Height, weight and age at menarche and the "critical weight" hypothesis

Factors that affect menarche in Japanese national-level track-and-field athletes

OBJECTIVES

The minimum body mass index (BMI) required to menarche and the relationship between the training onset age of sports and menarche is not fully understood. The aim of this study is to elucidate the minimum BMI required to attain menarche in female adolescent athletes competing at a national level, and to determine how the occurrence of menarche is associated with training onset age in track-and-field athletes.

METHODS

Overall, 134 sprinters and 44 long-distance (LD) runners of ninth-grade females at a national level were enrolled and an anonymous questionnaire was administered.

RESULTS

As BMI increased, the proportion of athletes who had attained menarche increased. The BMI cutoff values for menarche were 17.3 and 17.1 kg/m² for sprinters and LD runners, respectively. Menarche had not occurred in almost 50% of the LD runners who began training at elementary school, and among LD runners, those who began training at elementary school had 18.4 higher odds of not attaining menarche until the age of 15 years as opposed to those who started training after elementary school.

CONCLUSIONS

The BMI cutoff values could be an indicator for menarche in sprinters and LD runners. For LD runners, starting to compete at elementary school could be a risk factor for delayed menarche.

Birth weight, early life weight gain and age at menarche: a systematic review of longitudinal studies

BACKGROUND AND OBJECTIVE

Adiposity in pre- and postnatal life may influence menarcheal age. Existing evidence is primarily cross-sectional, failing to address temporality, for which the role of adiposity in early life remains unclear. The current study sought to systematically review longitudinal studies evaluating the associations between birth weight and infant/childhood weight status/weight gain in relation to menarcheal age.

METHODS

PubMed, EMBASE, Web of Science, Global Health (Ovid) and CINAHL were systematically searched. Selected studies were limited to English-language articles presenting multi-variable analyses. Seventeen studies reporting risk estimates for birth weight (n = 3), infant/childhood weight gain/weight status (n = 4) or both (n = 10), in relation to menarcheal age were included.

RESULTS

Lower vs. higher birth weight was associated with earlier menarche in nine studies and later menarche in one study, while three studies reported a null association. Greater BMI or weight gain over time and greater childhood weight were significantly associated with earlier menarche in nine of nine and six of seven studies, respectively.

CONCLUSIONS

Studies suggested that lower birth weight and higher body weight and weight gain in infancy and childhood may increase the risk of early menarche. The pre- and postnatal period may thus be an opportune time for weight control interventions to prevent early menarche, and its subsequent consequences.

Sex-Based Differences in Multiple Sclerosis (Part I): Biology of Disease Incidence

Multiple sclerosis (MS) is a chronic autoimmune demyelinating disease that leads to neuron damage and progressive disability. One major feature of multiple sclerosis (MS) is that it affects women three times more often than men. In this chapter, we overview the evidence that the autoimmune component of MS, which predominates in the early stages of this disease, is more robust in women than in men and undergoes a sharp increase with the onset of puberty. In addition, we discuss the common rodent models of MS that have been used to study the sex-based differences in the development of central nervous system (CNS) autoimmunity. We then address the biological underpinnings of this enhanced MS risk in women by first reviewing the autoimmune mechanisms that are thought to lead to the initiation of this disease and then honing in on how these mechanisms differ between the sexes. Finally, we review what is known about the hormonal and genetic basis of these sex differences in CNS autoimmunity.

Puberty in females enhances the risk of an outcome of multiple sclerosis in children and the development of central nervous system autoimmunity in mice

BACKGROUND

For reasons that remain unclear, three times more women develop multiple sclerosis (MS) than men. This preponderance among women is evident only after 12 years of age, implicating pubertal factors in the risk of MS.

OBJECTIVE

To investigate the influence of female puberty on central nervous system (CNS) autoimmunity.

METHODS

We examined the relationship between age of menarche on MS outcomes in 116 female children (< 16 years old) whom presented with incident 'acquired demyelinating syndromes' (ADS) and were followed prospectively in the national Canadian Pediatric Demyelinating Disease Study, from 2004-2013. Furthermore, we directly investigated the effects of puberty on susceptibility to experimental autoimmune encephalomyelitis (EAE) in two groups of female mice that differed only in their pubertal status.

RESULTS

In the ADS children, a later age of menarche was associated with a decreased risk of subsequent MS diagnosis. This relationship persisted, after accounting for patient age at ADS presentation and the presence of ≥1 T2 lesions on brain magnetic resonance imaging (MRI), with a hazard ratio (HR) of 0.64; and additional factors that associate with MS outcomes in ADS children, including low vitamin D levels. Furthermore, we found female mice that had transitioned through puberty were more susceptible to EAE than age-matched, pre-pubertal mice.

