Age at menarche, probability of ovulation and breast cancer risk

Hair Dye Ingredients and Potential Health Risks from Exposure to Hair Dyeing

Given the worldwide popularity of hair dyeing, there is an urgent need to understand the toxicities and risks associated with exposure to chemicals found in hair dye formulations. Hair dyes are categorized as oxidative and nonoxidative in terms of their chemical composition and ingredients. For several decades, the expert panel's Cosmetic Ingredient Review (CIR) has assessed the safety of many of the chemicals used in hair dyes; however, a comprehensive review of hair dye ingredients and the risk of exposure to hair dyeing has not been documented. Herein, we review the safety of the various chemicals in oxidative and nonoxidative hair dyes, toxicities associated with hair dyeing, and the carcinogenic risks related to hair dyeing. While many compounds are considered safe for users at the concentrations in hair dyes, there are conflicting data about a large number of hair dye formulations. The CIR expert panel has ratified a number of coloring ingredients for hair dyes and banned a series of chemicals as carcinogenic to animals and unsafe for this application. The use of these chemicals as raw materials for producing hair dyes may result in the synthesis of other contaminants with potential toxicities and increased risk of carcinogenesis. It is an open question whether personal or occupational hair dyeing increases the risk of cancer; however, in specific subpopulations, a positive association between hair dye use and cancer occurrence has been reported. To address this question, a better understanding of the chemical and mechanistic basis of the reported toxicities of hair dye mixtures and individual hair dye ingredients is needed. It is anticipated that in-depth chemical and systems toxicology studies harnessing modern and emerging techniques can shed light on this public health concern in the future.

Pubertal Growth, IGF-1, and Windows of Susceptibility: Puberty and Future Breast Cancer Risk

PURPOSE

Risk markers for breast cancer include earlier onset of menarche (age at menarche [AAM]) and peak height velocity (PHV). Insulin-like growth factor-1 (IGF-1) is associated with pubertal milestones, as well as cancer risk. This study examined the relationships between pubertal milestones associated with breast cancer risk and hormone changes in puberty.

METHODS

This is a longitudinal study of pubertal maturation in 183 girls, recruited at ages 6-7, followed up between 2004 and 2018. Measures included age at onset of puberty, and adult height attained; PHV; AAM; adult height, and serum IGF-1, and estrone-to-androstenedione (E:A) ratio.

RESULTS

PHV was greatest in early, and least in late maturing girls; length of the pubertal growth spurt was longest in early, and shortest in late maturing girls. Earlier AAM was related to greater PHV. IGF-1 concentrations tracked significantly during puberty; higher IGF-1 was related to earlier age of PHV, earlier AAM, greater PHV, and taller adult height. Greater E:A ratio was associated with earlier AAM.

CONCLUSIONS

Factors driving the association of earlier menarche and pubertal growth with breast cancer risk may be explained through a unifying concept relating higher IGF-1 concentrations, greater lifelong estrogen exposure, and longer pubertal growth period, with an expanded pubertal window of susceptibility.

Reproductive and hormonal factors and risk of cognitive impairment among Singapore Chinese women

BACKGROUND

Epidemiologic studies suggest that declining estrogen levels in menopause may play an important role in the pathogenesis of dementia and contribute to increased risk of cognitive impairment in women. Most previous studies have been conducted in Western populations to investigate the relationship of the length of reproductive periods and use of hormone-replacement therapy with risk of cognitive function and dementia, but the findings are inconclusive. Relevant evidence among Asian populations is limited.

OBJECTIVES

To evaluate the association between reproductive and hormonal factors and the risk of cognitive impairment in Chinese women with natural menopause.

STUDY DESIGN

The Singapore Chinese Health Study is a population-based study that recruited participants aged 45-74 years between 1993 and 1998, and the current study included 8222 women from this cohort who had natural menopause, complete data on reproductive factors and hormonal therapies at baseline (1993-1998), follow-up 1 (1999-2004) and follow-up 2 interviews (2006-2010), and cognitive function evaluated at ages 61-96 years using the Singapore Modified Mini-Mental State Examination during the follow-up 3 visits (2014-2016). Multivariable logistic regression models were used to estimate odds ratios and 95% confidence intervals for the risk of cognitive impairment.

RESULTS

Compared with women with menopause at 50-54 years of age, the odds ratios (95% confidence interval) were 1.67 (1.32-2.11), 1.24 (1.08-1.44), and 1.06 (0.87- 1.29) for women who experienced menopause before 45 years, at 45-49 years of age, and after 54 years, respectively. Compared with women with 35-39 reproductive years from menarche to menopause, the odds ratios (95% confidence interval) were 1.28 (1.11-1.48) for women with <35 reproductive years. Furthermore, compared with women who had 1-2 children, the odds ratios (95% confidence interval) were 1.27 (1.04-1.55) for women who had more than 5 children, and the risk increased significantly by 5% per child birth (odds ratio, 1.05; 95% confidence interval, 1.01-1.09). Compared with those who had never used oral contraceptives, women with short-term use (≤5 years) of oral contraceptives had 26% lower odds of having cognitive impairment (odds ratio, 0.74; 95% confidence interval, 0.63-0.87), whereas the association was not statistically significant for those used for more than 5 years (odds ratio, 0.87; 95% confidence interval, 0.68-1.13). Women who used hormone-replacement therapy had a 39% lower odd of getting cognitive impairment compared with nonusers (odds ratio, 0.61; 95% confidence interval, 0.46-0.80).

