Public health implications of altered puberty timing

Neuroendocrine pathways mediating nutritional acceleration of puberty: insights from ruminant models

The pubertal process is characterized by an activation of physiological events within the hypothalamic-adenohypophyseal-gonadal axis which culminate in reproductive competence. Excessive weight gain and adiposity during the juvenile period is associated with accelerated onset of puberty in females. The mechanisms and pathways by which excess energy balance advances puberty are unclear, but appear to involve an early escape from estradiol negative feedback and early initiation of high-frequency episodic gonadotropin-releasing hormone (GnRH) secretion. Hypothalamic neurons, particularly neuropeptide Y and proopiomelanocortin neurons are likely important components of the pathway sensing and transmitting metabolic information to the control of GnRH secretion. Kisspeptin neurons may also have a role as effector neurons integrating metabolic and gonadal steroid feedback effects on GnRH secretion at the time of puberty. Recent studies indicate that leptin-responsive neurons within the ventral premammillary nucleus play a critical role in pubertal progression and challenge the relevance of kisspeptin neurons in this process. Nevertheless, the nutritional control of puberty is likely to involve an integration of major sensor and effector pathways that interact with modulatory circuitries for a fine control of GnRH neuron function. In this review, observations made in ruminant species are emphasized for a comparative perspective.

Mendelian Randomisation Study of Childhood BMI and Early Menarche

To infer the causal association between childhood BMI and age at menarche, we performed a mendelian randomisation analysis using twelve established "BMI-increasing" genetic variants as an instrumental variable (IV) for higher BMI. In 8,156 women of European descent from the EPIC-Norfolk cohort, height was measured at age 39-77 years; age at menarche was self-recalled, as was body weight at age 20 years, and BMI at 20 was calculated as a proxy for childhood BMI. DNA was genotyped for twelve BMI-associated common variants (in/near FTO, MC4R, TMEM18, GNPDA2, KCTD15, NEGR1, BDNF, ETV5, MTCH2, SEC16B, FAIM2 and SH2B1), and for each individual a "BMI-increasing-allele-score" was calculated by summing the number of BMI-increasing alleles across all 12 loci. Using this BMI-increasing-allele-score as an instrumental variable for BMI, each 1 kg/m(2) increase in childhood BMI was predicted to result in a 6.5% (95% CI: 4.6-8.5%) higher absolute risk of early menarche (before age 12 years). While mendelian randomisation analysis is dependent on a number of assumptions, our findings support a causal effect of BMI on early menarche and suggests that increasing prevalence of childhood obesity will lead to similar trends in the prevalence of early menarche.

Exposure to polyfluoroalkyl chemicals during pregnancy is not associated with offspring age at menarche in a contemporary British cohort

INTRODUCTION

Polyfluoroalkyl chemicals (PFCs) are commercially synthesized chemicals used in consumer products. Exposure to certain PFCs is widespread, and some PFCs may act as endocrine disruptors. We used data from the Avon Longitudinal Study of Parents and Children (ALSPAC) in the United Kingdom to conduct a nested case-control study examining the association between age at menarche, and exposure to PFCs during pregnancy.

METHODS

Cases were selected from female offspring in the ALSPAC who reported menarche before the age of 11.5 years (n = 218), and controls were a random sample of remaining girls (n = 230). Serum samples taken from the girls' mothers during pregnancy (1991-1992) were analyzed using on-line solid-phase extraction coupled to isotope dilution high-performance liquid chromatography-tandem mass spectrometry for 8 PFCs. Logistic regression was used to determine association between maternal serum PFC concentrations, and odds of earlier age at menarche.

RESULTS

PFOS and PFOA were the predominant PFCs (median serum concentrations of 19.8 ng/mL and 3.7 ng/mL). All but one PFC were detectable in most samples. Total PFC concentration varied by number of births (inverse association with birth order; p-value < 0.0001) and race of the child (higher among whites; p-value = 0.03). The serum concentrations of carboxylates were associated with increased odds of earlier age at menarche; concentrations of perfluorooctane sulfonamide, the sulfonamide esters and sulfonates were all associated with decreased odds of earlier age at menarche. However, all confidence intervals included the null value of 1.0.

CONCLUSIONS

ALSPAC study participants had nearly ubiquitous exposure to most PFCs examined, but PFC exposure did not appear to be associated with altered age at menarche of their offspring.

