Does the potential for selection bias in semen quality studies depend on study design? Experience from a study conducted within an infertility clinic

Selection bias in a male-offspring cohort investigating fecundity: is there reason for concern?

STUDY QUESTION

Is there risk of selection bias in etiological studies investigating prenatal risk factors of poor male fecundity in a cohort of young men?

SUMMARY ANSWER

The risk of selection bias is considered limited despite a low participation rate.

WHAT IS KNOWN ALREADY

Participation rates in studies relying on volunteers to provide a semen sample are often very low. Many risk factors for poor male fecundity are associated with participation status, and as men with low fecundity may be more inclined to participate in studies of semen quality, a risk of selection bias exists.

STUDY DESIGN, SIZE, DURATION

A population-based follow-up study of 5697 young men invited to the Fetal Programming of Semen Quality (FEPOS) cohort nested within the Danish National Birth Cohort (DNBC), 1998-2019.

PARTICIPANTS/MATERIALS, SETTING, METHODS

Young men (age range: 18 years, 9 months to 21 years, 4 months) born 1998-2000 by mothers included in the DNBC were invited to participate in FEPOS. In total, 1173 men answered a survey in FEPOS (n = 115 participated partly); of those, 1058 men participated fully by also providing a semen and a blood sample at a clinical visit. Differential selection according to parental baseline characteristics in the first trimester, the sons' own characteristics from the FEPOS survey, and urogenital malformations and diseases in reproductive organs from the Danish registers were investigated using logistic regression. The influence of inverse probability of selection weights (IPSWs) to investigate potential selection bias was examined using a predefined exposure-outcome association of maternal smoking in the first trimester (yes, no) and total sperm count analysed using adjusted negative binomial regression. A multidimensional bias analysis on the same association was performed using a variety of bias parameters to assess different scenarios of differential selection.

MAIN RESULTS AND THE ROLE OF CHANCE

Participation differed according to most parental characteristics in first trimester but did not differ according to the prevalence of a urogenital malformation or disease in the reproductive organs. Associations between maternal smoking in the first trimester and male fecundity were similar when the regression models were fitted without and with IPSWs. Adjusting for other potential risk factors for poor male fecundity, maternal smoking was associated with 21% (95% CI: -32% to -9%) lower total sperm count. In the bias analysis, this estimate changed only slightly under realistic scenarios. This may be extrapolated to other exposure-outcome associations.

LIMITATIONS, REASONS FOR CAUTION

We were unable to directly assess markers of male fecundity for non-participants from, for example an external source and therefore relied on potential proxies of fecundity. We did not have sufficient power to analyse associations between prenatal exposures and urogenital malformations.

WIDER IMPLICATIONS OF THE FINDINGS

The results are reassuring when using this cohort to identify causes of poor male fecundity. The results may be generalized to other similar cohorts. As the young men grow older, they can be followed in the Danish registers, as an external source, to examine, whether participation is associated with the risk of having an infertility diagnosis.

STUDY FUNDING/COMPETING INTEREST(S)

The project was funded by the Lundbeck Foundation (R170-2014-855), the Capital Region of Denmark, Medical doctor Sofus Carl Emil Friis and spouse Olga Doris Friis's Grant, Axel Muusfeldt's Foundation (2016-491), AP Møller Foundation (16-37), the Health Foundation, Dagmar Marshall's Fond, Aarhus University and Independent Research Fund Denmark (9039-00128B). The authors declare that they have no conflict of interest.

TRIAL REGISTRATION NUMBER

N/A.

Use of paracetamol (acetaminophen) as a nonprescription analgesic and semen quality in young men: A cross-sectional study

BACKGROUND

Paracetamol (acetaminophen) is a frequently used nonprescription analgesic with suggested endocrine-disrupting properties. Epidemiological evidence on the effect of paracetamol on male fecundity is sparse.

OBJECTIVES

To investigate if the use of paracetamol as an oral nonprescription mild analgesic was associated with semen quality in young men.

MATERIALS AND METHODS

This cross-sectional study was based on data from the Fetal Programming of Semen Quality (FEPOS; 2017-2019) cohort of 1058 young men (18-21 years) included in the Danish National Birth Cohort. Participants completed a comprehensive online questionnaire on health behavior including analgesic use and provided a semen sample. Negative binomial regression models were used to estimate the percentage differences (adjusted mean ratios [aMR]) in semen quality characteristics according to paracetamol use (no; yes) and frequency of use (almost never; <1/month; ≥1/month; ≥1/week).

