Demonstration of a difference in urinary calcium, not calcium absorption, in black and white adolescents

Vitamin D/Bone Mineral Density and Triglyceride Paradoxes Seen in African Americans: A Cross-Sectional Study and Review of the Literature

Vitamin D is known to have a positive effect on bone health. Despite the greater frequency of vitamin D deficiency in African Americans (AA), they have a higher bone mineral density (BMD) compared to whites, demonstrating a disconnect between BMD and vitamin D levels in AA. Another intriguing relationship seen in AA is the triglyceride (TG) paradox, an unusual phenomenon in which a normal TG status is observed even when patients house conditions known to be characterized by high TG levels, such as Type II diabetes. To the best of our knowledge, no study has examined whether these two paradoxical relationships exist simultaneously in AA subjects with Type II diabetes. In this study, we compared levels of blood markers, including HbA1c, TG, and vitamin D, measured as serum 25-hydroxyvitamin D [25(OH)VD] µM/mL, [25(OH)VD]/TG, calcium, and BMD in AA (n = 56) and white (n = 26) subjects with Type II diabetes to see whether these relationships exist concurrently. We found that AA subjects had significantly lower TG and [25(OH)VD] levels and a significantly higher BMD status compared to white subjects, even when the ages, BMI, duration of diabetes, HbA1c, and calcium levels were similar between the two groups. This demonstrates that these two paradoxical relationships exist simultaneously in Type II diabetic AA subjects. In addition to these findings, we discuss the current hypotheses in the literature that attempt to explain why these two intriguing relationships exist. This review also discusses four novel hypotheses, such as altered circulating levels and the potential role of estrogen and hydrogen sulfide on BMD and HMG-CoA reductase as a possible contributor to the TG paradox in AA subjects. This manuscript demonstrates that there are still many unanswered questions regarding these two paradoxical relationships and further research is needed to determine why they exist and how they can be implemented to improve healthcare.

Endocrine Health and Health Care Disparities in the Pediatric and Sexual and Gender Minority Populations: An Endocrine Society Scientific Statement

Endocrine care of pediatric and adult patients continues to be plagued by health and health care disparities that are perpetuated by the basic structures of our health systems and research modalities, as well as policies that impact access to care and social determinants of health. This scientific statement expands the Society's 2012 statement by focusing on endocrine disease disparities in the pediatric population and sexual and gender minority populations. These include pediatric and adult lesbian, gay, bisexual, transgender, queer, intersex, and asexual (LGBTQIA) persons. The writing group focused on highly prevalent conditions-growth disorders, puberty, metabolic bone disease, type 1 (T1D) and type 2 (T2D) diabetes mellitus, prediabetes, and obesity. Several important findings emerged. Compared with females and non-White children, non-Hispanic White males are more likely to come to medical attention for short stature. Racially and ethnically diverse populations and males are underrepresented in studies of pubertal development and attainment of peak bone mass, with current norms based on European populations. Like adults, racial and ethnic minority youth suffer a higher burden of disease from obesity, T1D and T2D, and have less access to diabetes treatment technologies and bariatric surgery. LGBTQIA youth and adults also face discrimination and multiple barriers to endocrine care due to pathologizing sexual orientation and gender identity, lack of culturally competent care providers, and policies. Multilevel interventions to address these disparities are required. Inclusion of racial, ethnic, and LGBTQIA populations in longitudinal life course studies is needed to assess growth, puberty, and attainment of peak bone mass. Growth and development charts may need to be adapted to non-European populations. In addition, extension of these studies will be required to understand the clinical and physiologic consequences of interventions to address abnormal development in these populations. Health policies should be recrafted to remove barriers in care for children with obesity and/or diabetes and for LGBTQIA children and adults to facilitate comprehensive access to care, therapeutics, and technological advances. Public health interventions encompassing collection of accurate demographic and social needs data, including the intersection of social determinants of health with health outcomes, and enactment of population health level interventions will be essential tools.

Prebiotic to Improve Calcium Absorption in Postmenopausal Women After Gastric Bypass: A Randomized Controlled Trial

CONTEXT

The adverse skeletal effects of Roux-en-Y gastric bypass (RYGB) are partly caused by intestinal calcium absorption decline. Prebiotics, such as soluble corn fiber (SCF), augment colonic calcium absorption in healthy individuals.

OBJECTIVE

We tested the effects of SCF on fractional calcium absorption (FCA), biochemical parameters, and the fecal microbiome in a post-RYGB population.

METHODS

Randomized, double-blind, placebo-controlled trial of 20 postmenopausal women with history of RYGB a mean 5 years prior; a 2-month course of 20 g/day SCF or maltodextrin placebo was taken orally. The main outcome measure was between-group difference in absolute change in FCA (primary outcome) and was measured with a gold standard dual stable isotope method. Other measures included tolerability, adherence, serum calciotropic hormones and bone turnover markers, and fecal microbial composition via 16S rRNA gene sequencing.

RESULTS

Mean FCA ± SD at baseline was low at 5.5 ± 5.1%. Comparing SCF to placebo, there was no between-group difference in mean (95% CI) change in FCA (+3.4 [-6.7, +13.6]%), nor in calciotropic hormones or bone turnover markers. The SCF group had a wider variation in FCA change than placebo (SD 13.4% vs 7.0%). Those with greater change in microbial composition following SCF treatment had greater increase in FCA (r2 = 0.72, P = 0.05). SCF adherence was high, and gastrointestinal symptoms were similar between groups.

CONCLUSION

No between-group differences were observed in changes in FCA or calciotropic hormones, but wide CIs suggest a variable impact of SCF that may be due to the degree of gut microbiome alteration. Daily SCF consumption was well tolerated. Larger and longer-term studies are warranted.

Primary Hyperparathyroidism in Homozygous Sickle Cell Patients: A Hemolysis-Mediated Hypocalciuric Hypercalcemia Phenotype?

Primary hyperparathyroidism (pHPT) has been reported to have a higher prevalence in sickle cell disease (SCD) patients, including a high rate of recurrence following surgery. However, most patients are asymptomatic at the time of diagnosis, with surprisingly infrequent hypercalciuria, raising the issue of renal calcium handling in SCD patients. We conducted a retrospective study including (1) 64 hypercalcemic pHPT non-SCD patients; (2) 177 SCD patients, divided into two groups of 12 hypercalcemic pHPT and 165 non-pHPT; (3) eight patients with a diagnosis of familial hypocalciuric hypercalcemia (FHH). Demographic and biological parameters at the time of diagnosis were collected and compared between the different groups. Determinants of fasting fractional excretion of calcium (FeCa²⁺) were also analyzed in non-pHPT SCD patients. Compared to non-SCD pHPT patients, our data show a similar ionized calcium and PTH concentration, with a lower plasmatic calcitriol concentration and a lower daily urinary calcium excretion in pHPT SCD patients (p < 0.0001 in both cases). Fasting FeCa²⁺ is also surprisingly low in pHPT SCD patients, and thus inadequate to be considered hypercalcemia, recalling the FHH phenotype. FeCa²⁺ is also low in the non-pHPT SCD control group, and negatively associated with PTH and hemolytic biomarkers such as LDH and low hemoglobin. Our data suggest that the pHPT biochemical phenotype in SCD patients resembles the FHH phenotype, and the fasting FeCa²⁺ association with chronic hemolysis biomarkers strengthens the view of a potential pharmacological link between hemolytic by-products and calcium reabsorption, potentially through a decreased calcium-sensing receptor (CaSR) activity.

Vitamin D Supplementation in Elderly Black Women Does Not Prevent Bone Loss: A Randomized Controlled Trial

Black Americans have lower levels of serum 25(OH)D but superior bone health compared to white Americans. There is controversy over whether they should be screened for vitamin D deficiency and have higher vitamin D requirements than recommended by the Institute of Medicine (IOM). The purpose of this trial was to determine whether Vitamin D supplementation in elderly black women prevents bone loss. A total of 260 healthy black American women, 60 years of age and older were recruited to take part in a two-arm, double-dummy 3-year randomized controlled trial (RCT) of vitamin D₃ versus placebo. The study was conducted in an ambulatory clinical research center. Vitamin D₃ dose was adjusted to maintain serum 25(OH)D above 75 nmol/L. Bone mineral density (BMD) and serum were measured for parathyroid hormone (PTH), C-terminal crosslink telopeptide (CTX), and bone-specific alkaline phosphatase (BSAP) every 6 months. Baseline serum 25(OH)D₃ was 54.8 ± 16.8 nmol/L. There was no group × time interaction effect for any BMD measurement. For all BMD measurements, except for total body and spine, there was a statistically significant negative effect of time (p < 0.001). An equivalency analysis showed that the treatment group was equivalent to the control group. Serum PTH and BSAP declined, with a greater decline of PTH in the treatment group. The rate of bone loss with serum 25(OH)D above 75 nmol/L is comparable to the rate of loss with serum 25(OH)D at the Recommended Dietary Allowance (RDA) of 50 nmol/L. Black Americans should have the same exposure to vitamin D as white Americans. © 2018 American Society for Bone and Mineral Research.

