Adiposity and genetic admixture, but not race/ethnicity, influence bone mineral content in peripubertal children

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.

The role of racial genetic admixture with endometrial cancer outcomes: An NRG Oncology/Gynecologic Oncology Group study

PURPOSE

Racial genetic admixture (RGA), a measure to account for ancestral genetic background that correlates with individual's racial classification, could provide insights on causation of racial disparity in endometrial cancer (EC). Our objective is to evaluate the association of RGA with EC outcomes.

METHODS

EC patients enrolled onto the GOG-210 protocol were eligible. A randomized subcohort stratified by stage and self-reported race/ethnicity of black or white was used. Genotyping was performed using custom-selected Ancestry Informative Markers to calculate individual admixture estimates of African and European ancestral background.

RESULTS

A total of 149 patients were evaluated (self-reported race: 70 black & 79 white). Mean RGA for African ancestry for self-reported black patients was 0.65 (range 0.04-0.86); while mean RGA for European ancestry for self-reported white patients was 0.77 (range 0.12-0.88). Progression-free survival (PFS) analysis using proportional hazards models stratified by stage and race revealed that each 0.10 increase in African ancestry was associated with worse PFS with hazard ratio (HR) of 1.11 (95% CI 0.90-1.37). Each 0.10 increase in European RGA was associated with improved PFS with HR of 0.86 (95% CI 0.69-1.07). Using tertiles of African RGA showed increasing risk of progression of death with increasing African RGA (with 0-5% as reference), HR (95% CIs) for top two tertiles are: 6%-66%: 1.38 (0.64, 2.97), and 67%-86%: 2.27 (0.74, 6.95).

CONCLUSION

RGA demonstrated a trend with PFS in self-reported black and white patients with EC. Patients with increased levels of African ancestry showed a trend towards worse survival after stratifying by stage/race.

Vitamin D Associations With Renal, Bone, and Cardiovascular Phenotypes: African American-Diabetes Heart Study

CONTEXT

Vitamin D binding protein (DBP) is an important determinant of bioavailable vitamin D (BAVD) and may provide clues to racial variation in osteoporosis and atherosclerosis.

OBJECTIVE

The objective was to assess relationships between DBP, BAVD, 25-hydroxyvitamin D (25OHD), and 1,25 di-hydroxyvitamin D (1,25OH2D) with kidney, bone, adipose, and atherosclerosis phenotypes in African Americans with type 2 diabetes.

DESIGN

Cross-sectional (N = 545) and longitudinal (N = 288; mean 5.1 ± 0.9-year follow-up) relationships between vitamin D concentrations with renal phenotypes, vertebral bone mineral density, aorto-iliac, coronary artery, and carotid artery calcified plaque (CP), and adipose tissue volumes were studied.

SETTING

African American-Diabetes Heart Study.

PATIENTS

Participants were 56.7% female with mean ± standard deviation (sd) age 55.6 ± 9.6 years, diabetes duration 10.3 ± 8.2 years, and eGFR 90.9 ± 22.1 ml/min/1.73 m(2).

INTERVENTIONS

None.

MAIN OUTCOMES AND MEASURES

Associations tested between vitamin D and the previously mentioned phenotypes adjusting for age, sex, African ancestry proportion, diabetes duration, statins, smoking, changes in estimated glomerular filtration rate, body mass index, hemoglobin A1c, and blood pressure.

RESULTS

1,25OH2D was inversely associated with change in coronary artery CP (parameter estimate [β] -0.005, standard error [SE] 0.002; P = .037), with a trend for change in carotid artery CP (β -0.007, SE 0.004; P = .074). Further adjustment for renin-aldosterone-system blockade revealed inverse association between 1,25OH2D and change in albuminuria (β -0.004, SE 0.002; P = .037). DBP, BAVD, and 25OHD did not associate significantly with changes in albuminuria, CP, or bone mineral density. BAVD was inversely associated with visceral, subcutaneous, intermuscular, and pericardial adipose volumes.

CONCLUSIONS

In contrast to BAVD and 25OHD, only 1,25OH2D levels were significantly and inversely associated with changes in subclinical atherosclerosis and albuminuria in African Americans, suggesting potential beneficial effects.

