Environmental factors and puberty timing: expert panel research needs

Is early puberty triggered by catch-up growth following undernutrition?

Undernutrition during fetal and postnatal life is still a major problem in many low- and middle-income countries. Even in high-income countries malnutrition may exist in cases of intrauterine growth retardation, as well as in chronic conditions such as anorexia nervosa and inflammatory bowel disease. Children adopted from developing countries are often chronically malnourished. Nutritional rehabilitation, resulting in catch-up growth, is often complicated by influences originating in fetal life as well as during postnatal growth. This may result in hormonal and metabolic changes as well as alterations in pubertal development. The present review focuses on fetal, postnatal and fetal-postnatal undernutrition and subsequent catch-up growth as well as catch-up growth in relation to pubertal development. Catch-up growth in children can be associated with early puberty following fetal or combined fetal-postnatal undernutrition. However, early puberty does not seem to occur following catch-up growth after isolated postnatal undernutrition. Gonadotropins have been reported to be elevated in prepubertal adopted girls as well as during catch-up growth in animals. Even if other factors may contribute, linear catch-up growth seems to be associated with the timing of pubertal development. The mechanisms behind this are still unknown. Future research may elucidate how to carry out nutritional rehabilitation without risk for early pubertal development.

Association between chemical pattern in breast milk and congenital cryptorchidism: modelling of complex human exposures

During the past four decades, there has been an increase in the incidence rate of male reproductive disorders in some, but not all, Western countries. The observed increase in the prevalence of male reproductive disorders is suspected to be ascribable to environmental factors as the increase has been too rapid to be explained by genetics alone. To study the association between complex chemical exposures of humans and congenital cryptorchidism, the most common malformation of the male genitalia, we measured 121 environmental chemicals with suspected or known endocrine disrupting properties in 130 breast milk samples from Danish and Finnish mothers. Half the newborns were healthy controls, whereas the other half was boys with congenital cryptorchidism. The measured chemicals included polychlorinated biphenyls (PCBs), polybrominated diphenyl-ethers, dioxins (OCDD/PCDFs), phthalates, polybrominated biphenyls and organochlorine pesticides. Computational analysis of the data was performed using logistic regression and three multivariate machine learning classifiers. Furthermore, we performed systems biology analysis to explore the chemical influence on a molecular level. After correction for multiple testing, exposure to nine chemicals was significantly different between the cases and controls in the Danish cohort, but not in the Finnish cohort. The multivariate analysis indicated that Danish samples exhibited a stronger correlation between chemical exposure patterns in breast milk and cryptorchidism than Finnish samples. Moreover, PCBs were indicated as having a protective effect within the Danish cohort, which was supported by molecular data recovered through systems biology. Our results lend further support to the hypothesis that the mixture of environmental chemicals may contribute to observed adverse trends in male reproductive health.

Early-life soy exposure and age at menarche

This study examines the timing of menarche in relation to infant-feeding methods, specifically addressing the potential effects of soy isoflavone exposure through soy-based infant feeding. Subjects were participants in the Avon Longitudinal Study of Parents and Children (ALSPAC). Mothers were enrolled during pregnancy and their children have been followed prospectively. Early-life feeding regimes, categorised as primarily breast, early formula, early soy and late soy, were defined using infant-feeding questionnaires administered during infancy. For this analysis, age at menarche was assessed using questionnaires administered approximately annually between ages 8 and 14.5. Eligible subjects were limited to term, singleton, White females. We used Kaplan-Meier survival curves and Cox proportional hazards models to assess age at menarche and risk of menarche over the study period. The present analysis included 2920 girls. Approximately 2% of mothers reported that soy products were introduced into the infant diet at or before 4 months of age (early soy). The median age at menarche [interquartile range (IQR)] in the study sample was 153 months [144-163], approximately 12.8 years. The median age at menarche among early soy-fed girls was 149 months (12.4 years) [IQR, 140-159]. Compared with girls fed non-soy-based infant formula or milk (early formula), early soy-fed girls were at 25% higher risk of menarche throughout the course of follow-up (hazard ratio 1.25 [95% confidence interval 0.92, 1.71]). Our results also suggest that girls fed soy products in early infancy may have an increased risk of menarche specifically in early adolescence. These findings may be the observable manifestation of mild endocrine-disrupting effects of soy isoflavone exposure. However, our study is limited by few soy-exposed subjects and is not designed to assess biological mechanisms. Because soy formula use is common in some populations, this subtle association with menarche warrants more in-depth evaluation in future studies.

Dietary contaminant exposure affects plasma testosterone, but not thyroid hormones, vitamin A, and vitamin E, in male juvenile arctic foxes (Vulpes lagopus)

Levels of persistent organic pollutants (POP), such as polychlorinated biphenyls (PCB), are high in many Arctic top predators, including the Arctic fox (Vulpes lagopus). The aim of this study was to examine possible endocrine-disruptive effects of dietary POP exposure in male juvenile Arctic foxes in a controlled exposure experiment. The study was conducted using domesticated farmed blue foxes (Vulpes lagopus) as a model species. Two groups of newly weaned male foxes received a diet supplemented with either minke whale (Baleneoptera acutorostrata) blubber that was naturally contaminated with POP (exposed group, n = 5 or 21), or pork (Sus scrofa) fat (control group, n = 5 or 21). When the foxes were 6 mo old and had received the 2 diets for approximately 4 mo (147 d), effects of the dietary exposure to POP on plasma concentrations of testosterone (T), thyroid hormones (TH), thyroid-stimulating hormone (TSH), retinol (vitamin A), and tocopherol (viramin E) were examined. At sampling, the total body concentrations of 104 PCB congeners were 0.1 ± 0.03 μg/g lipid weight (l.w.; n = 5 [mean ± standard deviation]) and 1.5 ± 0.17 μg/g l.w. (n = 5) in the control and exposed groups, respectively. Plasma testosterone concentrations in the exposed male foxes were significantly lower than in the control males, being approximately 25% of that in the exposed foxes. There were no between-treatment differences for TH, TSH, retinol, or tocopherol. The results suggest that the high POP levels experienced by costal populations of Arctic foxes, such as in Svalbard and Iceland, may result in delayed masculine maturation during adolescence. Sex hormone disruption during puberty may thus have lifetime consequences on all aspects of reproductive function in adult male foxes.