Obesity and the pubertal transition in girls and boys

Childhood obesity has become a major health concern in recent decades, especially with regard to metabolic abnormalities that impart a high risk for future cardiovascular disease. Recent data suggest that excess adiposity during childhood may influence pubertal development as well. In particular, excess adiposity during childhood may advance puberty in girls and delay puberty in boys. Obesity in peripubertal girls may also be associated with hyperandrogenemia and a high risk of adolescent polycystic ovary syndrome. How obesity may perturb various hormonal aspects of pubertal development remains unclear, but potential mechanisms are discussed herein. Insulin resistance and compensatory hyperinsulinemia may represent a common thread contributing to many of the pubertal changes reported to occur with childhood obesity. Our understanding of obesity's impact on pubertal development is in its infancy, and more research into pathophysiological mechanisms and longer-term sequelae is important.

Association between lead and cadmium and reproductive hormones in peripubertal U.S. girls

BACKGROUND

Lead (Pb) and cadmium (Cd) are known reproductive toxicants thought to disrupt hormone production throughout sensitive developmental windows, although this has not been previously examined in nationally representative peripubertal children.

OBJECTIVES

We examined the association between blood Pb and urinary Cd concentrations and the reproductive hormones inhibin B and luteinizing hormone (LH) in girls 6-11 years of age who participated in the cross-sectional Third National Health and Nutrition Examination Survey (NHANES III) (1988-1994).

METHODS

Pb (micrograms per deciliter) was measured in whole blood, and Cd was measured in urine (nanograms per milliliter). Inhibin B (picograms per milliliter) and LH (milli-International units per milliliter) were measured in residual sera for 705 girls. Survey logistic regression was used to estimate associations with pubertal onset based on inhibin B concentration > 35 pg/mL or LH concentration > 0.4 mIU/mL, and multinomial logistic regression was used to estimate the association between Pb and increasing categories of hormone concentrations.

RESULTS

High Pb (≥ 5 µg/dL) was inversely associated with inhibin B > 35 pg/mL [odds ratio (OR) = 0.26; 95% confidence interval (CI), 0.11-0.60; compared with Pb < 1 µg/dL]. At 10 and 11 years of age, girls with low Pb (< 1 µg/dL) had significantly higher inhibin B than did girls with moderate (1-4.99 µg/dL) or high Pb (≥ 5 µg/dL). In the subsample of 260 girls with levels of inhibin B above the level of detection and using survey regression modeling, inhibin B levels were lower among girls with both high Pb and high Cd (ß= -0.52; 95% CI, -0.09 to -1.04) than among girls with high Pb alone (ß= -0.35; 95% CI, -0.13 to -0.57), relative to girls with low Pb and low Cd.

CONCLUSIONS

Higher Pb was inversely associated with inhibin B, a marker of follicular development, and estimated effects suggestive of pubertal delays appeared to be stronger in the context of higher Cd concentrations. These data underscore the importance of Pb and Cd as reproductive toxicants for young girls.

Pubertal assessment method and baseline characteristics in a mixed longitudinal study of girls

OBJECTIVES

The objective of this study was to describe the assessment methods and maturation status for a multisite cohort of girls at baseline recruitment and at ages 7 and 8 years.

METHODS

The method for pubertal maturation staging was developed collaboratively across 3 sites. Girls at ages 6 to 8 years were recruited at 3 sites: East Harlem, New York; greater Cincinnati metropolitan area; and San Francisco Bay area, California. Baseline characteristics were obtained through interviews with caregivers and anthropometric measurements by trained examiners; breast stage 2 was defined as onset of pubertal maturation. The kappa statistic was used to evaluate agreement between master trainers and examiners. Logistic regression models were used to identify factors that are associated with pubertal maturation and linear regression models to examine factors that are associated with height velocity.

RESULTS

The baseline cohort included 1239 girls. The proportion of girls who had attained breast stage 2 varied by age, race/ethnicity, BMI percentile, and site. At 7 years, 10.4% of white, 23.4% of black non-Hispanic, and 14.9% of Hispanic girls had attained breast stage>or=2; at 8 years, 18.3%, 42.9%, and 30.9%, respectively, had attained breast stage>or=2. The prime determinant of height velocity was pubertal status.

CONCLUSIONS

In this multisite study, there was substantial agreement regarding pubertal staging between examiners across sites. The proportion of girls who had breast development at ages 7 and 8 years, particularly among white girls, is greater than that reported from studies of girls who were born 10 to 30 years earlier.

