Have sperm counts been reduced 50 percent in 50 years? A statistical model revisited

Trends in sperm quality by computer-assisted sperm analysis of 49,189 men during 2015-2021 in a fertility center from China

Background

Sperm quality, including semen volume, sperm count, concentration, and total and progressive motility (collectively, "semen parameters"), has declined in the recent decades. Computer-assisted sperm analysis (CASA) provides sperm kinematic parameters, and the temporal trends of which remain unclear. Our objective is to examine the temporal trend of both semen parameters and kinematic parameters in Shanghai, China, in the recent years.

Methods

This retrospective study analyzed semen parameters and kinematic parameters of 49,819 men attending our reproductive center by using CASA during 2015-2021. The total sample was divided into two groups: samples that surpassed the WHO guideline (2010) low reference limits ("above reference limit" group, ARL; n = 24,575) and samples that did not ("below reference limit" group, BRL; n = 24,614). One-way analysis of variance, Kruskal-Wallis test, independent samples t-test, and covariance analysis were used to assess the differences among groups. Year, age, and abstinence time were included in the multiple linear regression model of the ARL group to adjust the confounders and depict the trends in sperm quality.

Results

Among all the total sample and the ARL and BRL groups, the age of subjects increased in recent years. Semen volume and sperm count showed declined tendency with years in the total sample, the ARL and BRL groups, and the subgroup of age or abstinence time, whereas sperm velocities showed increased tendency with years on the contrary. The multiple linear regression model of the ARL group, adjusting for age and abstinence time, confirmed these trends. Semen volume (β1= -0.162; CI: -0.172, -0.152), sperm count (β1= -9.97; CI: -10.813, -9.128), sperm concentration (β1 = -0.535; CI: -0.772, -0.299), motility (β1 = -1.751; CI: -1.830, -1.672), and progressive motility (β1 = -1.12; CI: -0.201, -0.145) decreased with year, whereas curvilinear line velocity (VCL) (β1 = 3.058; CI: 2.912, 3.203), straight line velocity (VSL) (β1 = 2.075; CI: 1.990, 2.161), and average path velocity (VAP) (β1 = 2.305; CI: 2.224, 2.386) increased over time (all p < 0.001). In addition, VCL, VSL, and VAP significantly declined with age and abstinence time.

Conclusion

The semen parameters declined, whereas the kinematic parameters increased over the recent years. We propose that, although sperm count and motility declined over time, sperm motion velocity increased, suggesting a possible compensatory mechanism of male fertility.

Spatiotemporal trends in human semen quality

Over the past four decades, studies of various designs have reported spatial and temporal trends in human semen quality. Several standardized-methodology studies in homogeneous populations that compare specific cities within a country or a continent provide clear evidence of geographical differences in sperm production, even over short distances within the same country. Human sperm production is widely believed to be declining over time, but evidence from the scientific literature is less clear. Studies based on repeated cross-sectional data from a single centre have shown mixed results. Among the numerous retrospective studies conducted in a single centre, only some included homogeneous groups of men and appropriate methods, and most of them suggest a temporal decrease in human sperm production in the geographical areas considered. Conclusions reporting temporal trends in sperm production that came from existing retrospective multicentre studies based on individual semen data and those using means, medians or estimates of sperm production are questionable, owing to intrinsic limitations in the studies performed. Regardless of study design, studies on the percentage of motile or morphologically normal spermatozoa are still limited by the inherent variability in assessment. Overall, available data do not enable us to conclude that human semen quality is deteriorating worldwide or in the Western world, but that a trend is observed in some specific areas. To understand these trends and contrasts in sperm and semen quality, prospective studies should be encouraged and combined with assessment of the male exposome.

Several studies over the past few decades have suggested that sperm quality varies by geographical region and might be subject to a temporal decline worldwide. However, the data supporting these conclusions have come from studies of various methodologies and heterogeneous populations, making them unreliable. In this in-depth Review, Chevrier and colleagues discuss the data surrounding discussion of spatiotemporal trends in semen parameters and consider how these trends and the factors promoting them interact.

The vast literature on human semen quality trends is extremely heterogeneous in terms of the populations studied and study designs, and so these studies have been unable to draw firm conclusions.

Understanding the data around spatiotemporal semen trends requires a focus on the methodological choices and application of criteria to filter findings from the studies with optimal design.

Numerous appropriately designed studies suggest unambiguous geographical contrasts in human sperm production; however, evidence of a decline in sperm production is reliable only in specific populations and cities in which studies with a complete set of quality criteria have been conducted.

By contrast, suggestions of a worldwide drop in human semen quality on the basis of retrospective multicentre studies cannot be substantiated, owing to intrinsic limitations in the studies performed.

Many and varied factors of variation, in particular the diverse modalities of assessment, do not enable us to conclude that clear temporal trends of sperm motility and normal morphology are present.

Progress in our understanding of the highlighted trends and their causal factors requires prospective studies that minimize all known biases combined with the assessment of men’s exposome.

Is seminal quality worsening? A 20-year experience in Córdoba, Argentina

PURPOSE

To assess the possible variations in semen quality during the last 20 years in Córdoba, Argentina, and to identify possible causal lifestyle or genitourinary factors.

METHODS

Retrospective study of 23,130 patients attending an andrology laboratory. The 20-year period (2001-2020) was divided into four quinquenniums. Seminal parameters (sperm concentration, motility, morphology, viability, and membrane functional integrity) were classified as normal or abnormal according to WHO, and results were expressed as percentage of patients abnormal for each parameter per quinquennium. In addition, the percentage of patients per quinquennium exposed to the different risk factors (daily alcohol and/or tobacco consumption; occupational exposure to heat or toxics; history of parotitis or varicocele; and high body mass index, BMI) was reported.

RESULTS

Patients included in our study did not show impairment in seminal quality over time. Beyond a transient decrease in normozoospermia in the second and third quinquennium, possibly explained by a parallel increase in teratozoospermia, other important parameters of the spermogram did not change. In fact, abnormalities in sperm concentration (oligozoospermia), total sperm count, viability and response to hypoosmotic test showed a decreasing trend over time. On the other hand, parotitis, varicocele, morbid obesity and regular exposition to heat/toxics were the factors more frequently associated with semen abnormalities; the last two increased their frequency over the study period.

CONCLUSION

The population included in this study did not show a clear impairment in semen quality during the last 20 years. The decreasing patterns found were associated with high BMI and exposure to heat/toxics.

An evaluation of changes over time in the semen parameters data used for the World Health Organization semen analysis reference ranges

BACKGROUND

Previous meta-analyses concluded that there is a decline in sperm parameters over time. This conclusion might be incorrect due to inherent biases or focusing only on a single parameter - sperm concentration.