Urinary mycoestrogens, body size and breast development in New Jersey girls

BACKGROUND

Despite extensive research and interest in endocrine disruptors, there are essentially no epidemiologic studies of estrogenic mycotoxins, such as zeranol and zearalenone (ZEA). ZEA mycoestrogens are present in grains and other plant foods through fungal contamination, and in animal products (e.g., meat, eggs, dairy products) through deliberate introduction of zeranol into livestock to enhance meat production, or by indirect contamination of animals through consumption of contaminated feedstuff. Zeranol is banned for use in animal husbandry in the European Union and other countries, but is still widely used in the US. Surprisingly, little is known about the health effects of these mycoestrogens, including their impact on puberty in girls, a period highly sensitive to estrogenic stimulation.

OBJECTIVES AND METHODS

We conducted a cross-sectional analysis among 163 girls, aged 9 and 10 years, participating in the Jersey Girl Study to measure urinary mycoestrogens and their possible relationship to body size and development.

RESULTS

We found that mycoestrogens were detectable in urine in 78.5% of the girls, and that urinary levels were predominantly associated with beef and popcorn intake. Furthermore, girls with detectable urinary ZEA mycoestrogen levels tended to be shorter and less likely to have reached the onset of breast development.

CONCLUSIONS

Our findings suggest that ZEA mycoestrogens may exert anti-estrogenic effects similar to those reported for isoflavones. To our knowledge, this was the first evaluation of urinary mycoestrogens and their potential health effects in healthy girls. However, our findings need replication in larger studies with more heterogeneous populations, using a longitudinal approach.

Changing age of acne vulgaris visits: another sign of earlier puberty?

The objective of the current study was to assess changes in the onset of pubertal maturation by determining whether acne is occurring at an earlier age. We assessed the age at which acne is occurring by assessing trends in the age of people seeking medical attention for acne. The National Ambulatory Medical Care Survey database was used to analyze physician visits for acne vulgaris in children aged 6 to 18 from 1979 to 2007. The data were used to assess trends in the mean age of children with acne and to compare these trends according to race and sex. Regression analysis revealed a significant decrease in the mean age of children seeking treatment for acne over this 28-year period (p < 0.001). There was no significant change in the mean age of black children seeking treatment for acne. Black girls had the lowest mean age whereas white boys had the highest mean age. There has been a decrease in the average age of children seeking treatment for acne that may be indicative of earlier acne onset. This finding provides supporting evidence of the increasingly earlier onset of puberty in girls.

Perinatal environmental exposures affect mammary development, function, and cancer risk in adulthood

Puberty is an important transition that enables reproduction of mammalian species. Precocious puberty, specifically early thelarche (the appearance of breast "buds"), in girls of multiple ethnic backgrounds is a major health problem in the United States and other countries. The cause for a continued decrease in the age of breast development in girls is unknown, but environmental factors likely play a major role. Laboratory and epidemiological studies have identified several individual environmental factors that affect breast development, but further progress is needed. Current research needs include increased attention to and recording of prenatal and neonatal environmental exposures, testing of marketed chemicals for effects on the mammary gland, and understanding of the mammary gland-specific mechanisms that are altered by chemicals. Such research is required to halt the increasing trend toward puberty at earlier ages.

Treating endometriosis in adolescents: does it matter?

Endometriosis has major physical and psychosocial impacts on teens, as well as long-term implications for their health. The hidden suffering of millions of adolescents worldwide calls on the medical profession to respond, despite the challenges. Given the increasing understanding of adolescent endometriosis, treating adolescents with endometriosis can be a most rewarding experience. Moreover, diagnosing and treating the disease early could prevent more complicated disease later, as well as comorbidities. Helping these girls may save them, their families, and their communities much physical and emotional pain, as well as lessen the huge burden on our health care systems and society.

Disruption of androgen receptor signaling in males by environmental chemicals

Androgen-disruptors are environmental chemicals in that interfere with the biosynthesis, metabolism or action of endogenous androgens resulting in a deflection from normal male developmental programming and reproductive tract growth and function. Since male sexual differentiation is entirely androgen-dependent, it is highly susceptible to androgen-disruptors. Animal models and epidemiological evidence link exposure to androgen disrupting chemicals with reduced sperm counts, increased infertility, testicular dysgenesis syndrome, and testicular and prostate cancers. Further, there appears to be increased sensitivity to these agents during critical developmental windows when male differentiation is at its peak. A variety of in vitro and in silico approaches have been used to identify broad classes of androgen disrupting molecules that include organochlorinated pesticides, industrial chemicals, and plasticizers with capacity to ligand the androgen receptor. The vast majority of these synthetic molecules act as anti-androgens. This review will highlight the evidence for androgen disrupting chemicals that act through interference with the androgen receptor, discussing specific compounds for which there is documented in vivo evidence for male reproductive tract perturbations. This article is part of a Special Issue entitled 'Endocrine disruptors'.

Vitamin D deficiency and age at menarche: a prospective study

BACKGROUND

Early menarche is a risk factor for cardiometabolic disease and cancer. Latitude, which influences sun exposure, is inversely related to age at menarche. This association might be related to vitamin D, but to our knowledge it has not been investigated in prospective epidemiologic studies.

