Trends In Semen Quality Research Articles

Downward trend in male reproductive health and fertility in Eastern Iran.

This study aimed to assess the ten-year trend in semen quality among couples referred to the Infertility Center in Kerman between 2008 and 2017. The study included 2952 semen samples from men 18 to 60 years old referred to the infertility center as infertile couples living in Kerman province, Iran, whether they had normal or abnormal semen analysis. A total of 2952 sperm samples were included. Statistically significant changes were observed in semen parameters. Particularly, significant changes were observed for volume (-0.08 mL/year), sperm concentration (-2.34 (mio/mL)/year), total sperm count (-13.17 (mio/ejaculate)/year), progressive motility (-2.62%/year), non-progressive motility (-0.59%/year), immotile sperm (2.49%/year), and normal morphology (-0.134%/year). In bivariate analysis, the prevalence of oligozoospermia in this study showed a statistically significant association with age (OR = 1.019; 95% CI = 1.007-1.032; p = 0.003). Likewise, there was a statistically significant association with the year (OR = 1.087; 95% CI = 1.050-1.125; p = 0.000). Semen quality parameters showed a downtrend during the last 10 years in this study, emphasizing the importance of male reproductive health monitoring and warning public health coordinators to pay more attention to this important issue.

SARS-CoV-2 Vaccination Improves Semen Quality in Men Recovered From COVID-19: A Retrospective Cohort Study.

Coronavirus disease 2019 (COVID-19) has been reported to decrease semen quality in reproductive-age men. Semen quality in vaccinated men after SARS-CoV-2 infection remains unclear. We recruited reproductive-age Chinese men scheduled for COVID-19 vaccination from December 2022 to March 2023. Among 1,639 vaccinated participants, an upward trend was found in sperm concentration (p < .001), progressive motility (p < .001), total motility (p < .001), total motile sperm count (TMSC) (p < .001), and normal morphology (p = .01) over time following COVID-19 recovery. Among men with an SARS-CoV-2 infection that lasted less than 30 days, men who received an inactivated vaccine booster had higher sperm progressive (p = .006) and total motility (p = .005) as well as TMSC (p = .008) than those without a booster vaccine, whereas no difference was found in semen parameters among men who received a recombinant protein vaccine. Similarly, an upward trend in semen quality was found among 122 men who provided semen samples before and after COVID-19. Higher risks of asthenozoospermia (odds ratio [OR] = 2.23, p < .001) and teratozoospermia (OR = 2.09, p = .03) were found among men who had an SARS-CoV-2 infection that lasted less than 30 days than among those without COVID-19. Collectively, after receiving SARS-CoV-2 vaccination, adverse but reversible semen parameters were observed in men recovering from COVID-19 over time. Recombinant protein vaccines and inactivated vaccine boosters should be recommended to all reproductive-age men.

Temporal Trends in Semen Quality, Hormone Levels, and Substance Use Among Infertile Men in Pre- and Post-Cannabis Legalization Eras in Canada.

Background: The Cannabis Act (Bill C-45) was enacted in 2018, to legalize and regulate the use, production, and sale of nonmedical cannabis in Canada. While public health and safety implications of cannabis legalization have yet to be elucidated, the wide availability of cannabis necessitates health care providers to be knowledgeable about therapeutic potential and side effects of use. This study aimed to examine the temporal trends over two decades and the impact of the Cannabis Act in Canada, implemented in October 2018, on substance use, semen parameters, and testosterone levels of infertile men. Methods: We conducted a retrospective cohort study from a prospectively maintained database of a single infertility clinic. Demographic, fertility, and substance use history were correlated with semen and hormone assessments. Temporal trends in cannabis use and semen quality between 2001 and 2021 were investigated and compared between pre-cannabis legalization eras (PRCL) and post-cannabis legalization eras (POCL). Results: Our cohort included 11,630 patients (9411 PRCL and 2230 POCL). Cannabis use increased by 8.4% per year (p<0.001), while alcohol and tobacco consumption declined (0.8% and 1.5% per year, p<0.05 and p=0.004, respectively). Similar trends were noticed in the POCL, with higher rates of cannabis use (22.4% vs. 12.9%, p<0.001) and decreased tobacco and alcohol intake (15.2% vs. 17.7%, p=0.005 and 50.5% vs. 55.2%, p<0.001, respectively) compared to the PRCL group. Semen concentration was lower in the POCL group (24.8±44.8 vs. 28.7±48.3 million/mL, p=0.03). Testosterone did not differ between the cohorts. Comparison between cannabis users (n=1715) and nonusers (n=9924) demonstrated a slight increase in sperm motility (25.9%±15.3% vs. 23.9%±15.0%, p=0.002) and decreased sperm concentration among users (27.6±53.5 vs. 23.9±15.0 million/mL, p=0.03). Conclusion: A nearly 10% rise in cannabis use in the POCL era was observed among men being investigated for infertility. Our data suggest cannabis use may be associated with an increase in testosterone, slightly improved sperm motility, and decreased sperm concentration.