CONCLUSION

Puberty in females enhances CNS autoimmune mechanisms that lead to MS in humans and EAE in mice.

[Does childhood obesity affect sexual development?]

The process of pubertal development is only partly understood and is influenced by many different factors. During the twentieth century there was a general trend toward earlier pubertal development. Fat mass is thought to be a major inducer of puberty. Owing to the rising epidemic of childhood obesity, the relationship between body composition in children and the rate and timing of puberty needs to be investigated. Some studies suggest that central obesity is associated with an earlier onset of pubertal development. Rapid weight gain in early life is linked to advanced puberty in both sexes. A clear correlation exists between increasing body mass index (BMI) and earlier pubertal development in girls. In boys the data are controversial: The majority of studies propose that there is an earlier puberty and voice break in obese boys, but some studies show the opposite. There are several factors and mechanisms that seem to link obesity and puberty, for example, leptin, adipocytokines, and gut peptides. Important players include genetic variation and environmental factors (e.g., endocrine-disrupting chemicals). This article presents the latest studies and evidence on this topic, underlining the inconsistencies in the data and, therefore, the need for further research in this area.

The timing of sexual maturation among boys and girls in eastern Poland, 1980-2000: a rural-urban comparison

The aim of this study was to determine secular changes in the sexual maturation of children and adolescents from Eastern regions of Poland between 1980 and 2000, with special attention paid to rural-urban differences. Our sample comprised 34,055 girls and 28,100 boys from 9 to 18 years of age. The age at which each gender reached each stage of sexual maturation was examined, along with menarcheal age in girls. An increase in the rate of sexual maturation was observed over the 20-year period of this study. Menarcheal age in girls decreased by 0.59 years. The length of sexual maturation decreased: from 6.58 years to 3.85 years in girls and from 5.84 years to 3.65 years in boys. A significantly faster rate of sexual maturation was observed between 1990 and 2000. Over the entire 20-year period, adolescents living in rural settings experienced a slower rate of sexual maturation than did their urban peers.

Effects of obesity on human sexual development

Puberty is a period of physical and psychological maturation, with long-term effects on health. During the 20(th) century, a secular trend towards earlier puberty occurred in association with improvements in nutrition. The worldwide pandemic of childhood obesity has renewed interest in the relationship between body composition in childhood and the timing and tempo of puberty. Limited evidence suggests that earlier puberty is associated with a tendency towards central fat deposition; therefore, pubertal status needs to be carefully considered in the categorization of childhood and adolescent overweight and obesity. In the other direction, rapid early weight gain is associated with advanced puberty in both sexes, and a clear association exists between increasing BMI and earlier pubertal development in girls. Evidence in boys is less clear, with the majority of studies showing obesity to be associated with earlier puberty and voice break, although a subgroup of boys with obesity exhibits late puberty, perhaps as a variation of constitutional delay in growth and puberty. The possible mechanisms linking adiposity with pubertal timing are numerous, but leptin, adipocytokines and gut peptides are central players. Other possible mediators include genetic variation and environmental factors such as endocrine disrupting chemicals. This Review presents current evidence on this topic, highlighting inconsistencies and opportunities for future research.

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.

Reproductive development and parental investment during pregnancy: moderating influence of mother's early environment

The association between a woman's age at menarche and the birth weight of her children is highly variable across human populations. Life history theory proposes that a woman's early environment may moderate this association and thus account for some of the variation between populations. According to one life history theory model, for individuals who develop in a childhood environment of high local mortality rates (experienced subjectively as psychosocial stress), it can be adaptive to mature earlier, have more offspring during their reproductive lifetime, and reduce investment in each offspring. In an environment of low psychosocial stress, however, it may be adaptive to mature later, have fewer offspring, and invest more in each. In this study, birth weight and proportionate birth weight (neonate's birth weight as a percentage of its mother's prepregnancy weight) were used as measures of parental investment during pregnancy. In a sample of 580 first-time mothers, we tested the hypothesis that the psychosocial stress experienced as a child would moderate the association between age at menarche and investment during pregnancy. We found that earlier menarche in those women who experienced stressful life events before 15 years of age was associated with a lower birth weight and proportionate birth weight. Conversely, in those who reported no childhood stressors, earlier menarche was associated with increased birth weight and proportionate birth weight. Our data suggest that the moderating influence of the childhood psychosocial environment on the association between age at menarche and parental investment throughout gestation operates in a dose-dependent manner.

