Differences in calcium metabolism between black and white men and women

Exploring ethnic differences in the distribution of blood test results in healthy adult populations to inform earlier cancer detection: a systematic review

BACKGROUND

In primary care, health professionals use blood tests to investigate nonspecific presentations to inform referral decisions. Reference ranges for the commonly used blood tests in western countries were developed in predominately White populations, and so may perform differently when applied to non-White populations. Knowledge of ethnic variation in blood test results in healthy/general populations could help address ethnic inequalities in cancer referral for diagnosis and outcomes.

OBJECTIVE

This systematic review explored evidence of ethnic differences in the distribution of selected blood test results among healthy/general populations to inform future research aimed at addressing inequalities in cancer diagnosis.

METHODS

We searched PubMed and EMBASE to identify studies reporting measures of haemoglobin, MCV, calcium, albumin, platelet count, and CRP in nondiseased adults from at least 2 different ethnic groups. Two reviewers independently screened studies, completed data extraction and quality assessment using an adapted Newcastle-Ottawa scale. Participants were stratified into White, Black, Asian, Mixed, and Other groups. Data were synthesised narratively and meta-analyses were conducted where possible.

RESULTS

A total of 47 papers were included. Black men and women have lower average values of haemoglobin, MCV, and albumin, and higher average values of CRP relative to their White counterparts. Additionally, Black men have lower average haemoglobin than Asian men, whereas Asian women have lower average CRP values when compared with White women.

CONCLUSIONS

There is evidence of ethnic differences in average values of haemoglobin, MCV, CRP, and albumin in healthy/general populations. Further research is needed to explore the reasons for these differences. Systematic review registration: CRD42021274580.

Vitamin D Metabolites: Analytical Challenges and Clinical Relevance

Recent research activities have provided new insights in vitamin D metabolism in various conditions. Furthermore, substantial progress has been made in the analysis of vitamin D metabolites and related biomarkers, such as vitamin D binding protein. Liquid chromatography tandem mass spectrometric (LC-MS/MS) methods are capable of accurately measuring multiple vitamin D metabolites in parallel. Nevertheless, only 25(OH)D and the biologically active form 1,25(OH)2D are routinely measured in clinical practice. While 25(OH)D remains the analyte of choice for the diagnosis of vitamin D deficiency, 1,25(OH)2D is only recommended in a few conditions with a dysregulated D metabolism. 24,25(OH)2D, free and bioavailable 25(OH)D, and the vitamin D metabolite ratio (VMR) have shown promising results, but technical pitfalls in their quantification, limited clinical data and the lack of reference values, impede their use in clinical practice. LC-MS/MS is the preferred method for the measurement of all vitamin D related analytes as it offers high sensitivity and specificity. In particular, 25(OH)D and 24,25(OH)2D can accurately be measured with this technology. When interpreted together, they seem to provide a functional measure of vitamin D metabolism beyond the analysis of 25(OH)D alone. The determination of VDBP, free and bioavailable 25(OH)D is compromised by unresolved analytical issues, lacking reference intervals and insufficient clinical data. Therefore, future research activities should focus on analytical standardization and exploration of their clinical value. This review provides an overview on established and new vitamin D related biomarkers including their pathophysiological role, preanalytical and analytical aspects, expected values, indications and influencing conditions.

Assessing vitamin D metabolism - four decades of experience

One hundred years ago, the role of vitamin D for bone mineralization and the prevention of rickets was discovered. Vitamin D comprises a group of over 50 metabolites with multiple functions that go far beyond calcium homeostasis and bone mineralization. Approximately 50 years ago, first methods for the measurement of 25-hydroxyvitamin D (25(OH)D) in human blood were developed. Over the years, different analytical principals were employed including competitive protein binding assays, high-performance liquid chromatography, various immunoassay and mass spectrometric formats. Until the recent standardization of serum 25(OH)D measurement, agreement between methods was unsatisfactory. Since then, comparability has improved, but substantial variability between methods remains. With the advent of liquid chromatography tandem mass spectrometry (LC-MS/MS), the accurate determination of 25(OH)D and other metabolites, such as 24,25(OH)2D, becomes increasingly accessible for clinical laboratories. Easy access to 25(OH)D testing has triggered extensive clinical research showing that large parts of the population are vitamin D deficient. The variable response of vitamin D deficient individuals to supplementation indicates that assessing patients' vitamin D stores by measuring 25(OH)D provides limited insight into the metabolic situation. Meanwhile, first evidence has emerged suggesting that the simultaneous measurement of 25(OH)D, 24,25(OH)2D and other metabolites allows a dynamic evaluation of patients' vitamin D status on metabolic principals. This may help to identify patients with functional vitamin D deficiency from those without. It can be expected that research into the assessment vitamin D status will continue for another 50 years and that this will help rationalizing our approach in clinical practice.