RESULTS

In total, 28% of the 913 participants with available data reported the use of paracetamol within the last 6 months. We found a slightly higher total sperm count (aMR 1.13 95% CI [0.99-1.30]) in users compared to nonusers but other semen characteristics were unaffected. The frequency of use was suggestive of lower total sperm count and morphologically normal sperm cells primarily among users ≥1/week, however, CIs were wide.

DISCUSSION

We were unable to account for the underlying reason for paracetamol use, which may induce confounding by indication. Exposure misclassification due to recall is likely but probably nondifferential due to the participants' young age and unawareness of semen quality. Due to the rapid plasma half-life of paracetamol and few frequent users, it was not possible to conclude on potential high-dose effects.

CONCLUSION

Our findings do not suggest any strong detrimental effect of paracetamol use on semen quality within this sample of young Danish men. However, the effects of high dose and frequent use cannot be excluded.

Environmental and occupational pesticide exposure and human sperm parameters: A Navigation Guide review

Global sperm counts have declined in recent decades, coinciding with the proliferation of endocrine-disrupting chemicals, of which pesticides are some of the most common. Previous systematic reviews of epidemiologic studies published between 1991 through 2013 have reported associations between environmental and occupational pesticide exposure and reduced sperm quality, particularly associations with reduced sperm concentration. This systematic review used the Navigation Guide to critically evaluate the current body of evidence examining sperm quality and pesticide exposure in epidemiological studies. PubMed, Scopus, and Web of Science databases were searched for all English-language articles published after September 2012 until August 2021. Original observational studies that assessed human sperm quality parameters, defined as concentration, motility, morphology, and DNA integrity, and individual-level pesticide exposure were included. The risk of bias for each included study and the strength of evidence were evaluated using the Navigation Guide protocol. Nineteen studies assessing environmental or occupational pesticide exposure and sperm parameters were included. Eighteen studies were cross-sectional studies and one prospective cohort; sample sizes ranged from 42 to 2122 men from 14 different countries. Fifteen (79 %) studies found at least one significant association between pesticide exposure and reduced sperm quality. The overall risk of bias across studies was classified as low to moderate. The quality of evidence was determined to be moderate based on systematic evaluation criteria. There were consistent adverse associations between pesticide exposure and sperm motility (63 % of studies) and DNA integrity (80 % of studies). For sperm concentration and morphology, 42 % and 36 % of studies found significant negative associations, respectively. The strength of the body of evidence overall was rated as having sufficient evidence of toxicity. Regarding specific sperm endpoints, there was sufficient evidence that pesticides are toxic for sperm motility and DNA integrity; limited evidence of toxicity for sperm concentration; and inadequate evidence of toxicity for sperm morphology. The studies reviewed here showed consistent associations between pesticide exposure and diminished sperm parameters, particularly sperm motility and sperm DNA integrity. These findings are largely consistent with results of previous reviews, which have found significant negative associations between pesticide exposure and sperm quality in 13 of 20 (65 %) studies published between 1991 and 2008, and in 14 of 17 (82 %) studies published between 2008 and 2012. After thirty years of mounting evidence, actions are needed to reduce pesticide risks to testicular function and male fertility.

Marijuana smoking and markers of testicular function among men from a fertility centre

STUDY QUESTION

Is marijuana smoking associated with semen quality, sperm DNA integrity or serum concentrations of reproductive hormones among subfertile men?

SUMMARY ANSWER

Men who had ever smoked marijuana had higher sperm concentration and count and lower serum FSH concentrations than men who had never smoked marijuana; no differences were observed between current and past marijuana smokers.

WHAT IS KNOWN ALREADY

Studies of marijuana abuse in humans and animal models of exposure to marijuana suggest that marijuana smoking adversely impacts spermatogenesis. Data is less clear for moderate consumption levels and multiple studies have found higher serum testosterone concentrations among marijuana consumers.

STUDY DESIGN, SIZE, DURATION

This longitudinal study included 662 subfertile men enroled at the Massachusetts General Hospital Fertility Center between 2000 and 2017. The men provided a total of 1143 semen samples; 317 men also provided blood samples in which we measured reproductive hormones.