CONCLUSION

Our data suggest that shorter reproductive years and greater parity were associated with a greater risk of cognitive impairment in late life, whereas the use of oral contraceptives and hormone-replacement therapy was associated with decreased risk. As the population ages, understanding how these factors affect late-life cognitive function in women may help health professionals develop preventive measures targeting lifetime estrogen exposure from endogenous or exogenous sources.

Menstrual Patterns in the First Gynecological Year: A Systematic Review

STUDY OBJECTIVE

Understanding what constitutes a normal menstrual cycle during the first gynecological year (GY1) is a common concern of adolescents and clinicians. However, limited high-quality evidence exists. We aimed to summarize published literature regarding menstrual and ovulatory patterns in GY1. DESIGN, SETTING, PARTICIPANTS, INTERVENTIONS, AND MAIN OUTCOME MEASURES: Electronic databases (MEDLINE, Pre-MEDLINE, Embase, Web of Science, CINAHL, Cochrane Library) were systematically searched from database inception to 2018. Eligible studies described menstrual cycles, symptoms, or validated ovulatory data in healthy adolescents in GY1. Two authors independently screened studies, extracted data, and assessed methodological quality.

RESULTS

Twenty-two studies involving more than 2000 adolescents were included. Thirteen recorded menstrual cycle and/or symptom data and 14 measured ovulation. Mean cycle length ranged from 32 to 61 days and decreased throughout GY1. Mean menses length was 4.9 to 5.4 days. Frequent menstrual bleeding was reported in up to 23% of participants, infrequent menstrual bleeding in up to one-third, and "irregular menstrual bleeding" in up to 43%. Dysmenorrhea was reported by 30%-89% of participants. Prevalence of ovulatory cycles identified using luteal phase serum or salivary progesterone or urinary pregnanediol was 0 to 45% and increased throughout GY1. However, all used definitions that would be considered subovulatory in clinical practice.

CONCLUSION

Menstrual and ovulatory patterns in GY1 are diverse and differ from those of adults. A transitional phase of menstrual and ovulatory immaturity is common. However, ovulation, irregular cycles, and dysmenorrhea are not uncommon. As such, safe sexual practice should be advocated and prompt medical management should be accessible.

Dynamics of body time, social time and life history at adolescence

Recent opposing trends towards earlier physical maturation and later social maturation present a conundrum of apparent biological-social mismatch. Here we use life history analysis from evolutionary ecology to identify forces that drive these shifts. Together with findings in developmental science, our life history analysis indicates that adolescence is a distinctive period for biological embedding of culture. Ethnographic evidence shows that mass education is a novel feature of the globalizing cultural configurations of adolescence, which are driven by transformations in labour, livelihood and lifestyle. Evaluation of the life history trade-offs and sociocultural ecologies that are experienced by adolescents may offer a practical basis for enhancing their development.

The LEP G-2548A gene polymorphism is associated with age at menarche and breast cancer susceptibility

Leptin is an adipocytokine made by fat cells and plays a key role in proliferation, cell survival, migration and immune response. It has a powerful effect on the initiation of puberty and in determining age at menarche. The current study is the first investigation to examine the effect of G-2548A leptin gene polymorphism on the age at menarche and breast cancer susceptibility. This case-control study was performed on 203 patients with breast cancer and 171 healthy women. The leptin genotypes were determined using the PCR-RFLP method and age at menarche was obtained by questionnaires. There was a significant difference between the leptin G-2548A genotypes between case and control groups (P<0.05). AA genotype is significantly higher in patients compared to the controls. Furthermore, women carrying the AA genotype had a significantly younger age at menarche (12.47 years) than women with the AG (12.94 years) and GG (13.47 years) genotypes. Also, we found that the AA genotype frequency in women with age at menarche <13 years was higher than in women with age at menarche ≥13 years (OR: 3.4, 95% CI: 1.7-6.7, P: 0.001). In conclusion, the G-2548A leptin gene polymorphism has an important role in the onset of menarche and breast cancer susceptibility.

Relationship of age at menarche on anthropometric index and menstrual irregularity in late adolescent girls in Seoul

PURPOSE

To examine the relationship between menarcheal age and anthropometric indices and menstrual irregularity in late adolescent girls in Seoul.

METHODS

We surveyed 4,218 fertile adolescent girls between the ages of 16 and 18 years to determine their anthropometric indices and menarcheal age. Measurements were taken from June 2008 to October 2009 at seven girl's high schools in Seoul, Korea. Participants were offered self-report questionnaire as a survey tool that included questions on anthropometric indices (height, weight, waist circumference), menarcheal age, menstrual pattern, frequency of menstruation per year.

RESULTS

THE PARTICIPANTS WERE CATEGORIZED INTO THREE GROUPS BASED ON MENARCHEAL AGE: early menarche group (younger than 2 standard deviations [SD]), mid menarche group (within ±2 SD), late menarche group (older than 2 SD). The mean age of early menarche group was 9.9±0.2 years, mid menarche group 12.5±0.9 years, late menarche group 15.1±0.3 years (P < 0.001). Heights were recorded as 160.4±5.2 cm, 161.8±4.9 cm, 162.3±4.7 cm in early, mid, and late menarche group, respectively (P = 0.001). Body mass index (BMI) and waist circumference significantly were lager in early menarche group than mid and late menarche ones (P < 0.001). The menarcheal age had a positive correlation with height and negative correlations with weight, BMI, waist circumference (P < 0.001). The prevalence of oligomenorrhea was more frequent in late menarche group than early and mid menarche group.