OBJECTIVE

We studied the association between vitamin D status and the occurrence of menarche in a prospective study in girls from Bogota, Colombia.

DESIGN

We measured plasma 25-hydroxyvitamin D [25(OH)D] concentrations in a random sample of 242 girls (mean ± SD age: 8.8 ± 1.6 y) and followed them for a median of 30 mo. Girls were asked periodically about the occurrence and date of menarche. Baseline 25(OH)D concentrations were categorized as <50 nmol/L (deficient), ≥50 and <75 nmol/L, or ≥75 nmol/L (sufficient). The incidence of menarche was compared between groups by using time-to-event analyses.

RESULTS

A total of 57% of girls in the vitamin D-deficient group reached menarche during follow-up compared with 23% of girls in the vitamin D-sufficient group (P-trend = 0.0004). The estimated mean (±SE) ages at menarche in the same groups were 11.8 ± 0.2 y and 12.6 ± 0.2 y, respectively (P = 0.0009). After adjustment for baseline age and BMI-for-age z score in a Cox proportional hazards model, the probability of menarche was twice as high in vitamin D-deficient girls than in girls who were vitamin D-sufficient (HR: 2.05; 95% CI: 1.03, 4.07; P = 0.04). Similar results were obtained in girls aged ≥9 y at baseline (HR: 2.39; 95% CI: 1.14, 5.00; P = 0.02).

CONCLUSION

Vitamin D deficiency is associated with earlier menarche.

Facing changes and changing faces in adolescence: a new model for investigating adolescent-specific interactions between pubertal, brain and behavioral development

Adolescence is a time of dramatic physical, cognitive, emotional, and social changes as well as a time for the development of many social-emotional problems. These characteristics raise compelling questions about accompanying neural changes that are unique to this period of development. Here, we propose that studying adolescent-specific changes in face processing and its underlying neural circuitry provides an ideal model for addressing these questions. We also use this model to formulate new hypotheses. Specifically, pubertal hormones are likely to increase motivation to master new peer-oriented developmental tasks, which will in turn, instigate the emergence of new social/affective components of face processing. We also predict that pubertal hormones have a fundamental impact on the re-organization of neural circuitry supporting face processing and propose, in particular, that, the functional connectivity, or temporal synchrony, between regions of the face-processing network will change with the emergence of these new components of face processing in adolescence. Finally, we show how this approach will help reveal why adolescence may be a period of vulnerability in brain development and suggest how it could lead to prevention and intervention strategies that facilitate more adaptive functional interactions between regions within the broader social information processing network.

Endocrine disrupting chemicals: Multiple effects on testicular signaling and spermatogenesis

In the past 200 years, an enormous number of synthetic chemicals with diverse structural features have been produced for industrial, medical and domestic purposes. These chemicals, originally thought to have little or no biological toxicity, are widely used in our daily lives as well as are commonly present in foods. It was not until the first World Wildlife Federation Wingspread Conference held in 1994 were concerns about the endocrine disrupting (ED) effects of these chemicals articulated. The potential hazardous effects of endocrine disrupting chemicals (EDCs) on human health and ecological well-being are one of the global concerns that affect the health and propagation of human beings. Considerable numbers of studies indicated that endocrine disruption is linked to "the developmental basis of adult disease," highlighting the significant effects of EDC exposure on a developing organism, leading to the propensity of an individual to develop a disease or dysfunction in later life. In this review, we intend to provide environmental, epidemiological and experimental data to associate pollutant exposure with reproductive disorders, in particular on the development and function of the male reproductive system. Possible effects of pollutant exposure on the processes of embryonic development, like sex determination and masculinization are described. In addition, the effects of pollutant exposure on hypothalamus-pituitary-gonadal axis, testicular signaling, steroidogenesis and spermatogenesis are also discussed.

Early life infections and onset of puberty: evidence from Hong Kong's children of 1997 birth cohort

As economic development increases, puberty occurs at younger ages, and this could contribute to an increase in the incidence of cardiovascular diseases and hormone-related cancers. The factors that determine pubertal timing are poorly understood. The growth axis that is active during puberty is active in the first 6 months of life and interacts with the immune system. The authors examined whether prior infections, proxied by number of hospital admissions for infections at different ages, were associated with age at pubertal onset (Tanner stage II) using interval-censored regression in the Children of 1997 cohort, which is a population-representative Chinese birth cohort (n = 7,527). Mediation by growth was also examined. Girls, but not boys, who were hospitalized for infections at least twice in the first 6 months of life experienced pubertal onset about 8 months later (mean = 10.3 years, time ratio = 1.08, 95% confidence interval: 1.04, 1.12) than did those without such hospitalizations (mean = 9.6 years) after adjustment for infant characteristics and socioeconomic position (sex interaction: P = 0.02). There were no such associations for infections at 6 months to ≤8 years of age. Growth did not mediate the association. Early infectious morbidity in girls may be associated with later puberty, perhaps via suppression of the gonadotropic axis. The lowering of the number of infections in early life that accompanies economic development could be an additional factor that contributes to earlier puberty.

Socio-environmental factors associated with pubertal development in female adolescents: the role of prepubertal tobacco and alcohol use

PURPOSE

Alcohol administered to laboratory animals has been shown to suppress puberty-related hormones and delay puberty by interfering with ovarian development and function. The effects of early substance use on human pubertal development are relatively unexplored.

METHODS

This cross-sectional study of 3,106 female adolescents, aged 11-21 years, evaluated the association between prepubertal alcohol and tobacco use and the onset of puberty. Ages at initial breast development, body hair growth, and menarche were self-reported. Prepubertal alcohol and tobacco use were defined as the age at first use before the age of pubertal development and accompanied by regular use. Hazard ratios (HR) and 95% confidence intervals (CI) were calculated using Cox proportional hazard models. Logistic regression was used to estimate the association between substance use and delayed puberty, defined as lack of breast development by the age of 13 years.

