Habitual alcohol consumption associated with reduced semen quality and changes in reproductive hormones; a cross-sectional study among 1221 young Danish men

OBJECTIVE

Study associations between three measures of alcohol consumption (recent, typical/habitual, binging), semen quality and serum reproductive hormones.

DESIGN

Cross-sectional population based study.

SETTING AND PARTICIPANTS

1221 young Danish men, aged 18-28 years were recruited when they attended a compulsory medical examination to determine their fitness for military service from 2008 to 2012. Total alcohol consumption: (1) in the week preceding (habitual/typical) the visit (recent alcohol intake), (2) in a typical week and (3) frequency of 'binge drinking' (consuming more than 5 units/day)) in the past 30 days was estimated.

MAIN OUTCOME MEASURES

Semen quality (volume, sperm concentration, total sperm count, and percentages of motile and morphologically normal spermatozoa) and serum concentration of reproductive hormones (follicle-stimulating hormone, luteinising hormone, testosterone, sex hormone binding globulin, oestradiol, free testosterone and inhibin B).

RESULTS

Sperm concentration, total sperm count and percentage of spermatozoa with normal morphology were negatively associated with increasing habitual alcohol intake. This association was observed in men reporting at least 5 units in a typical week but was most pronounced for men with a typical intake of more than 25 units/week. Men with a typical weekly intake above 40 units had a 33% (95% CI 11% to 59%) reduction in sperm concentration compared to men with an intake of 1-5 units/week. A significant increase in serum free testosterone with increasing alcohol consumption the week preceding the visit was found. Binging was not independently associated with semen quality.

CONCLUSIONS

Our study suggests that even modest habitual alcohol consumption of more than 5 units per week had adverse effects on semen quality although most pronounced associations were seen in men who consumed more than 25 units per week. Alcohol consumption was also linked to changes in testosterone and SHBG levels. Young men should be advised to avoid habitual alcohol intake.

Drinking-water disinfection by-products and semen quality: a cross-sectional study in China

BACKGROUND

Exposure to disinfection by-products (DBPs) has been demonstrated to impair male reproductive health in animals, but human evidence is limited and inconsistent.

OBJECTIVE

We examined the association between exposure to drinking-water DBPs and semen quality in a Chinese population.

METHODS

We recruited 2,009 men seeking semen analysis from the Reproductive Center of Tongji Hospital in Wuhan, China, between April 2011 and May 2012. Each man provided a semen sample and a urine sample. Semen samples were analyzed for sperm concentration, sperm motility, and sperm count. As a biomarker of exposure to drinking-water DBPs, trichloroacetic acid (TCAA) was measured in the urine samples.

RESULTS

The mean (median) urinary TCAA concentration was 9.58 (7.97) μg/L (interquartile range, 6.01-10.96 μg/L). Compared with men with urine TCAA in the lowest quartile, increased adjusted odds ratios (ORs) were estimated for below-reference sperm concentration in men with TCAA in the second and fourth quartiles (OR = 1.79; 95% CI: 1.19, 2.69 and OR = 1.51; 95% CI: 0.98, 2.31, respectively), for below-reference sperm motility in men with TCAA in the second and third quartiles (OR = 1.46; 95% CI: 1.12, 1.90 and OR = 1.30; 95% CI: 1.00, 1.70, respectively), and for below-reference sperm count in men with TCAA in the second quartile (OR 1.62; 95% CI: 1.04, 2.55). Nonmonotonic associations with TCAA quartiles were also estimated for semen parameters modeled as continuous outcomes, although significant negative associations were estimated for all quartiles above the reference level for sperm motility.

CONCLUSION

Our findings suggest that exposure to drinking-water DBPs may contribute to decreased semen quality in humans.