Progression through puberty in girls enrolled in a contemporary British cohort

PURPOSE

Patterns of pubertal development reflect underlying endocrine function and exposures, and could affect future health outcomes. We used data from a longitudinal cohort to describe factors associated with breast and pubic hair stage and estimate average duration of puberty.

METHODS

Data from the Avon Longitudinal Study of Parents and Children were used to describe timing and duration of pubertal development in girls. Self-reported Tanner stage of breast and pubic hair and menarche status were collected from ages 8-14 through mailed questionnaires. Factors associated with breast and pubic hair stage were identified using ordinal probit models. Age at entry into breast and pubic hair stages, and duration of puberty were estimated using interval-censored parametric survival analysis.

RESULTS

Among the 3,938 participants, being overweight or obese, of non-white race, being the firstborn, and younger maternal age at menarche were associated with more advanced breast and pubic hair stages. Having an overweight or obese mother was associated with more advanced breast stages. Time spent in breast stages 2 and 3 was longer (1.5 years) than time spent in pubic hair stages 2 and 3 (1 year). The average age at menarche was 12.9 (95% CI, 12.8-12.9) years, and average duration of puberty (time from initiation of puberty to menarche) was 2.7 years.

CONCLUSIONS

Girls in Avon Longitudinal Study of Parents and Children had a slightly longer duration of puberty compared to an earlier British cohort study. Various maternal and child characteristics were associated with breast and pubic hair stage, including both child and maternal body mass.

Role of prenatal characteristics and early growth on pubertal attainment of British girls

OBJECTIVES

The objective of this study was to explore the influence of maternal prenatal characteristics and behaviors and of weight and BMI gain during early childhood on the timing of various puberty outcomes in girls who were enrolled in the Avon Longitudinal Study of Parents and Children.

METHODS

Repeated self-assessments of pubertal development were obtained from approximately 4000 girls between the ages of 8 and 14. Data on prenatal characteristics and weight at birth and 2, 9, and 20 months of age were obtained from questionnaires, birth records, and clinic visits. Infants' weights were converted to weight-for-age and BMI SD scores (SDSs; z scores), and change values were obtained for the 0- to 20-month and other intervals within that age range. We used parametric survival models to estimate associations with age of entry into Tanner stages of breast and pubic hair and menarche.

RESULTS

Maternal initiation of menarche at age<12, smoking during pregnancy, and primiparity were associated with earlier puberty. A 1-unit increase in the weight SDS change values for the 0- to 20-month age interval was associated with earlier ages of entry into pubertal outcomes (0.19-0.31 years). Increases in the BMI SDS change values were also associated with earlier entry into pubertal outcomes (0.07-0.11 years).

CONCLUSIONS

Many of the maternal prenatal characteristics and weight and BMI gain during infancy seemed to have similar influences across different puberty outcomes. Either such early factors have comparable influences on each of the hormonal processes involved in puberty, or processes are linked and awakening of 1 aspect triggers the others.

Early age at menarche, lung function, and adult asthma

RATIONALE

hormonal and metabolic status appears to influence lung health in women, and there are findings suggesting that early menarche may be related to asthma, cardiovascular disease, diabetes, and breast cancer.

OBJECTIVES

this study investigates whether age at menarche is related to adult lung function and asthma.

METHODS

among participants in the European Community Respiratory Health Survey II, 3,354 women aged 27-57 years from random population samples in 21 centers responded to a questionnaire concerning women's health (1998-2002). Of these women, 2,873 had lung function measurements, 2,136 had measurements of bronchial hyperreactivity, and 2,743 had IgE measurements. Logistic, linear, and negative binomial regression analyses included adjustment for age, height, body mass index, education, smoking, family size, and center.

MEASUREMENTS AND MAIN RESULTS

FEV(1) and FVC were lower and asthma was more common in women with early menarche. Women reporting menarche at age 10 years or less, as compared with women with menarche at age 13 years (reference category), had lower FEV(1) (adjusted difference, -113 ml; 95% confidence interval [CI], -196 to -33 ml) and FVC (-126 ml; 95% CI, -223 to -28 ml); also lower FEV(1) expressed as a percentage of the predicted value (-3.28%; 95% CI, -6.25 to -0.30%) and FVC expressed as a percentage of the predicted value (-3.63%; 95% CI, -6.64 to -0.62%). Women with early menarche more often had asthma symptoms (odds ratio, 1.80; 95% CI, 1.09-2.97), asthma with bronchial hyperreactivity (odds ratio, 2.79; 95% CI, 1.06-7.34), and higher asthma symptom score (mean ratio, 1.58; 95% CI, 1.12-2.21).