RESULTS

Unadjusted models indicated prepubertal tobacco use was associated with a longer time required for breast development (HR = 0.74; 95% CI, 0.65-0.85) and body hair growth (HR = 0.81; 95% CI, 0.71-0.93). Prepubertal alcohol use was associated with late breast development (HR = 0.71; 95% CI, 0.57-0.88). The direction of the observed associations remained consistent after adjusting for covariates, but the magnitude of effects were attenuated and the upper bound of the 95% CIs exceeded the null value. Girls who used alcohol before puberty had four times the odds of having delayed puberty (OR = 3.99; 95% CI, 1.94-8.21) as compared with nonusers.

CONCLUSION

The results of this study suggest that the endocrine-disrupting effects of alcohol and tobacco use may alter the timing of pubertal development. These cross-sectional findings warrant further investigation.

Effects of environmental endocrine disruptors on pubertal development

The onset and course of puberty are under the control of the neuroendocrine system. Factors affecting the timing and regulation of the functions of this system may alter the onset and course of puberty. Several environmental endocrine disruptors (EDs) with significant influences on the normal course of puberty have been identified. Numerous animal and human studies concerning EDs have been conducted showing that these substances may extensively affect human health; nevertheless, there are still several issues that remain to be clarified. In this paper, the available evidence from animal and human studies on the effects of environmental EDs with the potential to cause precocious or delayed puberty was reviewed.

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.

Neuroendocrine disruption of pubertal timing and interactions between homeostasis of reproduction and energy balance

The involvement of environmental factors such as endocrine disrupting chemicals (EDCs) in the timing of onset of puberty is suggested by recent changes in age at onset of puberty and pattern of distribution that are variable among countries, as well as new forms of sexual precocity after migration. However, the evidence of association between early or late pubertal timing and exposure to EDCs is weak in humans, possibly due to heterogeneity of effects likely involving mixtures and incapacity to assess fetal or neonatal exposure retrospectively. The neuroendocrine system which is crucial for physiological onset of puberty is targeted by EDCs. These compounds also act directly in the gonads and peripheral sex-steroid sensitive tissues. Feedbacks add to the complexity of regulation so that changes in pubertal timing caused by EDCs can involve both central and peripheral mechanisms. In experimental conditions, several neuroendocrine endpoints are affected by EDCs though only few studies including from our laboratory aimed at EDC involvement in the pathophysiology of early sexual maturation. Recent observations support the concept that EDC cause disturbed energy balance and account for the obesity epidemic. Several aspects are linking this system and the reproductive axis: coexisting neuroendocrine and peripheral effects, dependency on fetal/neonatal programming and the many factors cross-linking the two systems, for instance leptin, adiponectin, Agouti Related Peptide (AgRP). This opens perspectives for future research and, hopefully, measures preventing the disturbances of homeostasis caused by EDCs.

Foetal hypothalamic and pituitary expression of gonadotrophin-releasing hormone and galanin systems is disturbed by exposure to sewage sludge chemicals via maternal ingestion

Animals and humans are chronically exposed to endocrine disrupting chemicals (EDCs) that are ubiquitous in the environment. There are strong circumstantial links between environmental EDC exposure and both declining human/wildlife reproductive health and the increasing incidence of reproductive system abnormalities. The verification of such links, however, is difficult and requires animal models exposed to 'real life', environmentally relevant concentrations/mixtures of environmental contaminants (ECs), particularly in utero, when sensitivity to EC exposure is high. The present study aimed to determine whether the foetal sheep reproductive neuroendocrine axis, particularly gondotrophin-releasing hormone (GnRH) and galaninergic systems, were affected by maternal exposure to a complex mixture of chemicals, applied to pasture, in the form of sewage sludge. Sewage sludge contains high concentrations of a spectrum of EDCs and other pollutants, relative to environmental concentrations, but is frequently recycled to land as a fertiliser. We found that foetuses exposed to the EDC mixture in utero through their mothers had lower GnRH mRNA expression in the hypothalamus and lower GnRH receptor (GnRHR) and galanin receptor (GALR) mRNA expression in the hypothalamus and pituitary gland. Strikingly, this, treatment had no significant effect on maternal GnRH or GnRHR mRNA expression, although GALR mRNA expression within the maternal hypothalamus and pituitary gland was reduced. The present study clearly demonstrates that the developing foetal neuroendocrine axis is sensitive to real-world mixtures of environmental chemicals. Given the important role of GnRH and GnRHR in the regulation of reproductive function, its known role programming role in utero, and the role of galanin in the regulation of many physiological/neuroendocrine systems, in utero changes in the activity of these systems are likely to have long-term consequences in adulthood and represent a novel pathway through which EC mixtures could perturb normal reproductive function.

Developmental and neurobehavioral effects of perinatal exposure to diets with different omega-6:omega-3 ratios in mice

OBJECTIVE

To investigate in mice the effect of diets enriched with soy or sunflower oil with different omega-6:omega-3 ratios on gestation, reproductive success, physical maturation, and the neurobiological development of the pups.

METHODS

Dams were assigned, throughout gestation and lactation, to different groups: a commercial diet (CD), a soy oil-enriched diet (SOD), or a sunflower oil-enriched diet (SFOD). Measurements during gestation were dams' body weights and daily food intakes. Measurements in the offspring were physical parameters (body weight, body length, body mass index, fur appearance, pinna detachment, incisor eruption, eye opening, and puberty onset) and behavioral preweaning tests (surface righting reflex, negative geotaxis, and cliff avoidance).