Deteriorating Semen Quality: The Role of the Environment.

Since the end of the last century, several reports have suggested that semen quality is declining, especially in Western countries. Furthermore, cross-sectional studies using similar protocols have suggested regional differences in semen quality of young and fertile men. Reasons for these regional differences and local adverse trends in semen quality are unknown, but environmental factors are suspected to have a role. Besides adulthood environmental exposures, those occurring during testicular development may also affect semen quality. Longitudinal follow-up studies and mixture risk analyses are needed to study the effect of fetal, childhood, and adult life environment on semen quality.

Global trends in semen quality of young men: a systematic review and regression analysis.

Many studies have reported declines in semen quality mainly focused on total sperm counts (TSC) and sperm concentration (SC), ignoring the importance of progressive motile sperm (PR), total motile sperm (TM), and normal morphological sperm (NM). Therefore, we performed a comprehensive meta-analysis to explore the trend in semen quality of young men. We searched 3 English databases and 4 Chinese databases from January 1980 to August 2022. Random-effect meta-analyses and weighted linear regression models were conducted to perform the trend in semen quality. Finally, 162 eligible studies including 264,665 men from 28 countries were got between 1978 and 2021. Significant decreases were observed in TSC (- 3.06 million/year, 95% CI - 3.28 to - 2.84), SC (- 0.47 million/ml/year, 95% CI - 0.51 to - 0.43), and PR (- 0.15%/year, 95% CI - 0.20 to - 0.09), and there was an upward trend in TM (0.28%/year, 95% CI 0.24 to 0.32). The results of meta-regression analyses indicated that age, continent, income, WHO criteria, and abstinence time significantly impacted on TSC, SC, PR, and TM. Positive regression coefficients were observed in some categories suggesting that outcomes might not be declining and even increasing in these subgroups. Downward trends in semen quality among global young men were observed in our study, including TSC, SC, and PR. But TM did not appear to be trending down or even to be leveling off. More studies are needed to focus on the causes of the declines.

Is there a temporal trend in semen quality in Belgian candidate sperm donors and in sperm donors' fertility potential from 1995 onwards?

A recent meta-regression analysis reported a temporal trend in sperm count showing a significant decline in sperm count between 1973 and 2011. This decline is thought to affect fecundity. Moreover, semen quality is considered of key interest to public health given its association with all-cause male morbidity/mortality. The issue requires ongoing investigation due to geographical variation in semen quality and methodological errors in semen analysis. To study whether there is a temporal trend in semen quality in Belgian candidate sperm donors and in sperm donors' fertility potential. Retrospective analysis of samples provided by 439 candidate donors and pregnancy outcome in acceptors over a period of 23years. A total of 807 specimens from 439 candidate donors were examined from January 1995 to December 2017 (Table S1). Sub-analyses performed with regard to TSC from 2010 onwards (weighing) revealed a significant negative trend (R2 =-0.033; β=-0.18; CI: -0.16 to 0.07; p<0.05). We found a statistically significant association between year of donation and morphology (R2 = 0.036; β= -0.19; CI: -0.26 to -0.08; p<0.0001). The mean (±SD) clinical pregnancy rate per effective donor recruited (n=104), defined as the number of women with a clinical pregnancy, per number of women who initiated treatment with a donor's spermatozoa, was 68.5 (± 24.9) %. This measure did not show a significant change in function of year of donation. Candidate sperm donors represent a select group of men; as such, these results are not to be interpreted as representative for the general population. The study did not show a significant change in sperm concentration or fertility potential in sperm donors over a period of 23years. However, a negative trend was found for TSC from 2010 onwards. Also, the results show a significant decrease in ideal morphology over time.

