Shift work and circadian dysregulation of reproduction

Association Between Sleep Quality and Semen Parameters and Reproductive Hormones: A Cross-Sectional Study in Zhejiang, China

BACKGROUND

The effects of sleep duration on semen quality have been documented in many epidemiological studies. However, the association between sleep quality and semen parameters and reproductive hormones is still unclear.

PATIENTS ENROLLMENT AND METHODS

We conducted a cross-sectional study among 970 outpatients from the Reproductive Medicine Center in Zhejiang, China between October 2017 and July 2019. All participants delivered a semen sample, underwent a physical examination, and answered a questionnaire to provide the following information: demographics, life habits, and sleep habits. Sleep quality was measured using the Pittsburgh Sleep Quality Index (PSQI). We first divided the patients into two groups according to sleep quality (good sleep: PQSI < 5 and poor sleep: PSQI ≥ 5). Then, we analyzed routine sperm parameters (semen volume, sperm total motility, progressive motility, sperm concentration, total sperm number, and normal sperm morphology) and reproductive hormones (follicle-stimulating hormone, luteinizing hormone, estrogen, testosterone, and prolactin) of each group. Finally, we used multivariate linear regression analysis and Spearman correlation coefficients to examine the relationship between sleep quality (discrete variable or dichotomous variable) and sperm parameters, reproductive hormones.

RESULTS

A negative correlation was found between the general PSQI scores and several semen parameters: total motility (r= -0.187979, p< 0.001), progressive motility (r= -0.192902, p< 0.001), concentration (r= -0.167063, p< 0.001), total sperm number (r= -0.160008, p< 0.001), and normal sperm morphology (r= -0.124511, p< 0.001). However, there was no significant correlation between the semen volume, all reproductive hormones and the general PSQI scores. After adjusting for confounders, men with poor sleep had lower total motility (β= -9.287; 95% CI, -12.050, -6.523), progressive motility (β= -8.853; 95% CI, -11.526, -6.180), concentration (log scale, β= -0.131; 95% CI, -0.181, -0.082), total sperm number (log scale, β= -0.137; 95% CI, -0.189, -0.084), and normal sperm morphology (β= -1.195; 95% CI, -1.844, -0.547), but semen volume and all reproductive hormones were not markedly altered.

CONCLUSION

Poor sleep quality might be related to impaired semen quality, but we found no evidence that poor sleep quality affects reproductive hormones.

The impact of occupational shift work and working hours during pregnancy on health outcomes: a systematic review and meta-analysis

BACKGROUD

An increasing number of original studies suggest that exposure to shift work and long working hours during pregnancy could be associated with the risk of adverse pregnancy outcomes, but the results remain conflicting and inconclusive.

OBJECTIVE

To examine the influences of shift work and longer working hours during pregnancy on maternal and fetal health outcomes.

DATA SOURCES

Five electronic databases and 3 gray literature sources were searched up to March 15, 2019.

METHODS OF STUDY SELECTION

Studies of all designs (except case studies and reviews) were included, which contained information on the relevant population (women who engaged in paid work during pregnancy); exposure (rotating shift work [shifts change according to a set schedule], fixed night shift [typical working period is between 11:00 pm and 11:00 am] or longer working hours [>40 hours per week]);comparator (fixed day shift [typical working period is between 8:00 am and 6:00 pm] or standard working hours [≤40 hours per week]); and outcomes (preterm delivery, low birthweight [birthweight <2500 g], small for gestational age, miscarriage, gestational hypertension, preeclampsia, intrauterine growth restriction, stillbirth, and gestational diabetes mellitus).

TABULATION, INTEGRATION, AND RESULTS

From 3305 unique citations, 62 observational studies (196,989 women) were included. "Low" to "very low" certainty evidence from these studies revealed that working rotating shifts was associated with an increased odds of preterm delivery (odds ratio, 1.13; 95% confidence interval, 1.00-1.28, I² = 31%), an infant small for gestational age (odds ratio, 1.18, 95% confidence interval, 1.01-1.38, I² = 0%), preeclampsia (odds ratio, 1.75, 95% confidence interval, 1.01-3.01, I² = 75%), and gestational hypertension (odds ratio, 1.19, 95% confidence interval, 1.10-1.29, I² = 0%), compared to those who worked a fixed day shift. Working fixed night shifts was associated with an increased odds of preterm delivery (odds ratio, 1.21; 95% confidence interval, 1.03-1.42; I² = 36%) and miscarriage (odds ratio, 1.23; 95% confidence interval, 1.03-1.47; I² = 37%). Compared with standard hours, working longer hours was associated with an increased odds of miscarriage (odds ratio, 1.38; 95% confidence interval, 1.08-1.77; I² = 73%), preterm delivery (odds ratio, 1.21; 95% confidence interval, 1.11-1.33; I² = 30%), an infant of low birthweight (odds ratio, 1.43; 95% confidence interval, 1.11-1.84; I² = 0%), or an infant small for gestational age (odds ratio, 1.16, 95% confidence interval, 1.00-1.36, I² = 57%). Dose-response analysis showed that women working more than 55.5 hours (vs 40 hours) per week had a 10% increase in the odds of having a preterm delivery.

CONCLUSION

Pregnant women who work rotating shifts, fixed night shifts, or longer hours have an increased risk of adverse pregnancy outcomes.

Impact of circadian rhythms on female reproduction and infertility treatment success

PURPOSE OF REVIEW

In recent years, new studies have investigated the role and influence of sleep on female fertility and early pregnancy outcomes, providing a growing body of knowledge demonstrating how regulation by sleep of hormones are important to reproduction, and how disruptions in sleep, circadian rhythms, and genes regulating circadian rhythmicity can negatively impact fertility and early pregnancy outcomes. This review aims to summarize the most recent research on the relationship among circadian rhythms, fertility, and early pregnancy outcomes in women, and to explore possible fertility interventions.

RECENT FINDINGS

Recent studies have found altered levels of FSH, LH, and prolactin with sleep disturbance or circadian dysrhythmia. Disruption of circadian rhythms in the form of shift work, jet lag, and daylight savings time changes have been associated with poorer fertility and early pregnancy outcomes. Alterations in the expression of circadian rhythm-regulating circadian locomotor output cycles kaput (CLOCK) genes have been associated with decreased fertility and increased rates of miscarriage.

SUMMARY

Overall, undisrupted sleep and circadian rhythmicity appear to optimize fertility and early pregnancy outcomes and may play an important role in the success of fertility treatment.

The influences of sleep duration, chronotype, and nightwork on the ovarian cycle

Despite research indicating that sleep disorders influence reproductive health, the effects of sleep on reproductive hormone concentrations are poorly characterized. We prospectively followed 259 regularly menstruating women across one to two menstrual cycles (the BioCycle Study, 2005-2007), measuring fasting serum hormone concentrations up to eight times per cycle. Women provided information about daily sleep in diaries and chronotype and night/shift work on a baseline questionnaire. We evaluated percent differences in mean hormone concentrations, the magnitude of shifts in the timing and amplitude of hormone peaks, and the risk for sporadic anovulation associated with self-reported sleep patterns and night/shift work. We estimated chronotype scores - categorizing women below and above the interquartile range (IQR) as "morning" and "evening" chronotypes, respectively. For every hour increase in daily sleep duration, mean estradiol concentrations increased by 3.9% (95% confidence interval [CI] 2.0, 5.9%) and luteal phase progesterone by 9.4% (CI 4.0, 15.2%). Receiving less than 7 hours of sleep per day was associated with slightly earlier rises in peak levels for several hormones. Women reporting night/shift work (n = 77) had lower testosterone relative to women employed without night/shift work (percent difference: -9.9%, CI -18.4, -0.4%). Women with morning chronotypes (n = 47) had earlier rises in estradiol during their cycles and potentially an earlier rise in luteinizing hormone. Compared to those who had intermediate chronotypes, women with evening chronotypes (n = 42) had a later luteinizing hormone peak of borderline statistical significance. A reduced risk for sporadic anovulation was suggested, but imprecise, for increasing hours of daily sleep leading up to ovulation (risk ratio 0.79, CI 0.59, 1.06), while an imprecise increased risk was observed for women with morning chronotypes (risk ratio 2.50, CI 0.93, 6.77). Sleep-related hormonal changes may not greatly alter ovarian function in healthy women, but have the potential to influence gynecologic health.

