| Total sperm count (millions), mean ± s.d. | 1349 | 262.6 ± 171.6 | 230.5 ± 136.7 | 185.3 ± 120.3 | < 0.001** |
*P < 0.05; **P < 0.001; EF: ejaculation frequency (times/week); PL: pregnancy loss; BMI: body mass index; DFI: DNA fragmentation index; s.d.:standard deviation
Adjusted regression coefficient of ejaculation frequency for semen parameters
After adjusting for confounding factors, the highest EF (EF3) was negatively associated with semen volume, sperm concentration and total progressive motility sperm count as shown in Table 3 (P < 0.001, respectively). Compared to EF1, EF3 was associated with a decrease of 0.45 mL in semen volume (95% CI: -0.70 to -0.21), a reduction of 12.66 million/mL in sperm concentration (95% CI: -19.32 to -6.00), and a decline of 18.02 million in total progressive motility sperm count (95% CI: -28.46 to -7.57). EF was negatively correlated with sperm DFI (EF2, P < 0.001; and EF3, P < 0.001) and total sperm count (EF2, P = 0.013; and EF3, P < 0.001). Compared with EF1, EF3 is associated with a decrease of 0.05 in sperm DFI (95% CI: -0.07 to -0.04) and a decrease of 72.78 million in total sperm count (95% CI: -96.96 million to -48.60 million). In addition, there was a significant positive linear association between EF and sperm vitality (EF2, P < 0.001; and EF3, P < 0.001). Compared with EF1, EF3 is associated with a 0.03 increase in sperm vitality (95% CI: 0.01 to 0.05).
Table 3.
Adjusted regression coefficient of ejaculation frequency for semen parameters
| Semen parameter | EF1 | EF2 | EF3 | ||||
|---|---|---|---|---|---|---|---|
| β (95% CI) | P value | β (95% CI) | P value | ||||
| DFI | Reference | -0.04 (-0.05- -0.02) | < 0.001 | -0.05 (-0.07- -0.04) | < 0.001** | ||
| Semen volume | Reference | -0.17 (-0.34- 0.01) | 0.060 | -0.45 (-0.70- -0.21) | < 0.001** | ||
| Sperm concentration | Reference | -2.56 (-7.26- 2.13) | 0.285 | -12.66 (-19.32- -6.00) | < 0.001** | ||
| Progressive motility | Reference | 0.01 (-0.01- 0.03) | 0.421 | -0.01 (-0.04- 0.02) | 0.551 | ||
| Sperm vitality | Reference | 0.03 (0.01–0.04) | < 0.001 | 0.03 (0.01–0.05) | < 0.001** | ||
| Total progressive motility sperm count | Reference | -1.19 (-8.55- 6.18) | 0.752 | -18.02 (-28.46- -7.57) | < 0.001** | ||
| Total sperm count | Reference | -28.09 (-45.13- -11.05) | 0.013 | -72.78 (-96.96- -48.60) | < 0.001** | ||
**P < 0.001; P values were derived from multiple linear regression model analyses adjusted for age, BMI, smoking, drinking, education level, abstinence time, duration of cohabitation, number of pregnancies and number of pregnancy losses. EF: ejaculation frequency; DFI: DNA fragmentation index; CI: confidence interval.
The odds ratio (95% confidence interval) of sperm ejaculation frequency on semen parameter values
The risk of sperm DFI > 15% (EF2, adjusted OR = 0.69, 95% CI: 0.54–0.89; EF3, adjusted OR = 0.41; 95% CI: 0.28–0.59) and DFI > 30% (EF2, adjusted OR = 0.24, 95% CI: 0.15–0.38; EF3, adjusted OR = 0.21; 95% CI: 0.10–0.48) was lower compared to EF1 (Fig. 2). The risk of necrozoospermia were also lower in EF2 (adjusted OR = 0.48, 95% CI: 0.28–0.72) and EF3 (adjusted OR = 0.45; 95% CI: 0.21–0.95) compared to EF1. There was no increased risk of oligozoospermia or asthenozoospermia with increased EF.
Fig. 2.