Sex-and race-specific burden of aortic valve calcification among older adults without overt coronary heart disease: The Atherosclerosis Risk in Communities Study

BACKGROUND AND AIMS

The prevalence of aortic valve calcification (AVC) increases with age. However, the sex-and race-specific burden of AVC and associated cardiovascular risk factors among adults ≥75 years are not well studied.

METHODS

We calculated the sex-and race-specific burden of AVC among 2283 older Black and White adults (mean age:80.5 [SD:4.3] years) without overt coronary heart disease from the Atherosclerosis Risk in Communities Study who underwent non-contrast cardiac-gated CT-imaging at visit 7 (2018-2019). Using Poisson regression with robust variance, we calculated the adjusted prevalence ratios (aPR) of the association of AVC with cardiovascular risk factors.

RESULTS

The overall AVC prevalence was 44.8%, with White males having the highest prevalence at 58.2%. The prevalence was similar for Black males (40.5%), White females (38.9%), and Black females (36.8%). AVC prevalence increased significantly with age among all race-sex groups. The probability of any AVC at age 80 years was 55.4%, 40.0%, 37.3%, and 36.2% for White males, Black males, White females, and Black females, respectively. Among persons with prevalent AVC, White males had the highest median AVC score (100.9 Agatston Units [AU]), followed by Black males (68.5AU), White females (52.3AU), and Black females (46.5AU). After adjusting for cardiovascular risk factors, Black males (aPR:0.53; 95%CI:0.33-0.83), White females (aPR:0.68; 95%CI:0.61-0.77), and Black females (aPR:0.49; 95%CI:0.31-0.77) had lower AVC prevalence compared to White males. In addition, systolic blood pressure, non-HDL-cholesterol, and lipoprotein (a) were independently associated with AVC, with no significant race/sex interactions.

CONCLUSIONS

AVC, although highly prevalent, was not universally present in this cohort of older adults. White males had ∼50-60% higher prevalence than other race-sex groups. Moreover, cardiovascular risk factors measured in older age showed significant association with AVC.

Race, Ancestry, and Vitamin D Metabolism: The Multi-Ethnic Study of Atherosclerosis

CONTEXT

A comprehensive characterization of racial/ethnic variations in vitamin D metabolism markers may improve our understanding of differences in bone and mineral homeostasis and the risk of vitamin D-related diseases.

OBJECTIVE

Describe racial/ethnic differences in vitamin D metabolism markers and their associations with genetic ancestry.

DESIGN, SETTING, PARTICIPANTS

In a cross-sectional study within the Multi-Ethnic Study of Atherosclerosis (MESA), we compared a comprehensive panel of vitamin D metabolism markers across self-reported racial/ethnic groups of Black (N = 1759), White (N = 2507), Chinese (N = 788), and Hispanic (N = 1411). We evaluated associations of proportion African and European ancestry with this panel of markers in Black and Hispanic participants using ancestry informative markers. Latent class analysis evaluated associations between patterns of vitamin D measurements with race/ethnicity.

RESULTS

Compared with Black participants, White participants had significantly higher serum concentrations of 25-hydroxyvitamin D and fibroblast growth factor-23; lower concentrations of parathyroid hormone and 1,25-dihydroxyvitamin D; circulating vitamin D metabolite ratios suggesting lower CYP27B1 and higher CYP24A1 activity; higher urinary concentrations of calcium and phosphorus with higher urinary fractional excretion of phosphorus; and differences in vitamin D binding globulin haplotypes. Higher percent European ancestry was associated with higher 25-hydroxyvitamin D and lower parathyroid hormone concentrations among Black and Hispanic participants. Latent classes defined by vitamin D measurements reflected these patterns and differed significantly by race/ethnicity and ancestry.

CONCLUSIONS

Markers of vitamin D metabolism vary significantly by race/ethnicity, may serve to maintain bone and mineral homeostasis across ranges of 25-hydroxyvitamin D production, and be attributable, at least partly, to genetic ancestry.

