Ethnic differences in androgens, IGF-I and body fat in healthy prepubertal girls

Overexpression of IGF-1 During Early Development Expands the Number of Mammary Stem Cells and Primes them for Transformation

Insulin-like growth factor I (IGF-1) has been implicated in breast cancer due to its mitogenic and anti-apoptotic effects. Despite substantial research on the role of IGF-1 in tumor progression, the relationship of IGF-1 to tissue stem cells, particularly in mammary tissue, and the resulting tumor susceptibility has not been elucidated. Previous studies with the BK5.IGF-1 transgenic (Tg) mouse model reveals that IGF-1 does not act as a classical, post-carcinogen tumor promoter in the mammary gland. Pre-pubertal Tg mammary glands display increased numbers and enlarged sizes of terminal end buds, a niche for mammary stem cells (MaSCs). Here we show that MaSCs from both wild type (WT) and Tg mice expressed IGF-1R and that overexpression of Tg IGF-1 increased numbers of MaSCs by undergoing symmetric division, resulting in an expansion of the MaSC and luminal progenitor (LP) compartments in pre-pubertal female mice. This expansion was maintained post-pubertally and validated by mammosphere assays in vitro and transplantation assays in vivo. The addition of recombinant IGF-1 promoted, and IGF-1R downstream inhibitors decreased mammosphere formation. Single-cell transcriptomic profiles generated from two related platforms reveal that IGF-1 stimulated quiescent MaSCs to enter the cell cycle and increased their expression of genes involved in proliferation, plasticity, tumorigenesis, invasion, and metastasis. This study identifies a novel, pro-tumorigenic mechanism, where IGF-1 increases the number of transformation-susceptible carcinogen targets during the early stages of mammary tissue development, and “primes” their gene expression profiles for transformation.

Skeletal maturation in relation to ethnic background in children of school age: The Generation R Study

Ethnicity is a well-established determinant of pediatric maturity, but the underlying genetic and environmental contributions to these ethnic differences are poorly comprehended. We aimed to evaluate the influence of ethnicity on skeletal age (SA), an assessment of pediatric maturation widely used in clinical settings. We included children from the Generation R Study, a multiethnic population-based pregnancy cohort, assessed at a mean age of 9.78 (±0.33) years. SA was evaluated by a trained observer on hand DXA scans using the Greulich and Pyle method. Ethnic background was defined as geographic ancestry (questionnaire-based assessment) (N = 5325) and genetic ancestry (based on admixture analysis) (N = 3413). Associations between the ethnic background and SA were investigated separately in boys and girls, using linear regression models adjusted for age, height and BMI. Based on geographic ancestry, 84% of the children were classified as European, 6% as Asian and 10% as African. Children of European background had on average younger SA than those of Asian or African descent. Asian boys had 0.46 (95% CI 0.26-0.66, p-value < 0.0001) and African boys 0.36 years (95% CI 0.20-0.53, p-value < 0.0001) older SA as compared to European boys. Similarly, Asian girls showed 0.64 (95% CI 0.51-0.77, p-value < 0.0001) and African girls 0.38 years (95% CI 0.27-0.48, p-value < 0.0001) older SA as compared to European girls. A similar pattern was observed in the analysis with genetically-defined ancestry. Furthermore, an increase in the proportion of Asian or African component was associated with older SA in both boys (log[Non-European/European]proportion = 0.10, 95% CI 0.06-0.13, p-value < 0.0001) and girls (log[Non-European/European]proportion = 0.06, 95% CI 0.04-0.08, p-value < 0.0001). In summary, children of Asian and African backgrounds have on average older SA as compared to children of European descent, partially explained by a genetic component.

Adrenal function links to early postnatal growth and blood pressure at age 6 in children born extremely preterm

BACKGROUND

Low birth weight in term-born individuals correlates with adverse cardiometabolic outcomes; excess glucocorticoid exposure has been linked to these relationships. We hypothesized that cortisol and adrenal androgens would correlate inversely with birthweight and directly with markers of cardiometabolic risk in school-aged children born extremely preterm; further, preterm-born would have increased cortisol and adrenal androgens compared to term-born children.

METHODS

Saliva samples were obtained at age 6 from 219 preterm-born children followed since birth and 40 term-born children and analyzed for dehydroepiandrosterone (DHEA) and cortisol. Cortisol was also measured at home (awakening, 30' later, evening).