PARTICIPANTS/MATERIALS, SETTING, METHODS

Use of marijuana and other drugs was self-reported at baseline. Standard protocols were followed for measuring semen quality, sex hormones and DNA integrity. We used linear mixed effect models with a random intercept to evaluate the associations of self-reported marijuana smoking at enrolment with semen parameters from subsequently collected samples, and linear regression models for sperm DNA integrity and serum reproductive hormones, while adjusting for confounders including smoking and cocaine use.

MAIN RESULTS AND THE ROLE OF CHANCE

Men who had ever smoked marijuana (N = 365) had significantly higher sperm concentration (62.7 (95% confidence interval: 56.0, 70.3) million/mL) than men who had never smoked marijuana (N = 297) (45.4 (38.6, 53.3) million/mL) after adjusting for potential confounders (P = 0.0003). There were no significant differences in sperm concentration between current (N = 74) (59.5 (47.3, 74.8) million/mL) and past marijuana smokers (N = 291) (63.5 (56.1, 72.0) million/mL; P = 0.60). A similar pattern was observed for total sperm count. Furthermore, the adjusted prevalence of sperm concentration and total sperm motility below WHO reference values among marijuana smokers was less than half that of never marijuana smokers. Marijuana smokers had significantly lower follicle stimulating hormone (FSH) concentrations than never marijuana smokers (-16% (-27%, -4%)) and there were no significant differences between current and past marijuana smokers (P = 0.53). Marijuana smoking was not associated with other semen parameters, with markers of sperm DNA integrity or with reproductive hormones other than FSH. Chance findings cannot be excluded due to the multiple comparisons.

LIMITATIONS, REASONS FOR CAUTION

Our results may not be generalisable to men from the general population. Marijuana smoking was self-reported and there may be misclassification of the exposure.

WIDER IMPLICATIONS OF THE FINDINGS

These findings are not consistent with a deleterious effect of marijuana on testicular function. Whether these findings are reflective of the previously described role of the endocannabinoid system in spermatogenesis or a spurious association requires confirmation in further studies.

STUDY FUNDING/COMPETING INTEREST(S)

The project was funded by grants R01ES009718 and P30ES000002 from the National Institute of Environmental Health Sciences (NIEHS). None of the authors has any conflicts of interest to declare.

TRIAL REGISTRATION NUMBER

N/A.

Semen quality of young men in Switzerland: a nationwide cross-sectional population-based study

BACKGROUND

Sperm counts have been steadily decreasing over the past five decades with regional differences in the Western world. The reasons behind these trends are complex, but numerous insights indicate that environmental and lifestyle factors are important players.

OBJECTIVE

To evaluate semen quality and male reproductive health in Switzerland.

MATERIALS AND METHODS

A nationwide cross-sectional study was conducted on 2523 young men coming from all regions of Switzerland, recruited during military conscription. Semen volume, sperm concentration, motility, and morphology were analyzed. Anatomy of the genital area and testicular volume was recorded. Testicular cancer incidence rates in the general population were retrieved from Swiss regional registries.

RESULTS

Median sperm concentration adjusted for period of sexual abstinence was 48 million/mL. Comparing with the 5th percentile of the WHO reference values for fertile men, 17% of men had sperm concentration below 15 million/mL, 25% had less than 40% motile spermatozoa, and 43% had less than 4% normal forms. Disparities in semen quality among geographic regions, urbanization rates, and linguistic areas were limited. A larger proportion of men with poor semen quality had been exposed in utero to maternal smoking. Furthermore, testicular cancer incidence rates in the Swiss general population increased significantly between 1980 and 2014.

DISCUSSION

For the first time, a systematic sampling among young men has confirmed that semen quality is affected on a national level. The median sperm concentration measured is among the lowest observed in Europe. No specific geographical differences could be identified. Further studies are needed to determine to what extent the fertility of Swiss men is compromised and to evaluate the impact of environmental and lifestyle factors.

CONCLUSION

A significant proportion of Swiss young men display suboptimal semen quality with only 38% having sperm concentration, motility, and morphology values that met WHO semen reference criteria.

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

BACKGROUND

Multiple meta-analyses have shown sperm count declines in Western countries spanning eight decades. Secular trends in other parameters remain unclear, as are potential predictors of these trends.

OBJECTIVE

To analyze secular trends in semen quality and to evaluate whether factors previously found to be related to semen quality were responsible for these patterns.