Effects of Different Dietary Interventions on Calcitriol, Parathyroid Hormone, Calcium, and Phosphorus: Results from the DASH Trial

The "Dietary Approaches to Stop Hypertension" (DASH) diet, rich in fiber and low-fat dairy, effectively lowers blood pressure. DASH's effect on calcitriol and other markers of bone-mineral metabolism is unknown. This secondary analysis of the DASH trial aimed to determine the effect of dietary patterns on blood concentrations of calcitriol, parathyroid hormone (PTH), ionized calcium, and urinary excretion of calcium and phosphorus. Outcomes were available in 334 participants in the trial. After a 3-week run-in on the control diet, participants were randomized to control, fruits and vegetables (F&V), or DASH diets. Outcomes were assessed at the end of run-in, and during the last week of the intervention period. Mean age of participants was 45.7 ± 10.7 years, 46% female, and 57% African-American. Mean ± Standard Deviation(SD) baseline serum concentrations of calcitriol, PTH, and ionized calcium were 37.8 ± 9.2 pg/mL, 46.1 ± 18.5 pg/mL and 5.2 ± 0.23 mg/dL, respectively. Mean (±SD) urinary calcium and phosphorus excretions were 150.1 ± 77.8 and 708.0 ± 251.8 mg/24 h, respectively. Compared with control, DASH reduced calcitriol -3.32 pg/mL (p = 0.004). Otherwise, there was no significant effect on other biomarkers. DASH lowered serum calcitriol perhaps more among African-Americans. These results raise important questions about the interpretation and clinical significance of low calcitriol concentrations in the setting of recommended diets.

Smoking habits and parathyroid hormone concentrations in young adults: The CARDIA study

Conflicting results have been reported concerning a relationship between smoking and serum PTH. Our study objective was to examine whether smoking was associated with serum PTH independent of correlates of PTH among young adults, and explore potential mechanisms. This was a cross-sectional study of healthy individuals, 24-36 years old, examined during 1992 through 1993 in California, USA (a subset of Coronary Artery Risk Development in Young Adults study). Linear regression was used to obtain adjusted means of PTH according to smoking habit (current, former, never). Biomarkers for calcium metabolism and bone turnover (including serum concentrations of osteocalcin, bone-specific alkaline phosphatase, and 24-hour urinary excretion of calcium) and bone mineral density were similarly compared by smoking. 376 participants were analyzed (171 women, 181 black). Over half reported never smoking. We observed lower PTH in current smokers compared to non-smokers and found no evidence of an interaction by race and sex. PTH was lowest in current smokers, intermediate in former smokers, and highest in never smokers (geometric mean PTH: 23.6, 26.7, 27.4 pg/mL, respectively: P for trend, 0.006) after adjusting for potential confounders including calcium intake. Among the biomarkers, serum osteocalcin concentration and 24-hour urinary excretion of calcium were lowest in current smokers. We observed no smoking-related difference in bone mineral density. In this community-based sample of young adult men and women, smoking was associated with significantly lower PTH concentration. The mechanism and clinical implication of the finding, however, remains uncertain.

Urinary calcium excretion in postmenopausal African American women

Aim: The objective of this study was to develop a reference range for urine calcium excretion (both 24-hour and fasting) for African American women compared to White women. In addition, the variables that determine urine calcium excretion were identified. Material: Data were analyzed for baseline studies of healthy postmenopausal volunteers who participated in seven separate studies conducted at one site. Methods: Some studies included fasting urine Ca/Cr and others 24-hour urine calcium excretion. 24-hour urine calcium was considered with and without correction for urinary creatinine excretion. Calcium was measured initially by atomic absorption spectrophotometry and more recently by an automated method (ADVIA 2400 Chemistry System). Results: Participants were considered healthy based on history and physical and routine laboratory studies. Those screened who had a history of nephrolithiasis were excluded. A reference range for 24-hour urine calcium and fasting urine calcium/creatinine was developed. Reference intervals of 11 – 197 mg/24-hour urine calcium excretion and of 0.007 – 0.222 of fasting Ca/Cr were found for African American women compared to 21 – 221 mg/24 hours and 0.019 – 0.264 in White women, respectively. Urine creatinine excretion was higher in African Americans consistent with their higher muscle mass. Conclusion: Urine calcium excretion is lower in postmenopausal African American than White women. The reference range developed should be considered in the diagnosis of hypocalciuric states and may also be useful in the diagnosis of hypercalciuria.

Role of vitamin D in uterine fibroid biology

OBJECTIVE

To provide a detailed summary of current scientific knowledge on uterine fibroids (leiomyomas) in vitro and in in vivo animal models, as well as to postulate the potential role of vitamin D3 as an effective, inexpensive, safe, long-term treatment option for uterine fibroids.

DESIGN

PubMed search articles were used to identify the most relevant studies on uterine fibroids, as well as effects of vitamin D3 on uterine fibroid cells and fibroid tumor growth in in vivo animal models.

SETTING

University research laboratory.

PATIENT(S)

Not applicable.

INTERVENTION(S)

None.

MAIN OUTCOME MEASURE(S)

Not applicable.