CONCLUSION

The menarcheal age have positive relationship with height and inverse relationship with BMI and waist circumference in late adolescent girls in Seoul. Late menarcheal girls are disposed to have menstrual irregularity compared to early menarcheal girls.

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.

Life-time estrogen exposure and cognitive functioning in later life

CONTEXT

While recent studies suggest that exogenous estrogen treatment could help reduce age-related cognitive decline and delay the onset of dementia, this has not been found consistently. Few studies have considered the influence of life-time estrogen exposure which may have an independent effect on cognition and/or modulate treatment response.

OBJECTIVE

The aim of this study was to examine whether factors related to estrogen exposure across the life-time were associated with cognitive function in postmenopausal women.

DESIGN

A battery of cognitive tests were administered at baseline and at 2 and 4 years of follow-up to evaluate cognitive performance among a population-based cohort of 996 French women aged 65 years or older, who were recruited as part of the ESPRIT study. Detailed reproductive histories were also obtained. Logistic regression models, controlling for an extensive range of potential confounding factors, were generated to determine whether hormone-related factors across a woman's lifetime were associated with poor cognitive performance in later life.

RESULTS

Age at first menses was negatively associated with performance on the tasks of visual memory and psychomotor speed, while a longer reproductive period was associated with better verbal fluency. Likewise, women who had their first child at a young age performed significantly worse on each of these tasks, as well as on a measure of global cognitive function. The results also suggest that current hormone therapy may be beneficial for a number of cognitive domains, however, in multivariate analysis, women performed significantly better on the task of visual memory only. In contrast, in analysis adjusted for baseline cognitive performance and a range of other factors, none of the reproductive variables were associated with a decline in cognitive performance or the incidence of dementia during the 4-year follow-up period.

CONCLUSIONS

In addition to hormone therapy, certain hormone-related events across the lifetime are also associated with cognitive functioning in later life. They were not observed in this study to modulate dementia risk; however, this should be verified over a longer follow-up period. Further studies will also be required to determine whether lifetime hormonal exposure may modify women's response to hormone therapy after the menopause.

Progesterone receptor isoform functions in normal breast development and breast cancer

Progesterone acting through two isoforms of the progesterone receptor (PR), PRA and PRB, regulates proliferation and differentiation in the normal mammary gland in mouse, rat, and human. Progesterone and PR have also been implicated in the etiology and pathogenesis of human breast cancer. The focus of this review is recent advances in understanding the role of the PR isoform-specific functions in the normal breast and in breast cancer. Also discussed is information obtained from rodent studies and their relevance to our understanding of the role of progestins in breast cancer etiology.

Reproductive factors and breast cancer risk among older women

Reproductive factors have been shown to affect pre- and postmenopausal breast cancer risk differently, but whether there are additional age-specific differences among menopausal women as they age has not been clarified. We analyzed data from a large population-based case-control study that included 1,508 breast cancer cases and 1,556 controls, aged 20-98 years, who completed an in-home interviewer-administered questionnaire. The following subgroups were created to examine if the associations between reproductive factors and breast cancer risk varied by age- and menopausal-status: premenopausal (n=968), postmenopausal <65 years (n=1,045), postmenopausal >or=65 years (n=958). Among postmenopausal women >or=65 years, ever having breastfed decreased risk (odds ratio (OR)=0.67, 95% confidence interval (CI)=0.48, 0.92), and a strong dose-response relationship was observed for longer durations of breastfeeding (P trend=0.02), with the most pronounced protective effect observed for >or=14 months of breastfeeding (OR=0.40, 95% CI=0.21,0.76). Late age at first birth (AFB) and older age at last birth (ALB) were associated with non-statistically significant increases in breast cancer risk in this older group, while late age at menarche and surgical menopause decreased risk. ORs for multiparity were close to the null. Among premenopausal women and postmenopausal women <65 years, multiparity significantly decreased risk, and older AFB nonsignificantly increased risk. Our findings suggest that the well-known protective effect of multiparity attenuates with older age. Moreover, breastfeeding, one of the few potentially modifiable risk factors for breast cancer, was an important factor in decreasing risk among older parous postmenopausal women.

Hormonal aspects in the causation of human breast cancer: epidemiological hypotheses reviewed, with special reference to nutritional status and first pregnancy

Epidemiology of breast cancer has identified early age at menarche, late first pregnancy, low parity and late menopause as risk factors, but in addition genetic factors, height, weight and living in western countries play a significant role. The international variation in incidence is almost exclusively due to non-genetic factors. Hypotheses in prevention-oriented research are reviewed: 1. obesity-related oestrogen production as a stimulus of the tumour in postmenopausal women; 2. nutritional status and energy expenditure during puberty and adolescence, developed for fertility and fecundity and extended later to breast cancer; 3. reproductive life during early adulthood, age at first pregnancy and its specific effects on breast tissues. The message of preventability of breast cancer is that mammary epithelial differentiation should come early. Our insight concerning events in puberty and early adulthood can be consolidated in one concept on the risk of extended proliferation of breast epithelium during early adulthood in the absence of full differentiation induced by pregnancy. The combined effects of Western-type nutrition, lack of exercise and Western-type women's emancipation sets the stage for breast cancer already at a young age. Since it is unlikely that emancipated women in affluent societies will return to the original life-style of getting pregnant as soon as it is biologically possible, a novel daring way of protection has to be considered. Could a "Breast Differentiation Pill" be developed to offer protection?