Serum calcium changes and risk of type 2 diabetes mellitus in Asian population

AIMS

We examined the association between changes in serum calcium levels with the incidence of type 2 diabetes mellitus (T2DM) in apparently healthy South Korean subjects.

METHODS

A retrospective longitudinal analysis was conducted with subjects who had participated in comprehensive health check-ups at least four times over a 7-year period (between 2006 and 2012). In total, 23,121 subjects were categorized into tertiles based on changes in their albumin-adjusted serum calcium levels. Multivariate Cox regression models were fitted to assess the association between changes in serum calcium levels during follow-up and the relative risk of diabetes incidence.

RESULTS

After a median follow-up of 57.4months, 1,929 (8.3%) new cases of T2DM occurred. Simple linear regression analysis showed serum calcium level changes correlated positively with changes in HbA1c and fasting plasma glucose (FPG) levels (B=5.72, p<0.001 for FPG; B=0.13, p<0.001 for HbA1c). An increase in albumin-adjusted serum calcium levels during follow-up was related to an increased risk of T2DM. After adjustment for potential confounders, the risk of T2DM was 1.6 times greater for subjects whose albumin-adjusted serum calcium levels were in the highest change tertile during follow-up than for subjects whose levels were in the lowest tertile (HR 1.65, 95% CI 1.44-1.88, P<0.001).

CONCLUSIONS

The elevation of albumin-adjusted serum calcium levels was associated with an increased risk of T2DM, independent of baseline glycemic status.

Risk of Stress Fracture Varies by Race/Ethnic Origin in a Cohort Study of 1.3 Million US Army Soldiers

Stress fractures (SF) are common and costly injuries in military personnel. Risk for SF has been shown to vary with race/ethnicity. Previous studies report increased SF risk in white and Hispanic Soldiers compared with black Soldiers. However, these studies did not account for the large ethnic diversity in the US military. We aimed to identify differences in SF risk among racial/ethnic groups within the US Army. A retrospective cohort study was conducted using data from the Total Army Injury and Health Outcomes Database from 2001 until 2011. SF diagnoses were identified from ICD-9 codes. We used Cox-proportional hazard models to calculate time to SF by racial/ethnic group after adjusting for age, education, and body mass index. We performed a sex-stratified analysis to determine whether the ethnic variation in SF risk depends on sex. We identified 21,549 SF cases in 1,299,332 Soldiers (more than 5,228,525 person-years of risk), revealing an overall incidence rate of 4.12 per 1000 person-years (7.47 and 2.05 per 1000 person-years in women and men, respectively). Using non-Hispanic blacks as the referent group, non-Hispanic white women had the highest risk of SF, with a 92% higher risk of SF than non-Hispanic black women (1.92 [1.81-2.03]), followed by American Indian/Native Alaskan women (1.72 [1.44-1.79]), Hispanic women (1.65 [1.53-1.79]), and Asian women (1.32 [1.16-1.49]). Similarly, non-Hispanic white men had the highest risk of SF, with a 59% higher risk of SF than non-Hispanic black men (1.59 [1.50-1.68]), followed by Hispanic men (1.19 [1.10-1.29]). When examining the total US Army population, we found substantial differences in the risk of stress fracture among racial/ethnic groups, with non-Hispanic white Soldiers at greatest risk and Hispanic, American Indian/Native Alaskan, and Asian Soldiers at an intermediate risk. Additional studies are needed to determine the factors underlying these race- and ethnic-related differences in stress fracture risk. © 2017 American Society for Bone and Mineral Research.

Assessing Vitamin D Status in African Americans and the Influence of Vitamin D on Skeletal Health Parameters

In the United States, there is a significant disparity in vitamin D status among individuals of African versus European descent. Despite having lower total 25-hydroxyvitamin D levels compared with white Americans, African Americans have higher bone mineral density and lower fracture risk. This article reviews classical and nonclassical vitamin D physiology, describes whether total versus free 25-hydroxyvitamin D is a better marker of vitamin D status in African Americans, and summarizes the influence of vitamin D status and vitamin D supplementation on markers of vitamin D bioactivity (intestinal calcium absorption, parathyroid hormone secretion, bone mineral density, fracture) in African Americans.

Parathyroid hormone and the risk of incident hypertension: the Atherosclerosis Risk in Communities study

BACKGROUND

Recent evidence suggests that parathyroid hormone (PTH) has effects on vascular smooth muscle cells, the rennin-angiotensin system and kidney function, but less is known about its role in the development of hypertension. The distribution of serum PTH also varies by race.

METHODS AND RESULTS

Therefore, we examined the relation between PTH and incident hypertension and tested for interaction by race among 7504 Atherosclerosis Risk in Communities participants (1264 black, 6240 white, median age 56 years) without initial hypertension in 1990-1992. During a median follow-up of 6 years, 1487 white and 509 black participants developed hypertension. In the overall study population, PTH was not associated with incident hypertension after adjustment for demographics and behavioral risk factors [hazard ratio highest vs. lowest quintiles, 95% confidence interval: 1.11 (0.96-1.28); P for linear trend 0.02]. Although the interaction was not statistically significant (P = 0.60), there was some evidence that the PTH-hypertension association differed by race. Among blacks, PTH was positively associated with incident hypertension, independent of demographics, and behavioral risk factors (P for linear trend 0.003). Among whites, PTH was not associated with hypertension risk. Results were similar when comparing participants with elevated versus nonelevated PTH (≥65 vs. <65 pg/ml): hazard ratio in blacks: 1.24 (1.02-1.54); hazard ratio in whites: 0.95 (0.78-1.16).

CONCLUSIONS

In this large community-based cohort, PTH levels, overall, were not independently associated with the risk of hypertension. However, we found some evidence that PTH may be associated with hypertension in blacks. Future research should continue to explore potential race differences in the PTH-hypertension association.

Serum calcium and incident type 2 diabetes: the Atherosclerosis Risk in Communities (ARIC) study

BACKGROUND

Elevated serum calcium has been associated with a variety of metabolic abnormalities and may be associated with a greater risk of diabetes.

OBJECTIVE

The purpose of this study was to test the hypothesis that serum calcium concentration is positively and independently associated with the incidence of diabetes and to evaluate the association of calcium-sensing receptor (CaSR) gene single nucleotide polymorphism (SNP) rs1801725 with incident diabetes.

DESIGN

Atherosclerosis Risk in Communities study participants free of diabetes at baseline (n = 12,800; mean age: 53.9 y; 22.6% black) were studied for incident diabetes. Serum calcium was measured at baseline and corrected for serum albumin. Diabetes was defined by use of glucose concentrations, self-report, or medication use. Cox proportional hazards regression was used.

RESULTS

During a mean 8.8 y of follow-up, 1516 cases of diabetes were reported. Participants in the highest compared with lowest calcium quintile were at greater risk of incident diabetes after adjustment for demographic and lifestyle factors [HR (95% CI): 1.34 (1.14, 1.57); P-trend across quintiles <0.0001] and with further adjustment for waist circumference and body mass index [1.26 (1.07, 1.48); P-trend = 0.004]. Additional adjustment for biomarkers on the metabolic pathway (e.g., 25-hydroxyvitamin D, parathyroid hormone, phosphorus) had little impact. The calcium-diabetes association was statistically significant in blacks [1.48 (1.11, 1.98); P-trend = 0.002] but not whites [1.17 (0.96, 1.43); P-trend = 0.17] after adjustment for adiposity. In whites, CaSR gene SNP rs1801725 was associated with serum calcium but not with risk of diabetes.

CONCLUSIONS

Consistent with 3 previous cohort studies, elevated serum calcium was found to be associated with a greater risk of type 2 diabetes. Further research is needed to understand the role, if any, that calcium plays in the pathogenesis of diabetes.

Genetic African Ancestry and Markers of Mineral Metabolism in CKD

BACKGROUND AND OBJECTIVES

Disorders of mineral metabolism are more common in African Americans with CKD than in European Americans with CKD. Previous studies have focused on the differences in mineral metabolism by self-reported race, making it difficult to delineate the importance of environmental compared with biologic factors.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

In a cross-sectional analysis of 3013 participants of the Chronic Renal Insufficiency Cohort study with complete data, we compared markers of mineral metabolism (phosphorus, calcium, alkaline phosphatase, parathyroid hormone, fibroblast growth factor 23, and urine calcium and phosphorus excretion) in European Americans versus African Americans and separately, across quartiles of genetic African ancestry in African Americans (n=1490).