Analysis of semen quality of 38 905 infertile male patients during 2008-2016 in Wenzhou, China.

This study analyzed the trend in semen quality of infertile male patients in Wenzhou, China, based on the data obtained from 38 905 patients during 2008–2016 in The First Affiliated Hospital of Wenzhou Medical University (Wenzhou, China). The results showed that only 24.9% of the patients had normal semen quality. For the semen quality of infertile male patients, that of the workers and 40-year-olds was significantly worse than the other occupational and age groups. For all the infertile patients, low semen volume, asthenozoospermia, and teratozoospermia accounted for 8.4%, 50.5%, and 54.1%, respectively. During 2008–2016, the annual mean percentage of fast forward motile spermatozoa, percentage of total forward motile spermatozoa, and percentage of spermatozoa with normal morphology decreased linearly with slopes of −2.11, −2.59, and −0.70, respectively. The proportion of patients with asthenozoospermia and multi-abnormal spermatozoa increased during 2008–2016 with slopes of 4.70 and 4.87, respectively, while for low semen volume, it decreased with a slope of −0.47 in the same time period. The proportion of patients with teratozoospermia increased from 2008 to 2011 and from 2011 to 2016 with slopes of 17.10 and 2.09, respectively. In general, the deteriorating trend of semen quality of infertile male patients in Wenzhou was obvious. Future efforts should be made to reveal the adverse influences on semen quality, such as occupational exposure, environmental quality, and living habits. Furthermore, more pervasive reproduction health education is necessary.

Temporal Trends in Semen Quality Among 271,545 Chinese Healthy Men From 1981 to 2019

Background: Recent studies reported a decrease of sperm count around the world, however, little data from China was included. In China, declines in sperm quality remain controversial. Therefore, this study attempted to explore the temporal trends in sperm quality of Chinese healthy males from 1981 to 2019. Methods: Based on the protocol provided by Levine et al, data extracted from Pubmed, Science Director, Embase, China National Knowledge Infrastructure (CNKI) and Wanfang Data were collected to assess changes of sperm concentration (SC) and total sperm count (TSC) in recent decades using simple liner regression and meta-regression before and after adjusting for potential covariates including fertility group, region group, mean age, abstinence time, sperm collection and counting methods and whether individual provides more than one sample selection of population. Moreover, subgroups, categorizing based on geographic region or fertility status, were also conducted. Findings: A total of 102 studies with 271,545 individuals who provided semen samples from 1981 to 2019 were finally extracted for the present meta-regression analysis. SC declined significantly, on average, 0.43% per year with an overall decline of 16.3% between 1981 and 2019 (slope in unadjusted simple regression models -0.848 million/ml/year; 95% CI: -1.392 to -0.304; P = 0.002; slope in adjusted meta-regression models = -0.854; −1.452 to -0.630; P < 0.001). Trends for TSC was similar to that for SC with 0.89% per year and 33.08% overall decline from 1981 to 2019 (slope in unadjusted simple regression models = -2.063 million/year; 95% CI: -3.840 to -0.287, P = 0.023; slope in adjusted meta-regression models = -2.536; -4.052 to -1.022; P = 0.001). In subgroup meta-regression analysis, the slopes in model could be modified by fertility and region group (PSC for interaction = 0.031 and PTSC for interaction = 0.006). Fertility males in northern China had continuous declines in both SC (slope= -2.393; -3.964 to -0.822; P = 0.006) and TSC (slope= -9.675; -16.295 to -3.054; P = 0.010). Similarity, unselected group (unknown fertility males) in northern China also showed significant decreases in both SC (slope= -0.866; -1.403 to -0.329; P = 0.002) and TSC (slope= -1.806; -3.744 to -0.131; P = 0.047). Meanwhile, in southern China, only SC had significant down trends in fertility individuals (slope= -0.997; -1.736 to -0.258; P = 0.008). No changes in SC or TSC were seen in other groups separately. Results changed minimally in multiple sensitivity analyses, and there was no statistical support for the use of a nonlinear model. Interpretation: The present study was the first study to assess semen quality among 271,545 Chinese general healthy men in the recent 4 decades and our result indicated a serious reproductive health warning that sperm quality in general healthy Chinese men decreases between 1981 and 2019. Further studies on causes of the decreases are urgently needed. Funding Statement: This research was financially supported by National Natural Science Funding of China (to DZ) and Natural Science Funding of Shaanxi Province (to DZ). Declaration of Interests: All authors declare no conflict of interest.