Vitamin D metabolites and bone mineral density: The multi-ethnic study of atherosclerosis

Previous studies demonstrate associations of low 25-hydroxyvitamin D (25(OH)D) concentrations with low bone mineral density (BMD) and fractures, motivating widespread use of vitamin D supplements for bone health. However, previous studies have been limited to predominantly White populations despite differences in the distribution and metabolism of 25(OH)D by race/ethnicity. We determined associations of serum 25(OH)D, 24,25-dihydroxyvitamin D (24,25(OH2)D3), and parathyroid hormone (PTH) with BMD among 1773 adult participants in the Multi-Ethnic Study of Atherosclerosis (MESA) in a staggered cross-sectional study design. Vitamin D metabolites were measured using liquid chromatography-mass spectroscopy and PTH using a 2-site immunoassay from serum collected in 2000-2002. Volumetric trabecular lumbar BMD was measured from computed tomography scans performed in 2002-2005 expressed as g/cm(3). We used linear regression and graphical methods to compare associations of vitamin D metabolite and PTH concentrations with BMD as the outcomes measure among White (n=714), Black (n=353), Chinese (n=249), and Hispanic (n=457) participants. Serum 25(OH)D and 24,25(OH2)D3 concentrations were highest among Whites and lowest among Blacks. BMD was greatest among Black participants. Higher serum 25(OH)D was only associated with higher BMD among Whites and Chinese participants (P-for-interaction=0.054). Comparing the lowest category of 25(OH)D (<20 ng/ml) to the highest (≥30 ng/ml), the adjusted mean difference in BMD was -8.1g/cm3 (95% CI -14.8, -1.4) for Whites; -10.2g/cm3 (-20.4, 0.0) for Chinese vs. 8.8 g/cm3 (-2.8, 20.5) for Black and -1.1g/cm3 (-8.3, 6.2) for Hispanic. Similar results were observed for serum 24,25(OH2)D3. Serum PTH was not associated with BMD. In a multi-ethnic population, associations of 25(OH)D with BMD were strongest among White and Chinese participants and null among Black and Hispanic participants. Further studies are needed to determine optimal biomarkers for bone health for multiple ethnic groups.

Vitamin D and calcium-sensing receptor polymorphisms differentially associate with resting energy expenditure in peripubertal children

Given that calcium metabolism is influenced by genes and is tightly linked to energy-utilizing pathways, this study evaluated the association of single nucleotide polymorphisms (SNPs) in the vitamin D receptor (VDR) and calcium-sensing receptor (CASR) with resting energy expenditure (REE). In 273 boys and girls, 7-12 years of age, cross-sectional REE was measured via indirect calorimetry, body composition by DXA, and dietary measures by 24-h recall. SNPs for VDR Cdx-2 (rs11568820) and CASR A986S (rs1801725) were genotyped using the Illumina Golden Gate assay. Multiple linear regression models were used to determine the association between SNPs and REE. African American carriers of the 'A' VDR Cdx2 allele had increased levels of REE in the overall sample, and this association was apparent among participants with an adiposity level of <25 % and 30 % body fat in males and females, respectively. For CASR, an association between carriers of the 'A' allele and REE was observed only in those in the upper median of calcium intake. VDR and CASR variants are associated with REE in children and are influenced by levels of calcium intake and adiposity. Our results bring awareness to mechanisms underlying the regulation of REE and biological and dietary influential factors.

Genetic admixture and obesity: recent perspectives and future applications

The process of the colonization of the New World that occurred centuries ago served as a natural experiment, creating unique combinations of genetic material in newly formed admixed populations. Through a genetic admixture approach, the identification and genotyping of ancestry informative markers have allowed for the estimation of proportions of ancestral parental populations among individuals in a sample. These admixture estimates have been used in different ways to understand the genetic contributions to individual variation in obesity and body composition parameters, particularly among diverse admixed groups known to differ in obesity prevalence within the United States. Although progress has been made through the use of genetic admixture approaches, further investigations are needed in order to explore the interaction of environmental factors with the degree of genetic ancestry in individuals. A challenge to confront at this time would be to further stratify and define environments in progressively more granular terms, including nutrients, muscle biology, stress responses at the cellular level, and the social and built environments.