RESULTS

Compared with European Americans, African Americans had higher blood concentrations of phosphorus, alkaline phosphatase, fibroblast growth factor 23, and parathyroid hormone, lower 24-hour urinary excretion of calcium and phosphorus, and lower urinary fractional excretion of calcium and phosphorus at baseline (P<0.001 for all). Among African Americans, a higher percentage of African ancestry was associated with lower 24-hour urinary excretion of phosphorus (Ptrend<0.01) in unadjusted analyses. In linear regression models adjusted for socio-demographic characteristics, kidney function, serum phosphorus, and dietary phosphorus intake, higher percentage of African ancestry was significantly associated with lower 24-hour urinary phosphorus excretion (each 10% higher African ancestry was associated with 39.6 mg lower 24-hour urinary phosphorus, P<0.001) and fractional excretion of phosphorus (each 10% higher African ancestry was associated with an absolute 1.1% lower fractional excretion of phosphorus, P=0.01).

CONCLUSIONS

A higher percentage of African ancestry was independently associated with lower 24-hour urinary phosphorus excretion and lower fractional excretion of phosphorus among African Americans with CKD. These findings suggest that genetic variability might contribute to racial differences in urinary phosphorus excretion in CKD.

Parathyroid hormone is associated with incident diabetes in white, but not black adults: The Atherosclerosis Risk in Communities (ARIC) Study

OBJECTIVE

Accumulating evidence has linked elevated parathyroid hormone (PTH) with insulin resistance, beta cell dysfunction and dysglycaemia, however, its role in the development of diabetes is largely unclear, particularly among non-whites. We sought to examine the association of PTH with the incidence of diabetes.

METHODS

We studied 8066 white and 2034 black adults aged 46-70 years at baseline (1990-92) from the ARIC Study with follow-up for incident diabetes ascertained during study visits conducted in 1993-95 and 1996-98. Hazard ratios (HR) and their 95% CIs for diabetes adjusted for demographics, lifestyle, and 25-hydroxyvitamin D were estimated according to PTH measured at baseline.

RESULTS

PTH was higher among blacks than whites (median [IQR], 43.8 [35.0-55.8] vs. 37.9 [30.4-47.3] pg/mL; P<0.001). During a median follow-up of 6 years, 498 white and 167 black participants developed diabetes. The association of PTH with diabetes varied significantly by race (P-interaction 0.02). PTH was not associated with risk for diabetes among black adults. Among whites, HRs according to quintiles of PTH were 1 (referent), 0.95 (0.71, 1.29), 0.95 (0.70, 1.28), 1.12 (0.84, 1.51), and 1.31 (0.98, 1.76) (P-trend 0.03). When a clinical cut-point for PTH was applied (≥65pg/mL; 5.7% of whites), the HR for diabetes among whites was 1.38 (1.01, 1.88). Results were similar when restricted to participants with normal baseline kidney function.

CONCLUSION

In this large, population-based study, elevated PTH was independently associated with risk for diabetes among white, but not black adults. Further studies are needed to elucidate the mechanisms that may underlie this differential association of PTH with diabetes across race groups.

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.

Bone Mineral Content as a Driver of Energy Expenditure in Prepubertal and Early Pubertal Boys

OBJECTIVE

To examine the associations of bone and bone-secreted factors with measures of energy metabolism in prepubertal and early pubertal boys.

STUDY DESIGN

Participants in this cross-sectional, observational study included 37 (69% black, 31% white) boys, aged 7-12 years (Tanner stage <III). Dual-energy X-ray absorptiometry was used to measure bone mineral content (BMC) and percent body fat. Indirect calorimetry was used to assess resting energy expenditure (REE). Fasting blood levels of osteocalcin (OCN), fibroblast growth factor 23 (FGF23), insulin, glucose, precursor product of type I collagen (N-terminal pro-peptide) and type I collagen, and C-terminal cross-linked telopeptide were measured. Pearson correlations were performed to evaluate relationships among BMC, OCN, FGF23, fasting insulin and glucose, and REE. Multiple linear regression models were used to test associations between OCN and BMC (independent variables) with fasting insulin and glucose and with REE, adjusting for bone turnover markers and further adjusted for percent body fat.

RESULTS

BMC was correlated with REE and insulin. OCN was correlated with glucose in blacks only (r = 0.45, P < .05). FGF23 was not correlated with any markers of energy metabolism. BMC was associated with insulin level in blacks (β = 0.95, P = .001), which was attenuated by percent body fat (β = 0.47, P = .081). BMC was associated with REE in whites (β = 0.496.7, P < .05) and blacks (β = 619.5, P < .0001); but accounting for percent body fat attenuated the association in whites (β = 413.2, P = .078).

CONCLUSION

Our findings suggest that BMC is a determinant of fasting insulin and REE, and that the contribution of body fat appears to be race-specific. Endocrine effects of FGF23 and OCN on energy metabolism were not apparent.

TRIAL REGISTRATION

Registered with ClinicalTrials.gov: NCT02040740, NCT02040727, and NCT01410643.

Ethnic differences in urinary calcium and phosphate excretion between Gambian and British older adults

Ethnic differences in renal calcium and phosphate excretion exist, which may depend on differences in their dietary intakes and regulatory factors. We report highly significant differences in urinary calcium and phosphate excretion between white British and Gambian adults after statistical adjustment for mineral intakes, indicating an independent effect of ethnicity.

INTRODUCTION

Populations vary in their risk of age-related osteoporosis. There are racial or ethnic differences in the metabolism of the bone-forming minerals calcium (Ca) and phosphate (P), with a lower renal Ca and P excretion in African-Americans compared to white counterparts, even at similar intakes and rates of absorption. Also, Africans in The Gambia have a lower Ca excretion compared to white British subjects, groups known to differ in their dietary Ca intake. Here, we report on differences in urinary Ca and P excretion between Gambian and white British adults while allowing for known predictors, including dietary intakes.

METHODS

Participants were healthy white British (n = 60) and Gambian (n = 61) men and women aged 60-75 years. Fasting blood and 2-h urine samples were collected. Markers of Ca and P metabolism were analysed. Dietary intake was assessed with country-specific methods.

RESULTS

White British older adults had higher creatinine-corrected urinary Ca and P excretion (uCa/uCr, uP/uCr) and lower tubular maximum of Ca and P compared to Gambian counterparts. The predictors of urinary Ca and P differed between groups. Multiple regression analysis showed that dietary Ca and Ca/P were predictors of uCa/uCr and uP/uCr, respectively. Ethnicity remained a significant predictor of uCa/uCr and uP/uCr after adjustment for diet and other factors.

CONCLUSIONS

Gambian older adults have higher renal Ca conservation than British counterparts. Dietary mineral intakes were predictors of the differences in urinary Ca and P excretion, but ethnicity remained a highly significant predictor after statistical adjustment. This suggests that ethnicity has an independent effect on renal Ca and P handling.

Ethnic differences in calcium, phosphate and bone metabolism

The prevalence of osteoporosis and the incidence of age-related fragility fracture vary by ethnicity. There is greater than 10-fold variation in fracture probabilities between countries across the world. Mineral and bone metabolism are intimately interlinked, and both are known to exhibit patterns of daily variation, known as the diurnal rhythm (DR). Ethnic differences are described for Ca and P metabolism. The importance of these differences is described in detail between select ethnic groups, within the USA between African-Americans and White-Americans, between the Gambia and the UK and between China and the UK. Dietary Ca intake is higher in White-Americans compared with African-Americans, and is higher in White-British compared with Gambian and Chinese adults. Differences are observed also for plasma 25-hydroxy vitamin D, related to lifestyle differences, skin pigmentation and skin exposure to UVB-containing sunshine. Higher plasma 1,25-dihydroxy vitamin D and parathyroid hormone are observed in African-American compared with White-American adults. Plasma parathyroid hormone is also higher in Gambian adults and, in winter, in Chinese compared with White-British adults. There may be ethnic differences in the bone resorptive effects of parathyroid hormone, with a relative skeletal resistance to parathyroid hormone observed in some, but not all ethnic groups. Renal mineral excretion is also influenced by ethnicity; urinary Ca (uCa) and urinary P (uP) excretions are lower in African-Americans compared with White-Americans, and in Gambians compared with their White-British counterparts. Little is known about ethnic differences in the DR of Ca and P metabolism, but differences may be expected due to known differences in lifestyle factors, such as dietary intake and sleep/wake pattern. The ethnic-specific DR of Ca and P metabolism may influence the net balance of Ca and P conservation and bone remodelling. These ethnic differences in Ca, P and the bone metabolism may be important factors in the variation in skeletal health.