RESULTS

For preterm-born children, cortisol and DHEA correlated inversely with weight and length Z-scores at 36 weeks PMA and positively with systolic BP. DHEA was higher in preterm-born than term-born children (boys p < 0.01; girls p = 0.04). Cortisol was similar between preterm-born and term-born at study visit; however, preterm-born children showed a blunted morning cortisol. In term-born children, DHEA correlated with BMI (p = 0.04), subscapular, and abdominal skinfold thicknesses (both p < 0.01).

CONCLUSION

Cortisol and DHEA correlated inversely with early postnatal growth and directly with systolic BP in extremely preterm-born children, suggesting perinatal programming. Blunted morning cortisol may reflect NICU stress, as seen after other adverse childhood experiences (ACEs).

Precocious pubertal events in Chilean children: ethnic disparities

PURPOSE

Puberty onset exhibits remarkable inter-individual and ethnic differences. 5% of Chileans are indigenous but puberty ethnic disparities have not been studied. We aim for evaluating precocious puberty prevalence in children with Mapuche ancestry vs non-indigenous Chilean children (according to their surnames).

METHODS

Longitudinal cohort study: 1003 children (50.2% girls) participating in the Growth and Obesity Chilean Cohort Study (GOCS) were studied. Annual anthropometry was measured since 4-7 years. Subsequently, Tanner staging and anthropometry were measured every 6 months. In girls, Tanner stage was assessed by breast palpation and in boys by testicular volume measurements. The cohort was stratified in three groups depending on Mapuche surname numbers as follows: (A) no indigenous surnames (n = 811), (B) one to two indigenous surnames (n = 147), and (C) three or more indigenous surnames (n = 45). We evaluated the prevalence of precocious thelarche, pubarche, menarche and gonadarche (testicular volume ≥ 4 ml-G2), using a cutoff age of 8 years in girls and 9 years in boys while controlling for socioeconomic status, body mass index, waist circumference, IGF-1 and DHEAS at 7 years.

RESULTS

In girls, no significant differences were observed. On the contrary, in boys, precocious gonadarche prevalence was higher in group C (29.2%) vs group A (6.0%) and vs group B (10.5%) (p =0.001, p = 0.004, respectively). Increased precocious gonadarche and pubarche risks in group C were observed even after adjustment [OR 7.31; 95% IC (2.32-23.51); p = 0.001] and [OR 6.17, 95% CI (1.62-23.49); p = 0.008], respectively.

CONCLUSION

Indigenous origin in Chile is an independent risk factor for precocious gonadarche and pubarche in boys but not in girls.

Circulating androgens and SHBG during the normal menstrual cycle in two ethnic populations

The objective of this study was to study possible ethnic differences in steroid hormones and sex hormone-binding globulin (SHBG) during the menstrual cycle. Serum levels of the ovarian steroids estradiol (E2) and progesterone (P) and of follicle-stimulating hormone (FSH), luteinizing hormone (LH), SHBG, dehydroepiandrosterone (DHEA) and testosterone (T-ria) were all measured by immunoassay during the menstrual cycle in 15 Swedish and 11 West Asian regularly menstruating women. Testosterone (T-ms) was also measured by LC-MS/MS and so were 4-androstene-3,17-dione (A-4) and 17-alpha-hydroxyprogesterone (17-OHP). There were no ethnic differences in levels of ovarian steroids, gonadotrophins, A-4, 17-OHP and T-ms. DHEA were significantly higher and SHBG significantly lower in West Asian than in Swedish women. Surprisingly, T-ria was significantly higher in West Asian than in Swedish women and higher than T-ms (47% in Swedish and 107% in West Asian women). The difference (T-ria - T-ms) showed strong positive correlations to DHEA in the total and in West Asian but not in Swedish women, indicating an influence of DHEA/DHEAS metabolites on the T-ria results. In conclusion, ethnic differences in cross reacting steroids may cause erroneous results in one ethnic group by a steroid immunoassay having reasonable specificity in another. The reasons for the lower SHBG and the higher DHEA levels in West Asian women are not known. The results raise the question about establishing different reference values for certain analytes in different ethnic groups.