The impact of sociodemographic characteristics, lifestyle, work exposure and medical history on semen parameters in young Chinese men: A cross-sectional study.

There is an ongoing debate on the declining semen quality, and unfortunately, existing evidence is inconclusive and inconsistence. We evaluated the impact of sociodemographic characteristics, lifestyle, medical history and work exposure on semen quality. Univariate and multivariate analysis was used to investigate the association between different risk factors and semen quality parameters. Total sperm count (p=0.041), sperm concentration (p=0.007), normal morphology (p=0.002), total motility (p=0.004) and progressive motility (p=0.009) decreased in men with varicocele. Sperm concentration increased in tea (p=0.044); progressive and total motility increased in cola (p=0.018, p=0.012) consumers. Progressive and total motility decreased in urogenital surgery (p=0.016, p=0.014) and infection (p=0.037, p=0.022). However, age, coffee and alcohol drinking, physical activities, sleep duration and cell phone use were unrelated to any of semen parameters. Interestingly, semen volume (p<0.0001), total sperm count (p<0.0001) and concentration (p<0.033) increased with longer abstinence period (>5days); normal morphology (p=0.013) improved in men with higher body mass index (BMI>24), curvilinear velocity (p=0.042) increased with smoking; semen volume (p=0.050) increased in manual labourers. This study highlights the importance of sociodemographic characteristics, lifestyle, occupational exposure and medical history and provides time trends in semen quality, its clinical importance and direction for further research.

Secular trends in semen parameters among men attending a fertility center between 2000 and 2017: Identifying potential predictors

BackgroundMultiple meta-analyses have shown sperm count declines in Western countries spanning eight decades. Secular trends in other parameters remain unclear, as are potential predictors of these trends. ObjectiveTo analyze secular trends in semen quality and to evaluate whether factors previously found to be related to semen quality were responsible for these patterns. MethodsThis is a prospective study including 936 men of couples seeking infertility treatment who provided 1618 semen samples at a single center (2000–2017). Self-reported demographic, nutritional and reproductive characteristics were collected using standardized questionnaires. Urinary concentrations of bisphenol A, parabens and phthalates were quantified by isotope-dilution tandem mass spectrometry. Semen samples were analyzed for volume, sperm concentration, count, motility and morphology following WHO guidelines. We estimated the differences in semen parameters over time by fitting generalized linear mixed models with random intercepts to account for repeated samples while adjusting for abstinence time. We also adjusted for demographic, nutritional and environmental factors to investigate these as potential predictors of time trends. ResultsSperm concentration and count declined by 2.62% per year (95% CI −3.84, −1.38) and 3.12% per year (95% CI: −4.42, −1.80), corresponding to an overall decline of 37% and 42%, respectively, between 2000 and 2017. Decreasing trends were also observed for total motility (per year: −0.44 percentage units, 95% CI −0.71, −0.17) and morphologically normal sperm (per year: −0.069 percentage units, 95% CI −0.116, −0.023). These decreases reflected relative percentage declines of 15% and 16% over the 17 year study period, respectively. When reproductive factors were included in the model, the downward trends in sperm concentration and sperm count were attenuated by 29% and 26%, respectively, while the trends in motility and morphology were attenuated by 54% and 53%, respectively. Also, the downward trends in both sperm concentration and sperm morphology over time were attenuated by 19% when including the DEHP and non-DEHP metabolites, respectively. ConclusionsSperm concentration, total count, motility and morphology significantly declined between 2000 and 2017 among subfertile men. These negative trends were attenuated when considering simultaneous changes in reproductive characteristics and urinary phthalates during the course of the study.