OBJECTIVE

To study trends in sperm parameters over the past twenty years using data from the trials that defined the reference ranges of the World Health Organization manual.

MATERIALS AND METHODS

Retrospective evaluation of the data used to define the World Health Organization reference ranges. The data from 11 studies, including 3589 participants between 1996-2016, were divided into three period groups based on the decade of study. Differences in semen parameters' distribution were presented in boxplot. P-values were calculated by the Kruskal Wallis rank-sum test followed by Dunn post-hoc test. Analyses were conducted using the R programming language.

RESULTS

A small decrease was noted in mean sperm concentrations (88.1 million/ml, 87.6 million/ml and 77.2 million/ml for the first second and third decades respectively) (p<0.01). However, the 5^th percentile of sperm concentration for the third decade was higher than the first or second decades (18 million/ml vs. 14.9 million/ml and 15 million/ml respectively). No significant differences were noted in progressive motility over the years (p = 0.32). The percent of morphologically normal sperm decreased between the first (24.2%) and the second (12.6%) periods of the study (p<0.001) and then increased in the third decade (14.2%) (p<0.01). While TMC declined between the second and third decades (189 million and 153.9 million respectively, p<0.001), at levels unlikely to decrease fertility. However, the 5^th percentile of the TMC remained stable at 24.9, 20.8 and 20.6 million, for the first, second and third decades respectively (p = 0.36).

DISCUSSION AND CONCLUSION AND RELEVANCE

Trends in sperm parameters over the last three decades do not seem to be clinically significant. This article is protected by copyright. All rights reserved.

Systematic Analysis of Breed, Methodological, and Geographical Impact on Equine Sperm Progressive Motility

Simple Summary

Semen quality is an important indicator of reproductive health and fertility. With adverse temporal trends in human semen quality over the past 50 years paralleled in male animals, there is increasing concern for the causes and implications of perturbed male reproductive health. The evaluation of equine progressive motility (PM), a parameter closely associated with fertility, provides information on the fertilising capacity of equine ejaculate and current reproductive health of the equine stallion. Using systematic analysis, recent trends in equine PM were determined from 696 estimates from 280 individual studies. Temporal trends indicate equine PM has not significantly changed between the years 1990 and 2018. Significant breed, methodological, and geographical variations observed in equine PM may considerably influence actual and reported stallion fertility potential. Information on stallion PM meaningfully contributes to the wider literature on semen quality and provides avenues for future stallion fertility research. This systematic analysis presents the wider challenges associated with semen quality assessment, particularly within the equine sector, and provides recommendations to promote consistency across industry and research.

Abstract

Over the past five decades, there has been increasing evidence to indicate global declines in human semen quality. Parallel adverse trends measured in male animals indicate a potential environmental aetiology. This study evaluated the progressive motility (PM) of stallion ejaculate through a systematic review and meta-analysis. A total of 696 estimates of equine PM from 280 studies, which collected semen samples between the years 1990 and 2018, were collated for meta-analysis. The method of motility analysis, breed, season of collection, and geographical location were extracted. Simple linear regression determined temporal trends in stallion PM. Studies using microscopy estimated PM to be significantly greater compared to computer-automated methods (p ≤ 0.001). For Arabian breeds, PM was consistently higher than other breeds. Over time, there was a significant decline in PM for studies from Europe (n = 267) but a significant increase for studies from North America (n = 259). Temporal trends indicate the fertilising capacity of equine ejaculate has remained consistently high in the last three decades. That being so, variations observed suggest methodological, geographical, and individual stallion differences may significantly influence actual and reported stallion fertility potential.

Un-riped fruit pods of Prosopis cineraria (L.) Druce ameliorates Cisplatin therapy-induced partial testicular atrophy in male Wistar rats

ETHNOPHARMACOLOGICAL RELEVANCE

Prosopis cineraria (L.) Druce is a plant that is widely found in dry parts of India. The unripe fruit pod has a very specific traditional claim of treating male infertility and increasing sperm volume and count.

AIM

The present work was endeavored to investigate the long-standing traditional claim of P. cineraria on meliorating male fertility. The study focussed on cancer therapy-induced male infertility and curative effect of the extract with an appraisal on any possible revitalizing effects on sperm count, morphology, motility, and viability combined with hormonal and histopathological investigations.

MATERIALS AND METHODS

Male Wistar rats were used for the study. Two different doses of 400 mg/kg/d and 800 mg/kg/d (both p.o.) of the Hydroalcoholic extract were chosen as test dose while Clomiphene (25 mg/kg/d; p.o.) treatment served as standard treatment. Animals were initially injected with cisplatin (1 mg/kg/d; i.p.) for 15 days and the drug treatment was begun at the 16^th day and continued till 43^rd day (28 days treatment). Later all male animals got cohabited with female animals in the ratio 1:3. On confirmation of mating, female animals were isolated. Male animals were euthanized on batches. Testis and epididymis were weighed and homogenized. Sperm count, motility, morphology, viability, and headcount. The serum collected was evaluated for serum FSH, LH, and testosterone levels. On day Gestational day 15, gravid uterus observations were calculated to evaluate male and female fertility parameters.

RESULTS

There were statistically significant improvements (p < 0.001) in sperm motility, sperm count, sperm viability, and improved morphological features. The same pace was also noticed in testosterone, FSH and LH levels in serum and LPO, CAT, GSH, GPx and SOD in testicular tissues. The extract treated male animals produced better and healthy litter compared to cisplatin-treated animals with less pre- and post-implantation loss.

CONCLUSION

Consolidating the results seen, the extract ameliorated the testicular toxicity caused by cisplatin in a dose-dependent manner. Further insight and evaluation of the phytochemicals of the pods should be performed to bring up commercial viability.

Regional difference in semen quality of young men: a review on the implication of environmental and lifestyle factors during fetal life and adulthood

The prevalence of low semen quality and the incidence of testicular cancer have been steadily increasing over the past decades in different parts of the World. Although these conditions may have a genetic or epigenetic origin, there is growing evidence that multiple environmental and lifestyle factors can act alone or in combination to induce adverse effects. Exposure to these factors may occur as early as during fetal life, via the mother, and directly throughout adulthood after full spermatogenic capacity is reached. This review aims at providing an overview of past and current trends in semen quality and its relevance to fertility as well as a barometer of men’s general health. The focus will be on recent epidemiological studies of young men from the general population highlighting geographic variations in Europe. The impact of some lifestyle and environmental factors will be discussed with their role in both fetal life and adulthood. These factors include smoking, alcohol consumption, psychological stress, exposure to electromagnetic radiation, and Endocrine Disrupting Chemicals (EDCs). Finally, the challenges in investigating the influence of environmental factors on semen quality in a fast changing world are presented.