The odds ratio (95% confidence interval) of penultimate ejaculatory abstinence on abnormal semen parameter values in adjusted model. *P < 0.05; **P < 0.001; The lower reference for sperm parameters is according to the World Health Organization guidelines: total sperm count < 39 × 106/ml (oligozoospermia), progressive motility sperm < 32% (asthenozoospermia), vitality sperm < 58% (necrozoospermia). Adjusted model adjusted for age, BMI, smoking, alcohol, education level, abstinence time, duration of cohabitation, number of pregnancies and number of pregnancy losses. EF: ejaculation frequency; DFI: DNA fragmentation index; OR: odds ratio; CI: confidence interval
Discussion
To the best of our knowledge, this is the first observational study to investigate the impact of EF on semen parameters. Ensuring the accuracy of semen analysis hinges on understanding the patient’s sample collection process. Key considerations before conducting semen analysis include abstinence period, method of semen collection, the patient’s mental state, and specimen integrity. Previous research also has suggested that the timing of semen collection can influence semen parameters [16]. Additionally, EF is also considered a potential factor affecting semen quality, though further related research is needed. Ejaculation is not a consistent behavior and carries a degree of randomness, making it a challenging factor for researchers to assess. To minimize variability in semen parameters due to irregular ejaculation, participants must meet specific grouping criteria to be included in the study.
To enhance natural fertility and ensure healthy offspring, couples should focus on two key factors: timing of sexual intercourse during ovulation and EF. Typically, couples overly emphasize ovulation timing while neglecting EF. Our study found that 81.4% of couples lack understanding of the relationship between EF and semen parameters. Moreover, 4.5% of couples chose to have intercourse only during ovulation, with minimal activity outside of this period. Therefore, we urgently need to figure out what kind of influence the EF has on semen parameters. After adjustment, we observed that as EF increased, there was a significant decrease in sperm DFI. Increasing EF had a negative impact on sperm concentration, total sperm count, and total progressive motility sperm count, but a positive effect on sperm vitality. However, no significant differences were found in sperm progressive motility across different ejaculatory frequencies. The seemingly contradictory decrease in sperm concentration and count, along with the improvement in sperm DFI and vitality, may be related to the oxidative stress damage caused by reactive oxygen species (ROS) in the epididymis, which leads to the accumulation of DNA damage and fragmentation over time [17]. An increase in EF reduces the duration of sperm retention in the epididymis, thereby decreasing damage and improving vitality and DFI. However, this also results in a reduction in sperm concentration and count per ejaculation.
While there are many researches on the relationship between abstinence period and semen parameters [9–11], studies investigating the association between EF and semen parameters are scarce. Nonetheless, there is a notable correlation between EF and abstinence period: an increase in EF correlates with a decrease in average abstinence period. Shortened abstinence periods have been shown to reduce semen volume, sperm concentration, and total sperm count [18, 19]. Similarly, our research has shown that increasing EF results not only in reduced semen concentration and total sperm count, but also in a significant decline in total progressive motility sperm count. This trend appears unfavorable for fertility outcomes. However, in studies of artificial insemination, it has been found that while reducing abstinence period decreases total number of motile sperm (TMS), it significantly improves success rates [20]. Of course, an adequate TMS is essential. We have also found an interesting result: after adjusting for confounding factors, there was no increased risk observed in oligozoospermic patients with increasing EF. This indicates that although sperm concentration and total sperm count significantly decrease with increasing EF, this reduction does not increase the clinical risk of oligospermia. Therefore, in this context, the statistical significance does not have an adverse impact on clinical outcomes. Similarly, a meta-analysis revealed that despite a decrease in sperm count, pregnancy success rates increased following a second ejaculation after a very short abstinence period [11]. Therefore, it is speculated that increasing EF may not diminish the success rate of natural conception. Nevertheless, further research is warranted to validate these findings.
This study also found that sperm progressive motility was not correlated with EF, contrary to most reports indicating a decrease in sperm progressive motility with longer abstinence periods [21]. This discrepancy may be because there was no difference in abstinence time among the different EF groups in this study. Studies by Sullivan et al. indicated that the proximal region, corpus, and cauda of the human epididymis showed distinct histological structures. The cauda epididymis is specialized in defense and immune responses and fertilization [12]. Sperm storage in the cauda epididymidis is significantly affected by the stasis of seminal fluids, accumulation of senescent and degenerating spermatozoa, and the accumulation of cells involved in the removal of aging spermatozoa [22]. Therefore, based on our study, we speculate sperm progressive motility is influenced by abstinence time rather than EF.