Average sperm count remains unchanged despite reduction in maternal smoking: results from a large cross-sectional study with annual investigations over 21 years.

How are temporal trends in lifestyle factors, including exposure to maternal smoking in utero, associated to semen quality in young men from the general population? Exposure to maternal smoking was associated with lower sperm counts but no overall increase in sperm counts was observed during the study period despite a decrease in this exposure. Meta-analyses suggest a continuous decline in semen quality but few studies have investigated temporal trends in unselected populations recruited and analysed with the same protocol over a long period and none have studied simultaneous trends in lifestyle factors. Cross-sectional population-based study including ~300 participants per year (total number = 6386) between 1996 and 2016. The study is based on men from the Greater Copenhagen area, Denmark, with a median age of 19 years, and unselected with regard to fertility status and semen quality. The men delivered a semen sample, had a blood sample drawn and a physical examination performed and answered a comprehensive questionnaire, including information on lifestyle and the mother's pregnancy. Temporal trends in semen quality and lifestyle were illustrated graphically, and trends in semen parameters and the impact of prenatal and current lifestyle factors were explored in multiple regression analyses. Throughout the study period, 35% of the men had low semen quality. Overall, there were no persistent temporal trends in semen quality, testicular volume or levels of follicle-stimulating hormone over the 21 years studied. The men's alcohol intake was lowest between 2011 and 2016, whereas BMI, use of medication and smoking showed no clear temporal trends. Parental age increased, and exposure in utero to maternal smoking declined from 40% among men investigated in 1996-2000 to 18% among men investigated in 2011-2016. Exposure to maternal smoking was associated with lower sperm counts but no overall increase in sperm counts was observed despite the decrease in this exposure. Information of current and prenatal lifestyle was obtained by self-report, and the men delivered only one semen sample each. The significant decline in in utero exposure to maternal smoking, which was not reflected in an overall improvement of semen quality at the population level, suggest that other unknown adverse factors may maintain the low semen quality among Danish men. The study has received financial support from the ReproUnion; the Research fund of Rigshospitalet, Copenhagen University Hospital; the European Union (Contract numbers BMH4-CT96-0314,QLK4-CT-1999-01422, QLK4-CT-2002-00603, FP7/2007-2013, DEER Grant agreement no. 212844); the Danish Ministry of Health; the Danish Environmental Protection Agency; A.P. Møller and wife Chastine McKinney Møllers foundation; and Svend Andersens Foundation. None of the funders had any role in the study design, collection, analysis or interpretation of data, writing of the paper or publication decisions. N/A.

Effect of Lifestyle Factors on Semen Quality

Effect of Lifestyle Factors on Semen Quality

Decline of semen quality among Chinese sperm bank donors within 7 years (2008-2014).

Semen from 5210 sperm bank donors was analyzed and trends in semen quality were evaluated at Shandong Human Sperm Bank between 2008 and 2014. After 2–7 days of abstinence, semen samples were collected. Measurements of semen volume, sperm concentration, sperm forward motility, and total sperm count were performed. There were significant declining trends in semen volume, sperm concentration, sperm forward motility, and total sperm count. Our results indicate that the quality of semen in this cohort of sperm donors had decreased during the study period.

Environmental toxicants perturb human Sertoli cell adhesive function via changes in F-actin organization mediated by actin regulatory proteins