Association between mobile phone use and semen quality: a systemic review and meta-analysis

Possible hazardous health effects of radiofrequency electromagnetic radiations emitted from mobile phone on the reproductive system have raised public concern in recent years. This systemic review and meta-analysis was prepared following standard procedures of the Cochrane Collaboration and the Preferred Reporting Items for Systematic Reviews and Meta-Analyses statement and checklist. Relevant studies published up to May 2013 were identified from five major international and Chinese literature databases: Medline/PubMed, EMBASE, CNKI, the VIP database and the Cochrane Central Register of Controlled Trials in the Cochrane Library. Eighteen studies with 3947 men and 186 rats were included in the systemic review, of which 12 studies (four human studies, four in vitro studies and four animal studies) with 1533 men and 97 rats were used in the meta-analyses. Systemic review showed that results of most of the human studies and in vitro laboratory studies indicated mobile phone use or radiofrequency exposure had negative effects on the various semen parameters studied. However, meta-analysis indicated that mobile phone use had no adverse effects on semen parameters in human studies. In the in vitro studies, meta-analysis indicated that radiofrequency radiation had detrimental effect on sperm motility and viability in vitro [pooled mean difference (MDs) (95% CI): -4.11 (-8.08, -0.13), -3.82 (-7.00, -0.65) for sperm motility and viability respectively]. As for animal studies, radiofrequency exposure had harmful effects on sperm concentration and motility [pooled MDs (95% CI): -8.75 (-17.37, -0.12), -17.72 (-32.79, -2.65) for sperm concentration and motility respectively]. Evidence from current studies suggests potential harmful effects of mobile phone use on semen parameters. A further multicentred and standardized study is needed to assess the risk of mobile phone use on the reproductive system.

Alcohol and male reproductive health: a cross-sectional study of 8344 healthy men from Europe and the USA

STUDY QUESTION

Is there an association between alcohol intake and semen quality and serum reproductive hormones among healthy men from the USA and Europe?

SUMMARY ANSWER

Moderate alcohol intake is not adversely associated with semen quality in healthy men, whereas it was associated with higher serum testosterone levels.

WHAT IS KNOWN ALREADY

High alcohol intake has been associated with a wide range of diseases. However, few studies have examined the correlation between alcohol and reproductive function and most have been conducted in selected populations of infertile men or have a small sample size and the results have been contradictory.

STUDY DESIGN, SIZE, DURATION

A coordinated international cross-sectional study among 8344 healthy men. A total of 1872 fertile men aged 18-45 years (with pregnant partners) from four European cities and four US states, and 6472 young men (most with unknown fertility) aged 18-28 years from the general population in six European countries were recruited.

PARTICIPANTS/MATERIALS, SETTING, METHODS

The men were recruited using standardized protocols. A semen analysis was performed and men completed a questionnaire on health and lifestyle, including their intake of beer, wine and liquor during the week prior to their visit. Semen quality (semen volume, sperm concentration, percentage motile and morphologically normal sperm) and serum reproductive hormones (FSH, LH, testosterone, sex hormone-binding globulin, and inhibin B and free testosterone) were examined.

MAIN RESULTS AND THE ROLE OF CHANCE

The participation rate for our populations was 20-30%. We found no consistent association between any semen variable and alcohol consumption, which was low/moderate in this group (median weekly intake 8 units), either for total consumption or consumption by type of alcohol. However, we found a linear association between total alcohol consumption and total or free testosterone in both groups of men. Young and fertile men who consumed >20 units of alcohol per week had, respectively, 24.6 pmol/l (95% confidence interval 16.3-32.9) and 19.7 pmol/l (7.1-32.2) higher free testosterone than men with a weekly intake between 1 and 10 units. Alcohol intake was not significantly associated with serum inhibin B, FSH or LH levels in either group of men. The study is the largest of its kind and has sufficient power to detect changes in semen quality and reproductive hormones.