RESULTS

The SOD and SFOD dams became significantly heavier than the CD dams from gestational days 14 and 19, respectively, to parturition. There were no significant differences in gestational length or food consumption during pregnancy or lactation or in maternal weight during lactation. Diets did not modify litter size, sex ratio, survival index at weaning, or body weight. The SFOD and SOD offspring were significantly shorter than the CD offspring at weaning. The mean offspring physical scores of SOD and SFOD offspring were higher than CD offspring and simple reflexes were earlier in the SOD and SFOD groups. In SFOD offspring, puberty onset was significantly delayed, at postnatal days 26 and 27 in male and female offspring, respectively.

CONCLUSION

This study suggests that the maintenance of an adequate omega-6:omega-3 ratio is necessary for the optimal growth and development of murine offspring. In populations that do not have sufficient provision of polyunsaturated fatty acids in the diet, their consumption would be advisable during gestation and lactation because these improve most neurodevelopmental outcomes included in this study.

Hypothesis: exposure to endocrine-disrupting chemicals may interfere with timing of puberty

A recent decline in onset of puberty - especially among girls - has been observed, first in the US in the mid-1990s and now also in Europe. The development of breast tissue in girls occurs at a much younger age and the incidence of precocious puberty (PP) is increasing. Genetic factors and increasing prevalence of adiposity may contribute, but environmental factors are also likely to be involved. In particular, the widespread presence of endocrine-disrupting chemicals (EDCs) is suspected to contribute to the trend of earlier pubertal onset. The factors regulating the physiological onset of normal puberty are poorly understood. This hampers investigation of the possible role of environmental influences. There are many types of EDCs. One chemical may have more than one mode of action and the effects may depend on dose and duration of the exposure, as well as the developmental stage of the exposed individual. There may also be a wide range of genetic susceptibility to EDCs. Human exposure scenarios are complex and our knowledge about effects of mixtures of EDCs is limited. Importantly, the consequences of an exposure may not be apparent at the actual time of exposure, but may manifest later in life. Most known EDCs have oestrogenic and/or anti-androgenic actions and only few have androgenic or anti-oestrogenic effects. Thus, it appears plausible that they interfere with normal onset of puberty. The age at menarche has only declined by a few months whereas the age at breast development has declined by 1 year; thus, the time span from initiation of breast development to menarche has increased. This may indicate an oestrogen-like effect without concomitant central activation of the hypothalamic-pituitary axis. The effects may differ between boys and girls, as there are sex differences in age at onset of puberty, hormonal profiles and prevalence of precocius puberty.

Genital anomalies in boys and the environment

The prevalence of male reproductive disorders, such as testicular cancer and impaired semen quality, is increasing in many, albeit not all, countries. These disorders are aetiologically linked with congenital cryptorchidism and hypospadias by common factors leading to perinatal disruption of normal testis differentiation, the testicular dysgenesis syndrome (TDS). There is recent evidence that also the prevalence of genital malformations is increasing and the rapid pace of increase suggests that lifestyle factors and exposure to environmental chemicals with endocrine disrupting properties may play a role. Recent prospective studies have established links between perinatal exposure to persistent halogenated compounds and cryptorchidism, as well as between phthalates and anti-androgenic effects in newborns. Maternal alcohol consumption, mild gestational diabetes and nicotine substitutes were also identified as potential risk factors for cryptorchidism. It may be the cocktail effect of many simultaneous exposures that result in adverse effects, especially during foetal life and infancy.

Contaminantes ambientais e os interferentes endócrinos

A toxicidade de diversos poluentes ambientais em seres humanos e demais espécies tem sido habitualmente investigada quanto aos seus efeitos teratogênicos e cancerígenos. Nas últimas décadas, muitos contaminantes têm demonstrado efeitos adversos sobre o sistema endócrino. Atualmente, cerca de onze milhões de substâncias químicas são conhecidas em todo mundo, sendo três mil delas produzidas em larga escala. Numerosos compostos químicos de uso doméstico, industrial e agrícola possuem comprovada atividade hormonal. Entre os produtos químicos com atividade estrogênica, destacam-se hormônios presentes em cosméticos, anabolizantes utilizados em rações animais, fitoestrógenos e poluentes orgânicos persistentes (POPs). Esses agentes que estão presentes nos efluentes industriais, residenciais e das estações de tratamento de água e esgoto representam uma importante fonte de contaminação ambiental. O Programa Internacional de Segurança Química (International Programme on Chemical Safety - IPCS) define como interferente endócrino substâncias ou misturas presentes no ambiente capazes de interferir nas funções do sistema endócrino, causando efeitos adversos em um organismo intacto ou na sua prole. No presente artigo, os autores apresentam uma revisão da literatura atual sobre o papel desses elementos nas doenças endócrinas e metabólicas, os prováveis mecanismos de ação envolvidos, discutindo-se perspectivas futuras em termos de investigação e estratégias para prevenção e redução dos seus possíveis danos.

Phthalate exposure and precocious puberty in females

OBJECTIVE

To determine whether phthalate exposure is associated with precocious puberty in girls.

STUDY DESIGN

This was a multicenter cross-sectional study in which 28 girls with central precocious puberty (CPP) and 28 age- and race-matched prepubertal females were enrolled. Nine phthalate metabolites and creatinine were measured in spot urine samples from these 56 children.

RESULTS

Levels of 8 of the 9 phthalate metabolites were above the limit of detection (LOD) in all 56 subjects. Mono (2-ethylhexyl) phthalate (MEHP) was below the LOD in 25/56 samples (14 subjects with precocious puberty and 11 controls). No significant differences between the children with CPP and the controls in either absolute or creatinine-normalized concentrations of any of the 9 phthalate metabolites were measured.