Relative Skeletal Maturation and Population Ancestry in Nonobese Children and Adolescents

More rapid skeletal maturation in African-American (AA) children is recognized and generally attributed to an increased prevalence of obesity. The objective of the present study was to evaluate the effects of population ancestry on relative skeletal maturation in healthy, non-obese children and adolescents, accounting for body composition and sexual maturation. To do this, we leveraged a multiethnic, mixed-longitudinal study with annual assessments for up to 7 years (The Bone Mineral Density in Childhood Study and its ancillary cohort) conducted at five US clinical centers. Participants included 1592 children, skeletally immature (45% females, 19% AA) who were aged 5 to 17 years at study entry. The primary outcome measure was relative skeletal maturation as assessed by hand-wrist radiograph. Additional covariates measured included anthropometrics, body composition by dual-energy X-ray absorptiometry (DXA), and Tanner stage of sexual maturation. Using mixed effects longitudinal models, without covariates, advancement in relative skeletal maturation was noted in self-reported AA girls (∼0.33 years, p < 0.001) and boys (∼0.43 years, p < 0.001). Boys and girls of all ancestry groups showed independent positive associations of height, lean mass, fat mass, and puberty with relative skeletal maturation. The effect of ancestry was attenuated but persistent after accounting for covariates: for girls, 0.19 years (ancestry by self-report, p = 0.02) or 0.29 years (ancestry by admixture, p = 0.004); and for boys, 0.20 years (ancestry by self-report, p = 0.004), or 0.29 years (ancestry by admixture, p = 0.004). In summary, we conclude that advancement in relative skeletal maturation was associated with AA ancestry in healthy, non-obese children, independent of growth, body composition, and puberty. Further research into the mechanisms underlying this observation may provide insights into the regulation of skeletal maturation. © 2016 American Society for Bone and Mineral Research.

Clinical presentation of children with premature adrenarche

OBJECTIVES

To describe the phenotype of premature adrenarche (PA) patients, elucidate historical and physical correlates, and distinguish PA from late-onset congenital adrenal hyperplasia (LOCAH).

STUDY DESIGN

Retrospective chart review of 122 patients (91 female and 31 male) with PA and 11 with LOCAH.

RESULTS

In PA patients, birth weight was <2 standard deviation scores (SDSs) in 6%, and 14% were premature. Body mass index SDSs were high (2.00 ± 1.84). Bone age (BA) SDS was >2 in 31% and was greater in boys than in girls; PA subjects were taller, and the predicted height was at or above genetic potential. Dehydroepiandrosterone sulfate (DHEAS) was higher in boys. LOCAH patients had earlier pubic hair, more advanced BA, lower height SDSs, lower adult height prediction, and higher adrenal androgen levels.

CONCLUSION

Patients with PA tend to be overweight with BA acceleration but normal height prediction. LOCAH is distinguished by earlier presentation and higher 17-hydrocyprogesterone and adrenal androgens.

Tanner Staging of Secondary Sexual Characteristics and Body Composition, Blood Pressure, and Insulin in Black Girls

OBJECTIVE

To assess Tanner staging (breast and pubic hair development) and its relationship to measures of body composition, blood pressure, and fasting insulin and glucose in young black girls.

RESEARCH METHODS AND PROCEDURES

Subjects were 138 black girls, 8 to 12 years of age, recruited from elementary schools in low socioeconomic status neighborhoods. Exclusion criteria included the presence of any acute/chronic medical conditions. Pubertal stages were assessed by one of two pediatricians and analyzed individually, as well as with a composite index (prepubertal, pubertal/premenarcheal, or pubertal/menarcheal). Glucose and insulin were measured after a 12-hour fast. Measures of body composition included height, weight, BMI, waist and hip circumferences, fat mass, fat-free soft tissue, bone mineral density (DXA), and visceral adipose tissue (magnetic resonance imaging). Resting systolic and diastolic blood pressure were measured by Dinamap.

RESULTS

With age in the model, breast development explained significant proportions of the variance in height, weight, fat-free soft tissue, bone mineral density, and insulin. Adding pubic hair development or menarche to those models did not significantly increase the proportion of variance that was explained by breast development. Furthermore, using a composite index of pubertal staging explained a smaller proportion of the variance compared with breast development alone.

DISCUSSION

Combined with age, breast development was a better predictor of body composition and fasting insulin than was pubic hair development or a composite index of pubertal staging.