RESULT(S)

Despite numerous publications available on uterine fibroids, information about the role that vitamin D3 plays in the regulation of uterine fibroids is limited. Most of the recent vitamin D3-related studies on uterine fibroids were published from our group. Recent studies have demonstrated that vitamin D deficiency plays a significant role in the development of uterine fibroids. Our recent studies have demonstrated that vitamin D3 reduces leiomyoma cell proliferation in vitro and leiomyoma tumor growth in in vivo animal models. These results postulate the potential role of vitamin D3 for an effective, safe, nonsurgical medical treatment option for uterine fibroids.

CONCLUSION(S)

This article reviews human and animal studies and uncovers new possibilities for understanding the vitamin D-based therapeutic option for an effective, safe, long-term treatment of uterine fibroids. On the basis of these results, a clinical trial with vitamin D3 or a hypocalcemic analog, paricalcitol, may be warranted for nonsurgical medical treatment of uterine fibroids.

Comparison of cellular and transcriptional responses to 1,25-dihydroxyvitamin d3 and glucocorticoids in peripheral blood mononuclear cells

Glucocorticoids (GC) and 1,25-dihydroxyvitamin D3 (1,25(OH)₂ D3) are steroid hormones with anti-inflammatory properties with enhanced effects when combined. We previously showed that transcriptional response to GCs was correlated with inter-individual and inter-ethnic cellular response. Here, we profiled cellular and transcriptional responses to 1,25(OH)₂ D3 from the same donors. We studied cellular response to combined treatment with GCs and 1,25(OH)₂ D3 in a subset of individuals least responsive to GCs. We found that combination treatment had significantly greater inhibition of proliferation than with either steroid hormone alone. Overlapping differentially expressed (DE) genes between the two hormones were enriched for adaptive and innate immune processes. Non-overlapping differentially expressed genes with 1,25(OH)₂ D3 treatment were enriched for pathways involving the electron transport chain, while with GC treatment, non-overlapping genes were enriched for RNA-related processes. These results suggest that 1,25(OH)₂ D3 enhances GC anti-inflammatory properties through a number of shared and non-shared transcriptionally-mediated pathways.

A cross-sectional association between bone mineral density and parathyroid hormone and other biomarkers in community-dwelling young adults: the CARDIA study

CONTEXT

Most association studies of bone-related biomarkers (BBMs) with bone mineral density (BMD) have been conducted in postmenopausal women.

OBJECTIVE

We tested whether the following BBMs were cross-sectionally associated with BMD among young adults: serum 1,25-dihydroxyvitamin D (1,25(OH)2D), 25-hydroxyvitamin D (25OHD), PTH, osteocalcin, bone-specific alkaline phosphatase (BAP), and urinary pyridinoline/urinary creatinine.

SETTING AND PARTICIPANTS

We studied 319 individuals (134 women, 149 black, 24-36 years) recruited during 1992 through 1993 in Oakland, California. BMD was assessed with dual-energy x-ray absorptiometry. Linear regression models estimated the association between BMD and each BBM.

RESULTS

1,25(OH)2D was inversely associated with all BMDs. 25OHD was positively, and PTH inversely, associated with lumbar spine, total hip, and whole-body BMD. BAP was inversely associated with left arm, right arm, and whole-body BMD but not with spine or hip BMD. Neither osteocalcin nor urinary pyridinoline/urinary creatinine was associated with BMD. When we placed all BBMs (including 1,25(OH)2D) in one model, the pattern and magnitude of association was similar except for PTH, which was attenuated. The association of BMD and BBMs did not differ significantly by race or sex.

CONCLUSIONS

In this cross-sectional study of healthy young men and women who had PTH levels considered normal in clinical practice, higher PTH was associated with lower BMD, particularly in weight-bearing sites (ie, spine and hip). The inverse association of 1,25(OH)2D, together with the attenuation of PTH, suggests that the observed association of PTH is mediated by 1,25(OH)2D. BAP was inversely associated with arm BMD. BBMs can be important markers of skeletal activity in young adults, but their clinical role on bone health among this population is yet to be fully determined.

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.

Vitamin D intake is inversely related to risk of developing metabolic syndrome in African American and white men and women over 20 y: the Coronary Artery Risk Development in Young Adults study

BACKGROUND

Vitamin D intake may play a key role in the prevention of cardiovascular disease.

OBJECTIVE

We evaluated associations of dietary and supplemental vitamin D intake with the 20-y incidence of metabolic syndrome.

DESIGN

Data from 4727 black and white young men and women from the Coronary Artery Risk Development in Young Adults study were used to examine relations of dietary plus supplemental vitamin D intake with the incidence of metabolic syndrome (as defined by Adult Treatment Panel, third report, guidelines) and the prevalence of its components, including abdominal obesity, elevated blood pressure, and high glucose, low HDL, and high triglyceride concentrations.