Adequate vitamin D status and adiposity contribute to bone health in peripubertal nonobese children

The dietary reference intake (DRI) of vitamin D for Korean children was reduced from 400 IU/day in 2005 to 200 IU/day in 2010. We evaluated the risk factors for low 25-hydroxyvitamin D [25(OH)D] status and its relationships with bone health in peripubertal nonobese children living in Seoul or Gyeonggi-do. One hundred children (9.3 ± 1.9 years, 71 prepubertal, 45 boys) participated in the winter (n = 38, December through March) and summer (June through September). Bone mineral content (Z_BMC), fat mass (Z_FM), lean mass (Z_LM), and bone mineral density for the total body (Z_TB) and lumbar spine (Z_L1-4) were measured using dual-energy X-ray absorptiometry. Twenty-nine percent of children (47.4 % in winter, 17.7 % in summer) were vitamin D deficient (25(OH)D level of <20 ng/mL). The winter season (P = 0.008) and low vitamin D intake (P = 0.044) were associated with low 25(OH)D level. The 25(OH)D level correlated positively with Z_BMC (P = 0.040), Z_TB (P = 0.027), and Z_L1-4 (P = 0.045) independently of sex, puberty, Z_FM, Z_LM, physical activity level, and calcium intake. Z_FM correlated independently with Z_BMC (P < 0.001), Z_TB (P = 0.037), and Z_L1-4 (P < 0.001). In conclusion, almost half of peripubertal nonobese children were vitamin D deficient in winter. Adequate vitamin D status and adiposity contributed to good bone health in nonobese children. Considering the beneficial effects of adequate vitamin D status on bone health, the current DRI may be insufficient for preventing vitamin D deficiency in winter among Korean children.

Getting to the height of the matter: the relationship between stature and adiposity in pre-pubertal children

OBJECTIVE

Height has been inversely associated with cardiometabolic disease, with adiposity as the proposed contributor. Childhood represents a time when underlying metabolic pathways converge to determine growth. Although the extent to which influence is relevant, insulin, as a key growth signaling factor, likely provides key insight into mechanisms linking height and adiposity. Insulin concentration displays well-established sex and racial differences, with hyperinsulinemia more common among African Americans (AA) females relative to European Americans (EA). The objective of our study was to evaluate the relationship between height and adiposity in children. In addition, a secondary objective was to evaluate potential moderation by insulin concentration.

DESIGN

Seventy-two pre-pubertal children aged 4-10 years (mu = 6.6 +/- .2) participated.

MAIN OUTCOME MEASURES

Percent fat was assessed by DXA and fasting insulin by serum assay.

RESULTS

Height was positively associated with percent fat in the overall sample (P = .04). When evaluated according to age, an association was identified at age seven years (P = .02). When evaluated by sex, a positive relationship was apparent only in AA girls (P = .05). Inclusion of insulin in the model attenuated all significant associations, barring marginal significance in those aged seven years (P = .08).

CONCLUSIONS

A positive relationship between height and adiposity is apparent, particularly among those in younger years, which is contrary to what has been consistently reported in adults. Interestingly, age seven years was identified as a point of race-associated divergence in body composition. The degree to which growth-related processes in childhood underlie developmental origins of health disparities warrants further study.

Calcium homeostasis may influence resting energy expenditure with effects most apparent in early pubertal girls

AIM

Perturbations in dietary and hormonal components of the calciotropic network may be mediated through the influence of calcium homoeostasis on resting energy expenditure (REE). We investigated the association of dietary and hormonal factors involved in the regulation of calcium homoeostasis with REE in girls.

METHODS

Thirty-six girls aged 7-11 years participated. REE was assessed by indirect calorimetry, and body composition, dietary intake (calcium, vitamins D and K, phosphorus) and serum hormones (PTH, osteocalcin, 25OHD) were evaluated by DXA, 24 h recall and serum assay, respectively.

RESULTS

  A positive association between vitamin K and REE and an inverse association of parathyroid hormone (PTH) with REE (p = 0.05) were observed. PTH and REE were positively related in those having normal adiposity (p = 0.03) and inversely related in those with excess adiposity (p = 0.01). The association of REE with vitamin K intake was evident in lean individuals (p = 0.001), but was null in those with excess adiposity.

CONCLUSION

Decreased calciotropic hormone levels along with increased related nutrient intakes were associated with greater REE, although these relationships differed according to adiposity. The physiologic response to the diet and subsequent energy partitioning needs to be considered in the context of puberty. In particular, regulation and signalling of the calciotropic network during pubertal maturation warrant investigation.