Racial variation in umbilical cord blood sex steroid hormones and the insulin-like growth factor axis in African-American and white female neonates

PURPOSE

To evaluate whether there is racial variation in venous umbilical cord blood concentrations of sex steroid hormones and the insulin-like growth factor (IGF) axis between female African-American and white neonates.

METHODS

Maternal and birth characteristics and venous umbilical cord blood samples were collected from 77 African-American and 41 white full-term uncomplicated births at two urban hospitals in 2004 and 2005. Cord blood was measured for testosterone, dehydroespiandrosterone-sulfate, estradiol, and sex steroid hormone-binding globulin (SHBG) by immunoassay. IGF-1, IGF-2, and IGF-binding protein-3 (IGFBP-3) were measured by ELISA. Crude and multivariable-adjusted geometric mean concentrations were computed for the hormones.

RESULTS

African-American neonates weighed less at birth (3,228 g vs. 3,424 g, p < 0.004) than whites. Birth weight was positively correlated with IGF-1, IGFBP-3, and the molar ratio of IGF-1 to IGFBP-3, but inversely correlated with the molar ratio of IGF-2 to IGFBP-3. Adjusted models showed higher testosterone (1.82 ng/ml vs. 1.47 ng/ml, p = 0.006) and the molar ratio of testosterone to SHBG (0.42 vs. 0.30, p = 0.03) in African-American compared to white female neonates. IGF-1, IGF-2, and IGFBP-3 were lower in African-American compared to white female neonates, but only the difference for IGF-2 remained significant (496.5 ng/ml vs. 539.2 ng/ml, p = 0.04).

CONCLUSION

We provide evidence of racial variation in cord blood testosterone and testosterone to SHBG in African-American compared to white female neonates, and higher IGF-2 in white compared to African-American female neonates. Findings suggest plausible explanations for a prenatal influence on subsequent breast cancer risk and mortality. Further work is needed to confirm these observations.

Higher DHEA-S (dehydroepiandrosterone sulfate) levels are associated with depressive symptoms during the menopausal transition: results from the PENN Ovarian Aging Study

The influence of sex hormones on mood during the menopausal transition has been the subject of ongoing investigation. Because dehydroepiandrosterone sulfate (DHEA-S) has been associated with several indicators of healthy aging, we conducted a population-based study of midlife women to determine the relationship between DHEA-S levels and depressive symptoms and major depression during the transition through menopause. Unexpectedly, the original report revealed a positive correlation between DHEA-S levels and depressive symptoms at baseline. The cohort was studied over 11 years to determine whether the positive association between DHEA-S levels and depression persists through the menopausal transition. We conducted a longitudinal cohort study with 11 assessments during an 11-year interval in Philadelphia, Pennsylvania, using a randomly identified, population-based sample of 436 African American and Caucasian premenopausal women aged 35 to 47 years at enrollment. For outcome measures, we used the Center for Epidemiologic Studies Depression Scale and standardized diagnosis of major depression. In a multivariable model, DHEA-S levels were positively associated with depressive symptoms when adjusted for age, menopausal stage, race, smoking status, and body mass index. There was no association between DHEA-S levels and a diagnosis of major depression. DHEA-S levels were positively associated with depressive symptoms through the menopausal transition. No association with major depression was apparent during the menopausal transition, but results may have limited power due to low prevalence of major depression in this cohort. These findings suggest that taking DHEA supplements may increase depressive symptoms for some women, and women and their physicians should be cautious about instituting DHEA replacement therapy during the menopausal transition.

Relationships between IGF-1 and IGFBP-1 and adiposity in obese African-American and Latino adolescents