RESULTS

The intake of vitamin D from dietary and supplemental sources was inversely related to the 20-y cumulative prevalence of abdominal obesity (P = 0.05) and high glucose (P = 0.02) and low HDL (P = 0.004) concentrations after adjustment for age, sex, race, education, center, and energy intake. In comparison with the lowest intake quintile (quintile 1), HRs (95% CIs) of developing incident metabolic syndrome for quintiles 2-5 of vitamin D intake were 0.82 (0.67, 1.00), 0.84 (0.68, 1.03), 0.70 (0.56, 0.88), and 0.82 (95% CI: 0.65, 1.02), respectively (P-trend = 0.03) after adjustment for demographic and lifestyle factors.

CONCLUSIONS

In young adults, the dietary plus supplemental vitamin D intake was inversely related to the development of incident metabolic syndrome over 20 y of follow-up. These findings support the recommendations of the Dietary Guidelines for Americans to increase intakes of vitamin D-rich foods, such as milk and fish.

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.

Socioeconomic status, race, and bone turnover in the Midlife in the US Study

Among a group of 940 US adults, economic adversity and minority race status were associated with higher serum levels of markers of bone turnover. These results suggest that higher levels of social stress may increase bone turnover.

INTRODUCTION

To determine socioeconomic status (SES) and race differences in levels of bone turnover.

METHODS

Using data from the Biomarker Substudy of the Midlife in the US (MIDUS) study (491 men, 449 women), we examined cross-sectional associations of SES and race with serum levels of bone turnover markers (bone-specific alkaline phosphatase [BSAP], procollagen type I N-terminal propeptide [PINP], and N-telopeptide [Ntx]) separately in men and women. Linear multivariable regression was used to control for body weight, menopausal transition stage, and age.

RESULTS

Among men, low family poverty-to-income ratio (FPIR) was associated with higher turnover, but neither education nor race was associated with turnover. Men with FPIR <3 had 1.808 nM BCE higher Ntx (P = 0.05), 3.366 U/L higher BSAP (P = 0.02), and 7.066 higher PINP (P = 0.02). Among women, neither education nor FPIR was associated with bone turnover, but Black women had 3.688 nM BCE higher Ntx (P = 0.001), 5.267 U/L higher BSAP (P = 0.005), and 11.906 μg/L higher PINP (P = 0.008) compared with non-Black women.

CONCLUSIONS

Economic adversity was associated with higher bone turnover in men, and minority race status was associated with higher bone turnover in women, consistent with the hypothesis that higher levels of social stresses cause increased bone turnover. The magnitude of these associations was comparable to the effects of some osteoporosis medications on levels of turnover.

Primary hyperparathyroidism in the underinsured: a study of 493 patients

BACKGROUND

Disparities may exist in the care of patients with primary hyperparathyroidism (HPT). This study examines the presentation and outcomes of underinsured patients undergoing parathyroidectomy.

METHODS

We divided 493 HPT patients who underwent initial parathyroidectomy from 2000 to 2008 at a single institution into 2 groups: underinsured patients (group 1; n = 94) evaluated and treated at a county hospital, and patients with insurance (group 2; n = 399). Univariate and multivariate analysis adjusting for race and ethnicity were conducted to determine the association of being underinsured with several clinical variables.

RESULTS

More patients in group 1 compared with group 2 were of black or Hispanic background (92% vs. 44%; P < .0001). Group 1 patients had higher mean preoperative serum calcium and PTH levels: 12.1 vs. 11.8 mg/dL (P = .009) and 263 vs. 198 pg/mL (P = .03), respectively. Seven group 1 (7.4%) and 7 group 2 (1.8%) patients presented with hypercalcemic crisis (P = .003). On multivariate analysis, underinsurance was associated with higher serum calcium levels (P = .011) and hypercalcemic crisis at presentation (odds ratio, 5.59; 95% confidence interval, 1.45-21.51; P = .012). Follow-up was shorter in group 1 patients (15 vs. 24 months; P < .001) and postoperative PTH levels were higher (76 vs. 48 pg/mL; P < .001). Other perioperative data were not different between the groups.

CONCLUSION

Underinsured patients with HPT may present with higher serum calcium and PTH levels, are more likely to have hypercalcemic crisis, and less likely to return for follow-up. Underfunded health insurance coverage may account for differences seen in this study.

Vitamin D: marker or mechanism of action?

The field of vitamin D and cancer research has been moving forward quickly. However, some challenges remain regarding the interpretation and integration of data collected from epidemiological investigations and laboratory experiments. These include consideration of vitamin D biology, a better understanding of characteristics that affect concentrations of the biomarker of vitamin D status, 25(OH)D, and elucidation of variation in response to vitamin D supplementation. To further the field of vitamin D and cancer prevention, future studies will need to bridge the gap between the epidemiology and molecular biology of vitamin D activity in carcinogenesis.