CONCLUSIONS

women with early menarche had lower lung function and more asthma in adulthood. This supports a role for metabolic and hormonal factors in women's respiratory health.

Pubertal development of the first cohort of young adults conceived by in vitro fertilization in the United States

OBJECTIVE

To characterize pubertal development of the first generation of young adults born as a result of in vitro fertilization (IVF). Demographic, clinical, and body size characteristics were examined regarding developmental milestones.

DESIGN

Cross-sectional.

SETTING

Academic center.

PATIENT(S)

Young adults (18-26 years) conceived by IVF (no gamete/embryo manipulation) 1981-1990.

INTERVENTION(S)

Self-administered questionnaire.

MAIN OUTCOME MEASURE(S)

Age at puberty onset, body size.

RESULT(S)

Of 560 eligible young adults, 173 completed the survey (response rate 30.9%). We analyzed data on 166 respondents (71 male and 95 female). No cases of delayed or precocious puberty were observed in the study sample. As expected, age at puberty onset was significantly higher among male subjects (12.3 years) compared with female subjects (11.5 years). A few developmental milestones were predicted by maternal age and infertility diagnoses. For both genders, a direct association was noted between age at puberty onset and height achieved in young adulthood. Structural equation models suggested an inverse relationship of female gender with age at puberty onset and body mass index.

CONCLUSION(S)

In vitro fertilization-conceived young adults did not exhibit pubertal abnormalities. Female gender and age at puberty onset independently predicted body mass index of IVF offspring in young adulthood.

Timing of sexual maturation and women's evaluation of men

Many antecedents and consequences of an accelerated sexual maturation are associated with negative experiences with the opposite sex. Here we show a connection between menarcheal age, a salient sign of female sexual maturation, and the implicit attitude toward men in later adulthood. In Study 1, earlier age at first menstruation was associated with automatic negative evaluations of male faces but not female ones. Study 2 revealed a relationship between early age of menarche and an implicit association between the concepts male and danger. In Study 3, the earlier the menarche, the larger was the estimated egocentric distance of virtual male voices and the shorter the estimated distance of female voices. These results, obtained about a decade after onset of menstruation, suggest that apparently subtle differences in the onset of sexual maturation may have long-lasting implications for intersexual relationships.

Longitudinal development of secondary sexual characteristics in girls and boys between ages 91/2 and 151/2 years

OBJECTIVES

To identify ages when adolescents were in sexual maturity stages 2 through 5; to explain the relations between breast (girls), genital (boys), and pubic hair (girls and boys) development between ages 9(1/2) and 15(1/2) years; and to evaluate synchrony of pubertal development across characteristics.

DESIGN

Annual pubertal assessments.

SETTING

Ten locations in the United States.

PARTICIPANTS

A total of 859 adolescents (427 boys [49.7%] and 432 girls [50.3%]; 737 white [85.8%] and 122 black [14.2%]).

MAIN OUTCOME MEASURES

Changes in the 5 stages of breast, genital, and pubic hair development.

RESULTS

Girls were in breast maturity stages 2 and 3 earlier than comparable pubic hair stages. Although breast development in girls started earlier than pubic hair development, girls completed breast and pubic hair development at approximately the same age. Black girls were in all stages of breast and pubic hair development earlier than white girls. Boys were in stages 2, 3, 4, and 5 of genital development before the comparable pubic hair stage. In boys, genital development started earlier than pubic hair development, but pubic hair development was completed in less time. Black boys were in genital and pubic hair development about 7 months earlier than white boys. Black and white boys completed genital development in approximately 4(1/2) years, but black boys took approximately 6 months longer than white boys to complete pubic hair development. At stage 2, for 66.2% of girls, breast development preceded their pubic hair development; for 91.1% of boys, genital development preceded their pubic hair development.

CONCLUSIONS

The results of this study are useful in understanding normative variation in the timing and change in the development of secondary sexual characteristics at puberty. They will help identify adolescents with atypical changes in sexual maturation and unusual progression of sexual maturation and growth disorders.