The purpose of this study was to examine interrelationships between insulin-like growth factor 1 (IGF-1), IGF binding proteins (IGFBPs), and adiposity in 49 African-American and 77 Latino obese adolescents (15.3 ± 0.1 and 15.4 ± 0.2 years; BMI: 33.0 ± 0.7 and 35.0 ± 1.0 kg/m(2), respectively). Immunoradiometric assays were used to measure IGF-1, IGFBP-1, and IGFBP-3. Total fat and soft lean tissue were measured by dual-energy X-ray absorptiometry and visceral adipose tissue (VAT), subcutaneous abdominal adipose tissue (SAAT), and hepatic fat fraction (HFF) were measured by magnetic resonance imaging. IGF-1 levels were 23.1% higher and IGFBP-1 were 40.4% higher in African Americans compared to Latinos after adjustment for total lean and total fat mass. IGF-1 and IGFBP-1 were inversely correlated with BMI, total fat mass, VAT, and HFF (r = -0.20 to -0.33, P < 0.05) while IGFBP-1 was inversely correlated with SAAT (r = -0.22, P < 0.05). These relationships did not differ by ethnicity, however, the relationship between IGF-1 and SAAT, as well as IGFBP-1 and HFF, differed by ethnicity. Predicted mean IGF-1 levels were 30.7% higher for African Americans at the 75th compared to 25th percentile of SAAT and only 11.7% higher for Latinos. Predicted mean IGFBP-1 levels were 158% higher for African Americans at the 25th compared to the 75th percentile of HFF while IGFBP-1 levels were 1.7% higher for Latinos at the 75th compared to the 25th percentile. These results demonstrate that the relationship between IGF-1 and SAAT as well as IGFBP-1 and HFF are different in African-American and Latino adolescents and may contribute to the higher IGF-1 levels in African-Americans.

Anthropometric and lifestyle associations of bone mass in healthy pre-menopausal Mexican and Asian American women

Few studies have established the lifestyle predictors of peak bone mineral density (BMD) in Mexican-American (MA) and Asian-American (AA) women. Pre-menopausal MA (n = 48) and AA (n = 58) women aged 30-45 years old were tested for BMD, body composition, aerobic fitness, and muscle function. Socio-demographic characteristics, health status, prevalence of osteoporosis risk factors, physical activity, and diet were determined via questionnaire. Pearson's correlations and multiple linear regressions were used to test the associations between various osteoporosis risk factors and BMD. Body composition, anthropometric, and BMD differences were noted between groups. Hip, but not spine BMD, remained significantly higher for the MA compared to the AA group after adjustment for age, BMI, income, and physical activity index. Lean body mass was a significant predictor of hip BMD for both groups and this relationship was stronger for the AA group. Lean body mass may explain ethnic differences in BMD.

Longitudinal analysis of the insulin-like growth factor system in African-American and European American children and adolescents

CONTEXT

IGF-I and its binding proteins influence growth, development, and disease risk. Studies have revealed ethnic variations in the IGF system.

OBJECTIVE

This longitudinal study was undertaken to test the hypothesis that the ethnic differences in the IGF system exist throughout the pubertal transition, and these differences are mediated at least in part by inherent differences in insulin dynamics.

DESIGN

This was a longitudinal study. Annual evaluations were conducted for pubertal maturation, body composition, acute insulin response to glucose (AIRg), and reproductive-endocrine profile. Hormones and binding proteins were determined using standard assays, the AIRg during a frequently sampled iv glucose tolerance test, and body composition by dual-energy x-ray absorptiometry. Mixed model analyses were used to identify and characterize ethnic differences in the IGF system across the pubertal transition after adjusting for ethnicity, sex, age, maturation status, body composition, and reproductive hormones, and to identify the contribution of insulin to IGF binding protein (IGFBP)-1.

PARTICIPANTS

Subjects included African-American (AA) and European American children (n = 162 at baseline) aged 7-16 yr, evaluated across the pubertal transition.

MAIN OUTCOME MEASURES

Annual data on IGF-I, IGFBP-1, and IGFBP-3 were examined.

RESULTS

IGF-I was higher in AA children at pubertal stage 1 only (P < 0.001). However, IGFBP-3 and IGFBP-1 concentrations were lower in AAs through much of puberty (P < 0.05). The lower IGFBP-1 of AAs was in part explained by greater AIRg.

CONCLUSIONS

Our data suggest that the higher IGF-I and lower IGFBP-1 and IGFBP-3 levels in AAs as compared with European Americans during puberty suggest potential ethnic differences in circulating bioavailable IGF-I. In addition, higher AIRg in AAs may lead to greater bioavailable IGF-I. Whether these differences in the IGF system account for disparities in disease risk warrants further investigation.