CONCLUSIONS

Although phthalates may be associated with certain other toxicities in humans, our study suggests that their exposure is not associated with precocious puberty in female children.

Pubertal development and behavior: hormonal activation of social and motivational tendencies

Adolescence is a time of dramatic changes including rapid physical growth, the onset of sexual maturation, the activation of new drives and motivations, and a wide array of social and affective changes and challenges. This review focuses on behavioral changes in this interval and is organized by the claim that a key set of these adolescent changes are part of a more general re-orientation of social behavior. More specifically we hypothesize that pubertal maturation is associated with the activation of social and motivational tendencies, which in turn influence behavior and emotion in adolescence depending upon interactions with social context. We focus on evidence for two examples of these motivational changes: (1) increases in sensation-seeking (motivational tendency to want to experience high-intensity, exciting experiences) and (2) stronger natural interest in--and pursuit of--contact with peers and potential romantic partners. We consider how these motivational changes contribute to the broader social re-orientation of adolescence, including exploration of social experiences, development of skills and knowledge relevant to taking on adult social roles, individuation from family, and establishment of an individual identity, all of which represent core developmental tasks during this period in the life span (Blakemore, 2008; Dahl & Spear, 2004; Steinberg & Morris, 2000). The paper also emphasizes the importance of investigating and understanding the direct influences of puberty on behavior and disentangling these from the broader set of changes during adolescent development.

Age at puberty and the emerging obesity epidemic

BACKGROUND

Recent studies have shown that puberty starts at younger ages than previously. It has been hypothesized that the increasing prevalence of childhood obesity is contributing to this trend. The purpose of this study was to analyze the association between prepubertal body mass index (BMI) and pubertal timing, as assessed by age at onset of pubertal growth spurt (OGS) and at peak height velocity (PHV), and the secular trend of pubertal timing given the prepubertal BMI.

METHODOLOGY/PRINCIPAL FINDINGS

Annual measurements of height and weight were available in all children born from 1930 to 1969 who attended primary school in the Copenhagen municipality; 156,835 children fulfilled the criteria for determining age at OGS and PHV. The effect of prepubertal BMI at age seven on these markers of pubertal development within and between birth cohorts was analyzed. BMI at seven years was significantly inversely associated with age at OGS and PHV. Dividing the children into five levels of prepubertal BMI, we found a similar secular trend toward earlier maturation in all BMI groups.

CONCLUSION/SIGNIFICANCE

The heavier both boys and girls were at age seven, the earlier they entered puberty. Irrespective of level of BMI at age seven, there was a downward trend in the age at attaining puberty in both boys and girls, which suggests that the obesity epidemic is not solely responsible for the trend.

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.

Exposure to a complex cocktail of environmental endocrine-disrupting compounds disturbs the kisspeptin/GPR54 system in ovine hypothalamus and pituitary gland

BACKGROUND

Ubiquitous environmental chemicals, including endocrine-disrupting chemicals (EDCs), are associated with declining human reproductive health, as well as an increasing incidence of cancers of the reproductive system. Verifying such links requires animal models exposed to "real-life," environmentally relevant concentrations/mixtures of EDC, particularly in utero, when sensitivity to EDC exposure is maximal.

OBJECTIVES

We evaluated the effects of maternal exposure to a pollutant cocktail (sewage sludge) on the ovine fetal reproductive neuroendocrine axes, particularly the kisspeptin (KiSS-1)/GPR54 (G-protein-coupled receptor 54) system.

METHODS

KiSS-1, GPR54, and ERalpha (estrogen receptor alpha) mRNA expression was quantified in control (C) and treated (T) maternal and fetal (110-day) hypothalami and pituitary glands using semiquantitative reverse transcription polymerase chain reaction, and colocalization of kisspeptin with LHbeta (luteinizing hormone beta) and ERalpha in C and T fetal pituitary glands quantified using dual-labeling immunohistochemistry.

RESULTS

Fetuses exposed in utero to the EDC mixture showed reduced KiSS-1 mRNA expression across three hypothalamic regions examined (rostral, mid, and caudal) and had fewer kisspetin immunopositive cells colocalized with both LHbeta and ERalpha in the pituitary gland. In contrast, treatment had no effect on parameters measured in the adult ewe hypothalamus or pituitary.

CONCLUSIONS

This study demonstrates that the developing fetus is sensitive to real-world mixtures of environmental chemicals, which cause significant neuroendocrine alterations. The important role of kisspeptin/GPR54 in regulating puberty and adult reproduction means that in utero disruption of this system is likely to have long-term consequences in adulthood and represents a novel, additional pathway through which environmental chemicals perturb human reproduction.

Timing of maturation and predictors of menarche in girls enrolled in a contemporary British cohort

This study describes the timing of puberty in 8- to 13-year-old girls enrolled in the Avon Longitudinal Study of Parents and Children (ALSPAC) and identifies factors associated with earlier achievement of menarche. Women were enrolled during pregnancy and their offspring were followed prospectively. We analysed self-reported Tanner staging and menstrual status information collected annually from daughters up to age 13. We used survival models to estimate median age of attainment of stage >1 and stage >2 of breast and pubic hair development and of menarche. We also constructed multivariable logistic regression models to identify factors associated with earlier achievement of menarche. About 12% of girls reported Tanner breast stage >1 at age 8; 98% of girls were above stage 1 by age 13. For pubic hair, 5% and 95% of girls had attained a stage >1 by 8 and 13 years, respectively. The estimated median age of entry into stage >1 of breast development was 10.14 years (95% confidence interval [CI], 10.08, 10.19), and for pubic hair development the median age was 10.92 years [95% CI, 10.87, 10.97]. One girl (out of 2953) had attained menarche by age 8; 60% had attained menarche by age 13. The estimated median age at menarche was 12.93 years [95% CI, 12.89, 12.98]. Prenatal predictors of menarche by age 11 (12% of girls) included earlier maternal age at menarche, high maternal pre-pregnancy body mass index, smoking during the third trimester, and non-white race; the single postnatal predictor was the girl's body size at 8 years. Age at attainment of breast and pubic hair Tanner stage and age at menarche in the ALSPAC cohort are similar to ages reported in other European studies that were conducted during overlapping time periods. The results also give added support to the strong influence of maternal maturation, pre-adolescent body size and race on the timing of a girl's menarche. This cohort will continue to be followed for maturational information until age 17.