Natural mixtures of persistent organic pollutants (POP) increase weight gain, advance puberty, and induce changes in gene expression associated with steroid hormones and obesity in female zebrafish

In the present study, developmental and reproductive effects of lifelong exposure to environmental relevant concentrations of two natural mixtures of persistent organic pollutants (POP) were investigated using classical and molecular methods in a controlled zebrafish model. The mixtures used were extracted from burbot (Lota lota) liver originating from freshwater systems in Norway: one mixture with high levels and one mixture with background levels of polybrominated diphenyl ethers (PBDE), polychlorinated biphenyls (PCB), and dichlorodiphenyltrichloroethane metabolites (DDT). The concentration of POP measured in the zebrafish ranged from levels detected in wild fish from Lake Mjøsa to concentrations reported in human and wildlife populations, indicating that the experimental fish were exposed to concentrations comparable with wild fish. Phenotypic effects observed in both exposure groups included earlier onset of puberty, increased male/female sex ratio, and differences in body weight at 5 mo of age. Interestingly, genome-wide transcription profiling showed changes in regulation of genes involved in endocrine signaling and growth. The transcriptomics changes include key regulator genes for steroid hormone functions (ncoa3), and growth (c/ebp, ncoa3). The effects observed in the experimental zebrafish model raise the question whether chemical pollution represents a risk to reproductive health of wild fish inhabitating the freshwater system.

Bisphenol-A and disparities in birth outcomes: a review and directions for future research

Racial disparities in pregnancy outcome in the United States are significant, persistent and costly, but the causes are poorly understood. We propose that disproportionate exposure of African-American women to environmental endocrine disrupting compounds (EDCs) may contribute to birth outcome disparities. Marked racial segregation, as well as health behaviors associated with poverty could result in differences in exposure to particular EDCs. One EDC that has aroused concern in recent years is bisphenol-A (BPA), a widely used industrial plasticizer with known estrogenic properties. Published studies indicate that excessive BPA exposure is associated with reduced fetal survival, as well as reductions in maternal weight and fetal body weight. Related findings include adverse effects of BPA exposure on ovarian function, mammary gland development, earlier age of puberty onset and some metabolic parameters. However, these findings are largely limited to experimental animal studies, and need to be validated in human populations. Our review supports the need to move beyond the currently dominant toxicological approach to examining the effects of BPA exposure, and rely more on observational human studies and epidemiological methods. Many of the risk factors for racial disparities in pregnancy outcome are global or difficult to modify, but exposure to BPA is a potentially malleable risk factor. If BPA contributes to racial disparities in pregnancy outcome, there are important implications for prevention. It is our hope that this review will stimulate further research in this important and neglected area.

The breast cancer and the environment research centers: transdisciplinary research on the role of the environment in breast cancer etiology

OBJECTIVES

We introduce and describe the Breast Cancer and the Environment Research Centers (BCERC), a research network with a transdisciplinary approach to elucidating the role of environmental factors in pubertal development as a window on breast cancer etiology. We describe the organization of four national centers integrated into the BCERC network.

DATA SOURCES

Investigators use a common conceptual framework based on multiple levels of biologic, behavioral, and social organization across the life span. The approach connects basic biologic studies with rodent models and tissue culture systems, a coordinated multicenter epidemiologic cohort study of prepubertal girls, and the integration of community members of breast cancer advocates as key members of the research team to comprise the network.

DATA EXTRACTION

Relevant literature is reviewed that describes current knowledge across levels of organization. Individual research questions and hypotheses in BCERC are driven by gaps in our knowledge that are presented at genetic, metabolic, cellular, individual, and environmental (physical and social) levels.

DATA SYNTHESIS

As data collection on the cohort, animal experiments, and analyses proceed, results will be synthesized through a transdisciplinary approach.

CONCLUSION

Center investigators are addressing a large number of specific research questions related to early pubertal onset, which is an established risk factor for breast cancer. BCERC research findings aimed at the primary prevention of breast cancer will be disseminated to the scientific community and to the public by breast cancer advocates, who have been integral members of the research process from its inception.

Early age at menarche associated with cardiovascular disease and mortality

CONTEXT

The relationship between age at menarche and cardiovascular disease remains unclear. Two recent studies found an inverse association between age at menarche and all-cause mortality.

OBJECTIVE

The aim of this study was to examine the relationship between age at menarche and cardiovascular disease risk factors, events, and mortality.

DESIGN, SETTING, AND PARTICIPANTS

A population-based prospective study involving 15,807 women, aged 40-79 yr in 1993-1997 and followed up to March 2007 for cardiovascular disease events (median follow-up 10.6 yr) and February 2008 for mortality (median follow-up 12.0 yr) was used.