Insulin-like growth factor-I is inversely related to adiposity in overweight Latino children

The purpose of this study was to examine interrelationships between IGF-I, IGF binding proteins (IGFBPs) and adiposity in 178 overweight Hispanic adolescents (11.2 +/- 1.7 yr; body mass index: 28.2 +/- 5.4 kg/m2). Immunoradiometric assays were used to measure IGF-I, IGFBP-1 and IGFBP-3. Total fat and lean tissue mass were measured by DEXA and visceral and subcutaneous adipose tissue by MRI. IGF-I and IGFBP-3 remained inversely correlated with total body fat mass (r = -0.52, p < 0.001 and r = -0.25, p < 0.01, respectively) after controlling for covariates. IGFBP-1 was inversely correlated to total fat mass (r = -0.55, p < 0.001) in simple correlations; however, this relationship was eliminated after controlling for covariates (r = 0.02, p = 0.85). Correlations with visceral and subcutaneous adipose tissue yielded similar results. These results demonstrate that IGF-I, IGFBP-1 and IGFBP-3 are all inversely related to adiposity in Hispanic children.

Racial differences in premenopausal endogenous hormones

Differences in breast cancer incidence across racial groups are well documented. African Americans have the highest rates of premenopausal breast cancer and Asians have lower breast cancer rates across all age groups. We hypothesized that levels of premenopausal endogenous hormones and growth factors, risk factors that have been predictive of breast cancer, would differ by race. Using a cross-sectional study design, we tested this hypothesis in the Nurses' Health Study II. We assayed estradiol, progesterone, prolactin, sex hormone binding globulin (SHBG), insulin-like growth factor-I (IGF-I), and IGFBP-3 in 111 African American and 111 Asian American women, matched to 111 Caucasian women on age, day of luteal phase, and day, time, and fasting status at blood collection. We analyzed the association between race and hormone levels using robust linear regression methods. In multivariate models, compared with Caucasians, African Americans had 18% higher levels of estradiol (P < 0.01), 17% higher free estradiol (P < 0.01), 11% lower SHBG (P = 0.05), 11% higher IGF-I (P < 0.01), 25% higher free IGF-I (P < 0.01), and 9% lower IGFBP-3 (P < 0.01) levels. In multivariate models, compared with Caucasian women, Asian Americans had 22% higher calculated free estradiol (P < 0.01), 31% lower SHBG (P < 0.01), and 25% higher free IGF-I (P < 0.01) levels. No racial differences were found in progesterone and prolactin levels. Our study showed hormone differences consistent with breast cancer risk between Caucasians and African Americans but inconsistent with breast cancer risk between Asian Americans and Caucasians. Further research is needed to explore differences across racial groups and the link between endogenous hormones and breast cancer risk.

Early ethnic difference in insulin-like growth factor-1 is associated with African genetic admixture

IGF-1 is a growth-promoting hormone. Numerous studies have reported higher systemic concentrations of IGF-1 among African Americans (AA) compared with European Americans (EA) before puberty. We conducted this cross-sectional analysis to determine whether African ancestral genetic background, dietary factors, energy expenditure, adiposity, and socioeconomic status contribute to this difference. Children were prepubertal, AA and EA males and females. Genetic admixture was assessed from approximately 20 ancestry informative genetic markers. Body composition was determined by dual-energy x-ray absorptiometry; intake of energy, carbohydrate, protein, and fat by 24-h dietary recall; activity-related energy expenditure by doubly labeled water and indirect calorimetry; and socioeconomic status (SES) according to the Hollingshead scale. IGF-1 and IGF binding protein-3 (IGFBP-3) were measured using immunoradiometric assays. AA children had significantly greater IGF-1 compared with EA children (p < 0.01). In addition, AA children had lower SES and greater protein intake relative to EAs (p < 0.05 for both). Multiple linear regression analysis revealed that the only significant independent predictors of IGF-1 were IGFBP-3 and African admixture (p < 0.01 for both). Thus, our data suggest that the greater IGF-1 of AA relative to EA children could have a genetic basis.

Dietary and Lifestyle Correlates of Plasma Insulin-Like Growth Factor-I (IGF-I) and IGF Binding Protein-3 (IGFBP-3): The Multiethnic Cohort