Interpreting the continued decline in the average age at menarche: results from two nationally representative surveys of U.S. girls studied 10 years apart

OBJECTIVES

To determine whether average age at menarche declined in the United States during the past decade, and whether associations between menarcheal timing, weight status, and race/ethnicity changed.

STUDY DESIGN

Relative weight, race/ethnicity, and menarcheal status of girls (n = 1577) in the National Health and Nutrition Examination Survey (NHANES) III (1988-1994) were compared with those of girls (n = 1720) in NHANES 1999-2002. Probit analysis estimated average age at menarche overall and also by race/ethnicity. Logistic regression assessed associations of relative weight and race/ethnicity with menarcheal status.

RESULTS

In the United States, average age at menarche declined from 12.53 years (95% confidence interval [CI] = 12.43 to 12.63 years) in 1988-1994 to 12.34 years (95% CI = 12.24 to 12.45 years) in 1999-2002. By race/ethnicity, average age at menarche estimates were as follows: non-Hispanic whites, 12.57 years (95% CI = 12.45 to 12.69 years) and 12.52 years (95% CI = 12.38 to 12.67 years); non-Hispanic blacks, 12.09 years (95% CI = 11.82 to 12.36 years) and 12.06 years (95% CI = 11.81 to 12.32 years); and Mexican Americans, 12.24 years (95% CI = 11.88 to 12.59 years) and 12.09 years (95% CI = 11.81 to 12.37 years). Higher relative weight was consistently associated with increased likelihood of having reached menarche.

CONCLUSIONS

Average age at menarche in the United States declined by 2.3 months between 1988-1994 and 1999-2002; by race/ethnicity, declines were considerably smaller. Changes in the population distribution of race/ethnicity and relative weight should be considered when interpreting trends in age at menarche.

Timing of pubertal maturation in girls: an integrated life history approach

Life history theory provides a metatheoretical framework for the study of pubertal timing from an evolutionary-developmental perspective. The current article reviews 5 middle-level theories--energetics theory, stress-suppression theory, psychosocial acceleration theory, paternal investment theory, and child development theory--each of which applies the basic assumptions of life history theory to the question of environmental influences on timing of puberty in girls. These theories converge in their conceptualization of pubertal timing as responsive to ecological conditions but diverge in their conceptualization of (a) the nature, extent, and direction of environmental influences and (b) the effects of pubertal timing on other reproductive variables. Competing hypotheses derived from the 5 perspectives are evaluated. An extension of W. T. Boyce and B. J. Ellis's (in press) theory of stress reactivity is proposed to account for both inhibiting and accelerating effects of psychosocial stress on timing of pubertal development. This review highlights the multiplicity of (often unrecognized) perspectives guiding research, raises challenges to virtually all of these, and presents an alternative framework in an effort to move research forward in this arena of multidisciplinary inquiry.

Analysis of menstrual, reproductive, and life-style factors for breast cancer risk in Turkish women: a case-control study

The aim of this study was to investigate the association between menstrual, reproductive, and life-style factors and breast cancer in Turkish women. In a hospital-based case-control study in Ankara, 622 patients with histologically confirmed breast cancer were compared with 622 age-matched controls, admitted to the same hospital for acute and non-neoplastic diseases. Unconditional logistic regression was used to estimate odds ratios (ORs) and 95% confidence intervals (CI) related to risk factors. Overall, menopausal status and age at menopause were found to be significantly associated with breast cancer. Having a full-term pregnancy and early age at first birth were associated with decreased breast cancer risk (OR = 0.45, 95% CI = 0.30-0.66; OR = 0.34, 95% CI = 0.22-0.53, respectively). Postmenopausal women with lactation longer than 48 mo had reduced risk of breast cancer (OR = 0.36, 95% CI = 0.14-0.93). In conclusion, decreased parity, late age at first birth, early menopause, and shorter duration of lactation were the most important determinants of breast cancer risk in Turkish women.

Pubertal maturation in girls and the relationship to anthropometric changes: pathways through puberty

OBJECTIVE

Patterns of pubertal maturation may have an impact on several risk factors associated with adult morbidity and mortality, such as obesity. We examined the relationship of the initial manifestation of puberty in girls with anthropometric measures, as well as age at menarche.

METHODS

White females (n = 1166, ages 9 and 10 at intake) were followed with annual visits for 10 years. Physical examinations included height, weight, skinfold thicknesses, and pubertal maturation assessment.

RESULTS

During the course of the study, 443 of 859 eligible females (51.6%) were observed to have asynchronous maturation in the development of puberty, that is, initial areolar/breast (thelarche pathway) or pubic hair (adrenarche pathway) development, without development of the other characteristic. Using a longitudinal regression model, significant interactions were noted between initial pubertal manifestation and years since onset of puberty on the following outcomes: sum of skinfolds thickness, percent body fat, waist-to-hip ratio, and body mass index (BMI). However, age of onset of pubertal maturation was the same in the 2 groups (10.7 years). Females in the thelarche pathway had earlier menarche (12.6 vs 13.1 years) as well as greater skinfolds, body fat, and BMI at the time of menarche. Females in the thelarche pathway also had greater body fat and BMI 1 year before puberty and throughout puberty compared with those in the adrenarche pathway.