LIMITATIONS, REASONS FOR CAUTION

The participation rate was low, but higher than in most previous semen quality studies. In addition, the study was cross-sectional and the men were asked to recall their alcohol intake in the previous week, which was used as a marker of intake up to 3 months before. If consumption in that week differed from the typical weekly intake and the intake 3 months earlier, misclassification of exposure may have occurred. However, the men were unaware of their semen quality when they responded to the questions about alcohol intake. Furthermore, we cannot exclude that our findings are due to unmeasured confounders, including diet, exercise, stress, occupation and risk-taking behavior.

WIDER IMPLICATIONS OF THE FINDINGS

Our study suggests that moderate alcohol intake is not adversely associated with semen quality in healthy men, whereas it was associated with higher serum testosterone levels which may be due to a changed metabolism of testosterone in the liver. Healthy men may therefore be advised that occasional moderate alcohol intake may not harm their reproductive health; we cannot address the risk of high alcohol consumption of longer duration or binge drinking on semen quality and male reproductive hormones.

STUDY FUNDING/COMPETING INTERESTS

All funding sources were non-profitable and sponsors of this study played no role in the study design, in data collection, analysis, or interpretation, or in the writing of the article. The authors have no conflicts of interest.

Air pollution and decreased semen quality: a comparative study of Chongqing urban and rural areas

To investigate the association and effects of air pollution level on male semen quality in urban and rural areas, this study examines the outdoor concentrations of particulate matter (PM10), sulfur dioxide (SO2), nitrous dioxide (NO2) and semen quality outcomes for 1346 volunteers in both urban and rural areas in Chongqing, China. We found the urban area has a higher pollution level than the rural area, contrasted with better semen quality in the rural residents, especially for sperm morphology and computer assistant semen analysis (CASA) motility parameters. A multivariate linear regression analysis demonstrates that concentrations of PM10, SO2, and NO2 significantly and negatively are associated with normal sperm morphology percentage (P < 0.001) and sperm kinetic parameters. In conclusion, exposure to higher concentrations of PM10, SO2, and NO2 in urban ambient air may account for worse semen quality in urban males.

In subfertile couple, abdominal fat loss in men is associated with improvement of sperm quality and pregnancy: a case-series

Background

The impact of overweight among men of reproductive-age may affect fertility. Abdominal fat, more than body mass index, is an indicator of higher metabolic risk, which seems to be involved in decreasing sperm quality.

This study aims to assess the relationship between abdominal fat and sperm DNA fragmentation and the effect of abdominal fat loss, among 6 men in subfertile couples.

Methods

Sperm DNA fragmentation, abdominal fat and metabolic and hormonal profiles were measured in the 6 men before and after dietary advices. Seminal oxidative stress and antioxidant markers were determined.

Results

After several months of a lifestyle program, all 6 men lost abdominal fat (patient 1: loss of 3 points of abdominal fat, patient 2: loss of 3 points, patient 3: loss of 2 points, patient 4: loss of 1 point, patient 5: loss of 4 points and patient 6: loss of 13 points). At the same time, their rate of sperm DNA fragmentation decreased: 9.5% vs 31%, 24% vs 43%, 18% vs 47%, 26.3% vs 66%, 25.4% vs 35% and 1.7% vs 25%. Also, an improvement in both metabolic (significant decrease in triglycerides and total cholesterol; p = 0.0139) and hormonal (significant increase in testosterone/oestradiol ratio; p = 0.0139) blood profiles was observed after following the lifestyle program. In seminal plasma, the amount of SOD2 has significantly increased (p = 0.0139) while in parallel carbonylated proteins have decreased. Furthermore, all spouses got pregnant. All pregnancies were brought to term.

Conclusion

This study shows specifically that sperm DNA fragmentation among men in subfertile couples could be affected by abdominal fat, but improvement of lifestyle factor may correct this alteration. The effect of specific abdominal fat loss on sperm quality needs further investigation. The reduction of oxidative stress may be a contributing factor.

Semen quality of 1559 young men from four cities in Japan: a cross-sectional population-based study

OBJECTIVES

To provide information of semen quality among normal young Japanese men and indicate the frequency of reduced semen quality.