MAIN OUTCOME MEASURES

Odds ratios for cardiovascular disease risk factors and hazard ratios for incident cardiovascular disease and mortality were calculated.

RESULTS

There were 3888 incident cardiovascular disease events (1323 coronary heart disease, 602 stroke, and 1963 other) and 1903 deaths (640 cardiovascular disease, 782 cancer, and 481 other) during follow-up. Compared with other women, those who had early menarche (<12 yr) had higher risks of hypertension [1.13 (1.02-1.24)], incident cardiovascular disease [1.17 (1.07-1.27)], incident coronary heart disease [1.23 (1.06-1.43)], all-cause mortality [1.22 (1.07-1.39)], cardiovascular disease mortality [1.28 (1.02-1.62)], and cancer mortality [1.25 (1.03-1.51)], adjusted for age, physical activity, smoking, alcohol, educational level, occupational social class, oral contraceptive use, hormone replacement therapy, parity, body mass index, and waist circumference.

CONCLUSIONS

Early age at menarche (before age 12 yr) was associated with increased risk of cardiovascular disease events, cardiovascular disease mortality, and overall mortality in women, and this association appeared to be only partly mediated by increased adiposity.

Abnormal timing of menarche in survivors of central nervous system tumors: A report from the Childhood Cancer Survivor Study

BACKGROUND

Children who receive high-dose radiotherapy to the hypothalamic-pituitary (H-P) axis may be at risk for both early and late puberty. To the authors' knowledge, data regarding the risk of altered timing of menarche after higher dose radiotherapy (RT), as used in the treatment of central nervous system (CNS) tumors, are limited.

METHODS

The authors evaluated 235 female survivors of CNS tumors, diagnosed between 1970 and 1986, and >1000 sibling controls who were participants in the Childhood Cancer Survivor Study, and provided self-reported data concerning age at menarche.

RESULTS

Survivors of CNS tumors were more likely to have onset of menarche before age 10 years compared with their siblings (11.9% vs 1.0%) (odds ratio [OR], 14.1; 95% confidence interval [95% CI], 7.0-30.9). Of the 138 survivors who received RT to the H-P axis, 20 (14.5%) had onset of menarche before age 10 years, compared with 4.3% of those who did not receive RT (OR, 3.8; 95% CI, 1.2-16.5). Age <or=4 years at the time of diagnosis was associated with an increased risk (OR, 4.0; 95% CI, 1.7-10.0) of early menarche. In addition, survivors of CNS tumors were more likely than siblings to have onset of menarche after age 16 years (10.6% vs 1.9%) (OR, 6.6; 95% CI, 3.4-11.4). Doses of RT to the H-P axis >50 gray OR, 9.0; 95% CI, 2.3-59.5) and spinal RT conferred an increased risk of late menarche, as did older age (>10 years) at the time of diagnosis (OR, 3.0; 95% CI, 1.3-7.0).

CONCLUSIONS

Survivors of CNS tumors are at a significantly increased risk of both early and late menarche associated with RT exposure and age at treatment.

Puberty onset in female rats: relationship with fat intake, ovarian steroids and the peptides, galanin and enkephalin, in the paraventricular and medial preoptic nuclei

Puberty is a time of rapid change, including a marked increase in fat consumption and body fat accrual, particularly in females. The mechanisms underlying these changes are unknown. Building on the results obtained in adult rats, the present study in pubertal rats focused on the orexigenic peptides, galanin (GAL) and enkephalin (ENK), in the paraventricular nucleus (PVN) and medial preoptic nucleus (MPN), which are known to be responsive to female steroids and have a role in both energy balance and reproductive function. The present study examined female rats maintained on pure macronutrient diets from before weaning (day 15) to day 70. After an initial burst in protein intake (days 21-35), rats showed an increase, specifically in preference for fat, from 15% to 30%. In rats examined at different ages before (day 30) and after (days 45 and 60) puberty, this rise in fat intake was associated with a marked increase, from days 30-45, in levels of oestradiol and progesterone and in GAL and ENK mRNA or peptide levels, specifically in the PVN and MPN, but not other hypothalamic areas examined. This positive relationship with increased fat intake, steroids and peptides across ages was also observed when comparing pubertal rats that naturally preferred fat (> 25% of total diet) with those consuming little fat (< 15%) or rats that reached puberty at an early age (days 30-34) with those that were late (days 37-40). These rats with early puberty onset exhibited a strong fat preference 3-4 days before vaginal opening, which was positively related to steroid levels, GAL, fat intake and body fat accrual after puberty. These findings suggest that, in addition to providing a signal for puberty onset, early fat ingestion acting through mechanisms involving the steroids and orexigenic peptides may be related to long-term patterns of eating and body weight regulation.