Can human Sertoli cells cultured in vitro and that have formed an epithelium be used as a model to monitor toxicant-induced junction disruption and to better understand the mechanism(s) by which toxicants disrupt cell adhesion at the Sertoli cell blood-testis barrier (BTB)? Our findings illustrate that human Sertoli cells cultured in vitro serve as a reliable system to monitor the impact of environmental toxicants on the BTB function. Suspicions of a declining trend in semen quality and a concomitant increase in exposures to environmental toxicants over the past decades reveal the need of an in vitro system that efficiently and reliably monitors the impact of toxicants on male reproductive function. Furthermore, studies in rodents have confirmed that environmental toxicants impede Sertoli cell BTB function in vitro and in vivo. We examined the effects of two environmental toxicants: cadmium chloride (0.5-20 µM) and bisphenol A (0.4-200 µM) on human Sertoli cell function. Cultured Sertoli cells from three men were used in this study, which spanned an 18-month period. Human Sertoli cells from three subjects were cultured in F12/DMEM containing 5% fetal bovine serum. Changes in protein expression were monitored by immunoblotting using specific antibodies. Immunofluorescence analyses were used to assess changes in the distribution of adhesion proteins, F-actin and actin regulatory proteins following exposure to two toxicants: cadmium chloride and bisphenol A (BPA). Human Sertoli cells were sensitive to cadmium and BPA toxicity. Changes in the localization of cell adhesion proteins were mediated by an alteration of the actin-based cytoskeleton. This alteration of F-actin network in Sertoli cells as manifested by truncation and depolymerization of actin microfilaments at the Sertoli cell BTB was caused by mislocalization of actin filament barbed end capping and bundling protein Eps8, and branched actin polymerization protein Arp3. Besides impeding actin dynamics, endocytic vesicle-mediated trafficking and the proper localization of actin regulatory proteins c-Src and annexin II in Sertoli cells were also affected. Results of statistical analysis demonstrate that these findings were not obtained by chance. (i) This study was done in vitro and might not extrapolate to the in vivo state, (ii) conclusions are based on the use of Sertoli cell samples from three men and (iii) it is uncertain if the concentrations of toxicants used in the experiments are reached in vivo. Human Sertoli cells cultured in vitro provide a robust model to monitor environmental toxicant-mediated disruption of Sertoli cell BTB function and to study the mechanism(s) of toxicant-induced testicular dysfunction.

Trans fatty acid intake is inversely related to total sperm count in young healthy men

Is intake of fatty acids related to semen quality among young men? The intake of trans fatty acids is inversely related to total sperm count in healthy young men. Spain has seen an increase in the proportion of calories consumed as fat over the same period that a downward trend in semen quality has been observed. In addition, rodent models suggest that trans fat intake may severely affect testicular function. Cross-sectional study of 209 men recruited between October 2010 and November 2011. A group of 209 healthy young university students 18-23 years of age provided a semen sample and completed a previously validated food frequency questionnaire. The association between intake of fatty acids with semen quality parameters (sperm concentration, motility, morphology and total count) was assessed using multivariate linear regression. Trans fatty acid intake was inversely related to total sperm count after adjusting for potential confounders (P, trend = 0.03). The multivariate adjusted mean (95% confidence interval) total sperm count in increasing quartiles of trans fat intake was 144 (110-190), 113 (87-148), 100 (18-130) and 89 (69-117). There also was an inverse association between cholesterol intake and ejaculate volume (P, trend = 0.04). No other statistically significant relations were observed. The cross-sectional design of the study limits causal inference, we cannot exclude the possibility of unmeasured confounding and there was insufficient statistical power to identify modest associations. The results of this study, together with previous experimental work in rodents and biomarker studies among infertility patients, suggest that intake of trans fatty acids may be related to lower semen quality. Although the data provide further evidence that diet is a modifiable factor that could impact male fertility, it is not known whether the observed differences in sperm count translate into differences in fertility. This work was supported by The Seneca Foundation, Regional Agency of Science and Technology, grant no 00694/PI/04, Ministerio de Ciencia e Innovación, Instituto de Salud Carlos III (FIS), grant no PI10/00985, and grant P30 DK46200 from the National Institutes of Health. The authors have no competing interests to declare.

Semen quality evaluation in a cohort of 28213 adult males from Sichuan area of south-west China