DESIGN

Cross-sectional, coordinated studies of Japanese young men included from university areas. The men had to be 18-24 years, and both the man and his mother had to be born in Japan. Background information was obtained from questionnaires. Standardised and quality-controlled semen analyses were performed, reproductive hormones analysed centrally and results adjusted for confounding factors.

SETTING

Four study centres in Japan (Kawasaki, Osaka, Kanazawa and Nagasaki).

PARTICIPANTS

1559 men, median age 21.1 years, included during 1999-2003.

OUTCOME MEASURES

Semen volume, sperm concentration, total sperm count, sperm motility, sperm morphology and reproductive hormone levels.

RESULTS

Median sperm concentration was 59 (95% CI 52 to 68) million/ml, and 9% and 31.9% had less than 15 and 40 million/ml, respectively. Median percentage of morphologically normal spermatozoa was 9.6 (8.8 to 10.3)%. Small, but statistically significant, differences were detected for both semen and reproductive hormone variables between men from the four cities. Overall, the semen values were lower than those of a reference population of 792 fertile Japanese men.

CONCLUSIONS

Assuming that the investigated men were representative for young Japanese men, a significant proportion of the population had suboptimal semen quality with reduced fertility potential, and as a group they had lower semen quality than fertile men. However, the definitive role-if any-of low semen quality for subfertility and low fertility rates remain to be investigated.

BMI in relation to sperm count: an updated systematic review and collaborative meta-analysis

BACKGROUND The global obesity epidemic has paralleled a decrease in semen quality. Yet, the association between obesity and sperm parameters remains controversial. The purpose of this report was to update the evidence on the association between BMI and sperm count through a systematic review with meta-analysis. METHODS A systematic review of available literature (with no language restriction) was performed to investigate the impact of BMI on sperm count. Relevant studies published until June 2012 were identified from a Pubmed and EMBASE search. We also included unpublished data (n = 717 men) obtained from the Infertility Center of Bondy, France. Abstracts of relevant articles were examined and studies that could be included in this review were retrieved. Authors of relevant studies for the meta-analysis were contacted by email and asked to provide standardized data. RESULTS A total of 21 studies were included in the meta-analysis, resulting in a sample of 13 077 men from the general population and attending fertility clinics. Data were stratified according to the total sperm count as normozoospermia, oligozoospermia and azoospermia. Standardized weighted mean differences in sperm concentration did not differ significantly across BMI categories. There was a J-shaped relationship between BMI categories and risk of oligozoospermia or azoospermia. Compared with men of normal weight, the odds ratio (95% confidence interval) for oligozoospermia or azoospermia was 1.15 (0.93-1.43) for underweight, 1.11 (1.01-1.21) for overweight, 1.28 (1.06-1.55) for obese and 2.04 (1.59-2.62) for morbidly obese men. CONCLUSIONS Overweight and obesity were associated with an increased prevalence of azoospermia or oligozoospermia. The main limitation of this report is that studied populations varied, with men recruited from both the general population and infertile couples. Whether weight normalization could improve sperm parameters should be evaluated further.

Modifiable and non-modifiable risk factors for poor semen quality: a case-referent study

STUDY QUESTION

Are common lifestyle factors associated with low-motile sperm concentration (MSC)?

SUMMARY ANSWER

Common lifestyle choices make little contribution to the risk of low MSC.

WHAT IS KNOWN AND WHAT THIS PAPER ADDS

Reviews of male subfertility often highlight how aspects of men's adult lifestyle can significantly increase their risk of subfertility but the strength of supporting evidence is weak. In this study, although low MSC was associated with a history of testicular surgery, being in manual work, not wearing loose underwear and black ethnicity, no relation was found to consumption of alcohol, use of tobacco or recreational drugs or high body mass index (BMI). These results suggest that delaying assisted conception to make changes to lifestyle is unlikely to enhance conception.