Impact of obesity on gynecology

Rising obesity rates around the world have had a profound impact on female reproductive health. Childhood obesity is associated with early onset of puberty, menstrual irregularities during adolescence and polycystic ovary syndrome. Women of reproductive age with high BMIs have a higher risk of ovulatory problems and tend to respond poorly to fertility treatment. Strategies for fertility control can also be complex since the efficacy and safety of hormonal contraceptives can be compromised by increased body weight. Obesity can aggravate symptoms of pelvic organ prolapse, stress urinary incontinence and increase the risk of endometrial polyps and symptomatic fibroids. Weight reduction enhances reproductive outcomes, diminishes symptoms of urinary incontinence and reduces morbidity following gynecological surgery. Sustained and substantial weight loss is difficult to achieve with the lifestyle and dietary measures that are currently available. A number of pharmacological treatment options are available, and there are emerging data on reproductive outcomes following surgical treatment for obesity.

Childhood obesity and the timing of puberty

The potential relationship between childhood obesity and earlier puberty onset has major public health implications. Earlier menarche in girls is associated with increased risk of adult obesity, type 2 diabetes and breast cancer. Current methods for assessing puberty are unreliable, with a lack of consensus regarding the impact of childhood obesity on breast development and/or age of menarche. Effects of obesity on early puberty in boys are more contentious, necessitating development of robust biomarkers. The possibility of the obesity epidemic lowering the age of puberty onset fuels concerns over the growing mismatch in age of sexual and social maturity. Here, we describe the biological basis linking childhood obesity to early puberty and consider evidence for a trend towards its earlier onset.

Menarche is related to fat distribution

The energy demands of pregnancy and lactation together with the accumulation of stored fat in human females during development suggest that a critical level of fat may be required for menarche; but multivariate analyses have supported the alternative view that skeletal growth is the main factor. However, significant differences between upper- and lower-body (gluteofemoral) fat suggest that fat distribution may be more relevant than total fat. Using cross-sectional data from the third National Health and Nutrition Examination Survey (NHANES III) for females aged 10-14, we show that menarche is more closely related to fat distribution than to skeletal maturity. Unit increases in hip circumference are associated with 24% higher odds of menarche while increases in waist circumference and triceps skinfold lower the odds by 7 and 9%, respectively. Those with menarche despite low levels of total body fat have relatively more fat stored in gluteofemoral depots than those without menarche or those with menarche and greater total amounts of fat. In young women with completed growth, age at menarche is negatively related to hip and thigh circumference and positively related to waist circumference, stature, and biiliac breadth; and blood leptin levels are much more strongly related to gluteofemoral than upper-body fat, suggesting that leptin may convey information about fat distribution to the hypothalamus during puberty. Fat distribution may be relevant because gluteofemoral fat may provide neurodevelopmentally important fatty acid reserves.

Reading the signs of starvation

Guidelines for managing malnutrition in adolescent eating disorders are based on limited evidence. Swenne and Engström's study explored the relationship between symptoms, signs and weight status in this patient group, towards refining clinical approaches to nutritional assessment in adolescents.

CONCLUSION

The need to compare findings across studies is crucial for research in nutritional assessment of adolescents

Confirmation of delayed menarche based on regression evaluation of age at menarche for age at MPV of height in female ball game players

A general delay in menarche in female athletes has been confirmed based on comparisons of mean ages between athletes and non-athletes; however, it has not been possible to judge such delays individually. If delayed menarche could be evaluated for an individual, the athlete could be advised as to necessary precautions. In this study, the age at maximum peak velocity (MPV) of height, adopted as an index of physical maturation, was identified by the wavelet interpolation method (WIM). The relationship between the age at menarche and age at MPV of height in female athletes and non-athletes was then examined. For the athlete group, health examination records of 90 female ball game players in the first year of university in the Tokai area, all of whom had participated in national level competitions, were reviewed for the period from the first grade of elementary school until the final year of high school (from 1985 to 1996). A similar examination was conducted for the control group, among whom a final group of 78 female non-athletes were selected. The age at menarche was determined by questionnaires, and the longitudinal data for height and weight were obtained from the health examination records. Based on a comparison of the difference between the age at MPV of height and age at menarche in ball game players and the control group, a tendency was seen for the difference between the two ages to narrow as the age at MPV of height rose. A corrected regression evaluation of age at menarche against age at MPV of height was derived in the control group, and the evaluation system was applied to ball game players. The delay in menarche in ball game players could be individually evaluated.