Declining Sperm Counts… or Rather Not? A Mini Review

Importance

Temporal global trends of sperm quality remain a matter of debate.

Objective

The aim of this study was to present a comprehensive review of studies reporting on sperm quality counts, summarize the main end points, and assess the main reasons for potential discrepancies.

Evidence Acquisition

An evidence-based review of PubMed and Scopus databases was performed regarding studies reporting on modification of sperm quality counts, independently of study character, study language, or date.

Results

Since the meta-analysis of Carlsen et al in 1992 (Br Med J 1992;305:609-613) that suggested an annual decline in sperm count of 1%, several reports confirmed the decline in sperm quality, whereas others disproved them, suggesting a slight increase or absence of change in sperm count. Such controversies may be attributed to geographical and time-related variability in sperm values and also to several confounding factors that influence the semen parameters. Intrinsic weaknesses of the studies include heterogeneity of subjects recruited, lack of adjustment for confounding factors, and samples that do not always represent the general population.

Conclusions

No consensus exists on whether sperm counts actually decrease because studies' results are often controversial or inconclusive with methodological deficiencies. More prospective, large-scale, population based studies are needed in order to provide sound evidence of possible global trends in sperm count.

Air pollution from natural and anthropic sources and male fertility

Exposure to air pollution has been clearly associated with a range of adverse health effects, including reproductive toxicity. However, a limited amount of research has been conducted to examine the association between air pollution and male reproductive outcomes, specially semen quality. We performed a systematic review (up to March 2017) to assess the impact of environmental and occupational exposure to air pollution on semen quality. Epidemiological studies focusing on air pollution exposures and male reproduction were identified by a search of the PUBMED, MEDLINE, EBSCO and TOXNET literature bases. Twenty-two studies were included which assess the impact of air pollutants (PM_2.5, PM₁₀, SO₂, NOx, O₃, PAHs) on main semen parameters (sperm concentration, motility, morphology), CASA parameters, DNA fragmentation, sperm aneuploidy and the level of reproductive hormones. The number of studies found significant results supporting the evidence that air pollution may affect: DNA fragmentation, morphology and motility.In summary, most studies concluded that outdoor air pollution affects at least one of the assessed semen parameters. However the diversity of air pollutants and semen parameters presented in the studies included in the review and different study design caused lack of consistency in results and difficulties in comparison.

Seasonal variation of semen parameters correlates with environmental temperature and air pollution: A big data analysis over 6 years

BACKGROUND

Male fertility is progressively declining in many developed countries, but the relationship between male infertility and environmental factors is still unclear.

OBJECTIVES

To assess the influence of environmental temperature and air pollution on semen parameters, using a big-data approach.

METHODS

A big data analysis of parameters related to 5131 men, living in a province of Northern Italy and undergoing semen analyses between January 2010 and March 2016 was performed. Ambient temperature was recorded on the day of analysis and the 90 days prior to the analysis and the average value of particulate matter (PM) and NO2 in the year of the test. All data were acquired by geocoding patients residential address. A data warehouse containing 990,904,591 data was generated and analysed by multiple regressions.

RESULTS

5573 semen analyses were collected. Both maximum and minimum temperatures registered on the day of collection were inversely related to total sperm number (p < .001), non-progressive motility (NPrM) (p < .005) and normal forms (p < .001). Results were confirmed considering temperature in the 30 and 60 days before collection, but not in the 90 days before collection. Total sperm number was lower in summer/autumn (p < .001) and was inversely related with daylight duration (p < .001). PM10 and PM2.5 were inversely related to PrM (p < .001 and p < .005) and abnormal forms (p < .001).

CONCLUSIONS

This is the first evaluation of the relationship between male fertility-related parameters and environment using a big-data approach. A seasonal change in semen parameters was found, with a fluctuation related to both temperature and daylight duration. A negative correlation between air pollution and semen quality is suggested. Such seasonal and environmental associations should be considered when assessing changes of male fertility-related parameters over time.

Temporal trends in sperm count: a systematic review and meta-regression analysis

BACKGROUND

Reported declines in sperm counts remain controversial today and recent trends are unknown. A definitive meta-analysis is critical given the predictive value of sperm count for fertility, morbidity and mortality.

OBJECTIVE AND RATIONALE

To provide a systematic review and meta-regression analysis of recent trends in sperm counts as measured by sperm concentration (SC) and total sperm count (TSC), and their modification by fertility and geographic group.

SEARCH METHODS

PubMed/MEDLINE and EMBASE were searched for English language studies of human SC published in 1981-2013. Following a predefined protocol 7518 abstracts were screened and 2510 full articles reporting primary data on SC were reviewed. A total of 244 estimates of SC and TSC from 185 studies of 42 935 men who provided semen samples in 1973-2011 were extracted for meta-regression analysis, as well as information on years of sample collection and covariates [fertility group ('Unselected by fertility' versus 'Fertile'), geographic group ('Western', including North America, Europe Australia and New Zealand versus 'Other', including South America, Asia and Africa), age, ejaculation abstinence time, semen collection method, method of measuring SC and semen volume, exclusion criteria and indicators of completeness of covariate data]. The slopes of SC and TSC were estimated as functions of sample collection year using both simple linear regression and weighted meta-regression models and the latter were adjusted for pre-determined covariates and modification by fertility and geographic group. Assumptions were examined using multiple sensitivity analyses and nonlinear models.

OUTCOMES

SC declined significantly between 1973 and 2011 (slope in unadjusted simple regression models -0.70 million/ml/year; 95% CI: -0.72 to -0.69; P < 0.001; slope in adjusted meta-regression models = -0.64; -1.06 to -0.22; P = 0.003). The slopes in the meta-regression model were modified by fertility (P for interaction = 0.064) and geographic group (P for interaction = 0.027). There was a significant decline in SC between 1973 and 2011 among Unselected Western (-1.38; -2.02 to -0.74; P < 0.001) and among Fertile Western (-0.68; -1.31 to -0.05; P = 0.033), while no significant trends were seen among Unselected Other and Fertile Other. Among Unselected Western studies, the mean SC declined, on average, 1.4% per year with an overall decline of 52.4% between 1973 and 2011. Trends for TSC and SC were similar, with a steep decline among Unselected Western (-5.33 million/year, -7.56 to -3.11; P < 0.001), corresponding to an average decline in mean TSC of 1.6% per year and overall decline of 59.3%. Results changed minimally in multiple sensitivity analyses, and there was no statistical support for the use of a nonlinear model. In a model restricted to data post-1995, the slope both for SC and TSC among Unselected Western was similar to that for the entire period (-2.06 million/ml, -3.38 to -0.74; P = 0.004 and -8.12 million, -13.73 to -2.51, P = 0.006, respectively).