Population ancestry and genetic risk for diabetes and kidney, cardiovascular, and bone disease: modifiable environmental factors may produce the cures

Variable rates of disease observed between members of different continental population groups may be mediated by inherited factors, environmental exposures, or their combination. This article provides evidence in support of differential allele frequency distributions that underlie the higher rates of nondiabetic kidney disease in the focal segmental glomerulosclerosis spectrum of disease and lower rates of coronary artery calcified atherosclerotic plaque and osteoporosis in populations of African ancestry. With recognition that these and other common complex diseases are affected by biological factors comes the realization that targeted manipulation of environmental exposures and pharmacologic treatments will have different effects based on genotype. The present era of precision medicine will couple one's genetic makeup with specific therapies to reduce rates of disease based on the presence of disease-specific alleles.

Racial differences in clinical use of cinacalcet in a large population of hemodialysis patients

BACKGROUND/AIMS

African-Americans with end-stage renal disease receiving dialysis have more severe secondary hyperparathyroidism than Whites. We aimed to assess racial differences in clinical use of cinacalcet.

METHODS

This retrospective cohort study used data from DaVita, Inc., for 45,589 prevalent hemodialysis patients, August 2004, linked to Centers for Medicare & Medicaid Services data, with follow-up through July 2007. Patients with Medicare as primary payer, intravenous vitamin D use, or weighted mean parathyroid hormone (PTH) level >150 pg/ml at baseline (August 1-October 31, 2004) were included. Cox proportional hazard modeling was used to evaluate race and other demographic and clinical characteristics as predictors of cinacalcet initiation, titration, and discontinuation.

RESULTS

Of 16,897 included patients, 7,674 (45.4%) were African-American and 9,223 (54.6%) were white; 53.2% of cinacalcet users were African-American. Cinacalcet was prescribed for 47.7% of African-Americans and 34.5% of Whites, and for a greater percentage of African-Americans at higher doses at each PTH strata. After covariate adjustment, African-Americans were more likely than Whites to receive cinacalcet prescriptions (hazard ratio 1.17, p < 0.001). The direction and magnitude of this effect appeared to vary by age, baseline PTH, and calcium, and by elemental calcium use. African-Americans were less likely than Whites to have prescriptions discontinued and slightly more likely to undergo uptitration (hazard ratio 1.09, 95% confidence interval 0.995-1.188), but this relationship lacked statistical significance.

CONCLUSION

Cinacalcet is prescribed more commonly and at higher initial doses for African-Americans than for Whites to manage secondary hyperparathyroidism.

Magnesium retention from metabolic-balance studies in female adolescents: impact of race, dietary salt, and calcium

BACKGROUND

Previously, we showed that black girls retained more calcium than white girls did and that salt loading negatively affected calcium retention. Racial differences likely exist in other bone minerals also, such as magnesium, in response to salt loading during growth.

OBJECTIVE

We studied racial differences in magnesium metabolism in response to dietary sodium and calcium during rapid bone growth.

DESIGN

Twenty-seven white and 40 black girls (11-15 y old) were studied for 3 wk while they consumed low-sodium (1.3 g/d) and high-sodium (3.8 g/d) diets by using a randomized-order, crossover metabolic study with 3 dietary calcium intakes; the magnesium dietary intake was fixed at 230 mg/d. Urine and feces were collected during each 3-wk period in 24-h pools and analyzed for magnesium. A mixed-model ANOVA was used to determine the effect of race and dietary sodium with calcium intake as a covariate.

RESULTS

Salt loading or calcium intake had no significant effect on urinary magnesium excretion. Blacks excreted significantly less urinary magnesium (mean ± SD: 83.8 ± 25.6 mg/d) than did whites (94.9 ± 27.3 mg/d; P < 0.05). No effects were observed in fecal magnesium excretion. Magnesium retention was higher with the low-sodium diet (50.1 ± 44.0 mg/d) than with the high-sodium diet (39.3 ± 49.8 mg/d) (P < 0.05), with no effects of race or calcium intake. Salt loading had no effect on biomarkers. Whites had higher 25-hydroxyvitamin D and insulin-like growth factor binding protein 3 but lower 1,25-dihydroxyvitamin D and parathyroid hormone concentrations.

CONCLUSIONS

Blacks excreted less urinary magnesium than did whites. Magnesium retention was similar between races but higher with the low-sodium diet. Kinetic studies are needed to fully explain magnesium homeostasis. This trial was registered at clinicaltrials.gov as NCT01564238.

Evaluation of markers of bone turnover during lactation in African-Americans: a comparison with Caucasian lactation

CONTEXT

The African-American skeleton is resistant to PTH; whether it is also resistant to PTHrP and the hormonal milieu of lactation is unknown.

OBJECTIVES

The objective of the study was to assess bone turnover markers in African-Americans during lactation vs Caucasians.

DESIGN AND PARTICIPANTS

A prospective cohort study with repeated measures of markers of bone turnover in 60 African-American women (3 groups of 20: lactating, bottle feeding, and healthy controls), compared with historic Caucasian women.

SETTING

The study was conducted at a university medical center.

OUTCOME MEASURES

Biochemical markers of bone turnover and calcium metabolism were measured.

RESULTS

25-Hydroxyvitamin D (25-OHD) and PTH were similar among all 3 African-American groups, but 25-OHD was 30%-50% lower and PTH 2-fold higher compared with Caucasians (P < .001, P < .002), with similar 1,25 dihydroxyvitamin D [1,25(OH)(2)D] values. Formation markers [amino-terminal telopeptide of procollagen-1 (P1NP) and bone-specific alkaline phosphatase (BSAP)] increased significantly (2- to 3-fold) in lactating and bottle-feeding African-American women (P1NP, P < .001; BSAP, P < .001), as did resorption [carboxy-terminal telopeptide of collagen-1 (CTX) and serum amino-terminal telopeptide of collagen 1 (NTX), both P < .001]. P1NP and BSAP were comparable in African-American and Caucasian controls, but CTX and NTX were lower in African-American vs Caucasian controls. African-American lactating mothers displayed quantitatively similar increases in markers of bone formation but slightly lower increases in markers of resorption vs Caucasians (P = .036).

CONCLUSIONS

Despite reported resistance to PTH, lactating African-American women have a significant increase in markers of bone resorption and formation in response the hormonal milieu of lactation. This response is similar to that reported in Caucasian women despite racial differences in 25-OHD and PTH. Whether this is associated with similar bone loss in African-Americans as in Caucasians during lactation is unknown and requires further study.

Fibroblast growth factor 23: state of the field and future directions

Fibroblast growth factor 23 (FGF23) is a bone-derived hormone that regulates and is regulated by blood levels of phosphate and active vitamin D. Post-translational glycosylation by the enzyme GALNT3 and subsequent processing by furin have been demonstrated to be a regulated process that plays a role in regulating FGF23 levels. In physiologic states, FGF23 signaling is mediated by an FGF receptor and the coreceptor, Klotho. Recent work identifying a role for iron/hypoxia pathways in FGF23 physiology and their implications are discussed. Beyond its importance in primary disorders of mineral metabolism, recent work implicates FGF23 in renal disease-associated morbidity, as well as possible roles in cardiovascular disease and skeletal fragility.

Effect of race and genetics on vitamin D metabolism, bone and vascular health

The pathophysiology of chronic kidney disease-mineral and bone disorder accounts for an inverse relationship between bone mineralization and vascular calcification in progressive nephropathy. Inverse associations between bone mineral density (BMD) and calcified atherosclerotic plaque are also observed in individuals of European and African ancestry without nephropathy, suggesting a mechanistic link between these processes that is independent of kidney disease. Despite lower dietary calcium intake and serum 25-hydroxyvitamin D (25(OH)D) concentrations, African Americans have higher BMD and develop osteoporosis less frequently than do European Americans. Moreover, despite having more risk factors for cardiovascular disease, African Americans have a lower incidence and severity of calcified atherosclerotic plaque formation than do European Americans. Strikingly, evidence is now revealing that serum 25(OH)D and/or 1,25 dihydroxyvitamin D levels associate positively with atherosclerosis but negatively with BMD in African Americans; by contrast, vitamin D levels associate negatively with atherosclerosis and positively with BMD in individuals of European ancestry. Biologic phenomena, therefore, seem to contribute to population-specific differences in vitamin D metabolism, bone and vascular health. Genetic and mechanistic approaches used to explore these differences should further our understanding of bone-blood vessel relationships and explain how African ancestry protects from osteoporosis and calcified atherosclerotic plaque, provided that access of African Americans to health care is equivalent to individuals of European ethnic origin. Ultimately, in our opinion, a new mechanistic understanding of the relationships between bone mineralization and vascular calcification will produce novel approaches for disease prevention in aging populations.