Biogeographic ancestry, self-identified race, and admixture-phenotype associations in the Heart SCORE Study

Large epidemiologic studies examining differences in cardiovascular disease (CVD) risk factor profiles between European Americans and African Americans have exclusively used self-identified race (SIR) to classify individuals. Recent genetic epidemiology studies of some CVD risk factors have suggested that biogeographic ancestry (BGA) may be a better predictor of CVD risk than SIR. This hypothesis was investigated in 464 African Americans and 771 European Americans enrolled in the Heart Strategies Concentrating on Risk Evaluation (Heart SCORE) Study in March and April 2010. Individual West African and European BGA were ascertained by means of a panel of 1,595 genetic ancestry informative markers. Individual BGA varied significantly among African Americans and to a lesser extent among European Americans. In the total cohort, BGA was not found to be a better predictor of CVD risk factors than SIR. Both measures predicted differences in the presence of the metabolic syndrome, waist circumference, triglycerides, body mass index, very low density lipoprotein cholesterol, lipoprotein A, and systolic and diastolic blood pressure between European Americans and African Americans. These results suggest that for most nongenetic cardiovascular epidemiology studies, SIR is sufficient for predicting CVD risk factor differences between European Americans and African Americans. However, higher body mass index and diastolic blood pressure were significantly associated with West African BGA among African Americans, suggesting that BGA should be considered in genetic cardiovascular epidemiology studies carried out among African Americans.

Recent insights into racial differences in bone and mineral metabolism

PURPOSE OF REVIEW

This study reviews recent insights into racial differences in bone from 2010 to 2011.

RECENT FINDINGS

Recent studies have focused on expanding our current understanding of responsible mechanisms for racial differences in osteoporotic fracture risk. Using newer, three-dimensional imaging techniques, these studies demonstrated that racial differences in bone mass and structure are apparent early in adolescence, even when accounting for differences in bone size and muscle mass by race. In addition, recent studies using genetic admixture analysis showed that greater percentage of African admixture was independently associated with higher bone mass and more favorable parameters of bone strength in children and adults. Furthermore, recent studies showed that the relationships between 25-hydoxyvitamin D and bone outcomes differed by race, with lower 25-hydroxyvitamin D levels being associated with lower bone quality and higher fracture risk in whites but not blacks.

SUMMARY

Racial differences in bone mass and strength are apparent early in life, are independently associated with genetic ancestry, and may be partly explained by differences in the relationships between vitamin D and bone metabolism. Further studies are needed to explore these findings, with the ultimate goal of better defining molecular and cellular mechanisms underlying racial differences in bone quality.

Parental feeding practices and socioeconomic status are associated with child adiposity in a multi-ethnic sample of children

Parental feeding practices have been associated with children's weight status, but results have been inconsistent across populations. Research is needed to elucidate the relationship between parental feeding practices and adiposity in diverse populations. The present study tested if: (1) parental feeding practices differed by race/ethnicity, (2) parental pressure to eat and parental restriction were associated with adiposity levels, and (3) to investigate the relationship between parental feeding practices and/or child adiposity with socioeconomic status (SES). Structural equations modeling was conducted to test the model in 267 children aged 7-12 years self-identified as African American (AA), European American (EA), or Hispanic American (HA) from economically diverse backgrounds. Dual energy X-ray absorptiometry and computed tomography scanning were used to determine body composition and abdominal fat distribution, respectively. Parental restriction was a significant predictor of child adiposity while parental pressure to eat had an inverse relationship with child adiposity. HA parents reported significantly higher levels of restriction and pressure to eat, whereas EA parents reported the lowest. SES was positively associated with child adiposity and inversely related to parental restriction and pressure to eat. Thus, parental feeding practices differ across racial/ethnic groups and SES and may contribute to population differences in child adiposity.

Beyond thriftiness: independent and interactive effects of genetic and dietary factors on variations in fat deposition and distribution across populations

The thrifty genotype hypothesis initiated speculation that feast and famine cycling throughout history may have led to group-specific alterations of the human genome, thereby augmenting the capacity for excessive fat mass accrual when immersed in the modern-day obesogenic environment. Contemporary work, however, suggests alternative mechanisms influencing fuel utilization and subsequent tissue partitioning to be more relevant in the etiology of population-based variation in adipose storage. The objective of this study was to evaluate the independent and interactive contribution of ancestral admixture as a proxy for population-based genetic variation and diet on adipose tissue deposition and distribution in peripubertal children and to identify differences in racial/ethnic and sex groups. Two-hundred seventy-eight children (53% male) aged 7-12 years, categorized by parental self-report as African- (n = 91), European- (n = 110), or Hispanic American (n = 77), participated. Ancestral genetic admixture was estimated using 140 ancestry informative markers. Body composition was evaluated by dual-energy X-ray absorptiometry; energy expenditure by indirect calorimetry and accelerometry; and diet by 24-h-recall. Admixture independently contributed to all adiposity parameters; i.e., estimates of European and Amerindian ancestries were positively associated with all adiposity parameters, whereas African genetic admixture was inversely associated with adiposity. In boys, energy intake was associated with adiposity, irrespective of macronutrient profile, whereas in girls, the relationship was mediated by carbohydrate. We also observed moderating effects of energy balance/fuel utilization of the interaction between ancestral genetic admixture and diet. Interactive effects of genetic and non-genetic factors alter metabolic pathways and underlie some of the present population-based differences in fat storage.