DESIGN

Unmatched case-referent study with 939 cases and 1310 referents. Cases had a low-MSC relative to the time since last ejaculation (<12 × 10(6) for 3 days of abstinence). Exposures included self-reported exposures to alcohol, tobacco, recreational drugs as well as occupational and other factors.

PARTICIPANTS AND SETTING

Eligible men, aged 18 or above, were part of a couple who had been attempting conception without success following at least 12 months of unprotected intercourse and also had no knowledge of any semen analysis. They were recruited from 14 fertility clinics across the UK during a 37-month period from 1 January 1999.

MAIN RESULTS AND THE ROLE OF CHANCE

Risk factors for low MSC, after adjustment for centre and confounding factors, included a history of testicular surgery [odds ratio = 2.39, 95% confidence interval (CI): 1.75, 3.28], being in manual work [odds ratio (OR) = 1.28, 95% CI: 1.07, 1.53] or not working (OR = 1.78, 95% CI: 1.22, 2.59) and having black ethnicity (OR = 1.99, 95% CI: 1.10, 3.63). Conversely, men who wore boxer shorts (OR = 0.76, 95% CI: 0.64, 0.92) or who had a previous conception (OR = 0.71, 95% CI: 0.60, 0.85) were less likely to be a case. No significant association was found with smoking and alcohol consumption, the use of recreational drugs, a high BMI or having a history of mumps or fever.

BIAS, CONFOUNDING AND OTHER REASONS FOR CAUTION

Data were collected blind to outcome, and exposure information should not have been subject to reporting bias. Among men attending the various clinics less than half met the study eligibility criteria and among those who did, two out of five were not recruited. It is not known whether any of those who refused to take part did so because they had a lifestyle they did not want subjected to investigation. Although the power of the study was sufficient to draw conclusions about common lifestyle choices, it cannot comment on exposures that are perhaps rare and poorly reported: the finding that use of street drugs was unrelated to low MSC cannot be assumed to apply to all such drugs and all patterns of use. The case definition did not consider sperm morphology or sperm DNA integrity.

GENERALIZABILITY TO OTHER POPULATIONS

All participating clinics saw patients at no cost (under the UK National Health Service) and the study population may differ from those in countries without such provision. Even within the UK, low-income couples may choose not to undertake any investigation believing that they would subsequently be unable to afford treatment.

Climatic influence on the reproductive characteristics of Japanese males

We previously performed a survey of the sperm characteristics of the partners of pregnant women in four cities in Japan. In the present study, we analyzed the sperm characteristics of these subjects and the correlations between these sperm characteristics and climatic changes or Y chromosome haplogroups. Our results showed that more haplogroup D2a1 males than O2b1 males were born in the first half of the year (January to June), whereas more O2b1 males were born in the last half of the year (July to December) (P<0.05). This was agreed and correlated with the seasonal variations in their mean sperm concentrations. The haplogroup C, D* and D2a1 males displayed lower sperm concentrations from March to May, followed by an increase in their sperm concentrations starting in June or July, while the O2b1 males displayed higher sperm concentrations in the first half of the year followed by a sudden decrease from July to August (P<0.05). We hypothesize that the Japanese climate has different effects on the sperm characteristics and reproductive seasonality of males from different lineages; and therefore, has influenced the modern population of Japan.