Low urine calcium excretion in African American patients with primary hyperparathyroidism

OBJECTIVE

To evaluate the prevalence of low urine calcium excretion in African American patients with primary hyperparathyroidism (PHPT), a common disorder associated with bone and renal complications, and to assess the distinction between PHPT and familial hypocalciuric hypercalcemia (FHH), a rare benign genetic disease.

METHODS

We conducted a retrospective study on a cohort of 1,297 patients in whom a 24-hour urine study was performed for measurement of urine calcium and creatinine. PHPT was diagnosed if the serum calcium concentration was ≥10.5 mg/dL and intact parathyroid hormone (PTH) was ≥40 pg/mL. Patients receiving medications that affect urine calcium or with glomerular filtration rate ≤30 mL/min were excluded.

RESULTS

Ninety-six patients satisfied the diagnostic criteria for PHPT. The African American (n = 70) and non-African American (n = 26) patients did not differ in their mean age, body mass index, glomerular filtration rate, serum PTH, 25-hydroxyvitamin D levels, and 24-hour urine creatinine values. Median values of urine calcium/creatinine (mg/g) were 122 for African American versus 214 for non-African American patients (P = .006). Thirty-one of 70 African American patients (44%) had a urine calcium/creatinine ratio ≤100 mg/g, whereas only 2 of 26 non-African American patients (8%) had this value (P = .001).

CONCLUSION

The prevalence of low urine calcium excretion among African American patients with PHPT is unexpectedly high. A threshold of 100 mg/g urine calcium/creatinine identified 44% of such patients with PHPT as having FHH in this cohort. Therefore, other clinical criteria and laboratory variables should be used to distinguish PHPT from FHH in African American patients with PTH-dependent hypercalcemia.

Racial differences in bone mineral density and fractures in men receiving androgen deprivation therapy for prostate cancer

PURPOSE

Whether race influences bone loss and fracture risk during androgen deprivation therapy for prostate cancer is unknown. Using data from a prospective clinical trial we compared bone mineral density and fracture between African-American and Caucasian men receiving androgen deprivation therapy.

MATERIALS AND METHODS

A total of 516 subjects were in the placebo group of a 2-year randomized placebo controlled fracture prevention trial, and were African-American (68) or Caucasian (448). We compared baseline characteristics, changes in bone mineral density and rates of new fractures between races.

RESULTS

Compared to Caucasian men, African-American men had higher baseline hip bone mineral density (mean ± SD 0.98 ± 0.15 vs 0.91 ± 0.15 gm/m(2), p = 0.001) and similar spine bone mineral density (1.09 ± 0.22 vs 1.11 ± 0.22, p = 0.51). There was no difference in prevalent vertebral fractures between African-American and Caucasian men (7.4% vs 15.0%, p = 0.13). The percentage change in hip bone mineral density at 2 years was similar between African-American and Caucasian men (mean ± SE -2.21% ± 0.59% vs -2.54% ± 0.26%, p = 0.65). Changes in bone mineral density of the lumbar spine were also similar between African-American and Caucasian men (-1.74% ± 0.69% vs -1.30% ± 0.33%, p = 0.64). No new vertebral fractures were reported in African-American men but 2 fractures were reported in Caucasian men.

CONCLUSIONS

In a clinical trial African-American men receiving androgen deprivation therapy for prostate cancer have a greater hip bone mineral density and tended to have fewer prevalent vertebral fractures than Caucasian men. Despite a lower baseline risk of osteoporosis and fracture, African-American men experience a decrease in bone mineral density similar to that of Caucasian men.

Racial differences in the relationship between vitamin D, bone mineral density, and parathyroid hormone in the National Health and Nutrition Examination Survey

It is unclear whether optimal levels of 25-hydroxyvitamin D (25(OH)D) in whites are the same as in minorities. In adult participants of NHANES, the relationships between 25(OH)D, bone mineral density (BMD), and parathyroid hormone (PTH) differed in blacks as compared to whites and Mexican-Americans, suggesting that optimal 25(OH)D levels for bone and mineral metabolism may differ by race.

INTRODUCTION

Blacks and Hispanics have lower 25-hydroxyvitamin D concentrations than whites. However, it is unclear whether 25(OH)D levels considered "optimal" for bone and mineral metabolism in whites are the same as those in minority populations.

METHODS

We examined the relationships between 25(OH)D and parathyroid hormone in 8,415 adult participants (25% black and 24% Mexican-American) in the National Health and Nutrition Examination Surveys 2003-2004 and 2005-2006; and between 25(OH)D and bone mineral density in 4,206 adult participants (24% black and 24% Mexican-American) in the 2003-2004 sample.

RESULTS

Blacks and Mexican-Americans had significantly lower 25(OH)D and higher PTH concentrations than whites (P < 0.01 for both). BMD significantly decreased (P < 0.01) as serum 25(OH)D and calcium intake declined among whites and Mexican-Americans, but not among blacks (P = 0.2). The impact of vitamin D deficiency (25(OH)D ≤ 20 ng/ml) on PTH levels was modified by race/ethnicity (P for interaction, 0.001). Whereas inverse relationships between 25(OH)D and PTH were observed above and below a 25(OH)D level of 20 ng/ml in whites and Mexican-Americans, an inverse association between 25(OH)D and PTH was only observed below this threshold in blacks, with the slope of the relationship being essentially flat (P = 0.7) above this cut-point, suggesting that PTH may be maximally suppressed at lower 25(OH)D levels in blacks than in whites or Mexican-Americans.

CONCLUSIONS

The relationships between 25(OH)D, BMD, and PTH may differ by race among US adults. Whether race-specific ranges of optimal vitamin D are needed to appropriately evaluate the adequacy of vitamin D stores in minorities requires further study.

Calcium intake and body composition in African-American children and adolescents at risk for overweight and obesity

This study examined the role of calcium intake on body composition in 186 African-American adolescents at risk for overweight and obesity. The average weight of 89.8 kg ± 23.6 (SD) had a mean BMI z score of 2.2. Females with a calcium intake of <314 mg/day had higher percent fat mass compared to those with the highest calcium intakes that were ≥634 mg/day. Compared to those with a low calcium intake (<365 mg/day), those with the highest calcium intake of >701 mg/day had higher intake of thiamin, folate, cobalamin, vitamin D, phosphorus, iron, zinc.

Bone mineral density in African&#x2013;American women with symptomatic uterine leiomyoma

OBJECTIVE

Uterine leiomyoma is associated with increased BMD in Caucasian women and is largely attributed to the state of hyperestrogenemia associated with disease. This relationship, however, has not been previously described in African-American women. We aim to assess BMD in African-American women with symptomatic uterine leiomyoma.

DESIGN

Case-control study.

MATERIALS & METHODS

29 African-American women with uterine leiomyoma signed an Institutional Review Board (IRB) approved consent form at a reproductive clinic of an inner city hospital in Brooklyn, NY, USA. BMD and T-score of lumbar spine was compared with a controlled group matched for age, race and BMI. BMD of lumbar spine was measured using Hologic QDR 4200 in both groups. Data are presented as mean ± SEM.

RESULTS

For the entire study population the mean age (years) was 42.07 ± 1.15, and the BMI (kg/m²) was 29.37 ± 0.93 in patients with uterine leiomyoma and 30.07 ± 1.06 for the control group (p = 0.07). There was a significant difference in the mean BMD (cm²) between the uterine leiomyoma group (1.17 ± 0.03) compared with control (1.05 ± 0.02 p < 0.01). The T-score for the uterine leiomyoma group was significantly higher compared with the control group (0.31 ± 0.25 and -0.74 ± 0.21 with p < 0.01). The prevalence of osteopenia (T-score <-1) was lower for the leiomyoma group when compared with controls, (p < 0.02).

CONCLUSION

Consistent with data from the white population with uterine leiomyoma, our data showed a significantly higher BMD in African-American women with uterine leiomyoma, compared with an age- and race-matched cohort. The implications of these findings remain to be investigated and further confirmed in future longitudinal studies.

Racial differences in postprandial mineral ion handling in health and in chronic kidney disease

BACKGROUND

Increased serum phosphate is associated with cardiovascular disease. Compared with whites, blacks have significantly higher serum phosphate and increased risk of hyperphosphataemia in health and chronic kidney disease (CKD). While population-based studies suggest that diminished urinary phosphorus excretion in blacks may explain these differences, few physiological studies explored the potential mechanisms. The aim of this study was to examine racial differences in postprandial urinary mineral ion excretion in health and in CKD.