Reduced Growth Hormone Secretion Prolongs Puberty But Does Not Delay the Developmental Increase in Luteinizing Hormone in the Absence of Gonadal Negative Feedback1

Previous studies have shown that the growth hormone (GH) axis is important for timing the later stages of puberty in female monkeys. However, it is not clear whether these growth-related signals are important for the initiation of puberty and early pubertal events. The present study, using female rhesus monkeys, used two approaches to answer this question. Experiment 1 tested the hypothesis that reduced GH secretion would blunt the rise in nocturnal LH secretion in young (17 mo; n = 7) but not older adolescent ovariectomized females (29 mo; n = 6). Reduced GH secretion was induced by treating females with the sustained release somatostatin analogue formulation, Sandostatin LAR (625 microg/kg). Morning (0900-0930 h) and evening (2200-2230 h) concentrations of bioactive LH were higher in older adolescent compared to young adolescent females. However, diurnal concentrations were not affected by the inhibition of GH secretion in either age group when compared to the placebo-treated, control condition. Experiment 2 tested the hypothesis that reduced GH secretion induced in young juvenile females would delay the initial increase in nocturnal LH secretion and subsequent early signs of puberty. In order to examine this hypothesis, puberty in control females (n = 7) was compared to those in which puberty had been experimentally arrested until a late adolescent age (29 mo) by the use of a depot GnRH analogue, Lupron (750 microg kg(-1) mo(-1); n = 7). Once the analogue treatment was discontinued, the progression of puberty was compared to a group treated in a similar fashion but made GH deficient by continuous treatment with Sandostatin LAR (n = 6). Puberty occurred as expected in control females with the initial rise in evening LH at 21 mo, menarche at 22 mo, and first ovulation at 30 mo. As expected, Lupron arrested reproductive maturation, but elevations in morning and evening LH and menarche occurred within 2 mo of the cessation of Lupron in both Lupron and Lupron-GH-suppressed females. In contrast, first ovulation was delayed significantly in the Lupron-GH-suppressed females (41 mo) compared to the Lupron-only females (36 mo). These data indicate that within this experimental model, reduced GH secretion does not perturb the early stages of puberty but supports previous observations that the GH axis is important for timing the later stages of puberty and attainment of fertility. Taken together, the data indicate that factors that reduce GH secretion may have a deleterious effect on the completion of puberty.

The role of craniofacial growth in leptin deficient (ob/ob) mice

OBJECTIVES

To elucidate the role of leptin on maxillo-facial morphological growth using hereditary obesity model ob/ob mice, and to examine the presence of the leptin receptor gene expression in the mouse condylar head cartilage.

DESIGN

Leptin was intraperitoneally administered once a day in 10 C57BL/6J (lean) and 10 C57BL/6J-ob (ob/ob) mice (leptin administration group), and phosphate-buffered saline (PBS) in 10 lean and 10 ob/ob mice (PBS administration group), between the fifth and 11th week after birth. The amount of fat, the body amount without fat, the rate of body fat, and the width of the condylar cervical area were measured during the 11th week, and roentgenographic cephalometric analysis was performed at the fifth, eighth, and 11th week. Furthermore, the condylar head cartilage in C57BL/6J mice was stereoscopically excised to extract total RNA, and RT-PCR method was performed regarding the leptin receptor gene.

RESULTS

The body fat amount in ob/ob mice with leptin production insufficiency was greater than that in lean mice, and significant differences were noted in every measurement item regarding maxillo-facial morphology. Recovery of bone length was noted in ob/ob mice by administering leptin. Furthermore, the expression of the leptin receptor gene in the condylar head cartilage was confirmed.

CONCLUSION

Exogenous leptin administration leads to significant increases in craniofacial dimensions; and leptin receptors are expressed in mandibular condylar cartilage. These results indicate an important role for leptin in craniofacial growth and morphology. We speculate that leptin's direct peripheral effect on bone and cartilage is closely involved in this role.

Relationship between change in BMI with age and delayed menarche in female athletes

Body mass index (BMI) is widely used as an index of obesity in people from the school age children to adults. However, the relationship between the change in BMI with age and the coming of menarche has not been discussed as there are few reports on the changes in BMI with age. In this study, the change in BMI with age was examined by applying the wavelet interpolation method (WIM), and a critical period for body fat in terms of the coming of menarche was estimated from the growth velocity. We investigated delayed menarche according to the influence of stress in athletes by comparing delayed menarche between athletes and non-athletes in relation to the critical period. Data were obtained from 144 female athletes in their first year at university in the Tokai area, all of whom had competed in a national sports competition in high school (athlete group). Health examination records showing these subjects' heights and weights from the first grade of elementary school to the final year of high school (1984-1995) were collected and BMI was calculated for each grade. Ages at menarche were ascertained from questionnaires. A control group of 73 non-athletes was similarly examined. The age at maximum peak velocity (MPV) derived from the growth (aging) distance curve of BMI was determined in the control group to be 11.96+/-0.97 years old. This age at MPV of BMI was almost the same as the age at menarche (12.11+/-0.93 years old). Therefore, this age at MPV of BMI is estimated to be the critical period of body fat for the coming of menarche. The interval between the age at MPV of BMI and age at menarche was 0.74+/-1.30 years in the athlete group and 0.15+/-0.81 years in the control group, so there was a significant difference (P<0.01) between the two groups. It is suggested that the delayed menarche in athletes is influenced by the stress of regular sports training.