The sperm DFI has become a novel parameter for assessing male fertility potential, surpassing traditional semen analysis in value. Besides its association with pregnancy loss and male infertility, sperm DFI demonstrates enhanced predictive value for pregnancy outcomes in ART. This study found that increasing EF significantly reduced sperm DFI. However, many factors such as age and abstinence time were found to have significant correlations with DFI [23]. After adjusting for confounding factors, both EF2 and EF3 groups showed a significant negative correlation between EF and DFI. Furthermore, using 15% and 30% as a critical threshold for analysis respectively, increasing EF was associated with a reduced risk of DFI > 15% and DFI > 30%. This finding emphasizes the importance of EF in male fertility. DFI tends to increase with a decrease in EF, due to oxidative stress reactions caused by ROS in the epididymal environment. Excessive ROS can lead to fragmentation of sperm DNA strands. The longer the storage time in the epididymis, the greater the impact on sperm. Additionally, external environmental factors that cause sperm damage also contribute to higher DFI. This is consistent with previous research on abstinence periods. However, relying solely on one ejaculation cannot completely empty the sperm stored in the epididymis. In this study, the EF3 group had lower sperm DFI compared to the EF2 group, indicating that frequent ejaculation was more beneficial. The study also found a positive correlation between sperm vitality and EF, suggesting that as EF decreases, the number of dead sperm and the risk of necrozoospermia were increased., which inevitably leaded to higher sperm DFI. It also indicated that EF was an important factor contributing to sperm DNA fragmentation, sperm aging, and sperm death.
Similar to the abstinence period, EF is readily accessible information and a simple method to quickly improve semen parameters. Therefore, this study investigated factors that may influence EF. We found that EF significantly decreased with increasing age, duration of cohabitation, number of pregnancies, and instances of pregnancy loss. Hence, when taking a medical history, it is important to inquire about EF when these risk factors are present. This is often overlooked yet critically important information that could impact reproductive outcomes.
The main strengths of this study include its relatively large sample size, which allowed for the evaluation of the relationship between EF and semen parameters. Considering numerous potential confounding factors such as age, body mass index, alcohol, smoking habits, abstinence duration, duration of cohabitation, number of pregnancies, and instances of pregnancy loss, which could affect semen parameters and EF, is another potential advantage.
This study indeed has several limitations that should be noted. Firstly, using samples from a single center may restrict the study’s ability to detect correlations effectively during adjusted analyses. Secondly, the frequency of ejaculation itself exhibits some degree of randomness, leading to potential recall biases during the survey process. Despite efforts to mitigate these biases by selecting participants with relatively consistent patterns and improving recall accuracy, complete error elimination remains unattainable. Therefore, future research directions should consider prospective randomized controlled study designs to obtain more precise and reliable information.
Conclusions
In conclusion, our study findings suggest that different EF affect both conventional and functional sperm parameters. Higher ejaculation frequency is associated with improved sperm vitality and lower DFI without negatively impacting motility. EF should be considered alongside abstinence in male fertility assessments. For males with low EF, personalized treatment should be based on semen parameters and specific clinical intervention needs.
Acknowledgements
The authors thank the patients enrolled in this study.
Abbreviations
- ANOVA
Analysis of variance
- ART
Assisted reproductive technology
- BMI
Body mass index
- DFI
DNA fragmentation index
- EF
Ejaculation frequency
- PL
Pregnancy loss
- ROS
Reactive oxygen species
- S.D.
Standard deviation
- TMS
Total number of motile sperm
Author contributions
Y.Y. and QK.K. designed and conceived the study; Q.X. and Y.Y. drafted the article; X.L. performed the statistical analysis; Data collected by QK.K. and Q.X.; RL.D. supervised the project; Y.Y. made critical revisions to the manuscript. All authors revised and commented on the article and approved the final version before submission.
Funding
This work was supported by grants from the Science and Technology Department of Jilin Province, China and Science and Technology Development Plan Project of Jilin Province, China (20210101354JC).
Data availability
The original contributions presented in the study are included in the article material. Further inquiries can be directed to the corresponding author.
Declarations
Ethics approval and consent to participate
This cross-sectional study was conducted with the approval of the medical ethics committee of the First Hospital of Jilin University (approval number: 23K227-001). The study is a registered clinical trial in ClinicalTrials.gov (identifier: NCT06172504). Written informed consent was obtained from all participating patients and the study was performed in accordance with the Declaration of Helsinki.
Consent for publication
Not applicable.
Competing interests
The authors declare no competing interests.
Footnotes
Publisher’s note
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Associated Data
This section collects any data citations, data availability statements, or supplementary materials included in this article.
Data Availability Statement
The original contributions presented in the study are included in the article material. Further inquiries can be directed to the corresponding author.