METHODS

This is a prospective study including 936 men of couples seeking infertility treatment who provided 1618 semen samples at a single center (2000-2017). Self-reported demographic, nutritional and reproductive characteristics were collected using standardized questionnaires. Urinary concentrations of bisphenol A, parabens and phthalates were quantified by isotope-dilution tandem mass spectrometry. Semen samples were analyzed for volume, sperm concentration, count, motility and morphology following WHO guidelines. We estimated the differences in semen parameters over time by fitting generalized linear mixed models with random intercepts to account for repeated samples while adjusting for abstinence time. We also adjusted for demographic, nutritional and environmental factors to investigate these as potential predictors of time trends.

RESULTS

Sperm concentration and count declined by 2.62% per year (95% CI -3.84, -1.38) and 3.12% per year (95% CI: -4.42, -1.80), corresponding to an overall decline of 37% and 42%, respectively, between 2000 and 2017. Decreasing trends were also observed for total motility (per year: -0.44 percentage units, 95% CI -0.71, -0.17) and morphologically normal sperm (per year: -0.069 percentage units, 95% CI -0.116, -0.023). These decreases reflected relative percentage declines of 15% and 16% over the 17 year study period, respectively. When reproductive factors were included in the model, the downward trends in sperm concentration and sperm count were attenuated by 29% and 26%, respectively, while the trends in motility and morphology were attenuated by 54% and 53%, respectively. Also, the downward trends in both sperm concentration and sperm morphology over time were attenuated by 19% when including the DEHP and non-DEHP metabolites, respectively.

CONCLUSIONS

Sperm concentration, total count, motility and morphology significantly declined between 2000 and 2017 among subfertile men. These negative trends were attenuated when considering simultaneous changes in reproductive characteristics and urinary phthalates during the course of the study.

Residential distance to major roadways and semen quality, sperm DNA integrity, chromosomal disomy, and serum reproductive hormones among men attending a fertility clinic

OBJECTIVE

We examined associations of residential distance to major roadways, as a proxy for traffic-related air pollution exposures, with sperm characteristics and male reproductive hormones.

DESIGN

The cohort included 797 men recruited from Massachusetts General Hospital Fertility Center between 2000 and 2015 to participate in fertility research studies.

MATERIALS AND METHODS

Men reported their residential addresses at enrollment and provided 1-6 semen samples and a blood sample during follow-up. We estimated the Euclidean distance to major roadways (e.g. interstates and highways: limited access highways, multi-lane highways (not limited access), other numbered routes, and major roads) using information from the Massachusetts Department of Geographic Information Systems. Semen parameters (1238 semen samples), sperm DNA integrity (389 semen samples), chromosomal disomy (101 semen samples), and serum reproductive hormones (405 serum samples) were assessed following standard procedures.

RESULTS

Men in this cohort were primarily Caucasian (86%), not current smokers (92%), with a college or higher education (88%), and had an average age of 36 years and BMI of 27.7 kg/m2. The median (interquartile range) residential distance to a major roadway was 111 (37, 248) meters. Residential proximity to major roadways was not associated with semen parameters, sperm DNA integrity, chromosomal disomy, or serum reproductive hormone concentrations. The adjusted percent change (95% CI) in semen quality parameters associated with a 500 m increase in residential distance to a major roadway was -1.0% (-6.3, 4.5) for semen volume, 4.3% (-5.8, 15.7) for sperm concentration, 3.1% (-7.2, 14.5) for sperm count, 1.1% (-1.2, 3.4) for % total motile sperm, and 0.1% (-0.3, 0.5) for % morphologically normal sperm. Results were consistent when we modeled the semen parameters dichotomized according to WHO 2010 reference values.

CONCLUSION

Residential distance to major roadways, as a proxy for traffic-related air pollution exposure, was not related to sperm characteristics or serum reproductive hormones among men attending a fertility clinic in Massachusetts.

Discrete survival model analysis of a couple's smoking pattern and outcomes of assisted reproduction

Background

Cigarette smoking has been associated with worse infertility treatment outcomes, yet some studies have found null or inconsistent results.