Time-of-day-dependent sensitivity of the reproductive axis to RFamide-related peptide-3 inhibition in female Syrian hamsters

In spontaneously ovulating rodent species, the timing of the luteinising hormone (LH) surge is controlled by the master circadian pacemaker in the suprachiasmatic nucleus (SCN). The SCN initiates the LH surge via the coordinated control of two opposing neuropeptidergic systems that lie upstream of the gonadotrophin-releasing hormone (GnRH) neuronal system: the stimulatory peptide, kisspeptin, and the inhibitory peptide, RFamide-related peptide-3 (RFRP-3; the mammalian orthologue of avian gonadotrophin-inhibitory hormone [GnIH]). We have previously shown that the GnRH system exhibits time-dependent sensitivity to kisspeptin stimulation, further contributing to the precise timing of the LH surge. To examine whether this time-dependent sensitivity of the GnRH system is unique to kisspeptin or a more common mechanism of regulatory control, we explored daily changes in the response of the GnRH system to RFRP-3 inhibition. Female Syrian hamsters were ovariectomised to eliminate oestradiol (E₂ )-negative-feedback and RFRP-3 or saline was centrally administered in the morning or late afternoon. LH concentrations and Lhβ mRNA expression did not differ between morning RFRP-3-and saline-treated groups, although they were markedly suppressed by RFRP-3 administration in the afternoon. However, RFRP-3 inhibition of circulating LH at the time of the surge does not appear to act via the GnRH system because no differences in medial preoptic area Gnrh or RFRP-3 receptor Gpr147 mRNA expression were observed. Rather, RFRP-3 suppressed arcuate nucleus Kiss1 mRNA expression and potentially impacted pituitary gonadotrophs directly. Taken together, these findings reveal time-dependent responsiveness of the reproductive axis to RFRP-3 inhibition, possibly via variation in the sensitivity of arcuate nucleus kisspeptin neurones to this neuropeptide.

The usefulness of melatonin in the field of obstetrics and gynecology

Disorders of the female reproductive system, including those associated with hormone regulation, fertility rate and fetal health, are issues of great concern worldwide. More recently, melatonin supplementation has been suggested as a therapeutic approach in gynecological practice. In both animal models and in women, melatonin supplementation suggests a therapeutic and preventative potential, effects attributed mainly to its antioxidant properties and action as hormone modulator. The aim of this literature review is to further investigate the evidence available on the effects of melatonin supplementation in animal and human studies, focusing on its potential application to gynecology. Melatonin-containing supplements are easily found in online and high street retailers, and despite its supplementation deemed to be relatively safe, no consensus has been reached on effective dosage and supplementation period. Short term supplementation studies, of up to six months, suggest that a daily posology of 2-18 mg of melatonin may have the potential to improve fertility rate, oocyte quality, maturation and number of embryos. However, the evidence available so far on the effects of melatonin supplementation covering gestational age and gestational outcomes is very scarce. Clinical trials and longer-term supplementation studies are required to assess any clinical outcome associated with melatonin supplementation in the field of gynecology.

Pregnancy Induces an Earlier Chronotype in Both Mice and Women

Daily rhythms generated by endogenous circadian mechanisms and synchronized to the light-dark cycle have been implicated in the timing of birth in a wide variety of species. Although chronodisruption (e.g., shift work or clock gene mutations) is associated with poor reproductive outcomes, little is known about circadian timing during pregnancy. This study tested whether daily rhythms change during full-term pregnancies in mice and women. We compared running wheel activity continuously in both nonpregnant ( n = 14) and pregnant ( n = 13) 12- to 24-week-old C57BL/6NJ mice. We also monitored wrist actigraphy in women ( N = 39) for 2 weeks before conception and then throughout pregnancy and measured daily times of sleep onset. We found that on the third day of pregnancy, mice shift their activity to an earlier time compared with nonpregnant dams. Their time of daily activity onset was maximally advanced by almost 4 h around day 7 of pregnancy and then shifted back to the nonpregnant state approximately 1 week before delivery. Mice also showed reduced levels of locomotor activity during their last week of pregnancy. Similarly, in women, the timing of sleep onset was earlier during the first and second trimesters (gestational weeks 4-13 and 14-27) than before pregnancy and returned to the prepregnant state during the third trimester (weeks 28 until delivery). Women also showed reduced levels of locomotor activity throughout pregnancy. These results indicate that pregnancy induces changes in daily rhythms, altering both time of onset and amount of activity. These changes are conserved between mice and women.

Time Restriction of Food Intake During the Circadian Cycle Is a Possible Regulator of Reproductive Function in Postadolescent Female Rats

BACKGROUND

We previously reported that skipping breakfast is associated with menstrual disorders of female college students during postadolescent maturation.

OBJECTIVE

In this study, we investigated the effects of meal timing during circadian cycle on the ovarian function using young female rats.

METHODS

Considering that rats are nocturnally active, 8-wk-old female Wistar rats were classified into 3 groups: fed during the daytime only (nonactive phase), night-time only (active phase), or control group I (without time or calorie restriction, free access to a standard caloric diet, 20.0% protein, 62.9% carbohydrate, and 7.0% fat, 3.95 kcal/g) for 4 wk. The changes in body weight and frequency of ovulation in each group were evaluated by a weight scale and a vaginal smear, respectively. At the end of the period of dietary restriction, ovaries were removed, and the numbers of growing follicles (mean diameter >250 µm) and corpora lutea (>600 µm) were examined using hematoxylin-eosin-stained tissue sections. In addition, 8-wk-old female rats were fed only during the night-time for 4 wk under a 20%-reduced food supply of the control group II (without any restriction).

RESULTS

In the daytime-fed group, the frequency and number of ovulations were significantly decreased compared with those in the control group I (P < 0.05), with a reduced body weight gain concomitant with about 20% of reduction in the daily food intake. In contrast, in the night-time-fed group, even when a 20% reduction in the daily food intake was loaded, their estrus cyclicity did not change despite significant reductions in weight gain and food intake compared with control group II.

CONCLUSION

These findings indicate that restricting food intake to the inactive phase impairs ovarian function in postadolescent female rats, suggesting that the timing of food intake during circadian cycle is one of the crucial factors interfering with the reproductive function.