Growth and puberty in German children: is there still a positive secular trend?

BACKGROUND

Since the mid-19th century, growth in German children has accelerated and final height increased. Possible causes of this secular trend include improvements in nutrition, hygiene, and health care. While the upward secular trend still continues in some parts of the world, it seems to be slowing in industrialized countries.

METHODS

Selective literature review.

RESULTS

Reliable data on growth that have been published since the middle of the 19th century reveal an increase in final height by 1 to 2 cm per decade in most European countries. Recent epidemiological studies, however, suggest that human height may be nearing an upper limit, beyond which it cannot increase even with further improvements in nutrition and health care. In Germany and other northern European countries, the upward trend in final height has slowed significantly over the last 30 years; in Germany, it now stands at less than 1 cm/decade. In the same interval, the age at menarche has remained constant at just under 13 years (currently 12.8).

CONCLUSIONS

In Germany, as elsewhere in northern Europe, the upward secular trend in height is slowing (ca. 2 cm/decade up to the mid-20th century, currently less than 1 cm/decade), and the age at menarche has stabilized at just under 13 years. It remains an open question whether the observed slowing will merely be temporary, or whether it indeed represents the near-attainment of an endpoint owing to relatively stable environmental conditions.

Endocrine-disrupting chemicals: an Endocrine Society scientific statement

There is growing interest in the possible health threat posed by endocrine-disrupting chemicals (EDCs), which are substances in our environment, food, and consumer products that interfere with hormone biosynthesis, metabolism, or action resulting in a deviation from normal homeostatic control or reproduction. In this first Scientific Statement of The Endocrine Society, we present the evidence that endocrine disruptors have effects on male and female reproduction, breast development and cancer, prostate cancer, neuroendocrinology, thyroid, metabolism and obesity, and cardiovascular endocrinology. Results from animal models, human clinical observations, and epidemiological studies converge to implicate EDCs as a significant concern to public health. The mechanisms of EDCs involve divergent pathways including (but not limited to) estrogenic, antiandrogenic, thyroid, peroxisome proliferator-activated receptor gamma, retinoid, and actions through other nuclear receptors; steroidogenic enzymes; neurotransmitter receptors and systems; and many other pathways that are highly conserved in wildlife and humans, and which can be modeled in laboratory in vitro and in vivo models. Furthermore, EDCs represent a broad class of molecules such as organochlorinated pesticides and industrial chemicals, plastics and plasticizers, fuels, and many other chemicals that are present in the environment or are in widespread use. We make a number of recommendations to increase understanding of effects of EDCs, including enhancing increased basic and clinical research, invoking the precautionary principle, and advocating involvement of individual and scientific society stakeholders in communicating and implementing changes in public policy and awareness.

Alternatives to animal experimentation for hormonal compounds research

Alternatives to animal testing and the identification of reliable methods that may decrease the need for animals are currently the subject of intense investigation worldwide. Alternative testing procedures are particularly important for synthetic and natural chemicals that exert their biological actions through binding nuclear receptors, called nuclear receptors-interacting compounds (NR-ICs), for which research is increasingly emphasizing the limits of several models in the accurate estimation of the physiological consequences of exposure to these compounds. In particular, estrogen receptor interacting compounds (ER-ICs) have a great impact on human health from the therapeutic, nutritional, and toxicological point of view due to the highly permissive nature of the estrogen receptors towards a large number of natural and synthetic compounds. Similar to in vitro systems, recently generated animal models (e.g., animal models generated for the study of estrogen receptor ligands) may fulfill the 3R principles: refine, reduce, and replace. If used correctly, NR-regulated models, such as reporter mice, xenopus, or zebrafish, and models obtained by somatic gene transfer in reporter systems, combined with imaging technologies, may contribute to strongly decreasing the overall number of animals required for NR-IC testing and research. With these models, flexible and highly standardized parameters and reporter marker quantification can be obtained. Here, we highlight the need for the substitution of currently used testing models with more appropriate ones that can reproduce the features and reactivity of specific mammalian target tissue/organs. We consider the promotion of this advancement a research priority bearing scientific, economic, social, and ethical relevance.

Neonatal exposure to bisphenol a alters reproductive parameters and gonadotropin releasing hormone signaling in female rats

BACKGROUND

Bisphenol A (BPA) is a component of polycarbonate plastics, epoxy resins, and polystyrene and is found in many products. Several reports have revealed potent in vivo effects, because BPA acts as an estrogen agonist and/or antagonist and as an androgen and thyroid hormone antagonist.

OBJECTIVES

We analyzed the effects of neonatal exposure to BPA on the reproductive axis of female Sprague-Dawley rats.

METHODS

Female rats were injected subcutaneously, daily, from postnatal day 1 (PND1) to PND10 with BPA [500 microg/50 microL (high) or 50 microg/50 microL (low)] in castor oil or with castor oil vehicle alone. We studied body weight and age at vaginal opening, estrous cycles, and pituitary hormone release in vivo and in vitro, as well as gonadotropin-releasing hormone (GnRH) pulsatility at PND13 and in adults. We also analyzed two GnRH-activated signaling pathways in the adults: inositol-triphosphate (IP(3)), and extracellular signal-regulated kinase(1/2) (ERK(1/2)).