Relationship of vitamin D and parathyroid hormone with obesity and body composition in African Americans

BACKGROUND

Obesity disproportionately affects African Americans (AA) (especially women), and is linked to depressed 25-hydroxyvitamin D (25-OH D) and elevated parathyroid hormone (PTH). The relationship of 25-OH D and PTH with body composition and size in AA is not well known.

OBJECTIVE

To determine the relationship of 25-OH D and PTH levels with body composition and anthropometric measures.

DESIGN

A cross-sectional study was conducted in 98 healthy, overweight, adult AA enrolled in an NIH/NIEHS-sponsored weight loss/salt-sensitivity trial.

MEASUREMENTS

Multivariable linear regression analyses were used to explore the relationship of 25-OH D and PTH with body composition, determined by dual-energy X-ray absorptiometry, and anthropometric measures. Body composition and size were contrasted across vitamin D/PTH groups using general linear models: (i) normal (25-OH D >50 nmol/l, PTH <or=65 pg/ml), (ii) low 25-OH D and normal PTH and (iii) low 25-OH D and high PTH.

RESULTS

Age, gender and season-adjusted regression analyses showed that PTH was directly correlated with total (P = 0.02), truncal (P = 0.03) and extremity (P = 0.03) fat mass, while 25-OH D was inversely related to truncal fat mass (P = 0.02). Total fat mass in groups 1-3, respectively, was 30.0, 34.0 and 37.4 kg (P = 0.008); truncal fat mass was 13.4, 15.9 and 17.6 kg (P = 0.006) and extremity fat mass was 15.8, 16.9 and 19.7 kg (P = 0.02). Lean mass did not differ across the three groups.

CONCLUSIONS

Our findings show that lower 25-OH D and raised PTH are both correlated, though in opposite directions, with fat mass, fat distribution and anthropometric measures in adult AA.

Screening for chronic kidney disease complications in US adults: racial implications of a single GFR threshold

BACKGROUND AND OBJECTIVES

An ideal and effective screening tool should perform equally across ethnic groups. The objective of this study was to determine whether the widely advocated creatinine-based estimated GFR (eGFR) threshold of 60 ml/min per 1.73 m(2) identifies the typical metabolic abnormalities related to chronic kidney disease equally well in minority and nonminority adults.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

This objective was addressed using data for 8918 minority and nonminority adult participants in the National Health and Nutrition Examination Survey 2003 through 2006, which used stratified, multistage, probability sampling methods to assemble a nationwide probability sample of the noninstitutionalized population of the United States. Metabolic abnormalities including BP, potassium, hemoglobin, bicarbonate, uric acid, calcium, phosphorus, and parathyroid hormone were defined by fifth or 95th percentile values.

RESULTS

Among participants with eGFR <60 ml/min per 1.73 m(2), black individuals were more likely than white individuals to have low hemoglobin (adjusted odds ratio [aOR] 3.76; 95% confidence interval [CI] 1.94 to 7.28), elevated uric acid (aOR 2.15; 95% CI 1.26 to 3.68), and elevated parathyroid hormone (aOR 3.93; 95% CI 2.33 to 6.66).

CONCLUSIONS

Metabolic consequences of reduced eGFR are more common in black individuals and seem to be present at levels well above 60 ml/min per 1.73 m(2); thus, black individuals should be screened for the metabolic complications of chronic kidney at higher GFR levels.

Genetic and environmental determinants of 25-hydroxyvitamin D and 1,25-dihydroxyvitamin D levels in Hispanic and African Americans

CONTEXT

Vitamin D deficiency is associated with many adverse health outcomes, yet little is known about the genetic epidemiology of vitamin D or its metabolites.

OBJECTIVE

Our objective was to examine the relationship among three vitamin D-related genes and levels of 25-hydroxyvitamin D [25(OH)D] and 1,25-dihydroxyvitamin D [1,25(OH)2D] in Hispanics (HAs) and African Americans (AAs).

DESIGN AND SETTING

The cross-sectional Insulin Resistance Atherosclerosis Family Study recruited and examined subjects in: Los Angeles, California (AAs; 513 individuals from 42 families); San Luis Valley (SLV), Colorado (HAs; 513 individuals from 30 families); and San Antonio (SA), Texas (HAs; 504 individuals from 58 families).

MAIN OUTCOME MEASURES

Plasma levels of 25(OH)D and 1,25(OH)2D were measured.