WIDER IMPLICATIONS

This comprehensive meta-regression analysis reports a significant decline in sperm counts (as measured by SC and TSC) between 1973 and 2011, driven by a 50-60% decline among men unselected by fertility from North America, Europe, Australia and New Zealand. Because of the significant public health implications of these results, research on the causes of this continuing decline is urgently needed.

Therapeutic and fertility restoration effects of Ionidium suffruticosum on sub-fertile male albino Wistar rats: effects on testis and caudal spermatozoa

CONTEXT

Ionidium suffruticosum (L.) Ging (Violaceae) is an important medicinal plant widely used as a herbal traditional medicine in Ayurveda for the treatment of infertility. Currently, little pharmacological information is available on its male fertility properties following prolonged use.

OBJECTIVE

To investigate I. suffruticosum leaf extracts for male fertility parameters.

MATERIALS AND METHODS

The ethanol lyophilized fraction was administered orally on carbendazim-induced sub-fertility rats (250 mg/kg body weight for 28 days). The effects of fractions on rat's fertility parameters i.e., body and testes weight, sperm motility, sperm vitality, epididymal sperm counts, its morphology, enzyme and antioxidant stress and histopathology were studied and compared with clomiphene citrate.

RESULTS

The sub-fertile male rats treated with I. suffruticosum leaf extract increased the body weight of 7 g, testis weight of 97 mg, increased cauda epididymal sperm counts of 34.2 × 10⁶ sperm/mL, motility of sperm 46% and vitality 28% also increased and normal sperm morphology also improved up to 32%. The carbendazim-treated group showed loss in body weight of 33 g, testis weight of 851 mg, decreased epididymal sperm counts of 15 × 10⁶ sperm/mL, with sluggish motility and a highly significant fall in the live sperms of about 57%.

DISCUSSION AND CONCLUSION

The leaf fraction of I. suffructicosum increased the testicular weight, spermatogenesis, sperm counts, lessened sperm agglutination, and increased testicular oxidative biomarkers, SOD, and CAT. This study therefore supports the usage of I. suffructicosum in traditional medicine for infertility.

Changes in the semen quality among 5739 men seeking infertility treatment in Northern Norway over past 20 years (1993–2012)

Semen quality plays a pivotal role in sustaining the fertility rate and healthy population growth. Therefore, assessment of temporal trends in the semen quality provides valuable public health information. We analyzed the semen quality parameters of 5739 North Norwegian men among consecutive couples attending the fertility clinic of University Hospital of North Norway for investigation and/or treatment from 1993 to 2012. The seminal fluid volume, sperm concentration, and total sperm count were found to have gradually decreased during the past 20 years. The proportion of hypospermic, azoospermic, and oligozoospermic men had increased by 24.6% ( p < 0.001), 109.5% ( p < 0.001), and 9.5% ( p = 0.05), respectively, in the last decade (2003–2012) compared to the first decade (1993–2002). The parameters of semen quality are rapidly deteriorating in North Norwegian men seeking fertility treatment.

Male Reproductive Disorders and Fertility Trends: Influences of Environment and Genetic Susceptibility

It is predicted that Japan and European Union will soon experience appreciable decreases in their populations due to persistently low total fertility rates (TFR) below replacement level (2.1 child per woman). In the United States, where TFR has also declined, there are ethnic differences. Caucasians have rates below replacement, while TFRs among African-Americans and Hispanics are higher. We review possible links between TFR and trends in a range of male reproductive problems, including testicular cancer, disorders of sex development, cryptorchidism, hypospadias, low testosterone levels, poor semen quality, childlessness, changed sex ratio, and increasing demand for assisted reproductive techniques. We present evidence that several adult male reproductive problems arise in utero and are signs of testicular dysgenesis syndrome (TDS). Although TDS might result from genetic mutations, recent evidence suggests that it most often is related to environmental exposures of the fetal testis. However, environmental factors can also affect the adult endocrine system. Based on our review of genetic and environmental factors, we conclude that environmental exposures arising from modern lifestyle, rather than genetics, are the most important factors in the observed trends. These environmental factors might act either directly or via epigenetic mechanisms. In the latter case, the effects of exposures might have an impact for several generations post-exposure. In conclusion, there is an urgent need to prioritize research in reproductive physiology and pathophysiology, particularly in highly industrialized countries facing decreasing populations. We highlight a number of topics that need attention by researchers in human physiology, pathophysiology, environmental health sciences, and demography.

Semen Quality Assessment in Fertile Men in Madrid During the Last 3 Decades

OBJECTIVE

To evaluate semen quality of men with proven fertility in Spain over the last 3 decades.

METHODS

We conduct a retrospective analysis of ejaculate samples of 992 men between 1985 and 2009. All patients had proven fertility as demonstrated by fathering at least 2 children and a semen analysis performed before they underwent vasectomy. A standardized procedure was used for the semen analysis. Semen volume, total sperm count, sperm concentration, motility, and percentage of morphologically normal spermatozoa were assessed. Mean values were calculated by examining microscopic fields of 100 spermatozoa.

RESULTS

Statistically significant differences were found in all semen parameters analyzed. For the periods 1985-1990, 1990-2000, and 2000-2009, the mean (standard deviation [SD]) sperm concentration was 27.7 (22.97), 20.73 (14.79), and 20.18 (20.79) × 10(6) (P <.0001). The mean (SD) progressive motility for each period was 53.19 (20.35), 47.22 (15.84), and 40.57 (15.15; P <.0001). The mean (SD) normal-shaped spermatozoa for each period was 67.69 (10.24), 58.87 (14.67), and 51.02 (15.76; P <.0001). Multivariate analysis using a logistic regression model showed that age had no significant effect in the variation of semen parameters at the cut-points analyzed, except for normal forms at percentile 25 (P = .001). Multivariate analysis revealed a trend for decline of semen in sperm concentration, progressive and nonprogressive motility, and the percentage of morphologically normal spermatozoa (P = .001-.002).

CONCLUSION

Over the last 3 decades, a decline in semen quality was found in all the parameters analyzed in Spanish men with proven fertility.