The trends in semen quality are conflicting. Although many previous surveys on semen quality indicated a decline, the trends in semen quality in Sichuan area of south-west China are not clear. We analysed the semen parameters in a cohort of 28,213 adult males close to general population in Sichuan between July 2007 and June 2012, and investigated the changes on semen quality. The semen parameters including pH, volume, concentration, motility, morphology were measured according to the World Health Organization (WHO) criteria. Kruskal-Wallis analysis of variance was used to examine the statistical differences of semen quality between groups. We found that the medians (5th and 95th percentiles) were 2.4 ml (1.0-5.0) for semen volume, 62.0 × 10(6) ml(-1) (15.0-142.0) for semen concentration, 39% (18-60%) for sperm progressive motility and 10.5% (1.0-34.5%) for normal morphology. In these 5 years, sperm concentration and the percentage of sperm normal morphology were decreased from 66.0 × 10(6 ) ml(-1) to 49.0 × 10(6) ml(-1) and from 13.5% to 4.5%, respectively; among different reproductive history groups, sperm concentration and the percentage of sperm normal morphology were also decreased in these 5 years. And the incidence of azoospermia was increasing. These may imply that there is a decline in semen quality of adult males in Sichuan area.

Dairy food intake in relation to semen quality and reproductive hormone levels among physically active young men

Is increased consumption of dairy foods associated with lower semen quality? We found that intake of full-fat dairy was inversely related to sperm motility and morphology. These associations were driven primarily by intake of cheese and were independent of overall dietary patterns. It has been suggested that environmental estrogens could be responsible for the putative secular decline in sperm counts. Dairy foods contain large amounts of estrogens. While some studies have suggested dairy as a possible contributing factor for decreased semen quality, this finding has not been consistent across studies. The Rochester Young Men's Study (n = 189) was a cross-sectional study conducted between 2009 and 2010 at the University of Rochester. Men aged 18-22 years were included in this analysis. Diet was assessed via food frequency questionnaire. Linear regression was used to analyze the relation between dairy intake and conventional semen quality parameters (total sperm count, sperm concentration, progressive motility, morphology and ejaculate volume) adjusting for age, abstinence time, race, smoking status, body mass index, recruitment period, moderate-to-intense exercise, TV watching and total calorie intake. Total dairy food intake was inversely related to sperm morphology (P-trend = 0.004). This association was mostly driven by intake of full-fat dairy foods. The adjusted difference (95% confidence interval) in normal sperm morphology percent was -3.2% (-4.5 to -1.8) between men in the upper half and those in the lower half of full-fat dairy intake (P < 0.0001), while the equivalent contrast for low-fat dairy intake was less pronounced [-1.3% (-2.7 to -0.07; P= 0.06)]. Full-fat dairy intake was also associated with significantly lower percent progressively motile sperm (P= 0.05). As it was a cross-sectional study, causal inference is limited. Further research is needed to prove a causal link between a high consumption of full-fat dairy foods and detrimental effects on semen quality. If verified our findings would mean that intake of full-fat dairy foods should be considered in attempts to explain secular trends in semen quality and that men trying to have children should restrict their intake. European Union Seventh Framework Program (Environment), 'Developmental Effects of Environment on Reproductive Health' (DEER) grant 212844. Grant P30 DK046200 and Ruth L. Kirschstein National Research Service Award T32 DK007703-16 from the National Institutes of Health. None of the authors has any conflicts of interest to declare.

Ignorance but not bliss: too little is known about the determinants of semen quality.