Shift Work Disrupts Circadian Regulation of the Transcriptome in Hospital Nurses

Circadian misalignment between sleep and behavioral/feeding rhythms is thought to lead to various health impairments in shift workers. Therefore, we investigated how shift work leads to genome-wide circadian dysregulation in hospital nurses. Female nurses from the University of Alabama at Birmingham (UAB) Hospital working night shift ( n = 9; 29.6 ± 11.4 y) and day shift ( n = 8; 34.9 ± 9.4 y) participated in a 9-day study measuring locomotor activity and core body temperature (CBT) continuously. Additionally, cortisol and melatonin were assayed and peripheral blood mononuclear cells (PBMCs) were harvested for RNA extraction every 3 h on a day off from work. We saw phase desynchrony of core body temperature, peak cortisol, and dim light melatonin onset in individual night-shift subjects compared with day-shift subjects. This variability was evident even though day- and night-shift nurses had similar sleep timing and scheduled meal times on days off. Surprisingly, the phase and rhythmicity of the expression of the clock gene, PER1, in PBMCs were similar for day-shift and night-shift subjects. Genome-wide microarray analysis of PBMCs from a subset of nurses revealed distinct gene expression patterns between night-shift and day-shift subjects. Enrichment analysis showed that day-shift subjects expressed pathways involved in generic transcription and regulation of signal transduction, whereas night-shift subjects expressed pathways such as RNA polymerase I promoter opening, the matrisome, and endocytosis. In addition, there was large variability in the number of rhythmic transcripts among subjects, regardless of shift type. Interestingly, the amplitude of the CBT rhythm appeared to be more consistent with the number of cycling transcripts for each of the 6 subjects than was melatonin rhythm. In summary, we show that shift-work patterns affect circadian alignment and gene expression in PBMCs.

Fetal Programming of Renal Dysfunction and High Blood Pressure by Chronodisruption

Adverse prenatal conditions are known to impose significant trade-offs impinging on health and disease balance during adult life. Among several deleterious factors associated with complicated pregnancy, alteration of the gestational photoperiod remains largely unknown. Previously, we reported that prenatal manipulation of the photoperiod has adverse effects on the mother, fetus, and adult offspring; including cardiac hypertrophy. Here, we investigated whether chronic photoperiod shifting (CPS) during gestation may program adult renal function and blood pressure regulation. To this end, pregnant rats were subjected to CPS throughout pregnancy to evaluate the renal effects on the fetus and adult offspring. In the kidney at 18 days of gestation, both clock and clock-controlled gene expression did not display a daily pattern, although there were recurrent weaves of transcriptional activity along the 24 h in the control group. Using DNA microarray, significant differential expression was found for 1,703 transcripts in CPS relative to control fetal kidney (835 up-regulated and 868 down-regulated). Functional genomics assessment revealed alteration of diverse gene networks in the CPS fetal kidney, including regulation of transcription, aldosterone-regulated Na+ reabsorption and connective tissue differentiation. In adult offspring at 90 days of age, circulating proinflammatory cytokines IL-1β and IL-6 were increased under CPS conditions. In these individuals, CPS did not modify kidney clock gene expression but had effects on different genes with specific functions in the nephron. Next, we evaluated several renal markers and the response of blood pressure to 4%NaCl in the diet for 4 weeks (i.e., at 150 days of age). CPS animals displayed elevated systolic blood pressure in basal conditions that remained elevated in response to 4%NaCl, relative to control conditions. At this age, CPS modified the expression of Nhe3, Ncc, Atp1a1, Nr3c1 (glucocorticoid receptor), and Nr3c2 (mineralocorticoid receptor); while Nkcc, Col3A1, and Opn were modified in the CPS 4%+NaCl group. Furthermore, CPS decreased protein expression of Kallikrein and COX-2, both involved in sodium handling. In conclusion, gestational chronodisruption programs kidney dysfunction at different levels, conceivably underlying the prehypertensive phenotype observed in the adult CPS offspring.

The Influence of Light Exposure in Ambiance during Pregnancy in Maternal and Fetal Outcomes: An Experimental Study

OBJECTIVE

 The aim of this study is to evaluate whether exposure to different environmental lighting conditions affects the reproductive parameters of pregnant mice and the development of their offspring.

METHODS

 Fifteen pregnant albino mice were divided into three groups: light/dark, light, and dark. The animals were euthanized on day 18 of pregnancy following the Brazilian Good Practice Guide for Euthanasia of Animals. Maternal and fetal specimens were measured and collected for histological evaluation. Analysis of variance (ANOVA) test was used for comparison of the groups considering p ≤ 0.05 to be statistically significant.

RESULTS

 There was no significant difference in the maternal variables between the three groups. Regarding fetal variables, significant differences were observed in the anthropometric measures between the groups exposed to different environmental lighting conditions, with the highest mean values in the light group. The histological evaluation showed the same structural pattern of the placenta in all groups, which was within the normal range. However, evaluation of the uterus revealed a discrete to moderate number of endometrial glands in the light/dark and light groups, which were poorly developed in most animals. In the fetuses, pulmonary analysis revealed morphological features consistent with the transition from the canalicular to the saccular phase in all groups.

CONCLUSION

 Exposure to different environmental lighting conditions had no influence on the reproductive parameters of female mice, while the offspring of mothers exposed to light for 24 hours exhibited better morphometric features.

Circadian Control of Neuroendocrine Function: Implications for Health and Disease

The circadian timing system orchestrates daily rhythms in physiology and behavior via the suprachiasmatic nucleus (SCN), the master brain clock. Because endocrine secretions have far-reaching influence on the brain and periphery, circadian regulation of hormones is essential for normal functioning and disruptions to circadian timing (e.g., irregular sleep patterns, limited exposure to sunlight, jet lag, nighttime light exposure) have detrimental health consequences. Herein, we provide an overview of circadian timing in three major endocrine axes, the hypothalamo-pituitary-gonadal (HPG), hypothalamo-pituitary-adrenal (HPA) and hypothalamo-pituitary-thyroid (HPT) axes, and then consider the negative health consequences of circadian disruptions in each of these systems. For example, disruptions to HPG axis circadian timing lead to a host of negative reproductive outcomes such as irregular menstrual cycles, low sperm density and increased rates of miscarriages and infertility. Dysregulation of HPA axis timing is associated with obesity and metabolic disease, whereas disruptions to the HPT axis are associated with dysregulated metabolic gene rhythms in the heart. Together, this overview underscores the significance of circadian endocrine rhythms in normal health and disease prevention.

Impact of Shift Work on the Circadian Timing System and Health in Women

Women who do shift work are a sizable part of the workforce. Shift workers experience circadian misalignment due to shifted sleep periods, with potentially far-reaching health consequences, including elevated risk of sleep disturbances, metabolic disorders, and cancer. This review provides an overview of the circadian timing system and presents the sex differences that can be observed in the functioning of this system, which may account for the lower tolerance to shift work for women compared with men. Recent epidemiologic findings on female-specific health consequences of shift work are discussed.

The menstrual cycle associated with insomnia in newly employed nurses performing shift work: a 12-month follow-up study

PURPOSE

This study aimed to investigate whether insomnia among newly-employed shift-working nurses is associated with menstrual cycle irregularity.

METHODS

We followed 287 nurses employed between 2015 and 2016 for 12 months. An Insomnia Severity Index (ISI) was completed to determine levels of insomnia 6 months after beginning work. At baseline and at 12-month follow-up, menstrual cycle information was obtained using clinical interviews. We analyzed baseline data separately by prevalence (participants with menstrual irregularity, n = 287) and incidence (participants with no reported menstrual irregularity, n = 238).

RESULTS

In a multivariate logistic regression analysis, including age, body mass index, and physical activity, insomnia was associated with a 2.05-fold increase in the odds of newly developing menstrual cycle irregularity compared with not having insomnia [odds ratio (OR) 2.05, 95% confidence interval (CI) 1.12-3.77]. Insomnia was associated with a 3.05-fold increase in the prevalence of menstrual cycle irregularity compared with not having insomnia (OR 3.05, 95% CI 1.81-5.13). As the ISI score increased, both the incidence and prevalence odds of menstrual cycle irregularity tended to increase.

CONCLUSIONS

Insomnia can induce menstrual cycle irregularity among nurses working shifts, and insomnia may have an important role in the pathway from shift work to menstrual dysfunction, aside from the possible effects of circadian rhythm disruption.