Methods

We followed 225 couples who underwent 354 fresh non-donor assisted reproductive technology (ART) cycles between 2006 and 2014. Smoking history was self-reported at study entry. We evaluated the associations between smoking patterns and ART success using multivariable discrete time Cox proportional hazards models with six time periods: cycle initiation to egg retrieval, retrieval to fertilization, fertilization to embryo transfer (ET), ET to implantation, implantation to clinical pregnancy, and clinical pregnancy to live birth to estimate hazard ratios (HR) and 95% CIs. Time-dependent interactions between smoking intensity and ART time period were used to identify vulnerable periods.

Results

Overall, 26% of women and 32% of men reported ever smoking. The HR of failing in the ART cycle without attaining live birth for male and female ever smokers was elevated, but non-significant, compared to never smokers regardless of intensity (HR = 1.02 and 1.30, respectively). Female ever smokers were more likely to fail prior to oocyte retrieval (HR: 3.37; 95% CI: 1.00, 12.73). Every one cigarette/day increase in smoking intensity for females was associated with a HR of 1.02 of failing ART (95% CI: 0.97, 1.08), regardless of duration or current smoking status. Women with higher smoking intensities were most likely to fail a cycle prior to oocyte retrieval (HR: 1.07; 95% CI: 1.00, 1.16). Among past smokers, every additional year since a man had quit smoking reduced the risk of failing ART by 4% (HR: 0.96; 95% CI: 0.91, 1.00) particularly between clinical pregnancy and live birth (HR: 0.86; 95% CI: 0.76, 0.96).

Conclusions

Female smoking intensity, regardless of current smoking status, is positively associated with the risk of failing ART cycles between initiation and oocyte retrieval. In men who ever smoked, smoking cessation may reduce the probability of failing ART, particularly between clinical pregnancy and live birth.

Trial registration

NCT00011713. Registered: 27 February 2001.

Electronic supplementary material

The online version of this article (doi:10.1186/s40738-017-0032-2) contains supplementary material, which is available to authorized users.

Self-reported mobile phone use and semen parameters among men from a fertility clinic

There is increasing concern that use of mobile phones, a source of low-level radio-frequency electromagnetic fields, may be associated with poor semen quality, but the epidemiologic evidence is limited and conflicting. The relationship between mobile phone use patterns and markers of semen quality was explored in a longitudinal cohort study of 153 men that attended an academic fertility clinic in Boston, Massachusetts. Information on mobile phone use duration, headset or earpiece use, and the body location in which the mobile phone was carried was ascertained via nurse-administered questionnaire. Semen samples (n=350) were collected and analyzed onsite. To account for multiple semen samples per man, linear mixed models with random intercepts were used to investigate the association between mobile phone use and semen parameters. Overall, there was no evidence for a relationship between mobile phone use and semen quality.

Pharmacological investigation of voltage-dependent Ca2+ channels in human ejaculatory sperm in vitro

The types of the voltage-dependent calcium channels (VDCCs) in human ejaculatory sperm and the effects of calcium channel blocker (CCB) on human sperm motility parameters in vitro were investigated. The human sperm motility parameters in vitro in response to the pharmacological agents nifedipine (NIF, inhibitor of L-type VDCC) and co-conotoxin (GVIA, inhibitor of N-type VDCC) were compared and analyzed statistically. The results showed that NIF (1, 5, 10 micromol/L) could not only significantly affect human sperm's shape but also spermatozoa motility after incubated at least 10 min in vitro (P<0.001). GVIA (0.1, 0.5 and 1 micromol/L) could just only significantly affect human sperm's progressive motility (a %+b %) after incubated for 20 min in vitro (P<0.01), but they both could not significantly affect spermic abnormality rate. It is suggested that L-type VDCC, non L-type VDCCs and isoform of L-type VDCC exist in the cell membrane of human sperm solely or together, and they participate in the spermic physiological processes especially the spermic motility.

Pyrethroid insecticide metabolites are associated with serum hormone levels in adult men

Experimental studies have reported that pyrethroid insecticides affect male endocrine and reproductive function, but human data are limited. We recruited 161 men from an infertility clinic between years 2000-2003 and measured serum reproductive and thyroid hormone levels, as well as the pyrethroid metabolites 3-phenoxybenzoic acid (3PBA) and cis- and trans-3-(2,2-dichlorovinyl)-2,2-dimethylcyclopropane carboxylic acid (cis-DCCA and trans-DCCA) in spot urine samples. When adjusting for potential confounders, categories for all three metabolites, as well as their summed values, were positively associated with FSH (all p-values for trend <0.05). Statistically significant or suggestive positive relationships with LH were also found. In addition, cis-DCCA and trans-DCCA were inversely associated with inhibin B (p for trend=0.03 and 0.02, respectively). Finally, there was evidence that trans-DCCA was inversely associated with testosterone and free androgen index (the ratio of testosterone to sex hormone binding globulin; p for trend=0.09 and 0.05, respectively). The observed relationships were consistent with previous findings, but further research is needed for a better understanding of the potential association between pyrethroid insecticides and male reproduction.