High frequency of TTTY2-like gene-related deletions in patients with idiopathic oligozoospermia and azoospermia

Genes located on Y chromosome and expressed in testis are likely to be involved in spermatogenesis. TTTY2 is a Y-linked multicopy gene family of unknown function that includes TTTY2L2A and TTTY2L12A at Yq11 and Yp11 loci respectively. Using PCR amplification, we screened for TTTY2L2A- and TTTY2L12A-associated deletions, in 94 Greek men with fertility problems. Patients were divided into three groups as following: group A (n = 28) included men with idiopathic moderate oligozoospermia, group B (n = 34) with idiopathic severe oligozoospermia and azoospermia, and group C (n = 32) with oligo- and azoospermia of various known etiologies. No deletions were detected in group C patients and 50 fertile controls. However, two patients from group A had deletions in TTTY2L2A (7.1%) and six in TTTY2L12A (21.4%), whereas from group B, four patients had deletions in TTTY2L2A (11.8%) and 10 in TTTY2L12A (29.4%). In addition, five patients from both groups A and B (8%) appeared to have deletions in both studied TTTY2 genes, although these are located very far apart. These results indicate that the TTTY2 gene family may play a significant role in spermatogenesis and suggest a possible mechanism of nonhomologous recombinational events that may cause genomic instability and ultimately lead to male infertility.

Shedding light on the controversy surrounding the temporal decline in human sperm counts: a systematic review

We systematically examined the evidence of declining sperm counts and the hypothesis that an increased exposure to environmental pollutants is responsible for such decline. Search engines, including PUBMED, MEDLINE, EMBASE, BIOSIS, and Cochrane library, were used to identify epidemiologic studies published from 1985 to 2013. We concluded that there is no enough evidence to confirm a worldwide decline in sperm counts. Also, there seems to be no scientific truth of a causative role for endocrine disruptors in the temporal decline of sperm production. Such assumptions are based on few meta-analyses and retrospective studies, while other well-conducted researches could not confirm these findings. We acknowledge that difficult-to-control confounding factors in the highly variable nature of semen, selection criteria, and comparability of populations from different time periods in secular-trend studies, the quality of laboratory methods for counting sperm, and apparently geographic variations in semen quality are the main issues that complicate the interpretation of the available evidence. Owing to the importance of this subject and the uncertainties still prevailing, there is a need not only for continuing monitoring of semen quality, reproductive hormones, and xenobiotics, but also for a better definition of fecundity.

Environmental toxins

This review comprehensively summarizes the effects of more than 15 mostly used pesticides on male reproductive physiology, as recent experimental and epidemiological research have indicated their alarming impact on overall human health. Mechanisms have described that pesticide exposure damages spermatozoa, alter Sertoli or Leydig cell function, both in vitro and in vivo and thus affects semen quality. But, the literature suggests a need for more intricate research in those pesticides that are defined as mutagens or carcinogens and directly affect the hypothalamic–pituitary–gonadal axis. This literature review also proposes specific solutions to overcome these health effects.

Sperm parameters: paradigmatic index of good health and longevity

Since the discovery of spermatozoon by Anton van Leeuwenhoek in 1677, there has been an ever increasing understanding of its role in reproduction. Many factors adversely affect sperm quality, including varicocele, accessory gland infection, immunological factors, congenital abnormalities, and iatrogenic systemic and endocrine causes, such as diabetes mellitus, obesity, metabolic syndrome, and smoking. The mechanisms responsible for the association between poor sperm parameters and ill health may include oxidative stress, low-grade inflammation, low testosterone, and low sex-hormone-binding globulin. Oxidative stress in the testicular microenvironment may result in decreased spermatogenesis and sperm DNA damage, loss of sperm motility, and abnormal sperm morphology. Low testosterone caused by advanced age, visceral obesity, and inflammation is associated with the development of cardiovascular disease. Hence, semen analysis has an important role in the routine evaluation of idiopathic male infertility, usually manifested as low sperm counts, impaired sperm motility, or absence of sperm, and remains the most common single diagnostic tool. Several studies have shown an inverse relationship between semen quality and medical disorders. This review elucidates the effect of medical disorders and social habits on sperm quality, the mechanisms that are involved in the impairment of sperm quality, and whether or not sperm quality can be used as an index of good health and longevity in a man.

Semen variation in a population of fertile donors: evaluation in a French centre over a 34-year period

Although it has been suspected that there is a decrease in semen quality over time, the results reported to date remain debatable because of methodological issues. The aim of the study reported here was to investigate the evolution of semen quality over time in a population of 1114 fertile candidates for sperm donation at CECOS, Tours, between 1976 and 2009. We investigated semen volume, sperm concentration, progressive motility, vitality, percentage of normal forms and multiple abnormalities index of the first ejaculate in this population. We did not find a decline in semen volume, whereas we observed a significant decrease in total sperm count (from 443.2 million in 1976 to 300.2 million in 2009), motility (from 64% in 1976 to 49% in 2009) and vitality (from 88% to 80%). Moreover, a significant decline in the percentage of normal forms was noted between 1976 and 1997 (from 67% to 26%) with a steady rise in the multiple abnormalities index between 1998 and 2009 (from 1.19 to 1.65). This study involving a population of fertile men from a restricted area revealed various degrees of decline in semen parameters over a period of 34 years. These findings will have to be compared with findings in other geographical areas.

Environmental chemical mediated male reproductive toxicity: Drosophila melanogaster as an alternate animal model

Industrialization and indiscriminate use of agrochemicals have increased the human health risk. Recent epidemiological studies raised a concern for male reproduction given their observations of reduced sperm counts and altered semen quality. Interestingly, environmental factors that include various metals, pesticides and their metabolites have been causally linked to such adversities by their presence in the semen at levels that correlate to infertility. The epidemiological observations were further supported by studies in animal models involving various chemicals. Therefore, in this review, we focused on male reproductive toxicity and the adverse effects of different environmental chemicals on male reproduction. However, it is beyond the scope of this review to provide a detailed appraisal of all of the environmental chemicals that have been associated with reproductive toxicity in animals. Here, we provided the evidence for reproductive adversities of some commonly encountered chemicals (pesticides/metals) in the environment. In view of the recent thrust for an alternate to animal models in research, we subsequently discussed the contributions of Drosophila melanogaster as an alternate animal model for quick screening of toxicants for their reproductive toxicity potential. Finally, we emphasized the genetic and molecular tools offered by Drosophila for understanding the mechanisms underlying the male reproductive toxicity.

No secular trend over the last decade in sperm counts among Swedish men from the general population

INTRODUCTION

Based on historical data, a decline in sperm counts during the years 1940-1990 has been suggested and aetiologically linked to a concomitant increase in the incidence of testicular cancer. This study, focusing on possible changes in sperm parameters among young Swedish men, during the past 10 years, was specifically designed in order to answer the question of whether there is a continuing decline in sperm counts.