An exploration of the association between male body mass index and semen quality

Obesity is becoming a serious problem, especially in industrialized societies. This study was designed to explore the association between body mass index (BMI) and semen quality. Semen analysis and demographic data were collected from male partners of couples undergoing fertility investigations in a referral fertility centre. Men were classified into groups according to their BMI (A, <18.5; B, 18.5-24.99; C, 25-29.99; D, ≥30 kg/m(2)). Data from 2035 men were analysed using logistic regression. There were 18, 839, 909 and 269 men in groups A, B, C and D, respectively. Taking group B as the reference, adjusted odds ratios (95% CI) for groups A, C and D for semen volume <2 ml were 1.57 (0.49-5.01), 1.06 (0.82-1.38) and 1.69 (1.20-2.38), respectively; for sperm morphology <15%, 1.44 (0.45-4.61), 1.07 (0.86-1.33) and 1.50 (1.06-2.09); for sperm concentration <20 million/ml, 0.46 (0.10-2.07), 1.03 (0.82-1.31) and 1.00 (0.72-1.41); and for motility <50%, 2.62 (0.73-9.45), 0.96 (0.78-1.18) and 0.75 (0.56-1.01). In conclusion, obese men are more likely to have lower semen volume and fewer morphologically normal spermatozoa than men with normal BMI.

Association between urinary polycyclic aromatic hydrocarbon metabolites and sperm DNA damage: a population study in Chongqing, China

BACKGROUND

Polycyclic aromatic hydrocarbons (PAHs), a class of the most ubiquitous environmental contaminants, may reduce male reproductive functions, but the data from human population studies are very limited.

OBJECTIVES

We designed this study to determine whether environmental exposure to PAHs contributes to the alteration in semen quality, sperm DNA damage, and apoptosis in the general male human population.

METHODS

We measured urinary levels of four PAH metabolites and assessed semen quality, sperm apoptotic markers with Annexin V assay, and sperm DNA damage with comet assay in 232 men from Chongqing, China.

RESULTS

We found that increased urinary 2-hydroxynaphthalene (2-OHNa) levels were associated with increased comet parameters, including the percentage of DNA in the tail (tail%) [β coefficient = 13.26% per log unit 2-OHNa (micrograms per gram creatinine); 95% confidence interval (CI), 7.97-18.55]; tail length (12.25; 95% CI, 0.01-24.52), and tail distribution (7.55; 95% CI, 1.28-18.83). The urinary level of 1-hydroxypyrene was associated only with increased tail% (5.32; 95% CI, 0.47-10.17). Additionally, the increased levels of four urinary PAH metabolites were significantly associated with decreased vital Annexin V negative sperm counts. However, there was no significant association between urinary PAH metabolite levels and human semen parameters or morphology of the sperm samples.

CONCLUSIONS

Our data indicate that the environmental level of PAH exposure is associated with increased sperm DNA damage but not with semen quality. These findings suggest that exposure to PAHs may disrupt sperm DNA and thereby interfere with human male fertility.

Association between socio-psycho-behavioral factors and male semen quality: systematic review and meta-analyses

OBJECTIVE

To identify the factors associated with male semen quality from many socio-psycho-behavioral factors.

DESIGN

Medline/PubMed, EMBASE, and CNKI were searched to identify relevant publications for systematic review and meta-analysis.

PATIENT(S)

None.

INTERVENTION(S)

None.

MAIN OUTCOME MEASURE(S)

Thirteen socio-psycho-behavioral factors in 57 cross-sectional studies with 29,914 participants from 26 countries/regions were involved in this review. Six factors (age, body mass index [BMI], psychological stress, smoking, alcohol, and coffee consumption) were included in meta-analyses.

RESULT(S)

Smoking can deteriorate all of the sperm parameters of both fertile and infertile men, but it is not risk factor for semen volume in Switzerland and Iran and for sperm density in the United States, Denmark, and Brazil; higher age and alcohol consumption are risk factors for lower semen volume; and psychological stress can lower sperm density and sperm progressive motility and increase abnormal sperm.

CONCLUSION(S)

This review further suggested that higher age, smoking, alcohol consumption, and psychological stress were risk factors for semen quality. These results indicated that health programs focusing on lifestyle and psychological health would be helpful for male reproductive health. Well-designed studies are needed to further identify the role of more socio-psycho-behavioral factors in male semen quality.