Sexual maturation data for Crl Sprague-Dawley rats: criteria and confounding factors

BACKGROUND

Considerable concern exists in the scientific community regarding potential effects of endocrine disruptive or modulating environmental agents on male and female reproductive development and capacity. Existing data show that in utero and postnatal exposure of rodents to endocrine modulating chemicals can influence the timing and progression of sexual differentiation and/or maturation (e.g., balanopreputial separation and vaginal opening).

METHODS

Sexual maturation data from various types of littering studies using International Gold Standard (IGS) Crl Sprague-Dawley rats were evaluated for consistency with both historical observations and published values from other laboratories. In addition, litters from two developmental neurotoxicology studies were statistically analyzed to identify whether increasing the numbers of pups per litter evaluated affected the interpretation of sexual maturation data sets.

RESULTS

Control values for preputial separation and vaginal opening ages ranged from PD 45.0 to 48.0 and from PD 32.0 to 34.0, respectively, regardless of the number of pups evaluated per litter. However, statistically significant delays in sexual maturation were present when three rats/sex/litter were evaluated that were not present when only one randomly selected rat/sex/litter was evaluated.

CONCLUSIONS

Standardized procedures and criteria are required to provide consistent intra-laboratory values and reduce inter-laboratory differences in sexual maturation observations. When such criteria are used, these endpoints provide sensitive measures for detecting alterations in sexual maturation. However, our analyses demonstrate that the ability to detect statistically significant and biologically important differences in these endpoints is sometimes impaired by the currently common practice of evaluating only one randomly selected rat/sex/litter. Evaluation of three rats/sex/litter improved the sensitivity of the statistical analysis in detection of treatment-related effects and reduced the probability of identifying a false negative result.

Body mass index and age at menarche in an adolescent clinic population

Body fatness as a determinant of menarche has been studied extensively, but limited to underweight females. Adolescent female patients were measured and interviewed. Subjects were divided into three groups based on body mass index (BMI) standard deviation score (SDS). Average age at menarche was 11.87 +/- 1.1 years in the obese group, 12.14 +/- 0.9 years in the overweight group, and 12.20 +/- 1.3 years in the normal weight group. Pearson correlation factor between BMI SDS and age at menarche was -0.24 (p < 0.01). These findings suggest an important role of increased body fatness on menarche that extends beyond underweight girls.

Gender-related differences in elite gymnasts: the female athlete triad

High-intensity training can alter the normal pattern of pubertal development in elite gymnasts. We investigated sex hormones, the ob gene product leptin, body composition, nutrition, and eating habits in female and male elite gymnasts from national cadres to elucidate gender-related differences. Serum leptin levels were decreased, particularly in pubertal girls, and did not show the normal developmental pattern. After leptin levels were transformed into standard deviation scores, mainly pubertal female gymnasts had significantly lower values than normal controls of the same gender, pubertal stage, and body mass index. The percentage of body fat was reduced compared with a normal age-matched population in both genders but to a higher degree in female gymnasts. When leptin standard deviation scores were based on percent body fat instead of body mass index, mean values were still significantly decreased compared with those of normal controls: -1.05 in girls (P < 0.001) and -0.60 in boys (P = 0.025). In both genders, total energy consumption and nutritional intake were insufficient, although to a lesser extent in male gymnasts. Pubertal development is influenced to a different degree in female and male elite gymnasts. In contrast to their male counterparts, high-intensity training takes place during the sensitive phase of pubertal maturation in female gymnasts. Whereas the girls displayed low estrogen levels, hypoleptinemia, reduced body fat mass, insufficient caloric intake, and retarded menarche, the pubertal development of male gymnasts remained almost unaltered.

Body fat mass, leptin and puberty

Leptin, the ob gene product, provides a molecular basis for the lipostatic theory of the regulation of energy balance. Leptin circulates as a monomeric 16 kDa protein in rodent and human plasma and is also bound to leptin binding proteins that may form large high molecular weight complexes. Initial models of leptin action included leptin-deficient ob/ob mice and leptin-insensitive db/db mice. Peripheral or central administration of leptin reduced body weight, adiposity, and food intake in ob/ob mice but not in db/db mice. In ob/ob mice leptin treatment restored fertility. Leptin interacts with many messenger molecules in the brain. For example, leptin suppresses neuropeptide Y (NPY) expression in the arcuate nucleus. Increased NPY activity has an inhibitory effect on the gonadotropin axis and represents a direct mechanism for inhibiting sexual maturation and reproductive function in conditions of food restriction and/or energy expenditure. By modulating the hypothalamo-pituitary-gonadal axis both directly and indirectly, leptin may thus serve as the signal from fat to the brain about the adequacy of fat stores for pubertal development and reproduction. Normal leptin secretion is necessary for normal reproductive function to proceed and leptin may be a signal allowing for the point of initiation of and progression toward puberty.