METHODS

Twenty-eight healthy (18 white and 10 black) and 19 CKD (9 white and 10 black) subjects consumed a standardized meal; after which, blood and urine samples were collected for 4 h for measurement of phosphate, calcium, parathyroid hormone (PTH) and fibroblast growth factor 23 (FGF23).

RESULTS

Although serum phosphate did not differ by race, blacks had ∼30% lower postprandial fractional excretion of phosphate than whites in health (P < 0.001) and CKD (P = 0.02). Similarly, blacks had ∼35% lower fractional excretion of calcium in health (P = 0.02) and CKD (P = 0.3). Moreover, the postprandial response in serum calcium among CKD subjects differed by race (P = 0.03), with serum calcium significantly decreasing in whites but not blacks.

CONCLUSIONS

Blacks had lower fractional excretion of phosphate than whites despite similar levels of PTH and FGF23 in health and in CKD, suggesting racial variability in renal sensitivity to phosphaturic hormones. Furthermore, blacks defend postprandial serum calcium more effectively than whites in CKD. Further studies are needed to define the mechanisms underlying these observations and evaluate whether racial differences in mineral ion handling may contribute to disparities in CKD outcomes.

Ethnicity, socioeconomic status, and attainment of clinical practice guideline standards in dialysis patients in the United kingdom

BACKGROUND AND OBJECTIVES

The role of socioeconomic status (SES) and its contribution to ethnic differences in standards attainment among dialysis patients is not known.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

We examined associations between area- level SES (Townsend index) and ethnicity (white, black, South Asian) and standards attainment in 14,117 incident dialysis patients (1997-2004) in the UK.

RESULTS

Deprived patients were less likely to achieve hemoglobin (Hb) > or = 10 g/dl (trend P < 0.001) but not after controlling for patient and center characteristics (trend P = 0.1). There was no association with hemodialysis dose and parathyroid hormone (PTH) standard but deprived patients had better attainment of phosphate (PO4) <5.6 mg/dl, calcium (Ca) and Calcium-phosphate (CaPO4) standard (e.g., most deprived versus least deprived adjusted odds ratio [OR] 1.25, 95% confidence intervals [CI] 1.12, 1.38). There was no association with SES using a lower limit for PO4 (3.5 - 5.5 mg/dl). Compared with Whites, Blacks had lower attainment of Hb (adjusted OR 0.57, 95% CI 0.45, 0.71) and PTH standards (adjusted OR 0.27, 95% CI 0.22, 0.33) but better attainment of PO4 and CaPO4, while South Asians experienced better or comparable outcomes for most standards except Ca and PTH.

CONCLUSIONS

There was no evidence of socioeconomic inequity in standards attainment or a consistent pattern of inequity by ethnic group. The lower attainment of some standards in ethnic minorities may reflect biologic differences rather than ethnicity-related inequity of care.

Imaging of metabolic bone diseases

Osteoporosis is a serious public health problem. The incidence of osteoporotic fractures increases with age. As life expectancy increases, social costs associated with osteoporotic fractures will multiply exponentially. The early diagnosis of osteoporosis, thanks to evermore precise devices, becomes, therefore, fundamental to prevent complications of disease and unnecessary suffering.

Vitamin D economy in blacks

The fact that fracture risk is lower and BMD is higher in blacks compared with whites is surprising in light of what is known about vitamin D status in blacks. Mean 25(OH)D levels are lower in blacks than whites at all stages of life, and a greater proportion of blacks meet criteria for vitamin D deficiency. The racial difference in serum 25(OH)D level is primarily caused by increased pigmentation reducing vitamin D production in the skin. In response to lower 25(OH)D levels and lower average calcium intake, blacks have higher average PTH levels and a higher prevalence of secondary hyperparathyroidism (twice the prevalence compared with whites for both sexes). This is associated with higher average levels of 1,25(OH)(2)D and lower urinary calcium excretion but not higher biochemical indices of bone turnover. In fact, in general, biochemical indices of bone formation (particularly osteocalcin levels) are lower in blacks. Bone formation rates assessed histomorphometrically are also lower, although wall thickness is maintained. During a 24-h PTH infusion, increments in levels of three different bone resorption markers are significantly lower in blacks than in whites, providing direct confirmation of the thesis that the black skeleton is resistant to the bone-resorbing effects of PTH, whereas renal sensitivity to PTH is maintained or perhaps even enhanced. Vitamin D supplementation studies in black women have shown inconsistent benefits to BMD. Skeletal and renal adaptations to vitamin D deficiency in blacks might be so effective that vitamin D supplementation might not confer any further benefit to the black skeleton. Benefits of vitamin D supplements in blacks may still play a role, however, in the prevention of other chronic diseases.

Ethnic Variation in Risk for Osteoporosis among Women: A Review of Biological and Behavioral Factors

Most studies of risk factors for osteoporosis and nontraumatic fracture involve white women, although more research is being geared toward bone health among various ethnic groups. The purpose of this review is to provide an overview of health disparity in osteoporosis, including assessment of bone mineral density (BMD), bone health screening, lifestyle risk factors, and treatment involving white, black, Hispanic, Asian, and Native American women. This review summarizes evidence that white, Asian, Hispanic, and Native American women are more at risk for osteoporosis than black women. These conclusions are supported by the disparity in BMD between white and black women, although the reason for this biological difference is not well characterized. Additional research is needed to determine if there is a significant difference in BMD among Hispanic, Asian, and Native American women independent of body weight and size. Similarly, there is also disparity in fracture rates, with the causes presumed to be multifactorial. Calcium intake is lower than recommended in all females at all ages; however, it is much lower in black and Native American women and highest in white and Hispanic women. Black women also have a lower vitamin D status than white women, with mean vitamin D status of Hispanic American women lying between that of black and white women. Similarly, although white women are more active than black and Hispanic women at all ages, data are lacking about physical activity habits of women of other ethnic backgrounds and how this impacts bone health. Finally, screening protocols for women of various ethnicities and effectiveness of treatments are not well established and remain a priority in women's health.

Idiopathic hypercalciuria in children--how valid are the existing diagnostic criteria?

Idiopathic hypercalciuria is a common metabolic abnormality in children of all ages. There is evidence of an association of idiopathic hypercalciuria with nephrolithiasis, hematuria, and osteoporosis. However, much of this evidence is anecdotal and the precise role of hypercalciuria in the pathogenesis of these conditions is far from clear. Furthermore, the precise definition of idiopathic hypercalciuria has not yet been established. The methodologies for quantitating urinary calcium excretion have also not been standardized, adding another potential confounding factor to the accurate interpretation of urinary calcium excretion. Long-term studies on the natural history of unselected children with idiopathic hypercalciuria are needed to establish the true clinical significance of this condition. The focus of this review is to critically evaluate the methods currently being used to measure urinary calcium excretion in children and to assess the validity of existing criteria for diagnosing idiopathic hypercalciuria.

Racial differences in bone mineral density in older men

Studies have examined factors related to BMD in older white, but not black, men. We measured BMD in older white and black men and examined factors related to racial differences in BMD. Black men had significantly higher adjusted BMD at all sites. These results may explain, in part, the lower incidence of fractures in older black men.

INTRODUCTION

Several studies have examined factors associated with bone mineral density (BMD)in older men. None, however, have had sufficient numbers of black men to allow for meaningful comparisons by race.

MATERIALS AND METHODS

A total of 503 white and 191 black men aged 65 and older(75.1 +/- 5.8 and 72.2 +/- 5.7 years, respectively) were recruited from the Baltimore metropolitan area. All men completed a battery of self-administered questionnaires, underwent a standardized examination, and had BMD measured at the femoral neck, lumbar spine, and total body. Data were analyzed using multiple variable linear regression models, adjusted for potential confounding variables; two-way interactions with main effects were included in models where appropriate.

RESULTS

Black men had significantly higher adjusted BMD at the femoral neck (difference 0.09 [95% CI: 0.07, 0.12] mg/cm2), lumbar spine (0.07 [0.04, 0.10] mg/cm2), and total body (0.06 [0.03, 0.08] mg/cm2) than white men.

CONCLUSIONS

Older black men have significantly higher BMD than older white men, even after adjustment for factors associated with BMD. These differences, especially at the femoral neck, may explain the reduced incidence of hip fracture in black compared with white men.

Glucocorticoid-induced osteoporosis in patients with sarcoidosis

BACKGROUND

Patients with sarcoidosis are at risk for osteoporosis caused by glucocorticoid therapy. However, because of potential hypercalciuria and hypercalcemia, the usual conservative treatment for low bone mass, calcium and vitamin D supplements, may not be well tolerated.