Criticisms of the data that have been presented to demonstrate a decline in sperm counts over time reveal problems with semen analysis methods and a lack of understanding of the genetic and environmental factors that determine a man's sperm count. Potential sources of error in the WHO semen analysis protocol and some areas of ignorance about the biological and environmental factors which can influence sperm counts are briefly discussed. I conclude that there is a need to include semen analyses in a large cohort study to fill the gaps in our knowledge. The paper by Carlsen et al.1 that is being marked in this issue of Asian Journal of Andrology stimulated widespread concern and considerable research effort. Together with other supportive studies, e.g. Auger et al.,2 strong evidence that testicular cancer was not only becoming more prevalent but was developing at lower ages3,4 and observations that other disorders of male development, e.g. cryptorchidism and hypospadias, were being more frequently reported, although this might be due to changes in clinical practice (see Thonneau et al.5), have raised serious concerns that something was going amiss with the human male. The proposition that oestrogen exposure in utero might be responsible by an effect on Sertoli cell development gave rise to the ‘testicular dysgenesis' hypothesis to explain these effects,6 although the role of oestrogen has been questioned recently. As most andrologists, I have followed developments in this area with keen interest but other contributors to this issue are far more knowledgeable than me, so I intend to say nothing about the testicular dysgenesis hypothesis or the latest consensus on whether sperm counts have indeed declined. Instead I will review some of the reasons why assessing trends in semen quality over time is difficult, and how these problems reveal gaps, or perhaps chasms, in our knowledge about the biology of human semen. First, although there is no better alternative, the standard semen analysis is inherently imprecise and is prone to many errors. The equipment used has changed over time and with it the nature of the error, making historical comparisons difficult. The errors introduced could be random, leading to imprecision and greater difficulty in demonstrating statistical significance but without effect on the nature of the trend, or systematic, leading to bias in the results. In theory systematic error could be corrected by direct comparison of former and current techniques. However, as discussed below results can potentially be affected by technical errors whose effects are difficult to predict. These can only be detected and eliminated by good quality control systems that have only been in place for at most two decades. Therefore doubt about older data will always remain. Secondly, the environmental factors that might influence a man's sperm count have changed over time and movements of populations have changed the genetic mix in many places. Moreover, social changes might affect the characteristics of the men recruited into semen studies. How these factors affect sperm count is very poorly understood. There are many excellent descriptions of how to do a semen analysis (e.g. Bjorndahl et al.7 and WHO Manual8), and I will not attempt to repeat these but will focus on what can so easily be done wrong in the laboratory. I will then discuss biological variation in semen quality in an attempt to highlight areas of ignorance.

Sperm counts may have declined in young university students in Southern Spain

Several studies have investigated temporal trends in semen quality in Northern Europe, but none has examined this question in Southern Europe. A prior study conducted in Almeria Province (Southern Spain) reported higher sperm count and concentration among Spanish young men recruited from 2001 to 2002 compared with young men from Northern Europe. The aim of this new study was to examine whether semen quality has changed among Spanish young men in the last decade. In this cross-sectional study, questionnaires and semen samples were collected from 215 healthy young university students from Murcia Region between 2010 and 2011. The 273 men from the Almeria study previously studied were included in a trend analysis of the two populations from Southern Spain. Descriptive statistics were calculated for the Murcia study population and these and semen variables for the Murcia and Almeria study populations were compared. Study methods and population characteristics were similar across the two studies. Therefore, we used multiple linear regression analyses on the combined population (controlling for study centre, age, ejaculation abstinence time, season, smoking, medication during the last 3months, Body mass index (BMI), presence of varicocoele and prenatal exposure to tobacco) to look for a birth-cohort effect over the combined study period (2001-2011). Sperm concentration and total sperm count declined significantly with year of birth in the pooled analysis (β=-0.04 and β=-0.06, respectively, both p<0.01). Sperm counts were significantly lower in Murcia study subjects than in the Almeria participants; sperm concentration median (5th-95th)=44.0 (8.9-129) million/mL vs. 51.0 (5.0-206) million/mL; p<0.01 and total sperm count=121 (17.8-400) million vs. 149 (8.0-599) million; p<0.01. Other semen variables did not differ significantly between the two studies. Our study suggests that total sperm count and sperm concentration may have declined in young Spanish men over the last decade.

Trends in global semen parameter values

Allegations for a worldwide decline in semen parameter values have not withstood scientific scrutiny. Methodological flaws in an influential 1992 paper are summarized here, and studies that have been published since 1992 are reviewed. Of the 35 major studies of time trends in semen quality reviewed here, eight (a total of 18 109 men) suggest a decline in semen quality; 21 (112 386 men) show either no change or an increase in semen quality; and six (26 007 men) show ambiguous or conflicting results. The cause (or causes) of the geographical and temporal variations in semen parameter values reported by these diverse studies deserve further investigation. This paper critically examines two related scientific assertions: that there have been worldwide declines in semen quality in recent decades and that these declines are related to environmental exposure to minute levels of ‘endocrine disruptors' (chemicals that exhibit some degree of estrogen-like activity in the body). The data supporting these assertions will be demonstrated to be weak, at best. Reported declines in semen parameter values are likely to be either highly local phenomena with an unknown etiology or the result of methodological errors arising from attempts to observe highly variable physical attributes (semen characteristics) with relatively low-resolution tools (retrospective analysis of nonrandomized study populations).