METHODS

During the period 2008-2010, 295 young (17-20 years; median 18) men born and raised in Sweden were recruited at the age they were supposed to undergo medical examination prior to military service. The participants filled in questionnaires, underwent andrological examination and delivered an ejaculate. Their semen parameters were compared with those of a similar cohort of men (n = 216) recruited in the year 2000-2001.

RESULTS

No significant changes (means; 2000-2001 versus 2008-2010) in sperm concentration (78 × 10⁶/ml versus 82 × 10⁶/ml; P = 0.54), semen volume (3.1 ml versus 3.0 ml; P = 0.26) or total sperm counts (220 × 10⁶ versus 250 × 10⁶; P = 0.18) were found. The proportion of progressively motile spermatozoa also remained unchanged.

CONCLUSIONS

Between the years 2000 and 2010 we found no evidence of time-related deterioration of semen parameters among young Swedish men from the general population. This finding does not exclude that such a decrease may have taken place before year 2000. If the risk of testicular cancer is linked to the sperm counts, the increase in incidence of this malignancy should be levelling off in southern Sweden in the next 10-15 years.

Alcohol, drugs, caffeine, tobacco, and environmental contaminant exposure: reproductive health consequences and clinical implications

Reproductive function and fertility are thought to be compromised by behaviors such as cigarette smoking, substance abuse, and alcohol consumption; however, the strength of these associations are uncertain. Furthermore, the reproductive system is thought to be under attack from exposure to environmental contaminants, particularly those chemicals shown to affect endocrine homeostasis. The relationship between exposure to environmental contaminants and adverse effects on human reproductive health are frequently debated in the scientific literature and these controversies have spread into the lay press drawing increased public and regulatory attention. Therefore, the objective of the present review was to critically evaluate the literature concerning the relationship between lifestyle exposures and adverse effects on fertility as well as examining the evidence for a role of environmental contaminants in the purported decline of semen quality and the pathophysiology of subfertility, polycystic ovarian syndrome, and endometriosis. The authors conclude that whereas cigarette smoking is strongly associated with adverse reproductive outcomes, high-level exposures to other lifestyle factors are only weakly linked with negative fertility impacts. Finally, there is no compelling evidence that environmental contaminants, at concentrations representative of the levels measured in contemporary biomonitoring studies, have any effect, positive or negative, on reproductive health in the general population. Further research using prospective study designs with robust sample sizes are needed to evaluate testable hypotheses that address the relationship between exposure and adverse reproductive health effects.

Light and transmission electron microscopic comparisons of sperms between petrochemical factory workers and public servants in a nonindustrialized area

In this study, we compared the semen characteristics on light microscopy and ultrastructural sperm morphology on transmission electron microscopy between workers in an industrialized area with petrochemical complexes and public servants in a nonindustrialized area. Occupational exposure to petrochemical compounds seems to decrease sperm motility and deteriorate the sperm ultrastructural arrangement, which may lead to this decrease in sperm motility.

Is human fecundity declining in Western countries?

Since Carlsen and co-workers reported in 1992 that sperm counts have decreased during the second half of the last century in Western societies, there has been widespread anxiety about the adverse effects of environmental pollutants on human fecundity. The Carlsen report was followed by several re-analyses of their data set and by many studies on time trends in sperm quality and on secular trends in fecundity. However, the results of these studies were diverse, complex, difficult to interpret and, therefore, less straightforward than the Carlsen report suggested. The claims that population fecundity is declining and that environmental pollutants are involved, can neither be confirmed nor rejected, in our opinion. However, it is of great importance to find out because the possible influence of widespread environmental pollution, which would adversely affect human reproduction, should be a matter of great concern triggering large-scale studies into its causes and possibilities for prevention. The fundamental reason we still do not know whether population fecundity is declining is the lack of an appropriate surveillance system. Is such a system possible? In our opinion, determining total sperm counts (as a measure of male reproductive health) in combination with time to pregnancy (as a measure of couple fecundity) in carefully selected populations is a feasible option for such a monitoring system. If we want to find out whether or not population fecundity will be declining within the following 20-30 years, we must start monitoring now.

Decreasing sperm quality: a global problem?

BACKGROUND

Carlsen and coworkers (1992) reviewed 61 heterogeneous observational studies on semen quality published between 1938 and 1990. This review indicates that mean sperm density decreased significantly between 1940 and 1990. An extended meta-analysis with 101 studies confirmed a decline in sperm density for the period from 1934 to 1996 (2000). The key message of the meta-analyses is that sperm counts have decreased globally by about 50% over the past decades. This assessment has been questioned.

DISCUSSION

A major methodological problem of the meta-analysis is the use of data collected in different countries, at different times, on different populations and with different methods of semen analysis. Furthermore, the results of studies concerning semen analysis are frequently biased e.g. by selection criteria of volunteers. In most studies on human semen characteristics the populations under study are insufficiently defined and the study participants are not a representative population sample. The incidence of testicular cancer has increased in Caucasian men worldwide. The investigation of common risk factors for male reproductive disorders requires well designed epidemiological studies and the collection of individual data.

SUMMARY

Former meta-analyses of sperm count data show a global downward trend. This conclusion should be interpreted with caution. The included studies are of great heterogeneity due to geographical and/or ethnical variation, different study designs and different methodological standards. Population-based prospective studies are needed to investigate secular trends in male reproductive disorders.

Etiologic factors in testicular germ-cell tumors

Globally, testicular cancer incidence is highest among men of northern European ancestry and lowest among men of Asian and African descent. Incidence rates have been increasing around the world for at least 50 years, but mortality rates, at least in developed countries, have been declining. While reasons for the decreases in mortality are related to improvements in therapeutic regimens introduced in the late 1970s, reasons for the increase in incidence are less well understood. However, an accumulating body of evidence suggests that testicular cancer arises in fetal life. Perinatal factors, including exposure to endocrine-disrupting chemicals, have been suggested to be related to risk.

Temporal trends in bull semen quality: a comparative model for human health?

INTRODUCTION

A decline in human semen quality over the past 30-60 years has been reported in numerous epidemiological studies from the United States and Europe. We evaluated temporal trends in semen quality parameters in dairy bulls. The long-term management of dairy bulls for artificial insemination presented a unique opportunity to evaluate temporal trends in semen quality and explore this relationship as a potential animal model for reproductive abnormalities in humans.