Human semen quality and sperm DNA damage in relation to urinary metabolites of pyrethroid insecticides

BACKGROUND

Exposure to synthetic pyrethroid insecticides is widespread, and is expected to increase among the general population due to the need to replace other common insecticides following regulatory use restrictions. On the basis of limited studies, there is animal and human evidence for altered reproductive or endocrine function following pyrethroid exposure.

METHODS

The present study measured urinary pyrethroid metabolites [3-phenoxybenzoic acid (3PBA) and cis- and trans-3-(2,2-dichlorovinyl)-2,2-dimethylcyclopropane carboxylic acid (CDCCA and TDCCA)], semen quality, sperm motion parameters and sperm DNA damage with the neutral comet assay in 207 men recruited from an infertility clinic.

RESULTS

In multivariate analysis, the highest 3PBA quartile was associated with a suggestive 20.2 million sperm/ml reduction (95% confidence interval -37.1 to + 2.6) in sperm concentration compared with men below the 3PBA median. There were significant inverse associations between TDCCA and sperm motility and sperm motion parameters when adjusting for CDCCA and other covariates. The highest TDCCA quartile was associated with a 15.5% decline (95% confidence interval -26.2 to -4.8) in sperm motility compared with men below the median. In multiple logistic analyses, there were dose-dependent increased odds for below reference sperm concentration, motility and morphology in relation to TDCCA. Among the comet assay measures, 3PBA and CDCCA were associated with increased sperm DNA damage, measured as percent DNA in the comet tail.

CONCLUSIONS

We found evidence for reduced semen quality and increased sperm DNA damage in relation to urinary metabolites of pyrethroid insecticides. These findings may be of concern due to increased pyrethroid use and prevalent human exposure.

Serum concentrations of estradiol and free T4 are inversely correlated with sperm DNA damage in men from an infertility clinic

Sperm DNA damage adversely affects male fertility and contributes to poorer embryo development and lower pregnancy rates. Endogenous hormones are critical to spermatogenesis and maintenance of male reproductive function and likely play an important role in human sperm DNA integrity, but this relationship is not fully understood. The present study measured serum hormone levels and sperm DNA damage with the neutral comet assay in 362 male partners of infertile couples. When sperm concentration and other potential confounding variables were included in multiple linear regression, serum estradiol and free T(4) levels were inversely associated with sperm DNA damage. Among other statistically significant associations that were observed, an interquartile range (IQR) increase in estradiol was associated with a 6.3% decline (95% confidence intervals: -9.7%, -2.9%) in comet extent and a 16.2% (-22.4%, -9.2%) decline in the percentage of DNA in the comet tail (Tail%), whereas an IQR increase in free T(4) was associated with a 24.4% (-31.5%, -17.4%) decline in Tail%. Likewise, in multiple logistic regression, men in the highest estradiol quartile had an 81% reduced risk of having a comet extent value in the highest quartile compared with men in the lowest estradiol quartile. Men in the highest free T(4) quartile had 92% decreased odds of being categorized in the highest Tail% quartile compared with men in the lowest free T(4) quartile. These results suggest that estradiol and free T(4) may have a protective effect against sperm DNA damage, but future mechanistic and epidemiologic studies are needed to confirm these findings.

Circulating estradiol in men is inversely related to urinary metabolites of nonpersistent insecticides

BACKGROUND

Estradiol plays an important role in male reproductive health as a germ cell survival factor. Chlorpyrifos and carbaryl, nonpersistent insecticides to which the general population are commonly exposed, were recently shown to inhibit estradiol metabolism in vitro which could lead to altered hormone balance.

METHODS

Subjects (N=322) were the male partners in couples presenting to a Massachusetts infertility clinic from years 2000-2003. 3,5,6-Trichloro-2-pyridinol (TCPY), the major urinary metabolite of chlorpyrifos and chlorpyrifos-methyl, and 1- and 2-naphthol (1N and 2N), urinary metabolites of carbaryl and naphthalene, were measured in a spot urine sample from each subject. Estradiol, sex hormone binding globulin (SHBG), and prolactin were measured in serum collected from subjects during the same clinic visit.