Integration of Circadian and Metabolic Control of Reproductive Function

Optimal fertility in humans and animals relies on the availability of sufficient metabolic fuels, information about which is communicated to the brain via levels of the hormones leptin and insulin. The circadian clock system is also critical; this input is especially evident in the precise timing of the female-specific surge of GnRH and LH secretion that triggers ovulation the next day. Chronodisruption and metabolic imbalance can both impair reproductive activity, and these two disruptions exacerbate each other, such that they often occur simultaneously. Kisspeptin neurons located in the anteroventral periventricular nucleus of the hypothalamus are able to integrate both circadian and metabolic afferent inputs and use this information to modulate the timing and magnitude of the preovulatory GnRH/LH surge. In an environment in which exposure to high caloric diets and chronodisruptors such as artificial night lighting, shift work, and transmeridian travel have become the norm, the implications of these factors for couples struggling to conceive deserve closer attention and more public education.

Regulation of the MAPK signaling pathway by miR-421-5p in rats under light pollution

The present study aimed to explore the difference in the expression profiles of ovarian microRNA sequences in rats in a light pollution environment and rats in a normal light environment. Rats in the control group were exposed to 12‑h light/dark cycles, while rats in the model group were continuously exposed to 24‑h light. The ovaries were extracted from the two groups of rats, and Illumina HiSeq 2500 high‑throughput sequencing technology was used to detect the differences in microRNA (miRNA) expression among the two groups. Fluorescence quantitative reverse transcription‑polymerase chain reaction was used to verify the differential expression of miRNA. The present study was designed to experimentally validate the interaction between miR‑421‑5p and mitogen‑activated protein kinase (MAPK) 7 by using the dual‑luciferase reporter system, and to explore the expression of proteins in the MAPK signaling pathway with a lentiviral vector‑mediated small hairpin RNA interference against microRNA‑421‑5p. The expression of 45 miRNAs was significantly different. In total, 13 miRNAs were upregulated, of which 5 miRNA sequences were known and 8 were predicted. Furthermore, 32 miRNAs were downregulated, of which 11 miRNA sequences were known and 21 were predicted. The results of the luciferase reporter assay confirmed the targeting association between miR‑421‑5p and MAPK7. The expression levels of MAPK and genes in its downstream signaling pathways, including c‑Fos, CREB and c‑Myc, were downregulated when miR‑421‑5p was overexpressed and upregulated when miR‑421‑5p was silenced. The differential expression of miRNAs may serve an important role in the development of the ovary in a light pollution environment. miR‑421‑5p may regulate ovarian growth and development by targeting the MAPK signaling pathway in light polluted rat ovaries.

Circadian disruption of food availability significantly reduces reproductive success in mice

Circadian disruptions impair reproductive health in human populations and in animal models. We tested the hypothesis that mistimed food, a common disruptive feature of shift work, impairs reproductive success in mice. Male and female mPer2^Luc mice on a C57BL/6 background were fed during the light or dark phase in two experiments. Food-induced internal misalignment of the liver clock was verified by in vivo bioluminescence in anesthetized mice in both experiments. In Experiment 1, food-restricted pairs were monitored for litters for 18 weeks. In the light-fed group, birth of the first litter was significantly delayed, and total reproductive output was significantly reduced by 38%. In Experiment 2, estrous cycling was monitored for 3 weeks, and then after pairing, copulatory plugs, pregnancy, litter sizes, and uterine implantation sites were measured. Fewer light-fed females birthed litters (25% versus 73%). This was attributable to a difference in behavior as mating success was significantly reduced in light-fed mice: 42% were observed with a copulatory plug compared to 82% for dark-fed mice. The proportion of mice displaying uterine implantation sites was the same as the proportion observed with copulatory plugs, suggesting no deficit in initiating pregnancy after mating. Estrous cycling and pregnancy maintenance did not differ between the groups. We conclude that mistimed feeding inhibits reproduction in mice by reducing successful mating behavior.

Training the Circadian Clock, Clocking the Drugs, and Drugging the Clock to Prevent, Manage, and Treat Chronic Diseases

Daily rhythms in behavior, physiology, and metabolism are an integral part of homeostasis. These rhythms emerge from interactions between endogenous circadian clocks and ambient light-dark cycles, sleep-activity cycles, and eating-fasting cycles. Nearly the entire primate genome shows daily rhythms in expression in tissue- and locus-specific manners. These molecular rhythms modulate several key aspects of cellular and tissue function with profound implications in public health, disease prevention, and disease management. In modern societies light at night disrupts circadian rhythms, leading to further disruption of sleep-activity and eating-fasting cycles. While acute circadian disruption may cause transient discomfort or exacerbate chronic diseases, chronic circadian disruption can enhance risks for numerous diseases. The molecular understanding of circadian rhythms is opening new therapeutic frontiers placing the circadian clock in a central role. Here, we review recent advancements on how to enhance our circadian clock through behavioral interventions, timing of drug administration, and pharmacological targeting of circadian clock components that are already providing new preventive and therapeutic strategies for several diseases, including metabolic syndrome and cancer.

The Effect of Shift Work on Urogenital Disease: a Systematic Review

PURPOSE OF REVIEW

Non-standard shift work schedules negatively impact the overall health of shift workers, and several studies have shown that shift work, specifically, is detrimental to urogenital health. The aims of this study are to systematically review the literature and determine the effect of shift work on the outcomes of hypogonadism, male infertility, lower urinary tract symptoms, and urogenital cancers.

RECENT FINDINGS

Recent evidence supports associations between non-standard shift work and an increase in the frequency of prostate cancer and the severity of erectile dysfunction, lower urinary tract symptoms, and hypogonadal symptoms, as well as worsening of semen parameters and fertility. These associations are strengthened by the presence of shift work sleep disorder (SWSD) which affects up to 20% of shift workers. No studies have assessed the impact of shift work on the frequency or severity of nephrolithiasis, interstitial cystitis, pelvic pain, prostatitis, or urinary tract infections. Non-standard shift work has been associated with a variety of negative health outcomes and urologic complications, especially with concurrent shift work sleep disorder. Recognition of these elevated risks among shift workers can aid in more effective screening for urologic conditions.

Genetic variation in the CLOCK gene is associated with idiopathic recurrent spontaneous abortion

Physiological studies in animals and human support an important role of circadian system in reproduction. The aim of this study was to investigate the potential association of CLOCK gene polymorphisms with idiopathic recurrent spontaneous abortion (IRSA). We performed a case-control study. The study group consisted of 268 women with a history of three or more idiopathic recurrent spontaneous abortions and 284 women with at least two live births and no history of pathologic pregnancies all from Slovenia and Serbia. Two SNPs in the CLOCK gene were chosen and genotyped. The results showed a statistically significant difference in genotype distribution between the two groups in the CLOCK gene for rs6850524 and rs11932595. Our analysis showed that G allele under dominant model (GG+GC/CC) for rs6850524 (p = 2∙10-4, OR = 2.28, 95%CI = 1.46-3.56) as well as G allele under dominant model (GA+AA/AA) for rs11932595 (p = 0.04, OR = 1.47, 95%CI = 1.01-2.04) might be risk factors against IRSA. Our data suggest that genetic variability in the CLOCK gene is associated with IRSA warranting further confirmation and mechanistic investigations.

The Relationship Between Shift Work and Men's Health

BACKGROUND

More than 21 million Americans and nearly 20% of the U.S. workforce are shift workers. Non-standard shift work, defined as work that falls outside of 6 am-6 pm, can lead to poor diet, exercise, and sleep habits that lead to decreased productivity, increased workplace accidents, and a variety of negative health outcomes.