MATERIALS AND METHODS

Bull semen analysis data from 1965 through 1995 were collected from a large artificial insemination organization. Semen analyses from 12- to 18-month-old Holstein dairy bulls were included in the study and consisted of daily sperm concentration, daily ejaculate volume, total daily sperm output, percentage of sperm with normal morphology, and percentage of sperm with normal post-thaw motility. Multiple regression analysis, logistic regression, and general linear modeling were used to determine temporal trends over the 30-year period.

RESULTS AND DISCUSSION

Semen quality appears to have declined from 1970 to 1980 or 1985 as manifested by declines in daily ejaculate volume, daily sperm concentration, and total daily sperm output. In contrast, sperm morphology and motility improved over the same period. In approximately 1980 or 1985, depending on the parameter, ejaculate volume, sperm concentration, total sperm, and motility improved. However, normal morphology began to deteriorate during this same period. Methodological inconsistencies over time introduce uncertainty in analyses of temporal trends in semen quality in this and previous human studies. However, changes in technology do not appear to be solely responsible for the temporal trends observed. The source of the decline in semen quality in the bulls studied is unknown. If the decline in semen quality were due to exposure to endocrine disrupting chemicals, then a continued decline or a leveling-off would be expected. Instead, a rise in semen quality was observed during the latter portion of the observation period.

Aneuploid sperm formation in rainbow trout exposed to the environmental estrogen 17{alpha}-ethynylestradiol

Environmental contaminants that mimic native estrogens (i.e., environmental estrogens) are known to significantly impact a wide range of vertebrate species and have been implicated as a source for increasing human male reproductive deficiencies and diseases. Despite the widespread occurrence of environmental estrogens and recognized detrimental effects on male vertebrate reproduction, no specific mechanism has been determined indicating how reduced fertility and/or fecundity is achieved. Previous studies show that male rainbow trout, Oncorhynchus mykiss, exposed to the environmental estrogen 17alpha-ethynylestradiol (EE2) before gamete formation and fertilization produce progeny with significantly reduced embryonic survival. To determine whether this observed decrease results from sperm chromosome alterations during spermatogenesis, male rainbow trout were exposed to 10 ng of EE2/l for 50 days. After exposure, semen was collected and sperm aneuploidy levels analyzed with two chromosome markers by fluorescent in situ hybridization. In vitro fertilizations were also conducted by using control and exposed sperm crossed to eggs from an unexposed female for offspring analysis. Evaluations for nucleolar organizer region number and karyotype were performed on developing embryos to determine whether sperm aneuploidy translated into embryonic aneuploidy. Results conclusively show increased aneuploid sperm formation due to EE2 exposure. Additionally, embryonic cells from propagated progeny of individuals possessing elevated sperm aneuploidy display high levels of embryonic aneuploidy. This study concludes that EE2 exposure in sexually developing male rainbow trout increases levels of aneuploid sperm, providing a mechanism for decreased embryonic survival and ultimately diminished reproductive success in EE2 exposed males.

Nonylphenol in the environment: a critical review on occurrence, fate, toxicity and treatment in wastewaters

Nonylphenol is a toxic xenobiotic compound classified as an endocrine disrupter capable of interfering with the hormonal system of numerous organisms. It originates principally from the degradation of nonylphenol ethoxylates which are widely used as industrial surfactants. Nonylphenol ethoxylates reach sewage treatment works in substantial quantities where they biodegrade into several by-products including nonylphenol. Due to its physical-chemical characteristics, such as low solubility and high hydrophobicity, nonylphenol accumulates in environmental compartments that are characterised by high organic content, typically sewage sludge and river sediments, where it persists. The occurrence of nonylphenol in the environment is clearly correlated with anthropogenic activities such as wastewater treatment, landfilling and sewage sludge recycling. Nonylphenol is found often in matrices such as sewage sludge, effluents from sewage treatment works, river water and sediments, soil and groundwater. The impacts of nonylphenol in the environment include feminization of aquatic organisms, decrease in male fertility and the survival of juveniles at concentrations as low as 8.2 microg/l. Due to the harmful effects of the degradation products of nonylphenol ethoxylates in the environment, the use and production of such compounds have been banned in EU countries and strictly monitored in many other countries such as Canada and Japan. Although it has been shown that the concentration of nonylphenol in the environment is decreasing, it is still found at concentrations of 4.1 microg/l in river waters and 1 mg/kg in sediments. Nonylphenol has been referred to in the list of priority substances in the Water Frame Directive and in the 3rd draft Working Document on Sludge of the EU. Consequently there is currently a concern within some industries about the possibility of future regulations that may impose the removal of trace contaminants from contaminated effluents. The significance of upgrading sewage treatment works with advanced treatment technologies for removal of trace contaminants is discussed.

Influence of endocrine disruptors on human male fertility

It has been suggested that during the past five decades human sperm counts have declined and the incidence of testicular cancer, hypospadias and cryptorchidism has increased. Furthermore, geographical differences, with respect to these markers of male reproductive function, have been reported. According to a recent hypothesis, all these abnormalities of the male genital system do have a common cause, namely exposure to endocrine disruptors affecting the male in early fetal life. Reduced sperm production as well as congenital abnormalities of male genitalia can be evoked in laboratory animals by exposing them to chemicals with endocrine-disrupting effect, and in humans similar effects have been seen following accidental exposures to very high concentrations of these environmental toxicants. However, the evidence for association between levels of exposure found in the general population and serious adverse effects on male reproduction, including fertility, is still lacking. A recent European Union-supported study, on the effect of persistent organohalogen pollutants on human reproduction, failed to show any correlation between post-natal exposure levels and fertility. Future studies will reveal whether prenatal exposure does more strongly affect male fertility and whether genetic predisposition regulates the susceptibility of an individual to the adverse effects of endocrine disruptors.

Endocrine disruptors and estrogenic effects on male reproductive axis

Endocrine disruptors (e.g., polychlorinated biphenyls [PCBs], dichlorodiphenyl-trichloroethane [DDT], dioxin, and some pesticides) are estrogen-like and anti-androgenic chemicals in the environment. They mimic natural hormones, inhibit the action of hormones, or alter the normal regulatory function of the endocrine system and have potential hazardous effects on male reproductive axis causing infertility. Although testicular and prostate cancers, abnormal sexual development, undescended testis, chronic inflammation, Sertoli-cell-only pattern, hypospadias, altered pituitary and thyroid gland functions are also observed, the available data are insufficient to deduce worldwide conclusions. The development of intra-cytoplasmic sperm injection (ICSI) is beyond doubt the most important recent breakthrough in the treatment of male infertility, but it does not necessarily treat the cause and may inadvertently pass on adverse genetic consequences. Many well-controlled clinical studies and basic scientific discoveries in the physiology, biochemistry, and molecular and cellular biology of the male reproductive system have helped in the identification of greater numbers of men with male factor problems. Newer tools for the detection of Y-chromosome deletions have further strengthened the hypothesis that the decline in male reproductive health and fertility may be related to the presence of certain toxic chemicals in the environment. Thus the etiology, diagnosis, and treatment of male factor infertility remain a real challenge. Clinicians should always attempt to identify the etiology of a possible testicular toxicity, assess the degree of risk to the patient being evaluated for infertility, and initiate a plan to control and prevent exposure to others once an association between occupation/toxicant and infertility has been established.