CONCLUSIONS

Females who enter puberty through the thelarche pathway, as compared with the adrenarche pathway, had greater sum of skinfold thicknesses, BMI, and percent body fat 1 year before the onset, as well as throughout, puberty. Because larger body composition and earlier age of menarche of females in the thelarche pathway parallel the epidemiologic profiles of women who are obese or at risk for obesity, these females may be at greater risk for adult obesity.

Cumulative number of menstrual cycles and breast cancer risk: results from the E3N cohort study of French women

OBJECTIVE

To examine the relationship between breast cancer risk and the cumulative number of cycles before a first full-term pregnancy (FTP) and lifetime, taking age at menarche and at onset of regular cycling, periodicity and regularity of cycles, duration of periods of pregnancy, and lactation, oral contraceptive (OC) use, and age at menopause into account.

METHODS

The data were taken from the E3N prospective cohort study of women aged 40-65 years in 1990. A total of 1718 breast cancer cases were identified during the 579,525 person-years of follow-up.

RESULTS

There was a highly significant linear relationship between breast cancer risk and both the cumulative number of cycles before a first FTP (p for trend < 0.0001) and lifetime (p for trend < 0.001), with multivariate relative risk (RR) of a similar magnitude for both variables. Compared to women with a lifetime number of cycles <402 (< or =30 years), the RR for those with a lifetime total of 403-441, 442-480, 481-520, and > or =521 cycles were 0.95 (0.75-1.21), 1.21 (0.97-1.52), 1.23 (0.96-1.58), and 1.60 (1.25-2.04), respectively. Results restricted to never OC users were similar.

CONCLUSIONS

Further investigation is needed to clarify whether the underlying factor is repeated exposure to fluctuating hormones, the number of anovular/ovular cycles, or the relative importance of the follicular and luteal phases.

Evolution of age at menarche and at onset of regular cycling in a large cohort of French women

BACKGROUND

Early exposure to ovarian hormones is considered to increase breast cancer incidence. The age at which the ovaries become functional is thus important.

METHODS

We explored the evolution of age at first menstruation and at onset of regular cycling in 86 031 women participating in the E3N-EPIC cohort study, part of the European Prospective Investigation into Cancer.

RESULTS

We observed an increase in mean age at menarche among women born between 1925 and 1930, followed by a steady decrease in the youngest birth cohorts. In contrast, age at onset of regular cycling increased gradually from 1925 onwards. There was thus a steady increase in the interval between age at menarche and at onset of regular cycling, mainly due to an increase in the percentage of women in whom regular cycling started at least 5 years after menarche (from 9.0% among women born in 1925-1929 to 20.8% in those born in 1945-1950). The increase in the interval between menarche and onset of regular cycling was even greater among women with a late menarche.

CONCLUSIONS

This increase might be due to a change in dietary intake and/or physical exercise aimed at achieving the slim silhouette desired by the younger generations.

CYP gene polymorphisms and early menarche

Early age at menarche is a risk factor for breast cancer. A previous study reported a significant positive association between the CYP3A4*1B variant allele and early puberty. We investigated whether polymorphisms of the CYP3A4, CYP17, CYP1B1, and CYP1A2 genes predict the age at onset of menarche. Five hundred eighty-three nulliparous women between ages 17 and 35, of various ethnic backgrounds, completed a questionnaire that included information about menstrual history. Samples of DNA were provided and used to genotype these women for polymorphic variants in the four genes. There was no significant difference in mean age at menarche between women who carried two variant CYP17 A2 alleles (12.5 years) and women who carried one or no variant allele (12.5 years) (P = 0.8, adjusted for ethnic group and year of birth). Similar results were found for the CYP1B1*3 variant allele and for the CYP1A2*1F variant allele. Women who carried two variant CYP3A4*1B alleles had an earlier mean age at menarche (12.0 years) than women who carried one or no variant allele (12.6 years) (P = 0.02). However, after adjusting for ethnic group and year of birth, no significant differences in mean age at menarche were found. The polymorphic variants of the CYP3A4, CYP17, CYP1B1, and CYP1A2 genes are unlikely to influence age of menarche.

The missing politics and unsettled science of the trend toward earlier puberty

The age of puberty in many populations has declined steeply over recent centuries and may be declining still. Consequently, today's children tend to experience the hormonal stresses of rapid development at younger ages than did their ancestors, around whose later, if not more gradual, maturation traditional behavioral expectations formed. Little has been made of this "rush to puberty" outside the life sciences. This article reviews its historical documentation, scholarly appreciation, epidemiological correlations, putative physiological and environmental explanations, sociological implications, and largely latent politics.