AIM

To investigate the associations between shift work exposure and chronic medical conditions such as metabolic syndromes, cardiovascular disease, gastrointestinal disturbances, and depression as well as urologic complications including hypogonadism, male infertility, lower urinary tract symptoms, and prostate cancer with a focus on the effects of shift work sleep disorder (SWSD) on the severity of these negative health outcomes.

METHODS

We reviewed the literature examining effects of shift work and SWSD on general and urologic health.

OUTCOMES

We produced a summary of effects of shift work on health with focus on the increased risk of negative health outcomes in non-standard shift workers, particularly those with SWSD, when compared to daytime workers or workers without SWSD.

RESULTS

Studies have associated non-standard shift work schedules and poor health outcomes, including increased risks of diabetes mellitus, dyslipidemia, hypertension, heart disease, peptic ulcer disease, and depression, in shift workers. However, few studies have focused on the role that shift work plays in men's urologic health. Current evidence supports associations between non-standard shift work and increased hypogonadal symptoms, poor semen parameters, decreased fertility, lower urinary tract symptoms, and prostate cancer. These associations are strengthened by the presence of SWSD, which affects up to 20% of shift workers. Unfortunately, interventions, such as planned naps, timed light exposure, melatonin, and sedative hypnotics, aimed at alleviating excessive nighttime sleepiness and daytime insomnia in non-standard shift workers experiencing SWSD, are limited and lack strong evidence to support their efficacy.

CONCLUSIONS

Non-standard shift work has been associated with a variety of negative health outcomes and urologic complications, especially with concurrent SWSD. Recognition of these increased risks among shift workers can potentially aid in more effective screening of chronic health and urologic conditions. Non-pharmacologic treatment of SWSD focuses on behavioral therapy and sleep hygiene while melatonin, hypnotics, and stimulants are used to alleviate insomnia and excessive sleepiness of SWSD. Further research into both pharmacologic and non-pharmacologic therapies for SWSD is needed to establish more definitive guidelines in the treatment of SWSD in order to increase productivity, minimize workplace accidents, and improve quality of life for shift workers. Deng N, Kohn TP, Lipshultz LI, et al. The Relationship Between Shift Work and Men's Health. Sex Med Rev 2018;6:446-456.

Circadian Rhythms and Clock Genes in Reproduction: Insights From Behavior and the Female Rabbit's Brain

Clock gene oscillations are necessary for a successful pregnancy and parturition, but little is known about their function during lactation, a period demanding from the mother multiple physiological and behavioral adaptations to fulfill the requirements of the offspring. First, we will focus on circadian rhythms and clock genes in reproductive tissues mainly in rodents. Disruption of circadian rhythms or proper rhythmic oscillations of clock genes provoke reproductive problems, as found in clock gene knockout mice. Then, we will focus mainly on the rabbit doe as this mammal nurses the young just once a day with circadian periodicity. This daily event synchronizes the behavior and the activity of specific brain regions critical for reproductive neuroendocrinology and maternal behavior, like the preoptic area. This region shows strong rhythms of the PER1 protein (product of the Per1 clock gene) associated with circadian nursing. Additionally, neuroendocrine cells related to milk production and ejections are also synchronized to daily nursing. A threshold of suckling is necessary to entrain once a day nursing; this process is independent of milk output as even virgin does (behaving maternally following anosmia) can display circadian nursing behavior. A timing motivational mechanism may regulate such behavior as mesolimbic dopaminergic cells are entrained by daily nursing. Finally, we will explore about the clinical importance of circadian rhythms. Indeed, women in chronic shift-work schedules show problems in their menstrual cycles and pregnancies and also have a high risk of preterm delivery, making this an important field of translational research.

Correlates of poor mental health in early pregnancy in obese European women

BACKGROUND

Depression during pregnancy is associated with higher maternal morbidity and mortality, and subsequent possible adverse effects on the cognitive, emotional and behavioral development of the child. The aim of the study was to identify maternal characteristics associated with poor mental health, in a group of overweight/obese pregnant women in nine European countries, and thus, to contribute to better recognition and intervention for maternal depression.

METHODS

In this cross-sectional observational study, baseline data from early pregnancy (< 20 weeks) of the DALI (Vitamin D and Lifestyle Intervention for gestational diabetes mellitus prevention) study were analyzed. Maternal mental health was assessed with the World Health Organization Well-Being Index (WHO-5). Women were classified as having a low (WHO-5 ≤ 50) or high wellbeing.

RESULTS

A total of 735 pregnant women were included. The prevalence of having a low wellbeing was 27.2%, 95% CI [24.0, 30.4]. Multivariate analysis showed independent associations between low wellbeing and European ethnicity, OR = .44, 95% CI [.25, .77], shift work, OR = 1.81, 95% CI [1.11, 2.93], insufficient sleep, OR = 3.30, 95% CI [1.96, 5.55], self-efficacy, OR = .95, 95% CI [.92, .98], social support, OR = .94, 95% CI [.90, .99], and pregnancy-related worries (socioeconomic: OR = 1.08, 95% CI [1.02, 1.15]; health: OR = 1.06, 95% CI [1.01, 1.11]; relationship: OR = 1.17, 95% CI [1.05, 1.31]).

CONCLUSIONS

Mental health problems are common in European overweight/obese pregnant women. The identified correlates might help in early recognition and subsequent treatment of poor mental health problems during pregnancy. This is important to reduce the unfavorable effects of poor mental health on pregnancy outcomes.

TRIAL REGISTRATION

ISRCTN70595832 , 02.12.2011.

Sleep duration is associated with sperm chromatin integrity among young men in Chongqing, China

This study explores whether sleep duration is associated with sperm chromatin integrity. To do so, we conducted a three-phase panel study of 796 male volunteers from colleges in Chongqing (China) from 2013 to 2015. Sleep duration was measured using a modified Munich Chronotype Questionnaire. Sperm DNA integrity was examined via Sperm Chromatin Structure Assay and Comet assay. Setting 7-7.5 h day^-1 of sleep duration as a reference, either longer or shorter sleep duration was associated negatively with high DNA stainability (HDS) (P = 0.009), which reflected the immaturity of sperm chromatin. The volunteers with > 9.0 h day^-1 sleep and those with ≤ 6.5 h day^-1 sleep had 40.7 and 30.3% lower HDS than did volunteers with 7-7.5 h day^-1 sleep. No association was found between sleep duration and DNA fragmentation index or Comet assay parameters. This study suggests that sleep duration is associated with sperm chromatin integrity. Further studies are required to validate these findings and investigate the mechanism underlying this association.

Daily rhythms count for female fertility

Female ovulation depends on a surge in circulating luteinizing hormone (LH) which occurs at the end of the resting period and requests high circulating estradiol. This fine tuning involves both an estradiol feedback as an indicator of oocyte maturation, and the master circadian clock of the suprachiasmatic nuclei as an indicator of the time of the day. This review describes the mechanisms through which daily time cues are conveyed to reproductive hypothalamic neurons to time the pre-ovulatory surge. In female rodents, neurotransmitters released by the suprachiasmatic nuclei activate the stimulatory kisspeptin neurons and reduce the inhibitory RFRP neurons precisely at the end of the afternoon of proestrus to allow a full surge in LH secretion. From these findings, the impact of circadian disruptions (during shift or night work) on female reproductive performance and fertility should now being investigated in both animal models and humans.