Crescimento pós-menarca

Embora a menarca seja um fenômeno tardio dentro do processo puberal, muitos pais percebem, só neste momento, que suas filhas não são mais crianças. Os pediatras são procurados nessa ocasião para esclarecer certas dúvidas e tranqüilizá-los. Com certa freqüência, indagam sobre o potencial de crescimento da menina e pedem que seja estimada sua estatura final. A literatura a respeito do crescimento pós-menarca é escassa, talvez devido às próprias características da adolescência que, por envolver inúmeras variáveis, dificulta a interpretação dos resultados. Esta revisão bibliográfica tem como objetivo focalizar alguns aspectos relacionados ao crescimento, que auxiliem o médico a oferecer um prognóstico um pouco mais preciso do que médias populacionais, para a adolescente que o questiona a respeito, considerando-se que ela já tenha menstruado. Não existe correlação entre a idade em que o pico de velocidade de crescimento ocorre e a estatura final. Na menarca, a adolescente já alcançou 95,5% da estatura final. Por mais 3 ou 4,8 anos, incrementos progressivamente menores irão ocorrer. As meninas que maturam mais cedo (menstruando antes da idade mediana de 12,6 anos para a ocorrência da menarca) provavelmente crescerão mais do que a média de 6 ou 7cm, e por mais tempo, do que as que maturam mais tarde, até atingirem sua estatura final.

The role of leptin in human growth and puberty

Experimental animal studies demonstrate the effects of leptin on appetite, weight gain and metabolism. The biological effects of leptin in human adults are still to be determined, but recent reports show that congenital leptin deficiency leads to hyperphagia and excessive weight gain from early infancy as well as failure of pubertal onset in adolescence. Our recently reported data from two longitudinal cohorts suggest a role for leptin in the normal regulation of childhood weight gain, maturation and the development of secondary sexual features and body composition. Low leptin levels in cord blood closely reflected decreased adiposity at birth and strongly predicted high rates of weight gain in infancy and catch-up growth. In adolescents, leptin levels rose gradually with age prior to puberty, suggesting that a threshold effect may trigger puberty. In girls, low leptin levels at the start of puberty predicted large gains in the percentage of fat mass, perhaps suggesting a role in the preparation for childbearing.

Leptin concentrations in precocious puberty or untimely puberty with and without GnRH analogue therapy

Nutritional status and body composition influence the development and maintenance of reproductive competence in mammals. It has been suggested that leptin concentrations communicate nutritional status to the neuroendocrine reproductive axis. To determine the interrelationship between circulating gonadotropin and leptin concentrations, leptin concentrations were measured in 39 children treated for GnRH dependent precocious or untimely puberty. Leptin concentrations were obtained during pubertal suppression with GnRH analogue therapy and during spontaneous pubertal gonadotropin secretion. The status of gonadotropin secretion (suppressed vs not suppressed) was verified by simultaneous GnRH stimulation tests and sex steroid concentrations. Leptin concentrations were similar at both time-points and correlated only with body mass index. Thus, no relationship was apparent between circulating concentrations of gonadotropins, sex steroids, and leptin.

Hypoleptinemia in female and male elite gymnasts

BACKGROUND

Elite gymnasts favour low body fat mass as the current aesthetic ideal required for complex movements in this sports discipline. Pubertal development and growth are retarded in juvenile gymnasts. Leptin, the protein product of the ob-gene, is secreted by fat cells. Besides its role in regulation of body weight, leptin also stimulates the reproductive axis. We investigated various serum hormones including leptin, body composition and nutrition in cohorts of female and male elite gymnasts to elucidate if there is a relationship between leptin levels and delayed puberty in elite gymnasts.

MATERIALS AND METHODS

Twenty-two female and 18 male elite gymnasts were enrolled in this study. Pubertal stage, various hormonal levels and body composition were determined and nutritional intake was assessed. Leptin was analysed using a specific RIA.

RESULTS

Pubertal development and growth were delayed in the study group, especially in girls. The percentage of body fat was reduced as compared to a normal age-matched population: 14.4% versus 21.9% in girls and 10.4% versus 15.1% in boys. Serum leptin levels were decreased, especially in pubertal girls, and did not show the normal developmental pattern with a steady increase in girls and a peak in boys of pubertal stage 2. In all gymnasts leptin levels correlated with the amount of fat mass (r = 0.6, P = 0.005 in girls; r = 0.44, P = 0.038 in boys). When leptin levels were transformed into standard deviation scores (SDS) it became obvious that the gymnasts, especially pubertal females, had significantly lower values than normal controls of the same sex, pubertal stage and body mass index (BMI): leptin SDS (BMI) = -1.21 and -3.99 in prepubertal and pubertal girls, - 0.94 and -0.91 in prepubertal and pubertal boys, respectively. When leptin SDS were based on % body fat instead of BMI, mean values were still significantly decreased compared to normal controls: -1.05 in girls (P < 0.001) and -0.60 in boys (P = 0. 025).