Overview of developmental and reproductive toxicity research in China: history, funding mechanisms, and frontiers of the research

Reproductive and developmental toxicology (DART) is the discipline that deals with adverse effects on male and female resulting from exposures to harmful chemical and physical agents. DART research in China boasted a long history, but presently has fallen behind the western world in education and research. The funding mechanisms for DART research in China were similar to that for other toxicological disciplines, and the funding has come from research grants and fellowships provided by national, ministerial, and provincial institutions. Finally, the frontiers of DART research in China could be summarized as follows: (1) use of model animals such as the zebrafish and roundworm, and use of cutting-edge techniques such as stem cell culture, as well as transgenic, metabonomic, and virtual screening to study the mechanisms of developmental toxicity for some important toxicants in China; (2) use of model animals and other lower-level sentinel organisms to evaluate and monitor the developmental toxicogical risk of environmental chemicals or pollutants; (3) epidemiological studies of some important reproductive hazards; (4) in-depth studying of the reproductive and developmental toxicity of some important environmental chemicals; and (5) evaluation and study of the reproductive and developmental toxicity of traditional Chinese medicines.

Male reproductive organs are at risk from environmental hazards

Male reproductive disorders that are of interest from an environmental point of view include sexual dysfunction, infertility, cryptorchidism, hypospadias and testicular cancer. Several reports suggest declining sperm counts and increase of these reproductive disorders in some areas during some time periods past 50 years. Except for testicular cancer this evidence is circumstantial and needs cautious interpretation. However, the male germ line is one of the most sensitive tissues to the damaging effects of ionizing radiation, radiant heat and a number of known toxicants. So far occupational hazards are the best documented risk factors for impaired male reproductive function and include physical exposures (radiant heat, ionizing radiation, high frequency electromagnetic radiation), chemical exposures (some solvents as carbon disulfide and ethylene glycol ethers, some pesticides as dibromochloropropane, ethylendibromide and DDT/DDE, some heavy metals as inorganic lead and mercury) and work processes such as metal welding. Improved working conditions in affluent countries have dramatically decreased known hazardous workplace exposures, but millions of workers in less affluent countries are at risk from reproductive toxicants. New data show that environmental low-level exposure to biopersistent pollutants in the diet may pose a risk to people in all parts of the world. For other toxicants the evidence is only suggestive and further evaluation is needed before conclusions can be drawn. Whether compounds as phthalates, bisphenol A and boron that are present in a large number of industrial and consumer products entails a risk remains to be established. The same applies to psychosocial stressors and use of mobile phones. Finally, there are data indicating a particular vulnerability of the fetal testis to toxicants-for instance maternal tobacco smoking. Time has come where male reproductive toxicity should be addressed form entirely new angles including exposures very early in life.

What has happened to human fertility?

Semen quality appears to have declined in recent decades in some populations, e.g. north-western Europe. At the same time, couple fertility may have increased. Hypotheses are suggested for this apparent inconsistency. Alongside the deterioration of spermatogenesis there is clear evidence of an increase in other related problems, notably testicular cancer. The sharply rising trend in this condition started a century ago--decades earlier than sometimes thought. This and other evidence clearly indicates an environmental origin, but there is also a definite genetic component. The relationship of genetics and environment is discussed in the context of the puzzle that infertility is inherited, which appears to be impossible from an evolutionary standpoint. Poor semen quality is related not only to testicular cancer but also to zygote development, in which cancer-like disruption of the genetic apparatus is observed, with serious implications for offspring health. This needs to be seen in the context that human reproduction is prone to a higher degree of impairment than that of other mammalian species, in relation to spermatogenesis, couple fertility, early pregnancy loss and embryonic aneuploidy; female- and male-mediated pathways are both implicated. It is unclear whether such human specificity originated on an evolutionary/genetic or a historico-social timescale, which is important in relation to pathogenesis. The evidence clearly indicates that the currently most popular explanation for male reproductive system impairment, the endocrine disruption hypothesis, cannot explain the main features of the descriptive epidemiology. An alternative pathogenesis is outlined, and some possible exposures considered that could be responsible.