Childhood abuse and early menarche: findings from the black women's health study

OBJECTIVES

We examined the association between childhood abuse and early menarche in a sample of US Black women.

METHODS

We conducted multivariable log-binomial regression on data from 35 330 participants in the Black Women's Health Study to estimate risk ratios and 95% confidence intervals for the relation of childhood physical and sexual abuse with early age at menarche (i.e., < 12 years).

RESULTS

In adjusted analyses, sexual abuse was positively associated with early menarche, and the risk of early menarche increased with increasing frequency of sexual abuse incidents. We observed a weak but statistically significant association between physical abuse and early menarche. Associations between sexual abuse and early menarche were stronger when we used a more stringent cutpoint for early menarche (i.e., < 11 years).

CONCLUSIONS

Our data suggest an increased risk of early menarche among Black women who experienced childhood sexual abuse. Evidence for an association between childhood physical abuse and early menarche was equivocal.

Endocrinology of female puberty

PURPOSE OF REVIEW

Puberty is the developmental process that culminates in reproductive capability. It is initiated by the release of gonadotropin-releasing hormone from specialized neurons of the hypothalamus to stimulate hormonal cascades and gonadal activation. The age of pubertal onset in girls may be younger than in previous decades, emphasizing the gaps in knowledge about pubertal onset and factors that modulate it. This review describes the state of the debate on the age of pubertal initiation, recent insights into the physiology of female puberty and its relationship to childhood obesity, and the regulation of gonadotropin-releasing hormone neurons at puberty.

RECENT FINDINGS

Recent studies suggest that the average age of pubertal onset is decreasing in American girls, sparking controversy in defining the age at which puberty is considered precocious. Obese girls have hyperinsulinemia and hyperandrogenemia prepubertally, but it is unclear whether these factors play a role in the early onset of puberty in obese girls. The kisspeptin/G protein-coupled receptor 54 pathway is important for pubertal initiation; an activating mutation in the pathway has been associated with precocious puberty.

SUMMARY

The recent trend toward obesity has been proposed to play a role in the cause of early puberty in girls. The molecular mechanisms that initiate puberty are slowly being elucidated, with the discovery of kisspeptin prompting a novel direction in reproductive research.

Transcriptional regulation in liver and testis associated with developmental and reproductive effects in male zebrafish exposed to natural mixtures of persistent organic pollutants (POP)

Persistent organic pollutants (POP) occur as mixtures in nature and it is difficult to predict the toxicity of such mixtures based on knowledge about toxicity and mechanisms of action for single compounds. The present knowledge on the combined toxic effects and modes of actions of exposure to mixtures is limited. Thus, the scientifically based hazard and risk assessment of POP requires analytical and toxicological data from studies with environmental mixtures of POP. The application of genome wide transcription profiling in toxicology, in combination with classical endpoints, will improve the current understanding of the mechanisms of toxic processes. Furthermore, gene expression data may be useful in establishing new hypothesis and discovering new biomarkers for known toxicity as well as not yet recognized toxicity endpoints. In the present study, developmental and reproductive effects of lifelong exposure to environmental relevant concentrations of two natural mixtures of POP were investigated using classical and molecular methods in a controlled zebrafish model. The mixtures used were extracted from burbot (Lota lota) liver originating from freshwater systems in Norway: one mixture with high levels and one mixture with background levels of polybrominated diphenyl ethers (PBD), polychlorinated biphenyls (PCB), and DDT. The concentration of POP in the zebrafish ranged from levels detected in wild fish from Lake Mjøsa, to concentrations reported in human and wildlife populations. Phenotypic effects observed in both exposure groups included (1) reduced survival, (2) earlier onset of puberty, (3) increased male/female sex ratio, and (4) differences in body weight at 5 mo of age. Interestingly, genome-wide transcription profiling showed changes in regulation of genes involved in endocrine signaling and growth. The transcriptomics changes included (1) key regulator genes for steroid and thyroid hormone functions (cga, ncoa3), (2) insulin signaling and metabolic homeostasis (pik3r1, pfkfb3, ptb1), and (3) p53 activation (mdm4). The effects observed in the experimental zebrafish model raise the question of whether chemical pollution represents a risk to the reproductive health of wild fish inhabiting the freshwater system.