RESULTS

Exposure to BPA altered pituitary function in infantile rats, lowering basal and GnRH-induced luteinizing hormone (LH) and increasing GnRH pulsatility. BPA dose-dependently accelerated puberty onset and altered estrous cyclicity, with the high dose causing permanent estrus. In adults treated neonatally with BPA, GnRH-induced LH secretion in vivo was decreased and GnRH pulsatility remained disrupted. In vitro, pituitary cells from animals treated with BPA showed lower basal LH and dose-dependently affected GnRH-induced IP(3) formation; the high dose also impaired GnRH-induced LH secretion. Both doses altered ERK(1/2) activation.

CONCLUSIONS

Neonatal exposure to BPA altered reproductive parameters and hypothalamic-pituitary function in female rats. To our knowledge, these results demonstrate for the first time that neonatal in vivo BPA permanently affects GnRH pulsatility and pituitary GnRH signaling.

Recent decline in age at breast development: the Copenhagen Puberty Study

OBJECTIVE

Recent publications showing unexpectedly early breast development in American girls created debate worldwide. However, secular trend analyses are often limited by poor data comparability among studies performed by different researchers in different time periods and populations. Here we present new European data systematically collected from the same region and by 1 research group at the beginning and end of the recent 15-year period.

METHODS

Girls (N = 2095) aged 5.6 to 20.0 years were studied in 1991-1993 (1991 cohort; n = 1100) and 2006-2008 (2006 cohort; n = 995). All girls were evaluated by palpation of glandular breast, measurement of height and weight, and blood sampling (for estradiol, luteinizing hormone, and follicle-stimulating hormone). Age distribution at entering pubertal breast stages 2 through 5, pubic hair stages 2 through 5, and menarche was estimated for the 2 cohorts.

RESULTS

Onset of puberty, defined as mean estimated age at attainment of glandular breast tissue (Tanner breast stage 2+), occurred significantly earlier in the 2006 cohort (estimated mean age: 9.86 years) when compared with the 1991 cohort (estimated mean age: 10.88 years). The difference remained significant after adjustment for BMI. Estimated ages at menarche were 13.42 and 13.13 years in the 1991 and 2006 cohorts, respectively. Serum follicle-stimulating hormone and luteinizing hormone did not differ between the 2 cohorts at any age interval, whereas significantly lower estradiol levels were found in 8- to 10-year-old girls from the 2006 cohort compared with similarly aged girls from the 1991 cohort.

CONCLUSIONS

We found significantly earlier breast development among girls born more recently. Alterations in reproductive hormones and BMI did not explain these marked changes, which suggests that other factors yet to be identified may be involved.

Sustainability, substance-flow management, and time, Part II: Temporal impact assessment (TIA) for substance-flow management

High-quality food and general good health are fundamental needs that have to be satisfied if society is to attain a high standard of living. Accordingly, a great deal of effort is expended in order to guarantee a high quality of food and ensure healthy living conditions. Among other things, these efforts entail massive substance flows. Significant substance flows are connected with the production and consumption of food and can be regarded from an economic, social, or environmental point of view. Substance flows are a part of both nature and the anthroposphere. This study demonstrates that food production at present is not linked to societal issues of production and sustainability; rather, it shows that a systematic approach and an analysis of issues and measures to be taken are required. This interconnectedness can be described as a timescape, in analogy to a landscape. For proper orientation in a landscape, a map is helpful, especially in combination with a compass. In the same way, we need a temporal orientation. Time scales serve as a compass to give orientation. A complete temporal analysis that includes all relevant temporalities provides the information that is encoded in a map. What has to be learned and exercised is the reading of such temporal maps. One method of doing this is temporal impact analysis (TIA). Temporal impact analysis brings issues that are not normally focused on into the foreground. It allows a better understanding of the implications of certain substance flows and the measures necessary for their management, and it provides an opportunity to develop a more sustainable management of substance flows.

The influence of endocrine disruptors on pubertal timing

PURPOSE OF REVIEW

Overview of the effects of endocrine disruptors on pubertal timing.

RECENT FINDINGS

Epidemiologic studies in humans support animal data demonstrating that exposures to endocrine-disrupting compounds have pronounced effects on pubertal timing and that the timing of endocrine-disrupting compound exposure and the specific agent causes different outcomes. Recent studies confirm subtle effects of lead, dioxins, and phytoestrogens on delaying onset of puberty and demonstrate an association of phthalates and polychlorinated biphenyls with earlier breast development and menarche, respectively. These studies, however, are complicated by mixed exposures of compounds which individually may have opposing actions on the reproductive axis.

SUMMARY

Animal and human data confirm perturbations in pubertal onset with exposures to endocrine-disrupting compounds.

Hormonal regulation of hepatic drug-metabolizing enzyme activity during adolescence

Activities of drug-metabolizing enzymes (DMEs) are known to change throughout the course of physical and sexual maturation, with the greatest variability noted during infancy and adolescence. The mechanisms responsible for developmental regulation of DME are currently unknown. However, the hormonal changes associated with puberty/adolescence provide a theoretical framework for understanding the biochemical regulation of DME activity during growth and maturation. Important information regarding potential influences of growth and sex hormones can also be extrapolated from studies that evaluate changes in activities of DMEs occurring as a consequence of physiological, pathological, and/or pharmacological hormonal fluctuations. Collectively, current data support the hypothesis that isoform-specific alterations in DME activity during adolescence are mediated by sex and/or growth hormones. Characterization of the underlying biochemical alterations responsible for developmental changes in DME activity will require additional studies in which relationships between DMEs and important hormonal axes are evaluated during the course of pubertal development.

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.