RESULTS

Using multiple linear regression, an interquartile range (IQR) increase in TCPY was associated with a 1.36 pg/mL decline (95% confidence interval=-2.91 to -0.22) in estradiol concentration. When estradiol and TCPY were divided into quintiles, there was a dose-dependent increase in the odds of being in the lowest estradiol quintile with increasing TCPY quintiles.

CONCLUSION

On a population level, these reductions in estradiol levels are of potential public health importance because of widespread exposure to TCPY and its parent insecticides.

Altered semen quality in relation to urinary concentrations of phthalate monoester and oxidative metabolites

BACKGROUND

Phthalates are multifunctional chemicals used in a variety of consumer, medical, and personal care products. Previously, we reported dose-response associations of decreased semen quality with urinary concentrations of monobutyl phthalate (MBP) and monobenzyl (MBzP) phthalate, which are metabolites of dibutyl phthalate and butylbenzyl phthalate, respectively. The present study extends our work in a larger sample of men and includes measurements of di(2-ethylhexyl) phthalate (DEHP) oxidative metabolites.

METHODS

Between January 2000 and May 2004, we recruited 463 male partners of subfertile couples who presented for semen analysis to the Massachusetts General Hospital. Semen parameters were dichotomized based on World Health Organization reference values for sperm concentration (<20 million/mL) and motility (<50% motile) and the Tygerberg Kruger Strict criteria for morphology (<4% normal). The comparison group was men with all 3 semen parameters above the reference values. In a single spot urine sample from each man, phthalate metabolites were measured using solid-phase extraction coupled to high-performance liquid chromatography isotope-dilution tandem mass spectrometry.

RESULTS

There were dose-response relationships of MBP with low sperm concentration (odds ratio per quartile adjusted for age, abstinence time, and smoking status = 1.00, 3.1, 2.5, 3.3; P for trend = 0.04) and motility (1.0, 1.5, 1.5, 1.8; P for trend = 0.04). There was suggestive evidence of an association between the highest MBzP quartile and low sperm concentration (1.00, 1.1, 1.1, 1.9; P for trend = 0.13). There were no relationships of monoethyl phthalate, monomethyl phthalate, and the DEHP metabolites with these semen parameters.

CONCLUSION

The present study confirms previous results on the relationship of altered semen quality with exposure to MBP at general population levels. We did not find associations between semen parameters and 3 DEHP metabolites.

Exposure to Nonpersistent Insecticides and Male Reproductive Hormones

BACKGROUND

Urinary metabolites of several nonpersistent insecticides have been measured in a high percentage of men in the general population, suggesting widespread environmental exposures to these compounds. The present study explored the association of urinary concentrations of 3,5,6-trichloro-2-pyridinol (TCPY), a metabolite of chlorpyrifos and chlorpyrifos-methyl, and 1-naphthol (1N), a metabolite of carbaryl and naphthalene, with serum reproductive hormone levels in adult men.

METHODS

Subjects (n = 268) were the male partners in couples presenting to a Massachusetts infertility clinic in years 2000 through 2003. TCPY and 1N were measured in a spot urine sample from each subject and adjusted for dilution using specific gravity. Reproductive hormones (follicle-stimulating hormone, leuteinizing hormone, inhibin B, testosterone, and sex hormone-binding globulin) were measured in serum collected from subjects during the same clinic visit.

RESULTS

Multiple linear regression models showed an inverse association between TCPY and testosterone concentration. An interquartile range (IQR) increase in TCPY was associated with a decline of 25 ng/dL (95% confidence interval = -40 to -10) in testosterone concentration. The association appeared to be dose-dependent when exposure was divided into quintiles. The highest TCPY quintile was associated with a testosterone decline of 83 ng/dL (-128 to -39) compared with the lowest TCPY quintile. We also found inverse associations between TCPY and free androgen index and between 1N and testosterone, and suggestive inverse associations between TCPY and leuteinizing hormone and between 1N and free androgen index.

CONCLUSION

In adult men, TCPY and 1N were associated with reduced testosterone levels. On a population level, these reductions are of potential public health importance because of widespread exposure to these nonpersistent insecticides.