CONCLUSIONS

Adjustment of serum leptin levels in elite gymnasts for gender, pubertal stage and BMI or % body fat reveals inappropriately low values. The reason for this hypoleptinemia is most probably insufficient caloric intake. The data suggest that hypoleptinemia in turn causes delayed puberty and growth in this particular group of athletes.

Heart 'growth stagnation' during the year following menarche

During puberty, most body structures show an acceleration followed by deceleration in growth, while some grow at a constant rate. This study analyses heart growth dynamics during puberty. The focus was directed towards detection of 'unexpected' events in pubertal physiological growth, such as an episode of a heart growth stagnation or even a temporary reduction in size. A longitudinal study was performed in 173 healthy children (81 girls and 92 boys), aged 11.5 years at the beginning and 14.5 years at the end of the study. Changes in echocardiographic (parasternal M-mode) cardiac dimensions and in anthropometric and ergometric size of related body structures and functions were recorded annually. Direction (positive, zero or negative) and sizes of yearly increments were determined from the measurements, and three annual growth rates were compared for each variable by paired sample t-test. All observed variables increased following the usual growth velocity curve in boys. In girls, body height and weight, lean body mass, aortal root and left atrium, as well as diastolic blood pressure changed in the expected way during puberty, but cardiac left ventricle and endurance time did not. At the age of 13, thickness of the left ventricular walls and length of endurance time did not increase; later the growth of these variables resumed. Menarche onset (12.6 years) immediately precedes these events. Possible mechanisms are: temporary reduction of myocardial cells growth and division, and physiological heart "remodelling' due to changed growth pattern favouring longitudinal instead of transverse myofibrils growth, increased myocardial diastolic compliance and oscillatory blood volume increase.

Critical anthropometry for menarche

The objective of the study was to determine if any anthropometric measurements, including weight, height, and upper arm circumference, or the calculated body mass index observed at the time of menarche may be used as a threshold for menarche. The sample was randomly selected from 1133 girls aged 10-18 years from two groups, one residing in Lima, Peru, at 150 m above sea level, and the second in Cerro de Pasco, Peru, at 4340 m above sea level. For the purpose of this study, all girls who reached menarche at least 1 month before the study (n = 93) were considered as cases (girls at menarche); 88 girls without menarche at the time of the study were randomly matched by age and place of residence, and designated as controls. All subjects came from the same low socioeconomic status. Body weight at menarche was 44.6 +/- 5.09 kg (mean +/- SD; coefficient of variation [CV], 11.4%). Height at menarche was 151.6 +/- 5.5 cm (CV, 3.7%). Body mass index, defined as weight/height2.15, was 18.26 +/- 1.96 kg/m2.15 at menarche (CV, 10.7%). Upper arm circumference at menarche was 21.8 +/- 1.6 cm (CV, 7.3%). The logistic regression analysis showed that any of the four anthropometric measurements analyzed were critical for menarche; i.e., any of the four could be used as a threshold for menarche. Data from the present study do not support the hypothesis that there are anthropometric markers that are critical for menarche.

Differential fertility and body build in !Kung San and Kavango females from northern Namibia

The study examines the impact of body build on differential fertility patterns in 93 !Kung San and 85 Kavango females from northern Namibia. In both groups shorter females had more offspring, but also more dead offspring, than taller females. The interaction between body weight and fertility was different in both groups and may be due to different nursing behaviour. There was a positive relationship between the typical pedomorphy and fertility in the !Kung San, and directional selection processes may be important.

Genetic correlates of menarcheal age: a multivariate twin study

Multivariate genetic models were fitted to data from 44 pairs of MZ and 42 pairs of DZ twin girls on weight, height, and skeletal maturation at the age of menarche, in order to obtain information on genetic relationships of those measures with the age of menarche. The relationships of all three physical measures with this age were largely genetically controlled, but a genetic system controlling skeletal maturity was identified as the only genetic determinant of menarcheal age, independent of those systems of the two remaining physical measures. Heritabilities of all individual traits considered in the study were uniformly high. Possible links of genetic information with hormonal functions determining menarche are discussed.

Expected gain in body mass and onset of the menarche

Fertility is dependent on sexual maturity, which is associated with a number of factors, including body mass. In this study the Body Mass Index (BMI) was used to estimate body fat in a large sample of 13-year-old New Zealand girls. Nearly half of the subjects (46%) had experienced the menarche. Expected gain in body mass was calculated from growth rates at earlier ages and used to examine whether deviation from the expected gain was associated with the onset of the menarche. In general, the results show an association between the menarche and gain in body mass. However, many girls who failed to achieve their expected gain had experienced the menarche (18%), indicating that the relationship between body weight and the menarche may not be causal or is mediated by other factors.