Genetic and environmental correlates of semen quality: a twin study

BACKGROUND

The influences of environmental factors on the male reproductive system have been much debated over the last 3 decades. We studied the impact of genes and environment on semen quality, sex hormone levels, and sperm chromatin stability by using a twin design.

METHODS

The study population consisted of monozygotic and dizygotic twins from the population-based Danish Twin Registry and a random selection of pairs of singleton brothers from the Danish Civil Registration System. All men were 20 to 45 years of age. The study population comprised 100 monozygotic twin brothers (50 pairs), 102 dizygotic twins (51 pairs), and 102 single-born brothers (51 pairs). A semen sample and blood sample were collected from all participants.

RESULTS

Heritability was estimated to account for 20% (95% confidence interval = 0% to 68%) of the variation in sperm density. A higher heritability was found for the hormones reflecting Sertoli cell function (inhibin B, 76% [36% to 84%] and follicle-stimulating hormone, 81% [40% to 88%]) and for percent morphologic normal cells (41% [0% to 60%] and sperm chromatin parameters (mean alphaT, 68% [34% to 81%] and COMP alphaT, 72% [25% to 82%], respectively).

CONCLUSION

Our study indicates a substantial hereditary component in plasma levels of hormones reflecting Sertoli cell function and in sperm cell chromatin stability and morphology. The environmental contribution (including the prenatal environment) appeared to be largest for sperm count.

Semen quality in a population of volunteers from the province of Barcelona

A prospective study was carried out on 1005 male volunteers residing in the province of Barcelona. Participants were asked to complete a questionnaire concerning their health status and lifestyle, and provided a semen sample for analysis. Sperm concentration and percentages of motile, and normal forms were evaluated. The effect of smoking, alcohol consumption, stress and previous disease on semen parameters was also evaluated. Normal parameters were found in 22% of volunteers and sperm counts and/or percentage motility below normal threshold values were found in 78%. Asthenozoospermia detected in 62% and oligozoospermia in 17% of volunteers. No statistically significant association was found between semen quality and age, with the exception of a decrease in semen volume (P = 0.04) and progressive motility (P = 0.01). No statistically significant differences in semen parameters were found between smokers and non-smokers or between males who consumed alcohol versus those that did not. However, stress had a negative effect on sperm concentration. In conclusion, the prevalence of normal semen parameters in the study population evaluated was markedly lower than that reported for the general population (60-70%). Since sperm concentration did not appear to decrease with age, the decrease observed in the last decades may be related to exposure to environmental toxicants during the fetal period, as previously suggested.

Semen quality and sperm functional parameters in fertile Indian men

The reports of a decline in the reproductive health of men worldwide prompted the present study to be undertaken so that baseline semen parameters could be established in Indian men. Semen profile and sperm function parameters were evaluated in 368 Indian men of proven fertility, settled in Delhi. The results of the study were compared with available published information from Indian men. The mean sperm concentration and semen volumes were 68.22 +/- 15.14 x 10(6) ml(-1) and 3.20 +/- 0.94 ml, respectively. Rapid, linear progressive motility and sluggish linear motility were 40.95 +/- 9.15% and 24.95 +/- 7.01%, respectively. A comparison of the results of the present study with earlier published data did not support the contention of a decrease in the semen quality in Indian men.

Exposure to environmental ozone alters semen quality

Idiopathic male infertility may be due to exposure to environmental toxicants that alter spermatogenesis or sperm function. We studied the relationship between air pollutant levels and semen quality over a 2-year period in Los Angeles, California, by analyzing repeated semen samples collected by sperm donors. Semen analysis data derived from 5,134 semen samples from a sperm donor bank were correlated with air pollutant levels (ozone, nitrogen dioxide, carbon monoxide, and particulate matter < 10 microm in aerodynamic diameter) measured 0-9, 10-14, and 70-90 days before semen collection dates in Los Angeles between January 1996 and December 1998. A linear mixed-effects model was used to model average sperm concentration and total motile sperm count for the donation from each subject. Changes were analyzed in relationship to biologically relevant time points during spermatogenesis, 0-9, 10-14, and 70-90 days before the day of semen collection. We estimated temperature and seasonality effects after adjusting for a base model, which included donor's date of birth and age at donation. Forty-eight donors from Los Angeles were included as subjects. Donors were included if they collected repeated semen samples over a 12-month period between January 1996 and December 1998. There was a significant negative correlation between ozone levels at 0-9, 10-14, and 70-90 days before donation and average sperm concentration, which was maintained after correction for donor's birth date, age at donation, temperature, and seasonality (p < 0.01). No other pollutant measures were significantly associated with sperm quality outcomes. Exposure to ambient ozone levels adversely affects semen quality.

Increase in scrotal temperature in laptop computer users

BACKGROUND

Scrotal hyperthermia has been identified as a risk factor for male infertility. Laptop computers (LC) have become part of a contemporary lifestyle and have gained popularity among the younger population of reproductive age. LC are known to reach high internal operating temperatures. We evaluated the thermal effect of LC on the scrotum.

METHODS

Right and left scrotal temperature (ScT) was measured in 29 healthy volunteers in two separate 60 min sessions. ScT was recorded from thermocouples on a digital datalogger every 3 min with the working LC in a laptop position and in the same sitting position with approximated thighs without LC.

RESULTS

ScT increased significantly on the right and left side in the group with working LC (2.8 degrees C and 2.6 degrees C, respectively; P<0001) and without LC (2.1 degrees C, P<0.0001). However, ScT elevation with working LC was significantly higher (P<0.0001).

CONCLUSIONS

Working LC in a laptop position causes significant ScT elevation as a result of heat exposure and posture-related effects. Long-term exposure to LC-related repetitive transient scrotal hyperthermia is a modern lifestyle feature that may have a negative impact upon spermatogenesis, specifically in teenage boys and young men. Further studies of such thermal effects on male reproductive health are warranted.