Signal transduction through the Ras/Erk pathway is essential for the mycoestrogen zearalenone-induced cell-cycle progression in MCF-7 cells

Zearalenone is a naturally occurring estrogenic contaminant of moldy feeds and is present in high concentrations in dairy products and cereals. Zearalenone was postulated to contribute to the overall estrogen load of women, but the mechanisms of its action are not known. We demonstrated that zearalenone could stimulate the growth of estrogen receptor-positive human breast carcinoma cell line MCF-7. In addition, zearalenone functioned as an antiapoptotic agent by increasing the survival of MCF-7 cell cultures undergoing apoptosis caused by serum withdrawal. Treatment of these cells with 100 nM zearalenone induced cell-cycle transit after increases in the expression of c-myc mRNA and cyclins D1, A, and B1 and downregulation of p27(Kip-1). G(1)/G(2)-phase kinase activity and phosphorylation of the retinoblastoma gene product was also evident. Flow cytometric analysis demonstrated entry of cells into the S and G(2)/M phases of the cell cycle, and phosphorylation of histone H3 occurred 36 h after zearalenone treatment. Ectopic expression of a dominant-negative p21(ras) completely abolished the zearalenone-induced DNA synthesis in these cells, and the specific inhibitor PD98059 for mitogen/extracellular-regulated protein kinase kinase arrested S-phase entry induced by zearalenone. These data suggest that the mitogen-activated protein kinase signaling cascade is required for zearalenone's effects on cell-cycle progression in MCF-7 cells. Given the presence of this mycotoxin in cereals, milk, and meat, the possibility that zearalenone is a potential promoter of breast cancer tumorigenesis should be investigated further. Mol. Carcinog. 30:88-98, 2001.

Protein kinase expression during murine mammary development

The susceptibility of the mammary gland to carcinogenesis is influenced by its normal development, particularly during developmental stages such as puberty and pregnancy that are characterized by marked changes in proliferation and differentiation. Protein kinases are important regulators of proliferation and differentiation, as well as of neoplastic transformation, in a wide array of tissues, including the breast. Using a RT-PCR-based cloning strategy, we have identified 41 protein kinases that are expressed in breast cancer cell lines and in the murine mammary gland during development. The expression of each of these kinases was analyzed throughout postnatal mammary gland development as well as in a panel of mammary epithelial cell lines derived from distinct transgenic models of breast cancer. Although the majority of protein kinases isolated in this screen have no currently recognized role in mammary development, most kinases examined were found to exhibit developmental regulation. After kinases were clustered on the basis of similarities in their temporal expression profiles during mammary development, multiple distinct patterns of expression were observed. Analysis of these patterns revealed an ordered set of expression profiles in which successive waves of kinase expression occur during development. Interestingly, several protein kinases whose expression has previously been reported to be restricted to tissues other than the mammary gland were isolated in this screen and found to be expressed in the mammary gland. In aggregate, these findings suggest that the array of kinases participating in the regulation of normal mammary development is considerably broader than currently appreciated.

Identification of the woman at risk for breast cancer: problem solved?

The clinical availability of antiestrogens to reduce breast cancer incidence has focused increased attention on the ability to identify women at increased risk for breast cancer development. Multiple risk factors, which can be grouped under the headings of genetic and familial factors, hormonal factors, benign breast disease, and environmental factors have been described. However, of these risk factors, only genetic mutations and atypical hyperplasia, lobular carcinoma in situ, and ductal carcinoma in situ have a relative risk of four or more. Many of the other risk factors, although associated with statistically significant increases in risk in large populations, are of little practical significance for the individual woman. Lack of knowledge of the interactions among various positive and negative risk factors also complicates the evaluation of risk. In addition, the impact of some risk factors may not be constant over time, and the majority of data on risk come from studies of white women, and little is known about the impact of ethnic diversity on these factors. Finally, there is no consensus about what level of increase in risk is necessary for a women to be labeled "high risk." It is important to recognize that only 50% of breast cancers occur in women with identifiable risk factors other than age. Thus, an improved ability to define risk status is needed if prevention studies directed at high-risk women are to have a major impact on breast cancer incidence and mortality.

Possible mechanisms mediating an association between physical activity and breast cancer

The epidemiologic, methodologic, and biologic evidence that physical activity may be related inversely to breast cancer risk was the focus of a recent workshop. This article presents the workshop summary on biologic mechanisms that may mediate this association between physical activity and breast cancer. There is some evidence that physical activity may reduce breast cancer risk, although the exact biologic pathways have not been determined. Among the potential mechanisms discussed at the workshop were reductions in endogenous steroid exposure, alterations in menstrual cycle patterns, delay of age at menarche, increased energy expenditure and reduction in body weight, changes in insulin-like and other growth factors, and enhancement of natural immune mechanisms. Although physical activity may prove to be a modifiable risk factor for breast cancer, further mechanistically oriented research is necessary to both verify whether this is the case and to clarify the details of this association so that public health recommendations can be developed.

Menstrual cycle length preceding menopause in relation to age at menopause

OBJECTIVES

In one of the earlier hypotheses of the etiology of breast cancer (Korenman's 'oestrogen window' hypothesis (1981)), it was assumed that women with a later age at menopause have a longer period with irregular cycles preceding menopause than women with an early menopause. This assumption was tested in a prospective study.

METHODS

Subjects were 628 women, born between 1932 and 1941, who had participated in a breast cancer screening project in Utrecht, The Netherlands (the DOM-project) in 1982-1985, and who were still menstruating at that time. The women had filled out a questionnaire and a menstrual calendar every 2 years to determine their age at menopause prospectively. The women had not used oral contraceptives or medicines for menopausal complaints and had reached natural menopause by 1992. The median of the mean menstrual cycle length per woman and the median of the standard deviation of the mean menstrual cycle length per woman were plotted against number of years prior to menopause in three categories of age at menopause (44-49; 50-54; 55-59).

RESULTS

During the 9 years prior to menopause, women with a late age at menopause have a somewhat higher mean menstrual cycle length than women with a younger age at menopause (P = 0.0008). Cycle length variability in the 9 years prior to menopause is not statistically significantly different between the three categories of age at menopause (P = 0.16).