RESULTS

Levels of 25(OH)D were highest in SLV-HAs [18.3 +/- 7.7 ng/ml (45.7 +/- 19.2 nmol/liter)], lower in SA-HAs [14.6 +/- 6.4 ng/ml (36.4 +/- 16.0 nmol/liter)], and lowest in AAs [11.0 +/- 5.4 ng/ml (27.5 +/- 13.5 nmol/liter)]. Levels of 1,25(OH)2D were similar in AAs [43.5 +/- 13.9 pg/ml (113.1 +/- 36.1 pmol/liter)] and SLV-HAs [43.2 +/- 13.3 pg/ml (112.3 +/- 34.6 pmol/liter)], but higher in SA-HAs [48.6 +/- 17.0 pg/ml (126.4 +/- 44.2 pmol/liter)]. After adjusting for gender and age within the site, two single nucleotide polymorphisms (SNPs) in the vitamin D binding protein gene (DBP), rs4588 and rs7041, were associated with 25(OH)D, and one SNP in the DBP, rs4588, was associated with 1,25(OH)2D at all three study centers.

CONCLUSIONS

SNPs in the DBP are associated with levels of 25(OH)D and 1,25(OH)2D in HA and AA participants in the Insulin Resistance Atherosclerosis Family Study.

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.

Macro- and micronutrients in African-Americans with heart failure

An emerging body of evidence suggests secondary hyperparathyroidism (SHPT) may be an important covariant of congestive heart failure (CHF), especially in African-Americans (AA) where hypovitaminosis D is prevalent given that melanin, a natural sunscreen, mandates prolonged exposure of skin to sunlight and where a housebound lifestyle imposed by symptomatic CHF limits outdoor activities and hence sunlight exposure. In addition to the role of hypovitaminosis D in contributing to SHPT is the increased urinary and fecal losses of macronutrients Ca(2+) and Mg(2+) associated with the aldosteronism of CHF and their heightened urinary losses with furosemide treatment of CHF. Thus, a precarious Ca(2+) balance seen with reduced serum 25(OH)D is further compromised when AA develop CHF with circulating RAAS activation and are then treated with a loop diuretic. SHPT accounts for a paradoxical Ca(2+) overloading of diverse tissues and the induction of oxidative stress at these sites which spills over to the systemic circulation. In addition to SHPT, hypozincemia and hyposelenemia have been found in AA with compensated and decompensated heart failure and where an insufficiency of these micronutrients may have its origins in inadequate dietary intake, altered rates of absorption or excretion and/or tissue redistribution, and treatment with an ACE inhibitor or AT(1) receptor antagonist. Zn and Se deficiencies, which compromise the activity of several endogenous antioxidant defenses, could prove contributory to the severity of heart failure and its progressive nature. These findings call into question the need for nutriceutical treatment of heart failure and which is complementary to today's pharmaceuticals, especially in AA.

Vitamin D and African Americans

Vitamin D insufficiency is more prevalent among African Americans (blacks) than other Americans and, in North America, most young, healthy blacks do not achieve optimal 25-hydroxyvitamin D [25(OH)D] concentrations at any time of year. This is primarily due to the fact that pigmentation reduces vitamin D production in the skin. Also, from about puberty and onward, median vitamin D intakes of American blacks are below recommended intakes in every age group, with or without the inclusion of vitamin D from supplements. Despite their low 25(OH)D levels, blacks have lower rates of osteoporotic fractures. This may result in part from bone-protective adaptations that include an intestinal resistance to the actions of 1,25(OH)2D and a skeletal resistance to the actions of parathyroid hormone (PTH). However, these mechanisms may not fully mitigate the harmful skeletal effects of low 25(OH)D and elevated PTH in blacks, at least among older individuals. Furthermore, it is becoming increasingly apparent that vitamin D protects against other chronic conditions, including cardiovascular disease, diabetes, and some cancers, all of which are as prevalent or more prevalent among blacks than whites. Clinicians and educators should be encouraged to promote improved vitamin D status among blacks (and others) because of the low risk and low cost of vitamin D supplementation and its potentially broad health benefits.

Low vitamin D status in children with sickle cell disease

OBJECTIVES

To examine vitamin D status in children with sickle cell disease (SCD)-SS and its relation to season and dietary intake.

STUDY DESIGN

Growth, dietary intake, 25-hydroxyvitamin D (25-OHD), and parathyroid hormone levels were measured. Children with low and normal vitamin D status were compared. Low vitamin D status was defined as a serum concentration of 25-OHD <27.5 nmol/L. Serum 25-OHD and parathyroid hormone levels were compared among children with SCD-SS and healthy children.