BMAL1 facilitates trophoblast migration and invasion via SP1-DNMT1/DAB2IP pathway in recurrent spontaneous abortion

The underlying mechanism about rhythms and epigenetics leading to aberrant trophoblast migration and invasion in recurrent spontaneous abortion (RSA) remains unknown. Brain and muscle ARNT-like protein 1 (BMAL1) is considered as a crucial role in fertility, and polymorphism of BMAL1 gene has been reported to be associated with risk of miscarriage. However, the functional role of BMAL1 in RSA is not fully understood. Previous study shows the descended expression of DNA 5′-cytosine-methyltransferases 1 (DNMT1) in the villous of early pregnancy loss. Thus, understanding of the regulation of DNMT1 expression may be of significance for the elucidation of the process of RSA. Using HTR-8/SVneo and JEG-3 cell lines, we certified the induction of specificity protein 1 (SP1) to DNMT1 and DAB2 interaction protein (DAB2IP), respectively, both of which further activated matrix metallo-proteinase 2/9 (MMP2/9), bringing out changes in trophoblast migration and invasion. Notably, BMAL1 functioned as a positive upstream factor of SP1 only in HTR-8/SVneo cells but not in JEG-3 cells, inducing SP1-DNMT1/DAB2IP pathway and facilitating migration and invasion of trophoblasts. In addition, progesterone might restore the down-regulation of BMAL1 and downstream pathway in a dose-dependent manner. Last but not least, the decreased abundance of BMAL1 was correlated positively with that of SP1, DNMT1, DAB2IP, MMP2 and MMP9 in human villous specimens of RSA. Our results demonstrate that the induction of BMAL1 to SP1 contributes to the expression of DNMT1 and DAB2IP, respectively, activating trophoblast migration and invasion. The deregulation of the BMAL1-mediated pathway in RSA can be rescued by progesterone.

Maternal and Early-Life Circadian Disruption Have Long-Lasting Negative Consequences on Offspring Development and Adult Behavior in Mice

Modern life involves chronic circadian disruption through artificial light and these disruptions are associated with numerous mental and physical health maladies. Because the developing nervous system is particularly vulnerable to perturbation, we hypothesized that early-life circadian disruption would negatively impact offspring development and adult function. Pregnant mice were subjected to chronic circadian disruption from the time of uterine implantation through weaning. To dissociate in utero from postnatal effects, a subset of litters was cross-fostered at birth from disrupted dams to control dams and vice versa. Postnatal circadian disruption was associated with reduced adult body mass, social avoidance, and hyperactivity. In utero disruption resulted in more pronounced social avoidance and hyperactivity, phenotypes not abrogated by cross-fostering to control mothers. To examine whether circadian disruption affects development by acting as an early life stressor, we examined birthweight, litter size, maternal cannibalism, and epigenetic modifications. None of these variables differed between control and disrupted dams, or resembled patterns seen following early-life stress. Our findings indicate that developmental chronic circadian disruption permanently affects somatic and behavioral development in a stage-of-life-dependent manner, independent of early life stress mechanisms, underscoring the importance of temporal structure during development, both in utero and early postnatal life.

The Circadian System: A Regulatory Feedback Network of Periphery and Brain

Circadian rhythms are generated by the autonomous circadian clock, the suprachiasmatic nucleus (SCN), and clock genes that are present in all tissues. The SCN times these peripheral clocks, as well as behavioral and physiological processes. Recent studies show that frequent violations of conditions set by our biological clock, such as shift work, jet lag, sleep deprivation, or simply eating at the wrong time of the day, may have deleterious effects on health. This infringement, also known as circadian desynchronization, is associated with chronic diseases like diabetes, hypertension, cancer, and psychiatric disorders. In this review, we will evaluate evidence that these diseases stem from the need of the SCN for peripheral feedback to fine-tune its output and adjust physiological processes to the requirements of the moment. This feedback can vary from neuronal or hormonal signals from the liver to changes in blood pressure. Desynchronization renders the circadian network dysfunctional, resulting in a breakdown of many functions driven by the SCN, disrupting core clock rhythms in the periphery and disorganizing cellular processes that are normally driven by the synchrony between behavior and peripheral signals with neuronal and humoral output of the hypothalamus. Consequently, we propose that the loss of synchrony between the different elements of this circadian network as may occur during shiftwork and jet lag is the reason for the occurrence of health problems.

Occupational factors and markers of ovarian reserve and response among women at a fertility centre

OBJECTIVES

To explore whether work schedules and physically demanding work were associated with markers of ovarian reserve and response.

METHODS

This analysis included women (n=473 and n=313 for ovarian reserve and ovarian response analysis, respectively) enrolled in a prospective cohort study of couples presenting to an academic fertility centre (2004-2015). Information on occupational factors was collected on a take-home questionnaire, and reproductive outcomes were abstracted from electronic medical records. Generalised linear models and generalised linear mixed models were used to evaluate the associations.

RESULTS

Women who reported lifting or moving heavy objects at work had 1.0 fewer total oocytes (p=0.08), 1.4 fewer mature oocytes (p=0.007) and 0.7 fewer antral follicles (p=0.06) compared with women who reported never lifting or moving heavy objects at work. The inverse association between heavy lifting and oocyte yield was stronger in women >37 years and with a Body Mass Index ≥25 kg/m². Women who worked evening/night/rotating shifts had 2.3 (p<0.001) fewer mature oocytes, on average, compared with women who worked day-only shifts. None of the occupational exposures were associated with day 3 follicle-stimulating hormone or peak oestradiol levels.

CONCLUSIONS

Women working non-daytime shifts and those with physically demanding jobs had fewer mature oocytes retrieved after controlled ovarian hyperstimulation. Our results provide insight into possible mechanisms linking these occupational exposures with decreased fecundity.

Impact of daylight savings time on spontaneous pregnancy loss in in vitro fertilization patients

Transition into daylight savings time (DST) has studied negative impacts on health, but little is known regarding impact on fertility. This retrospective cohort study evaluates DST impact on pregnancy and pregnancy loss rates in 1,654 autologous in vitro fertilization cycles (2009 to 2012). Study groups were identified based on the relationship of DST to embryo transfer. Pregnancy rates were similar in Spring and Fall (41.4%, 42.2%). Pregnancy loss rates were also comparable between Spring and Fall (15.5%, 17.1%), but rates of loss were significantly higher in Spring when DST occurred after embryo transfer (24.3%). Loss was marked in patients with a history of prior spontaneous pregnancy loss (60.5%).

Loss of Bmal1 decreases oocyte fertilization, early embryo development and implantation potential in female mice

Biological clock genes expressed in reproductive tissues play important roles in maintaining the normal functions of reproductive system. However, disruption of female circadian rhythm on oocyte fertilization, preimplantation embryo development and blastocyst implantation potential is still unclear. In this study, ovulation, in vivo and in vitro oocyte fertilization, embryo development, implantation and intracellular reactive oxygen species (ROS) levels in ovary and oviduct were studied in female Bmal1+/+ and Bmal1-/- mice. The number of naturally ovulated oocyte in Bmal1-/- mice decreased (5.2 ± 0.8 vs 7.8 ± 0.8, P < 0.001), with an increasing abnormal oocyte ratio (20.4 ± 3.5 vs 11.7 ± 2.0%, P = 0.001) after superovulation. Significantly lower fertilization rate and obtained blastocyst number were observed in Bmal1-/- female mice either mated with wild-type in vivo or fertilized by sperm from wild-type male mice in vitro (all P < 0.05). Interestingly, in vitro fertilization rate of oocytes derived from Bmal1-/- increased significantly compared with in vivo study (P < 0.01). After transferring blastocysts derived from Bmal1+/+ and Bmal1-/- female mice to pseudopregnant mice, the implantation sites of the latter decreased 5 days later (8.0 ± 0.8 vs 5.3 ± 1.0, P = 0.005). The intracellular ROS levels in the ovary on proestrus day and in the oviduct on metestrus day increased significantly in Bmal1-/- mice compared with that of Bmal1+/+ mice. Deletion of the core biological clock gene Bmal1 significantly decreases oocyte fertilization rate, early embryo development and implantation potential in female mice, and these may be possibly caused by excess ROS levels generated in ovary and oviduct.