CONCLUSIONS

The assumption that women with a late age at menopause have a longer period with irregular cycles than women with an earlier age at menopause was not corroborated by our results.

Physical activity and the primary prevention of cancer

Evidence has been accumulating that suggests that physical activity may help reduce the risk of cancer. Physically active people have been shown to have a decreased rate of all-cancer mortality. The incidence of colon, breast, and perhaps prostate cancer are decreased in more active people when compared with their sedentary peers. Chronic physical activity may decrease tumor risk by its effect on natural immunity, antioxidant defenses, improved energy balance, hormonal changes, or by other unknown mechanisms.

Impaired ovulation and breast cancer risk

Conflicting results have been reported on the association between breast cancer risk and symptoms of luteal insufficiency, such as irregular or prolonged menstrual cycles and difficulty in becoming pregnant. Studies on the association between breast cancer risk and hormonal markers of impaired ovulation have also yielded conflicting results. Inadequate allowance for body mass and fat distribution may lead to inconsistent results when assessing the association between luteal insufficiency in premenopausal women and breast cancer risk. Ovulatory function is impaired by obesity, especially if it is predominantly abdominal in distribution. The Western diet and lifestyle favour early manifestation of hyperinsulinaemic insulin resistance in genetically-predisposed women. It is commonly associated with obesity which is predominantly abdominal in distribution. In a subset of premenopausal women, the concomitants of hyperinsulinaemia may impair maturation of ovarian follicles by a direct effect of insulin or insulin-like growth factors on ovarian tissue. Even when women are ovulating regularly, obesity may be associated with luteal insufficiency as shown by decreased levels of progestins or other changes in the sex steroid profile. Insulin resistance is likely to be involved and might explain the weak reduction in breast cancer risk associated with overweight in premenopausal Western women, in contrast with the increased risk widely reported in obese post menopausal women.

Regularity and length of menstrual cycles in women aged 41-46 in relation to breast cancer risk: results from the DOM-project

The effect of regularity and length of the menstrual cycle on breast cancer risk was studied prospectively in 78 cases and 383 age-matched controls who participated in a breast cancer screening programme, the DOM-project, in Utrecht, the Netherlands. Before entering the screening programme when they were aged 41-46, the women kept a menstrual calendar during at least three consecutive cycles. Cycles were considered to be irregular if any of three cycles was shorter than 21 days or longer than 35 days and/or if variation between cycle lengths was more than five days. Women with irregular cycles had a significantly reduced risk of breast cancer (odds ratio = 0.44; 95% confidence interval 0.22-0.86) after adjustment for age at menarche, age at first birth, parity, Quetelet's index and family history of breast cancer. Among regularly menstruating women, long cycles (28 days or more) were not significantly associated with increased risk of breast cancer (odds ratio 1.17; 95% confidence interval 0.66-2.09). To the extent that irregular menstrual cycles reflect anovulatory cycles, our findings support the hypothesis that the cumulative number of regular ovulatory cycles increases breast cancer risk.

Reproductive factors and breast cancer risk. Effect of age at diagnosis

The data from a French case-control study of 495 patients with breast cancer and 542 control subjects interviewed in five French public hospitals, were analyzed to assess the effect of reproductive factors (age at menarche, age at first full-term pregnancy, the time interval between these two ages, and parity) on the risk of breast cancer. Age at menarche, age at first full-term pregnancy, the time interval between these two ages, and parity appeared to have a limited influence on breast cancer risk. However, the relationship between these factors and the risk of breast cancer varied according to the age at breast cancer diagnosis. In the youngest group of women, the most consistent effects came from factors occurring early in life (menarche, first full-term pregnancy, and consequently the time interval between these two events). These factors had a null or weak effect on the oldest group of women. The protective effect of high parity was confined to the oldest group of women.

Strenuous physical activity in young adulthood and risk of breast cancer (United States)

The epidemiologic data on the relation between strenuous physical activity and breast cancer are limited and inconsistent. Because risk of breast cancer may be influenced by ovarian function which, in turn is modulated by physical activity, the hypothesis that exercise may be associated with a reduced risk of breast cancer merits further investigation. We, therefore, conducted a large case-control study in 1988-1991, and interviewed 6,888 women (17 to 74 years of age) with breast cancer in Maine, Massachusetts, New Hampshire, and Wisconsin (United States). Interviewed controls (9,539 women, 18 to 74 years of age) were selected randomly from lists of licensed drivers (for younger women) or from a roster of Medicare enrollees (for older women). We used multivariate adjusted odds ratios (OR) and 95 percent confidence intervals (CI) from logistic regression models to estimate relative risks between self-reported physical activity when 14 to 22 years of age and breast cancer. When compared with sedentary controls, women who reported any strenuous physical during ages 14 to 22 years had a modest reduction in the risk of breast cancer (OR = 0.95, CI = 0.93-0.97). However, those who exercised vigorously at least once a day had a 50 percent reduction in risk of breast cancer (OR = 0.5, CI = 0.4-0.7). These data support the hypothesis that women who are physically active have a reduced risk of breast cancer.