RESULTS

Children with SCD-SS (n=65), 5 to 18 years of age, were evaluated. Mean (+/-SD) serum 25-OHD concentration was 25.5 +/- 12.8 nmol/L; 65% of subjects had low vitamin D status. Low vitamin D prevalence was highest during spring (100%). Children with SCD-SS were at higher risk for low vitamin D status than healthy children. Vitamin D intake was lower in subjects with SCD-SS and low vitamin D than those with normal serum vitamin D status (P <.05).

CONCLUSIONS

Low serum vitamin D status was highly prevalent in black children with SCD-SS. Vitamin D status was associated with season and dietary intake.

Is There a Racial Difference in Presentation of Primary Hyperparathyroidism?

Nearly 50,000 new cases of primary hyperparathyroidism (PHPT) are diagnosed annually in the United States. Most information about the disease focuses on the white population. We evaluated African American (AA) and white patients at our tertiary care university medical center to determine whether there was a racial difference in presentation of PHPT. A retrospective chart review of patients treated surgically for PHPT between 1997 and 2002 was performed. Demographic data, laboratory values, objective symptoms, surgical procedure, and histologic findings were recorded. The AA participants were matched to whites by age and gender. The effect of race was adjusted for the matching variables by including them in regression models. ANOVA χ2 tests were performed on the race effects. Thirty-six (14.4%) of the 286 patients treated for PHPT at Wake Forest University Baptist Medical Center during this 5-year period were AA. There was no difference in serum calcium or presence of objective symptoms, but PTH levels were significantly higher for blacks (207.5 vs 143.5 pg/mL; P = 0.02). In our study, AA patients had significantly higher parathyroid hormone levels at time of surgical intervention but did not present with a difference in symptoms or more advanced disease. Further research is recommended to characterize ethnic differences in patients with PHPT.

Racial differences in the effect of early milk consumption on peak and postmenopausal bone mineral density

Studies of the effect of milk consumption on bone density have focused on white women. The applicability to other races is unclear. This study of 4316 women found a racial difference in the effect of early milk consumption on bone. Further study is required to evaluate the etiology of this difference.

INTRODUCTION

Early milk consumption has been found to influence bone mineral density positively throughout life. Previous studies leading to this finding focused on white women; there are no data to support the view that black women also gain an equivalent benefit from early milk consumption.

MATERIALS AND METHODS

Using data from the Third National Health and Nutrition Examination Survey (NHANES III), we analyzed the relationship between reported childhood and teenage milk consumption and current hip bone mineral density at four sites (femoral neck, trochanter, intertrochanter, and total hip) among postmenopausal and 20- to 39-year-old non-Hispanic white (NHW) and black (NHB) women. Potential confounding variables were accounted for in the analysis.

RESULTS

Controlling for age and body mass index, teenage milk consumption was significantly associated with higher bone mineral density at all four sites among both postmenopausal and 20- to 39-year-old white women, but was not associated with bone mineral density at any site among black women. A similar pattern was observed for childhood milk intake. The interaction between race and teenage milk consumption significantly explained postmenopausal bone mineral density at all sites, whereas the interaction between race and teenage milk consumption was significant at two of the four sites among the 20- to 39-year-old women.

CONCLUSION

The results show racial differences in the effect of early milk consumption on peak and postmenopausal bone mineral density.

Hypovitaminosis D prevalence and determinants among African American and white women of reproductive age: third National Health and Nutrition Examination Survey, 1988-1994

BACKGROUND

Recent reports of rickets among African American children drew attention to the vitamin D status of these infants and their mothers. African American women are at higher risk of vitamin D deficiency than are white women, but few studies have examined determinants of hypovitaminosis D in this population.

OBJECTIVE

We examined the prevalence and determinants of hypovitaminosis D among African American and white women of reproductive age.

DESIGN

We examined 1546 African American women and 1426 white women aged 15-49 y who were not pregnant and who participated in the third National Health and Nutrition Examination Survey (1988-1994). Hypovitaminosis D was defined as a serum 25-hydroxyvitamin D concentration < or =37.5 nmol/L. Multiple logistic regression was used to examine the independent association of dietary, demographic, and behavioral determinants of hypovitaminosis D.

RESULTS

The prevalence of hypovitaminosis D was 42.4 +/- 3.1% ( +/- SE) among African Americans and 4.2 +/- 0.7% among whites. Among African Americans, hypovitaminosis D was independently associated with consumption of milk or breakfast cereal <3 times/wk, no use of vitamin D supplements, season, urban residence, low body mass index, and no use of oral contraceptives. Even among 243 African Americans who consumed the adequate intake of vitamin D from supplements (200 IU/d), 28.2 +/- 2.7% had hypovitaminosis D.

CONCLUSIONS

The high prevalence of hypovitaminosis D among African American women warrants further examination of vitamin D recommendations for these women. The determinants of hypovitaminosis D among women should be considered when these women are advised on dietary intake and supplement use.