METHODS

Patients with sarcoidosis referred to a metabolic bone clinic were compared with other sarcoidosis patients studied prospectively and patients with chronic obstructive pulmonary disease (COPD) or asthma. The subjects underwent bone mineral density (BMD) testing, and the sarcoidosis patients underwent mobility testing and measurements of serum and urine chemistries, vitamin D levels, bone turnover markers, and sex hormone levels.

RESULTS

The subjects were mostly male African Americans in the 6th decade of life. Many took chronic oral glucocorticoid therapy and often used home oxygen therapy. Low hip BMD was common among the referred group, comparable with patients with COPD. Surprisingly, hypercalciuria and hypercalcemia were uncommon, and serum testosterone levels were frequently low. The use of calcium supplements, multivitamins containing vitamin D, and glucocorticoids had no impact on serum or urine calcium levels. From univariate analysis, potential risk factors for low hip BMD were low weight, low body mass index (BMI), advanced age, and current use of glucocorticoids. However, in stepwise multiple regression analysis, only low BMI predicted about 40% of hip BMD.

CONCLUSIONS

Despite calcium and vitamin D supplements, this group of patients with sarcoidosis had low BMD but relatively infrequent hypercalciuria and hypercalcemia. No prediction model of BMD was adequate. Therefore, we conclude that each patient needs to be assessed individually, including measurement of BMD, serum and urine calcium, and sex steroid status.

Vitamin D deficiency and secondary hyperparathyroidism in the elderly: consequences for bone loss and fractures and therapeutic implications

Vitamin D deficiency is common in the elderly, especially in the housebound and in geriatric patients. The establishment of strict diagnostic criteria is hampered by differences in assay methods for 25-hydroxyvitamin D. The synthesis of vitamin D3 in the skin under influence of UV light decreases with aging due to insufficient sunlight exposure, and a decreased functional capacity of the skin. The diet contains a minor part of the vitamin D requirement. Vitamin D deficiency in the elderly is less common in the United States than elsewhere due to the fortification of milk and use of supplements. Deficiency in vitamin D causes secondary hyperparathyroidism, high bone turnover, bone loss, mineralization defects, and hip and other fractures. Less certain consequences include myopathy and falls. A diet low in calcium may cause an increased turnover of vitamin D metabolites and thereby aggravate vitamin D deficiency. Prevention is feasible by UV light exposure, food fortification, and supplements. Vitamin D3 supplementation causes a decrease of the serum PTH concentration, a decrease of bone turnover, and an increase of bone mineral density. Vitamin D3 and calcium may decrease the incidence of hip and other peripheral fractures in nursing home residents. Vitamin D3 is recommended in housebound elderly, and it may be cost-effective in hip fracture prevention in selected risk groups.

Race and sex effects on the association between muscle strength, soft tissue, and bone mineral density in healthy elders: the Health, Aging, and Body Composition Study

Two factors generally reported to influence bone density are body composition and muscle strength. However, it is unclear if these relationships are consistent across race and sex, especially in older persons. If differences do exist by race and/or sex, then strategies to maintain bone mass or minimize bone loss in older adults may need to be modified accordingly. Therefore, we examined the independent effects of bone mineral-free lean mass (LM), fat mass (FM), and muscle strength on regional and whole body bone mineral density (BMD) in a cohort of 2,619 well-functioning older adults participating in the Health, Aging, and Body Composition (Health ABC) Study with complete measures. Participants included 738 white women, 599 black women, 827 white men, and 455 black men aged 70-79 years. BMD (g/cm2) of the femoral neck, whole body, upper and lower limb, and whole body and upper limb bone mineral-free LM and FM was assessed by dual-energy X-ray absorptiometry (DXA). Handgrip strength and knee extensor torque were determined by dynamometry. In analyses stratified by race and sex and adjusted for a number of confounders, LM was a significant (p < 0.001) determinant of BMD, except in white women for the lower limb and whole body. In women, FM also was an independent contributor to BMD at the femoral neck, and both FM and muscle strength contributed to limb BMD. The following were the respective beta-weights (regression coefficients for standardized data, Std beta) and percent difference in BMD per unit (7.5 kg) LM: femoral neck, 0.202-0.386 and 4.7-5.9%; lower limb, 0.209-0.357 and 2.9-3.5%; whole body, 0.239-0.484 and 3.0-4.7%; and upper limb (unit = 0.5 kg), 0.231-0.407 and 3.1-3.4%. Adjusting for bone size (bone mineral apparent density [BMAD]) or body size BMD/height) diminished the importance of LM, and the contributory effect of FM became more pronounced. These results indicate that LM and FM were associated with bone mineral depending on the bone site and bone index used. Where differences did occur, they were primarily by sex not race. To preserve BMD, maintaining or increasing LM in the elderly would appear to be an appropriate strategy, regardless of race or sex.

Bone mineral content in girls perinatally infected with HIV

BACKGROUND

Early diagnostic efforts and advances in multidrug therapy have considerably prolonged the survival time of children infected perinatally with HIV. Despite these advances, few studies have addressed calcium status and bone growth in HIV-infected children.

OBJECTIVE

Our objective was to examine the effect of HIV infection on calcium status and bone growth in children.

DESIGN

We measured calcitropic hormones, urinary calcium excretion, bone mineral content, and body composition in 19 young girls aged 9.2 +/- 2.6 y (range: 5.9-15.2 y) who were infected perinatally with HIV.

RESULTS

Serum concentrations of 1,25-dihydroxyvitamin D [1,25(OH)(2)D] and parathyroid hormone concentrations were elevated above normal ranges in 25% and 12% of these girls, respectively. Urinary calcium excretion normalized for creatinine excretion was also elevated (Ca/Cr >0.18) in 17% of these children despite suboptimal calcium intakes (679 +/- 437 mg/d). Total-body bone mineral content, measured with the use of dual-energy X-ray absorptiometry, averaged 845.1 +/- 279.0 g and was on average 2.7 z scores below age- and race-matched values reported in non-HIV-infected healthy girls. Significant positive correlations were found between an indirect marker of bone resorption in urine (N:-telopeptide) and 1,25(OH)2D (P < 0.02, r2 = 0.586, n = 9), and between serum N-telopeptide and total alkaline phosphatase (P < 0.001, r2 = 0.541, n = 17), suggesting that calcium insufficiency may be increasing bone resorption in this group.

CONCLUSIONS

Young girls with HIV infection had low bone mass and evidence of calcium insufficiency. Nutritional counseling of children with HIV infection should emphasize adequate calcium intakes because of the importance of this age period in bone mineral acquisition.

Insulin-like growth factors and bone mineral density in African American and White girls

OBJECTIVES

African American children have greater bone mineral density (BMD) and bone mineral content (BMC) than white children. We examined the hypothesis that differences in insulin-like growth factors (IGFs) are important determinants of BMD during childhood.

METHODS

We measured IGFs and IGF binding proteins in 59 African American and 59 white girls matched for age, body mass index, socioeconomic status, and pubertal stage. BMD and BMC were determined by dual emission x-ray absorptiometry.

RESULTS

African American girls had greater total BMD (P <.001), BMC (P <.01), total IGF-1 (P <.001), and free IGF-1 (P <.01) than white girls. IGFBP-1, IGFBP-2, and IGFBP-3 were similar in both groups or lower in African Americans. IGF-1 was positively correlated with IGF-2 in white girls (P =.012) but was negatively correlated with IGF-2 in African Americans (P =.015). IGF-1 and free IGF-1 were positively correlated with BMD/BMC. Multiple regression analyses showed 80% of the variance in BMC could be accounted for by the use of body weight, height, and IGF-1 in the model. When IGF-1 was included as a factor, race did not add to the model's predictive power.

CONCLUSION

IGF-1 and free IGF-1 are greater in African American than in white girls and may contribute to the greater BMD of African Americans.

Bone mineral density in older non-Hispanic Caucasian and Mexican-American women: relationship to lean and fat mass

PRIMARY OBJECTIVE

The prevalence of osteoporotic fracture is higher in non-Hispanic Caucasian (NHC) than Mexican-American (MA) women in the USA. The present study examined bone mineral density (BMD) in these two ethnic groups and the association between BMD and body composition.

RESEARCH DESIGN

Cross-sectional.

SUBJECTS

Sixty-two NHC and 54 MA women, aged 60-86 years, with a body mass index (kgm(-2)) of <30.

METHODS

BMD (gcm(-2)) of the spine (L2-4), hip (femoral neck, trochanter, Ward's triangle) and whole body was determined by dual-energy X-ray absorptiometry (DXA). Bone mineral-free lean mass (LM) and fat mass (FM) and several ratios of body fat distribution were also assessed by DXA.