Parental infertility and sexual maturation in children

BACKGROUND

The reproductive health of children born of infertile couples may be affected by infertility treatment or factors associated with infertility. We examined sexual maturation in children of parents with infertility.

METHODS

We used data from a follow-up of 3382 girls and 2810 boys born between 1984 and 1987 in the Aalborg-Odense Birth Cohort. We had mothers' report of time to pregnancy (TTP) and infertility treatment (at the time, mostly hormonal) from the pregnancy questionnaire administered in 1984-1987, and the children's report of their own sexual maturation from the follow-up questionnaire administered in 2005, when they were between 18 and 21 years old. Many reported age only in year when they had the events related to sexual maturation, and for each event, we imputed the month based on the median month at each year of age among those reporting both years and months.

RESULTS

In girls, the mean age at menarche was 13.3 years and, in boys, the mean age at appearance of acne, voice break, regular shaving and first nocturnal emission were 14.5, 14.5, 17.2 and 14.7 years, respectively. We saw no significant differences in age at these events among children born of either fertile (with TTP of 0-12 months and no treatment), untreated infertile (with TTP of more than 12 months and no treatment) or treated infertile couples (with a history of examination or treatment for infertility).

CONCLUSIONS

Our data suggest no significant association between parental infertility or hormonal treatment and timing of sexual maturation in the offspring.

Forty years trends in timing of pubertal growth spurt in 157,000 Danish school children

BACKGROUND

Entering puberty is an important milestone in reproductive life and secular changes in the timing of puberty may be an important indicator of the general reproductive health in a population. Too early puberty is associated with several psychosocial and health problems. The aim of our study was to determine if the age at onset of pubertal growth spurt (OGS) and at peak height velocity (PHV) during puberty show secular trends during four decades in a large cohort of school children.

METHODS AND FINDINGS

Annual measurements of height were available in all children born from 1930 to 1969 who attended primary school in the Copenhagen Municipality. 135,223 girls and 21,612 boys fulfilled the criteria for determining age at OGS and age at PHV. These physiological events were used as markers of pubertal development in our computerized method in order to evaluate any secular trends in pubertal maturation during the study period (year of birth 1930 to 1969). In this period, age at OGS declined statistically significantly by 0.2 and 0.4 years in girls and boys, respectively, whereas age at PHV declined statistically significantly by 0.5 and 0.3 years in girls and boys, respectively. The decline was non-linear with a levelling off in the children born between 1940 and 1955. The duration of puberty, as defined by the difference between age at OGS and age at PHV, increased slightly in boys, whereas it decreased in girls.

CONCLUSION

Our finding of declining age at OGS and at PHV indicates a secular trend towards earlier sexual maturation of Danish children born between 1930 and 1969. Only minor changes were observed in duration of puberty assessed by the difference in ages at OGS and PHV.

Role of environmental factors in the timing of puberty

Puberty-timing measures have historically been used as indicators of adequate nutrition and growth. More recently, these measures have been examined in relation to exposure to estrogenic or antiandrogenic agents, as well as other environmental factors. The scientific community has debated whether puberty timing is occurring earlier today than in the mid-1900s in the United States and, if so, whether environmental factors play a role; however, no one has asked a multidisciplinary panel to resolve this question. Thus, a multidisciplinary expert panel jointly sponsored by the US Environmental Protection Agency, the National Institute of Environmental Health Sciences, and Serono Symposia International was convened to examine the evidence of a secular trend, identify potential environmental factors of concern, and identify research needs regarding environmental factors and puberty timing at "The Role of Environmental Factors on the Timing and Progression of Puberty" workshop. The majority of the panelists concluded that the girls' data are sufficient to suggest a secular trend toward earlier breast development onset and menarche from 1940 to 1994 but that the boys' data are insufficient to suggest a trend during this same period. The weight-of-the-evidence evaluation of human and animal studies suggest that endocrine-disrupting chemicals, particularly the estrogen mimics and antiandrogens, and body fat are important factors associated in altered puberty timing. A change in the timing of puberty markers was considered adverse from a public health perspective. The panel recommended research areas to further our understanding of the relationships among environmental factors, puberty-timing outcomes, and other reproductive and adult disease at the individual and population levels.