Lack of linkage between height and weight and age at menarche during the secular shift in growth of Japanese children

During the past century, Japanese children have shown a most dramatic secular trend toward earlier menarche and accelerated tempo of growth. In order to assess the inter-relationship between these dual secular trends, we analysed the data on height and weight measurements of Japanese children, collected by the Japanese Ministry of Education in the years from 1900 through 1986, with reference to various retrospective studies on the age of menarche among Japanese. Between 1950 and 1983, both the mean height and weight at menarche varied significantly but percentage of the mean height achieved at menarcheal age, as compared with the mature height, remained relatively stable at approximately 95%. The results indicate that the secular trend toward earlier menarche reflects largely, if not solely, the secular change in tempo of physical growth in Japanese children.

Sexual maturation in underfed weight-matched rats. A test of the "critical body weight" theory of pubertal timing in males

A popular current theory proposes that the timing of puberty is related to attainment of a critical level of body weight or body fatness. These critical body weight and critical body fat theories have been studied almost exclusively in females. To explore these theories in males, we tested a corollary of these hypotheses: are male rats of the same weight all at the same level of sexual maturation irrespective of prior growth rate? Male rats growing in body weight at five different rates due to various degrees of underfeeding (beginning at weaning) were sacrificed at body weight milestones of 123 and 279 grams. At the first weight milestone, significant (P less than 0.01) inverse correlations were observed among these weight-matched rats between the preceding rate of body weight growth and prostate weight, seminal vesicle weight, testis weight, serum testosterone, and daily sperm production rate, indicating that the underfed animals were more sexually mature. Testis histology also showed that spermatogenic development increased progressively as the prior rate of body weight growth was reduced. These parameters of sexual maturation tended to correlate inversely with body fatness (i.e., leaner animals were more sexually mature) and directly with body length (i.e., longer animals were more sexually mature). By the second body weight milestone, however, the degree of prior underfeeding exerted little effect on those indices of sexual development. We conclude that the degree of sexual maturation in weight-matched animals with varying previous patterns of body weight growth correlates inversely with body fatness and the rate of body weight growth but correlates directly with body length.(ABSTRACT TRUNCATED AT 250 WORDS)

[Growth rate and development in feed restricted female rats]

Age and weight were determined by direct measure in 30 feed-restricted female rats studied from weaning to first estrus, and compared to well fed controls. At the first estrus the average weight of well fed rats did not differ from that of the feed-restricted groups. Mean ages at vaginal opening and first estrus in the feed-restricted animals were however greater.

Body weight and/or fatness as potential determinants of the onset of egg production in broiler breeder hens

In four trials during consecutive years individually-caged birds were weighed at first egg, and in the first two trials they were then killed to determine abdominal and skin fat, in order to establish whether there is a minimal body weight and/or body fat pool required for the start of egg production in broiler breeder hens. There were negative correlations ranging from significant to negligible between body weight and age at first egg. For birds of the same strain on a conventional food restriction regimen, the average weight range at first egg in the four trials was 3.3 to 3.7 kg, which may be a strain characteristic. In spite of severe food restriction, all birds were very fat at first egg. The correlations between fat concentration and age at first egg were negative. In mature pullets a minimum concentration of stored, easily mobilised fat may be essential for yolk formation and ovulation.

Sex hormone profiles of premenarcheal athletes

Female gymnasts have a delayed onset and probably retarded progression of puberty. The aim of this study was to test the hypothesis that the delay in onset of puberty in gymnasts as compared to girl swimmers is modulated by a lower estrone level due to a smaller amount of body fat. The sex-hormone and gonadotropin levels of 46 gymnasts and 37 girl swimmers of the same biological maturation (breast development: M = 1 or M = 2) were studied. In each subject the following hormones were measured in plasma: estrone, 17-beta-estradiol, DHEAS, testosterone, androstenedione, LH, and FSH. In prepubertal children (M = 1) the levels of estrone, testosterone, and androstenedione were lower in the gymnastic group as compared to the swimming group. In the early pubertal (M = 2) gymnastic and swimming groups these hormone levels were no longer different. The other hormone levels were not significantly different in either the prepubertal groups or the early pubertal ones. Within the total prepubertal group there is a clear relationship between the estrone levels and the levels of testosterone and androstenedione, but not between estrone and 17-beta-estradiol, nor between the calculated fat mass and any of the hormone levels. It appears that the androstenedione and testosterone levels are responsible for the difference in estrone level, rather than the amount of body fat.