African genetic admixture is associated with body composition and fat distribution in a cross-sectional study of children

OBJECTIVE

Although differences in body composition parameters among African American (AA), Hispanic American (HA) and European American (EA) children are well documented, the factors underlying these differences are not completely understood. Environmental and genetic contributors have been evaluated as contributors to observed differences. This study evaluated the extent to which African or European ancestral genetic background influenced body composition and fat distribution in 301 peripubertal AA (n = 107), HA (n = 79) and EA (n = 115) children aged 7-12.

DESIGN

Estimates of African admixture (AFADM) and European admixture (EUADM) were obtained for every subject using 142 ancestry informative DNA markers. Dual energy X-ray absorptiometry and computed tomography scanning were used to determine body composition and abdominal fat distribution, respectively. Multiple regression models were conducted to evaluate the contribution of admixture estimates to body composition and fat distribution.

RESULTS

Greater AFADM was associated with lower fat mass (P = 0.0163), lower total abdominal adipose tissue (P = 0.0006), lower intra-abdominal adipose tissue (P = 0.0035), lower subcutaneous abdominal adipose tissue (P = 0.0115) and higher bone mineral content (BMC) (P = 0.0253), after adjusting for socio-economic status, sex, age, height, race/ethnicity and pubertal status. Greater EUADM was associated with lower lean mass (LM) (P = 0.0056).

CONCLUSION

These results demonstrate that ancestral genetic background contributes to racial/ethnic differences in body composition above and beyond the effects of racial/ethnic classification and suggest a genetic contribution to total body fat accumulation, abdominal adiposity, LM and BMC.

Does fat fuel the fire: independent and interactive effects of genetic, physiological, and environmental factors on variations in fat deposition and distribution across populations

Markers of inflammation (MOI) have been reported to influence bone health in adults, with reports of inverse associations. Adipose has also been linked to bone. In children, the interrelationships are unclear. The objective of this study was to evaluate the relationship between MOI (i.e. CRP, TNFR2, IL-6) and bone mineral content (BMC) and determine the contribution of fat deposition/distribution in children. Forty-nine children (59% male) 7-12 y participated. Body composition was evaluated by DXA, and MOI and insulin sensitivity (S(I)) were obtained during an IVGTT. Multiple linear regression was used for analyses. TNFR2 was inversely associated with BMC. In boys, TNFR2 was inversely associated with BMC, and in girls IL-6 was inversely associated with BMC, and total and percent fat influenced the relationships. Our results suggest a potential inhibitory role of inflammation on bone as well as a negative impact of adiposity. Future investigations are warranted to further investigate these relationships.

The role of European genetic admixture in the etiology of the insulin resistance syndrome in children: are the effects mediated by fat accumulation?

OBJECTIVES

To evaluate the contribution of European genetic admixture (EUADM) to insulin resistance syndrome (IRS) in a multiethnic sample of children age 7-12 years, and to explore whether body fat affects this relationship.

STUDY DESIGN

Anthropometric measurements and blood pressure were assessed in 243 children. After an overnight fast, an intravenous glucose tolerance test was conducted, and measures of fasting insulin/glucose, lipids, insulin sensitivity (SI), and acute insulin response to glucose (AIRg) were obtained. The proportion of EUADM was determined by maximum likelihood estimation using 140 ancestry informative markers. Subjects were stratified into tertiles according to the proportion of EUADM for analyses. Subjects were categorized as lean or obese using body fat percentage cutpoints (25% in boys, 30% in girls).

RESULTS

Among lean subjects (72%), the tertile representing the greatest proportion of EUADM was associated with higher SI (P<.001) and serum glucose (P<.05) and lower insulin (P<.05), AIRg (P<.001), high-density lipoprotein cholesterol (P=.05), and blood pressure (P<.05). However, among obese subjects, EUADM was associated only with SI (P<.05).

CONCLUSIONS

Our results suggest that population differences in IRS likely have a genetic component, but that the influence of genetic background may be masked by obesity.