RESULTS

There was no difference in age (NHC, 69.5+/-0.7; MA 69.5+/-0.9 years; mean +/- SEM) or body mass, but MA women were shorter with a higher truncal adiposity (p < 0.001). There was no significant difference in BMD between groups, however, adjusting for height resulted in higher hip and whole body BMD in MA women (p < 0.01). When volumetric bone density was calculated (bone mineral apparent density; BMAD, gcm(-3)), a trend for higher values in MA women was observed at the femoral neck (p = 0.018). LM contributed independently to BMD at the spine and hip in NHC women, with FM also contributing at the femoral neck. In MA women, LM was an independent contributor to lumbar spine and trochanter BMD, and both LM and FM contributed to whole body BMD. However, the effects of LM and FM were removed in both groups when BMD was adjusted for body or bone size, the only exception being at the trochanter in NHC women.

CONCLUSIONS

These results indicate that MA women have higher bone density at the proximal femur than NHC women, which may partially account for their lower rate of hip fracture. Further, differences in bone density between the two ethnic groups do not appear to be dependent on soft-tissue composition.

Osteoporosis and African American women

The incidence of osteoporosis and related fractures in African American women is half that of Caucasian women. African American women who sustain osteoporosis-related fractures have increased disability and decreased survival. Given the exponential increase in hip fracture rate among African American women over the age of 70 years, the risk of osteoporosis among this population may be underestimated. This review focuses on racial differences in women's bone mineral density (BMD) and bone metabolism and on various explanations for these observed differences. Environmental risk factors for osteoporosis and related fractures among African American women and modalities for prevention and treatment of osteoporosis are discussed. African American women begin menopause with higher BMD and have lower rates of women's bone loss after menopause, which account for their decreased incidence of osteoporosis and related fractures. The risk factors for osteoporosis among African American women are similar to those found in Caucasian women. Lifestyle interventions, such as calcium and vitamin D supplementation, smoking cessation, and increased physical activity, should be encouraged to enhance peak bone mass and to decrease bone loss. These interventions and other treatment modalities, such as hormone replacement therapy, bisphosphonates, and selective estrogen receptor modulators, should be studied further in African American women.

Oligofructose stimulates calcium absorption in adolescents

BACKGROUND

In rats, nondigestible oligosaccharides stimulate calcium absorption. Recently, this effect was also found in human subjects.

OBJECTIVE

The objective of the study was to investigate whether consumption of 15 g oligofructose/d stimulates calcium absorption in male adolescents.

DESIGN

Twelve healthy, male adolescents aged 14-16 y received, for 9 d, 15 g oligofructose or sucrose (control treatment) daily over 3 main meals. The treatments were given according to a randomized, double-blind, crossover design, separated by a 19-d washout period. On the 8th day of each treatment period, 44Ca was given orally with a standard breakfast containing approximately 200 mg Ca. Within half an hour after administration of 44Ca, 48Ca was administered intravenously. Fractional calcium absorption was computed from the enrichment of 44Ca:43Ca and 48Ca:43Ca in 36-h urine samples, which was measured by inductively coupled plasma mass spectrometry.

RESULTS

An increase in true fractional calcium absorption (%) was found after consumption of oligofructose (mean difference +/- SE of difference: 10.8+/-5.6; P < 0.05, one sided). The results are discussed in relation to the methods used.

CONCLUSION

Fifteen grams of oligofructose per day stimulates fractional calcium absorption in male adolescents.

Calcium absorption and kinetics are similar in 7- and 8-year-old Mexican-American and Caucasian girls despite hormonal differences

To assess the possibility of ethnic differences in mineral metabolism in prepubertal children, we compared measures of calcium metabolism in 7- and 8-y-old Mexican-American (MA) and non-Hispanic Caucasian (CAU) girls (n = 38) living in southeastern Texas. We found similar fractional calcium absorption, urinary calcium excretion, calcium kinetic values and total-body bone mineral content in the MA and CAU girls. In contrast, parathyroid hormone (PTH) concentrations were greater in MA girls (4.01 +/- 0.47 vs. 1. 96 +/- 0.50 pmol/L, P = 0.005) than in CAU girls. Serum 25-hydroxyvitamin D concentrations were lower in MA girls (68.9 +/- 7.7 vs. 109.4 +/- 8.4 nmol/L, P = 0.001) than in CAU girls, but 1, 25-dihydroxyvitamin D concentrations did not differ between groups. Seasonal variability was seen for 25-hydroxyvitamin D concentrations in girls of both ethnic groups, but values in all of the girls were >30 nmol/L (12 ng/mL). We conclude the following: 1) greater PTH levels in MA girls than CAU girls are present without evidence of vitamin D deficiency; and 2) differences in 25-hydroxyvitamin D and PTH concentrations between MA and CAU girls do not have a large effect on calcium absorption, excretion or bone calcium kinetics. These data do not provide evidence for adjusting dietary recommendations for mineral or vitamin D intake by MA girls.

Effects of calcium supplementation on calcium homeostasis and bone turnover in lactating women

Lactation is a time of calcium flux, because women secrete approximately 210 mg calcium/day in breast milk, and they experience a transient bone loss. The objectives of this study were to determine the effect of calcium supplementation on adaptive responses in calcium homeostasis during lactation and after weaning. Two cohorts of women participated in a 6-month randomized calcium supplementation trial. Lactation cohort women (97 lactating, 99 nonlactating) were studied during the first 6 months post partum, and weaning cohort women (95 lactating, 92 nonlactating) were studied during the second 6 months post partum. Lactating women in the weaning cohort weaned approximately 1.5 months after enrollment. PTH was 18-30% lower in lactating than in nonlactating women (P < 0.01). Serum 1,25-dihydroxyvitamin D was 11-16% higher in lactating than in nonlactating women and remained elevated for approximately 1.5 months after weaning (P = 0.06). Calcium supplementation decreased serum PTH and 1,25-dihydroxyvitamin D in lactating and nonlactating women similarly. At 6 months, the calciuric response to calcium supplementation was less in lactating (compared with nonlactating) women (P = 0.06). Biomarkers of bone turnover were higher in lactating than in nonlactating women during lactation and after weaning but were not effected by calcium supplementation. Calcium supplementation has little effect on lactation-induced changes in the calcium economy.

Ultrasound measurements of the calcaneus: effects of ethnicity

This study investigated whether there were differences in quantitative ultrasound (QUS) of the calcaneus between African-American and Caucasian females. QUS-1X, an ultrasonometer by Metra Biosystems Inc., was used to determine broadband ultrasound attenuation (UBI-4) using Burg Spectral Estimation in decibels/megahertz. The average transit time through the heel (TTH) in microseconds was used to estimate bone size. A multiple factor index taking into account bone size, UBI-4T, was calculated by dividing UBI-4 by TTH in decibels/(Megahertz x microseconds). Results showed that premenopausal Caucasian females (n = 37) have approx 6-8% lower values (p < 0.05) of QUS indices than their African-American (n = 54) counterparts. However, after adjusting for bone size, the differences in attenuation disappeared. Pilot data for males (Caucasian: n = 16, African-American: n = 18) suggest that the differences in QUS appear to be related to bone size. The limited scope of our study supports the fact that there are differences in QUS between premenopausal Caucasian and African-American females, but not with the same magnitude as evidenced by dual X-ray absorptiometry. We recommend that more data be collected on ethnic differences across all age ranges, to help understand how QUS may be used to assess bone mass and determine its value either as a screening tool to diagnose low bone mass or as a tool to predict osteoporotic fracture within various ethnic groups.

Bone mass and hip axis length in healthy Asian, black, Hispanic, and white American youths

The primary objective of this study was to examine the associations of ethnicity, diet (calcium, protein, energy), and weight-bearing activity with dual-energy X-ray absorptiometry (DXA)-measured bone mass and hip axis length (HAL) in 423 Asians, blacks, Hispanics, and non-Hispanic Caucasians, aged 9-25 years. Bone mass was expressed as bone mineral content (BMC), bone mineral density (BMD), and bone mineral apparent density (BMAD). The data were analyzed using multiple linear regression, after stratifying for gender and pubertal stage and adjusting for height and weight. With few exceptions, Asians and Hispanics had comparable bone mass to whites at all pubertal stages. Greater femoral neck BMAD in black than white females was observed at all pubertal stages. Black males displayed greater BMD and BMAD than white males at all sites in early puberty and at the femoral neck in maturity. Calcium was positively and protein negatively related to BMAD at the femoral neck in early pubertal females. Among males, calcium was negatively associated with whole body BMC and BMD and spine BMD and BMAD in midpuberty. Weight-bearing activity was not associated with bone mass in females; in males, it was positively related only to femoral neck BMC in early puberty. There was an absence of evidence for ethnic differences in HAL among females. In males, we observed shorter HAL in mature Asians and blacks than whites. Neither diet nor activity was associated with HAL.