High circulating concentration of insulin-like growth factor-I (IGF-I) and low circulating concentration of IGF binding protein-3 (IGFBP-3) have been associated with increased risk for breast, prostate, and colorectal cancers. Building on previous work in the Multiethnic Cohort (MEC) showing significant differences in IGF-I levels across racial/ethnic groups, we investigated which lifestyle and dietary factors are associated with levels of IGF-I and IGFBP-3 in a random sample of 1,000 MEC participants, which included Native Hawaiian, African American, Japanese, Latino, and White men and women. Crude analyses confirmed the existence of differences in protein levels with race/ethnicity, sex, age, and body size. Reproductive, physical activity, smoking, and diet variables had less consistent effects. In multivariate analyses, IGF-I levels were lower and IGFBP-3 were higher in females versus males. IGF-I and IGFBP-3 declined with increasing age in both genders. Women in the highest quartile of body mass index showed depressed IGF-I and IGFBP-3 levels; in men, height was significantly positively associated with both proteins. In women, alcohol was directly associated with IGFBP-3. Both proteins were lowest among female Latinos. IGF-I was highest among female African Americans. In men, IGFBP-3 was lowest among African Americans. Overall, although these factors were statistically significant determinants of IGF-related protein levels, they did not explain much of the variation in these levels. A positive correlation was found between IGF-I levels (ng/mL) and colon cancer incidence rates (per 100,000) within the MEC by race/ethnicity for both sexes but not for either breast or prostate cancer.

Ultrasound bone measurements in pre-adolescent girls: interaction between ethnicity and lifestyle factors

AIM

We obtained calcaneal ultrasound measurements in 198 girls between 7.5 and 11.7 y of age, representing ethnic groups (black [n = 80], white [n = 41], mixed ancestral origin [n = 77]) in South Africa.

METHODS

Anthropometry was assessed. Demographics, physical activity, habitual dietary calcium intake and pubertal development were quantified by questionnaires. Broadband ultrasound attenuation (BUA) and speed of sound (SOS) of the left calcaneus were measured. Girls in Tanner breast stage 5 and/or those menstruating were excluded from analysis.

RESULTS

Black girls were lighter than white girls (31.4 +/- 7.8 vs 34.8 +/- 7.5 kg; p < 0.05), and shorter than girls of mixed ancestral origin (1.29 +/- 0.08 vs 1.34 +/- 0.07 m; p < 0.001) and white girls (1.35 +/- 0.07 m; p < 0.001), after adjusting for age. Reported calcium intake scores were higher in black than white girls (21.6 +/- 11.1 vs 16.1 +/- 8.4; p < 0.01). Total peak bone strain score (TPBSS) was higher in white compared to black girls (6.8 +/- 4.8 vs 5.0 +/- 4.7; p < 0.05), while walking energy expenditure (MET h/wk) was higher in black girls compared to the other groups (p < 0.001). BUA and SOS were higher in the black girls (59.6 +/- 13.7 dB/MHz; 1575.1 +/- 22.6 m/s; p < 0.001) and girls of mixed ancestral origin (59.0 +/- 12.5 dB/MHz; 1567.8 +/- 26.1 m/s; p < 0.01) than in the white girls (50.4 +/- 8.7 dB/MHz; 1552.1 +/- 19.5 m/s). Co-varying for age and weight did not affect these results. Walking energy expenditure (r = 0.20) and calcium score (r = 0.17) were correlated (p < 0.05) with SOS for the whole group.

CONCLUSION

Ultrasound parameters were lower in the white compared to the black girls, who consumed more calcium on average, but who were lighter, shorter and performed less impact activity. This suggests that interactions between ethnicity and lifestyle factors determine bone quality in premenarcheal girls.

Prepubertal girls with premature adrenarche have greater bone mineral content and density than controls

Body composition in premature adrenarche (PA) has not been described. We hypothesized that the increased adrenal androgens in PA would have a trophic effect on lean body components. We studied 14 PA subjects and 16 controls, all prepubertal Hispanic girls. The body composition parameters tested included height, weight, bone mineral density (BMD), bone mineral content (BMC), nonbone fat-free mass, total body potassium, total body water, and extracellular water. Bone age was determined in all PA subjects. Compared with controls, PA subjects had significantly higher BMC (P = 0.02) and BMD (P = 0.03) when adjusted for age, weight, height, and fat mass, but were not different in the following lean body components: fat-free mass, total body potassium, total body water, and extracellular water. There was no difference in BMD or BMC between the PA subjects with and without advanced bone age. These data suggest a specific effect of PA on bone mineral, but not on other lean body components. The absence of a correlation between bone age and bone mineral in this small group leads us to propose there are separate promoters of bone age advancement and bone mineral accrual. Candidate hormones for these processes include adrenal androgens, E, and IGF-I. The findings of this study suggest that hormonal alterations associated with PA affect bone mineral accrual and may elucidate the mechanisms involved in this process.