Reproductive factors in breast cancer epidemiology

There is abundant epidemiologic evidence showing that early menarche, late menopause, low parity and late age at first birth are related to increased risk of breast cancer. However, in younger age groups, uniparous women seem to be at higher risk than nulliparous, and the effect of later pregnancies is less clear in this group. Intervals between pregnancies may modify the general protective effect. Some studies have indicated an adverse effect of late age at pregnancies after the first. Further studies are necessary to determine if the general protective effect of pregnancies after the first is preceded by a transient increase in breast cancer risk. No clear association has been established with number of abortions. Results from two large prospective studies suggest that breast feeding is not strongly related to risk of breast cancer among Western populations.

The international variation in breast cancer rates: an epidemiological assessment

Part of the international differences in breast cancer incidence rates can be explained by geographic variation in reproductive and other breast cancer risk factors. Age at menarche and age at onset of regular ovulatory menstrual cycles are two such factors; both vary across populations directly according to breast cancer risk, and both are acknowledged as breast cancer risk factors. Consideration of the body of evidence on these factors, as well as that on age at menopause, suggests that the cumulative frequency of ovulatory menstrual cycles is a critical determinant of breast cancer risk. Although age at first term pregnancy explains the majority of the protective effect of parity on breast cancer risk, two recent studies have demonstrated a small residual protective effect of increasing number of births. It appears that pregnancy has paradoxical effects on breast cancer risk in terms of hormone production and metabolism. The initial effect is an increased risk associated with first trimester estrogen exposure. However, the hormonal consequences of completing the pregnancy counteract this negative effect of early pregnancy. The effect of body weight, a breast cancer risk factor for postmenopausal women, can be explained in terms of increased extraglandular conversion of androstenedione to estrone. Further evidence supporting a pathogenic role of estrogens in the development of breast cancer comes from international studies of endogenous hormones in populations with differing risks of breast cancer. These risk factors have been incorporated into a mathematical model which is based on the concept that breast tissue ages according to hormonal (primarily estrogen) exposure; this model closely predicts the incidence rates throughout the world.

Nutrition and breast cancer

International comparisons have provided striking correlations between fat consumption and risk of breast cancer, but these comparisons do not often consider variations in life style. Case-control studies carried out in several countries showed no real association between fat intake and breast cancer. There is some evidence that vitamin A or carotenoid intake may exert a protective effect. Alcohol intake, on the other hand, seems to be positively associated with breast cancer risk. Elevated body weight, body mass, stature, and frame size have been found to be associated as risk factors for breast cancer in women. Animal studies found that caloric restriction inhibits growth of spontaneous and induced mammary tumors, an observation that held up even when the calorie-restricted animals ingest more fat than the ad-libitum-fed controls. College women who exercise have a lower incidence of breast cancer than their more sedentary classmates. Exercise is another means of reducing caloric availability.

Serum hormone levels in pre-menopausal Chinese women in Shanghai and white women in Los Angeles: results from two breast cancer case-control studies

To assess whether risk of breast cancer in young women is associated with differences in luteal-phase hormone production and to attempt to explain differences in risk of breast cancer of young Shanghai Chinese and Los Angeles white women, two concurrent case-control studies of serum hormone concentrations were conducted. Both studies were carefully controlled for the possible confounding effects of age, weight, height, pregnancy history, and day of the menstrual cycle, by individually matching cases and controls on these factors. Case eligibility was limited to women with localized breast cancer. Sixteen of 39 Shanghai breast-cancer cases were sampled prior to the histologic diagnosis of their disease. The remaining 23 Shanghai cases and all 42 Los Angeles cases were diagnosed, and treated by surgery only, at least six months prior to hormonal evaluation. All subjects were sampled on day 22 of the menstrual cycle. Overall, cases had 13.5% higher serum estradiol concentrations (p = 0.038) with a case-to-control excess of 16.6% in Shanghai subjects (p = 0.089) and 10.8% in Los Angeles subjects (p = 0.23). There were no appreciable differences in amounts of sex-hormone binding globulin between cases and controls. Cases had lower progesterone levels than controls, but the situation was reversed when the analysis was restricted to subjects with evidence of ovulation. Los Angeles controls had 20.6% greater estradiol concentrations than Shanghai controls (p = 0.036); adjustment for body weight accounted for only 25.7% of this difference.(ABSTRACT TRUNCATED AT 250 WORDS)

Some endocrine characteristics of early menarche, a risk factor for breast cancer, are preserved into adulthood

Early menarche is a risk factor for breast cancer. In a longitudinal manner, we have investigated the endocrine features of girls with early menarche. This study extends our investigations to the third decade of life in a cohort of girls followed up for 13 years. The group studied comprised 44 women, 20-31 years of age. Eleven women had had their menarche before 12.0 years, 14 women at 12.0-12.9 years and 19 women at 13.0 years or more. The women who had had early menarche had higher serum oestradiol concentrations during the follicular phase of the menstrual cycle than the women who had had their menarche later. The serum oestradiol concentrations increased rapidly at the beginning of cycle in these "early menarche" women. If there is a threshold which serum oestradiol concentrations must exceed to increase the risk of breast cancer, then these women have more days at risk than other women. In addition, the serum SHBG (sex-hormone-binding globulin) concentration was about 30% lower in the follicular-phase specimens of the women who had had their menarche before 12.0 years compared with those who had had their menarche at 13.0 years. Our data therefore indicate that women with early menarche are subject to a high degree of oestrogen stimulation at least until approximately 30 years of age. Our findings may have important consequences for the design of intervention programs for breast cancer prevention.