The Circadian Timing System and Environmental Circadian Disruption: From Follicles to Fertility

The internal or circadian timing system is deeply integrated in female reproductive physiology. Considerable details of rheostatic timing function in the neuroendocrine control of pituitary hormone secretion, adenohypophyseal hormone gene expression and secretion, gonadal steroid hormone biosynthesis and secretion, ovulation, implantation, and parturition have been reported. The molecular clock, an autonomous feedback loop oscillator of interacting transcriptional regulators, dictates the timing and amplitude of gene expression in each tissue of the female hypothalamic-pituitary-gonadal (HPG) axis. Although multiple targets of the molecular clock have been identified, many associated with critical physiological functions in the HPG axis, the full extent of clock-driven gene expression and physiology in this critical system remains unknown. Environmental circadian disruption (ECD), the disturbance of temporal relationships within and between internal clocks (brain and periphery), and external timing cues (eg, light, nutrients, social cues) due to rotating/night shift work or transmeridian travel have been linked to reproductive dysfunction and subfertility. Moreover, ECD resulting from exposure to endocrine disrupting chemicals, environmental toxins, and/or irregular hormone levels during sexual development can also reduce fertility. Thus, perturbations that disturb clock function at the molecular, cellular or systemic level correlate with significant declines in female reproductive function. Here we briefly review the evidence for molecular clock function in each tissue of the female HPG axis (GnRH neuron, pituitary, uterus, oviduct, and ovary), describe the human epidemiological and animal data supporting the negative effects of ECD on fertility, and explore the potential for novel chronotherapeutics in women's health and fertility.

Association between the CLOCK gene 3111 T > C polymorphism and an irregular menstrual cycle in Korean adolescents

The menstrual cycle is an example of a human infradian rhythm, but an altered sleep-wake cycle or a disrupted circadian rhythm can change the regularity of the menstrual cycle. In this study, we investigated whether an irregular menstrual cycle is associated with polymorphisms in the CLOCK (3111T > C) and/or PER3 (variable number tandem repeat, VNTR) genes, which are known to have an impact on the circadian rhythm. One hundred ninety-seven postmenarchal, adolescent girls from two girls' high schools in Seoul, Korea, were studied. All participants were requested to complete the Perceived Stress Scale (PSS), the State-Trait Anxiety Inventory (STAI), and the Beck Depression Inventory (BDI) to assess the emotional distress that might cause menstrual irregularity. Every participant donated a blood sample from which DNA was extracted and genotyped for the CLOCK 3111T > C and PER3 VNTR polymorphisms. A significant association was found between the CLOCK 3111T > C genotype and irregular menstrual cycles. Subjects with the 3111T > C genotype had a high risk of an irregular menstrual cycle compared with 3111T/T homozygous subjects (odds ratio [OR] = 2.88; 95% confidence interval [CI]: 1.26-6.55). When multivariate logistic regression analysis was performed to adjust for age, PSS, STAI, BDI and BMI, subjects with the 3111T > C polymorphism showed a significantly increased OR for irregular menstrual cycles (OR = 3.09; 95% CI: 1.32-7.21). There was no significant association between the PER3 VNTR polymorphism and the irregularity of the menstrual cycle (p > 0.05). The results of this study suggest that the CLOCK 3111T > C polymorphism could be an independent risk factor for irregular menstrual cycles, irrespective of psychological distress and endocrine or metabolic conditions, and could be used as a molecular marker for gynecological studies on this aspect.

Rotating shift work and menstrual characteristics in a cohort of Chinese nurses

Background

Shift work disrupts the circadian rhythm and may cause menstruation disorders. This study assessed the impact of shift work on menstrual cycle in a population of Chinese nurses.

Methods

Questionnaires on menstrual characteristics and shift schedules were sent to female nurses of the First Affiliated Hospital of Sun Yat-sen University (FAHSYSU) and Guanghua Hospital of Stomatology (GHHS), affiliated to Sun Yat-sen University. Part I was a cross-sectional study and included 139 nurses in GHHS who had regular 8:00–17:30 working (non-shift group), and 334 nurses from FAHSYSU who worked shifts, a response rate of 67.5 % and 59.6 %, respectively (age ≤ 50 years). Menstrual patterns were compared and age-adjusted relative risks of shift work were analyzed. Part II was a nested case–control study. Cases were nurses in Part I who had regular cycle with mean cycle length (MCL) of 25–31 days and but at least 3 days variation in MCL after starting shift work (n = 45). Controls consisted of 67 nurses with matching shift patterns and age, but no MCL changes. A control non-shift age-matched group consisted of 30 GHHS nurses with no MCL changes. A follow-up second questionnaire was sent 2 years later.

Results

In Part I, the shift group had a significantly higher proportion of nurses with menstrual cycle irregularity. The proportion of nurses with a cycle of 25–31 days decreased from 81.7 to 67.8 % after changing to shift work. Logistic regression analysis showed that night shift frequency was the only risk factor associated with cycle shortening. After adjusting for age, MCL was shorter when night work was performed > 7 times per month. In Part II, the mean change in MCL in the case group, including prolongation or shortening, was 4.115 ± 2.084 days after shift working. In the 2 years’ follow-up, the MCL of the study group did not recover to the original length.

Conclusions

Rotating shift work can increase the prevalence of menstrual cycle irregularity. Night shift frequency was the only risk factor associated with cycle reduced. Changes in MCL did not show recovery over a follow-up period of 2 years.

Electronic supplementary material

The online version of this article (doi:10.1186/s12905-016-0301-y) contains supplementary material, which is available to authorized users.

Work schedule and physical factors in relation to fecundity in nurses

OBJECTIVES

To evaluate the association of work schedule and physical factors with fecundity.

METHODS

Women currently employed outside the home and trying to get pregnant (n=1739) in the Nurses' Health Study 3 cohort (2010-2014) were included in this analysis. Work schedule and physical labour were self-reported on the baseline questionnaire, and every 6 months thereafter the women reported the duration of their ongoing pregnancy attempt. Multivariable accelerated failure time models were used to estimate time ratios (TR) and 95% CIs.

RESULTS

Among the 1739 women (median age=33 years, 93% Caucasian) the estimated proportions of women not pregnant after 12 and 24 months were 16% and 5%, respectively. None of the various shift work patterns were associated with duration of pregnancy attempt (as a surrogate for fecundity). However, women working >40 h/week had a 20% (95% CI 7 to 35%) longer median duration of pregnancy attempt compared to women working 21-40 h/week (p-trend=0.005). Women whose work entailed heavy lifting or moving (ie, 25+ pounds) >15 times/day also had a longer median duration of pregnancy attempt (adjusted TR=1.49; 95% CI 1.20 to 1.85) compared to women who never lifted or moved heavy loads (p-trend=0.002). The association between heavy moving and lifting and duration of pregnancy attempt was more pronounced among overweight or obese women (body mass index, BMI<25: TR=1.17; 95% CI 0.88 to 1.56; BMI≥25: TR=2.03, 95% CI 1.48 to 2.79; p-interaction=0.007).

CONCLUSIONS

Working greater than 40 h per week and greater frequency of lifting or moving a heavy load were associated with reduced fecundity in a cohort of nurses planning pregnancy.

Effect of arousing stimuli on circulating corticosterone and the circadian rhythms of luteinizing hormone (LH) surges and locomotor activity in estradiol-treated ovariectomized (ovx+EB) Syrian hamsters

In most proestrous hamsters, novel wheel exposure phase advances activity rhythms and blocks the preovulatory LH surge, which occurs 2h earlier the next day. Because wheel immobilization does not prevent these effects we hypothesized that arousal alone blocks and phase advances the LH surge. Ovariectomized (ovx) hamsters received a jugular vein cannula and estradiol benzoate (EB) or vehicle was injected sc. The next day (Day 1), at zeitgeber time (ZT) 4-5 (ZT 12 = lights off), after obtaining a blood sample, each hamster was exposed to constant darkness (DD), and either remained in her home cage or was transferred to a new cage and exposed to a running wheel or a 2-hour arousal paradigm. Blood samples were obtained in dim red light and activity was recorded hourly until ~ZT 10-11 on Days 1 and 2. For the next 1-2 weeks, activity was monitored in DD. Plasma LH and corticosterone were assessed by RIA. Novel wheel exposure or arousal at ZT 4 greatly attenuated the Day 1 LH surge in ovx+EB hamsters, and phase advanced the Day 2 LH surge by about 2h. In proestrous hamsters, novel wheel exposure led to a prolonged (>2h) increase in corticosterone levels only when LH surges were blocked. Phase advances in activity rhythms were enhanced by estradiol and arousal. The results suggest that estradiol modulates the effectiveness of non-photic stimuli. The role of the increased activity of the hypothalamic-pituitary-adrenal axis associated with novel wheel-induced attenuation of LH surges in ovx+EB hamsters remains to be determined.

A Multi-Oscillatory Circadian System Times Female Reproduction

Rhythms in female reproduction are critical to insure that timing of ovulation coincides with oocyte maturation and optimal sexual arousal. This fine tuning of female reproduction involves both the estradiol feedback as an indicator of oocyte maturation, and the master circadian clock of the suprachiasmatic nuclei (SCN) as an indicator of the time of the day. Herein, we are providing an overview of the state of knowledge regarding the differential inhibitory and stimulatory effects of estradiol at different stages of the reproductive axis, and the mechanisms through which the two main neurotransmitters of the SCN, arginine vasopressin, and vasoactive intestinal peptide, convey daily time cues to the reproductive axis. In addition, we will report the most recent findings on the putative functions of peripheral clocks located throughout the reproductive axis [kisspeptin (Kp) neurons, gonadotropin-releasing hormone neurons, gonadotropic cells, the ovary, and the uterus]. This review will point to the critical position of the Kp neurons of the anteroventral periventricular nucleus, which integrate both the stimulatory estradiol signal, and the daily arginine vasopressinergic signal, while displaying a circadian clock. Finally, given the critical role of the light/dark cycle in the synchronization of female reproduction, we will discuss the impact of circadian disruptions observed during shift-work conditions on female reproductive performance and fertility in both animal model and humans.

The impact of rotating night shifts on the breast milk collection volume among employed breastfeeding mothers

OBJECTIVES

The health benefits of breastfeeding are widely recognized. The World Health Organization recommends exclusive breastfeeding for six months after birth and for two years or longer together with nutritionally adequate complementary foods. To respond to the needs of industry, employed breastfeeding mothers must adapt to the rotating night shift (RNS). However, the RNS is associated with a higher risk of health problems in career women. We investigated the relationship between the RNS and breast milk volume.

METHODS

Mothers who used a breastfeeding room while working at a technology company in Taiwan voluntarily participated in this study from March 1 through April 30, 2013. We compared two groups: breastfeeding mothers on (RNS(+)) and not on a RNS (RNS(-)) to determine independent predictors for breast milk volume. We analyzed data from 109 participants: RNS(+) group n=56; RNS(-) group n=53.

RESULTS

There was no significant difference in daily milk collection volume between the groups. Daily milk collection frequency and exclusive breastfeeding were independent predictors for a daily breast milk collection volume >350 ml.

CONCLUSIONS

The RNS may not affect the breast milk volume. This result may help the government and employers make policies more appropriate for supporting employed breastfeeding mothers.

Loss of BMAL1 in ovarian steroidogenic cells results in implantation failure in female mice

The circadian clock plays a significant role in many aspects of female reproductive biology, including estrous cycling, ovulation, embryonic implantation, onset of puberty, and parturition. In an effort to link cell-specific circadian clocks to their specific roles in female reproduction, we used the promoter that controls expression of Steroidogenic Factor-1 (SF1) to drive Cre-recombinase-mediated deletion of the brain muscle arnt-like 1 (Bmal1) gene, known to encode an essential component of the circadian clock (SF1-Bmal1(-/-)). The resultant SF1-Bmal1(-/-) females display embryonic implantation failure, which is rescued by progesterone supplementation, or bilateral or unilateral transplantation of wild-type ovaries into SF1-Bmal1(-/-) dams. The observation that the central clock, and many other peripheral clocks, are fully functional in this model allows the assignment of the implantation phenotype to the clock in ovarian steroidogenic cells and distinguishes it from more general circadian related systemic pathology (e.g., early onset arthropathy, premature aging, ovulation, late onset of puberty, and abnormal estrous cycle). Our ovarian transcriptome analysis reveals that deletion of ovarian Bmal1 disrupts expression of transcripts associated with the circadian machinery and also genes critical for regulation of progesterone production, such as steroidogenic acute regulatory factor (Star). Overall, these data provide a powerful model to probe the interlocking and synergistic network of the circadian clock and reproductive systems.

Circadian clock control of endocrine factors

Organisms experience dramatic fluctuations in demands and stresses over the course of the day. In order to maintain biological processes within physiological boundaries, mechanisms have evolved for anticipation of, and adaptation to, these daily fluctuations. Endocrine factors have an integral role in homeostasis. Not only do circulating levels of various endocrine factors oscillate over the 24 h period, but so too does responsiveness of target tissues to these signals or stimuli. Emerging evidence suggests that these daily endocrine oscillations do not occur solely in response to behavioural fluctuations associated with sleep-wake and feeding-fasting cycles, but are orchestrated by an intrinsic timekeeping mechanism known as the circadian clock. Disruption of circadian clocks by genetic and/or environmental factors seems to precipitate numerous common disorders, including the metabolic syndrome and cancer. Collectively, these observations suggest that strategies designed to realign normal circadian rhythmicities hold potential for the treatment of various endocrine-related disorders.

Day-night contrast as source of health for the human circadian system

Modern societies are characterized by a 24/7 lifestyle (LS) with no environmental differences between day and night, resulting in weak zeitgebers (weak day light, absence of darkness during night, constant environmental temperature, sedentary LS and frequent snacking), and as a consequence, in an impaired circadian system (CS) through a process known as chronodisruption. Both weak zeitgebers and CS impairment are related to human pathologies (certain cancers, metabolic syndrome and affective and cognitive disorders), but little is known about how to chronoenhance the CS. The aim of this work is to propose practical strategies for chronoenhancement, based on accentuating the day/night contrast. For this, 131 young subjects were recruited, and their wrist temperature (WT), activity, body position, light exposure, environmental temperature and sleep were recorded under free-living conditions for 1 week. Subjects with high contrast (HC) and low contrast (LC) for each variable were selected to analyze the HC effect in activity, body position, environmental temperature, light exposure and sleep would have on WT. We found that HC showed better rhythms than LC for every variable except sleep. Subjects with HC and LC for WT also demonstrated differences in LS, where HC subjects had a slightly advanced night phase onset and a general increase in day/night contrast. In addition, theoretical high day/night contrast calculated using mathematical models suggests an improvement by means of LS contrast. Finally, some individuals classified as belonging to the HC group in terms of WT when they are exposed to the LS characteristic of the LC group, while others exhibit WT arrhythmicity despite their good LS habits, revealing two different WT components: an exogenous component modified by LS and another endogenous component that is refractory to it. Therefore, intensifying day/night contrast in subject's LS has proven to be a feasible measure to chronoenhance the CS.