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The association of 25 hydroxyvitamin D and parathyroid hormone with metabolic syndrome in two ethnic groups in South Africa.

ABSTRACT: Though inconsistent, a number of studies have shown an association between vitamin D (25(OH)D) status, parathyroid hormone (PTH) and the metabolic syndrome (Met S). These have largely been carried out in Caucasians or black subjects living in high income countries. There no data on the relationship of 25(OH)D and PTH status with Met S in populations resident in Africa. The aims of this study were to evaluate if there was an association of 25(OH)D or PTH with Met S in non-Caucasian populations in South Africa, and whether these molecules explained ethnic differences in the prevalence of Met S and its individual components.We measured anthropometry, serum 25(OH)D and PTH levels and the components of Met S, plus related metabolic variables, in 374 African and 350 Asian Indian healthy adults from the greater Johannesburg metropolitan area.Met S was diagnosed in 29% of the African and 46% of the Asian Indian subjects (p<0.0001). Subjects with Met S had higher PTH than those without Met S, (p<0.0001), whilst 25(OH)D levels were not significantly different (p = 0.50). In multivariate analysis, 25(OH)D was not associated with any components of the Met S however PTH was shown to be positively associated with systolic (p = 0.018) and diastolic (p = 0.005) blood pressures and waist circumference (p<0.0001) and negatively associated with HOMA (p = 0.0008) levels. Logistic regression analysis showed that Asian Indian ethnicity (OR 2.24; 95% CIs 1.57, 3.18; p<0.0001) and raised PTH (OR 2.48; 95% CIs 1.01, 6.08; p = 0.04; adjusted for 25(OH)D) produced an increased risk of Met S but 25(OH)D did not (OR 1.25; 95% CI 0.67, 2.24; p = 0.48).Plasma PTH but not 25(OH)D is an independent predictor of the Met S in African and Asian Indians in South Africa.

SUBMITTER: George JA

PROVIDER: S-EPMC3626636 | biostudies-other | 2013

REPOSITORIES: biostudies-other

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Project description:Increases in 25-hydroxyvitamin D concentrations are shown to improve strength in adults; however, data in pediatric populations are scant and equivocal. In this ancillary study of a larger-scale, multi-sited, double-blind, randomized, placebo-controlled vitamin D intervention in US children and adolescents, we examined the associations between changes in vitamin D metabolites and changes in muscle mass, strength, and composition after 12 weeks of vitamin D3 supplementation. Healthy male and female, black and white children and adolescents between the ages of 9 and 13 years from two US states (Georgia 34°N and Indiana 40°N) were enrolled in the study and randomly assigned to receive an oral vitamin D3 dose of 0, 400, 1000, 2000, or 4000 IU/d for 12 weeks between the winter months of 2009 to 2011 (N = 324). Analyses of covariance, partial correlations, and regression analyses of baseline and 12-week changes (post-baseline) in vitamin D metabolites (serum 25(OH)D, 1,25(OH)2 D, intact parathyroid hormone [iPTH]), and outcomes of muscle mass, strength, and composition (total body fat-free soft tissue [FFST], handgrip strength, forearm and calf muscle cross-sectional area [MCSA], muscle density, and intermuscular adipose tissue [IMAT]) were assessed. Serum 25(OH)D and 1,25(OH)2 D, but not iPTH, increased over time, as did fat mass, FFST, forearm and calf MCSA, forearm IMAT, and handgrip strength (p < 0.05). Vitamin D metabolites were not associated with muscle strength at baseline nor after the 12-week intervention. Changes in serum 25(OH)D correlated with decreases in forearm IMAT, whereas changes in serum iPTH predicted increases in forearm and calf MCSA and IMAT (p < 0.05). Overall, increases in 25(OH)D did not influence muscle mass or strength in vitamin D-sufficient children and adolescents; however, the role of iPTH on muscle composition in this population is unknown and warrants further investigation. © 2018 American Society for Bone and Mineral Research.

Project description:Studies have shown altered vitamin D metabolism in obesity. We assessed differences between obese and normal-weight subjects in total, free, and bioavailable 25-hydroxyvitamin D (25(OH)D, 25(OH)DFree, and 25(OH)DBio, respectively), vitamin D binding protein (DBP), parathyroid hormone (PTH) and bone traits.595 37-47-year-old healthy Finnish men and women stratified by BMI were examined in this cross-sectional study. Background characteristic and intakes of vitamin D and calcium were collected. The concentrations of 25(OH)D, PTH, DBP, albumin and bone turnover markers were determined from blood. 25(OH)DFree and 25(OH)DBio were calculated. pQCT was performed at radius and tibia.Mean±SE (ANCOVA) 25(OH)DFree (10.8±0.6 vs 12.9±0.4 nmol/L; P = 0.008) and 25(OH)DBio (4.1±0.3 vs 5.1±0.1 nmol/L; P = 0.003) were lower in obese than in normal-weight women. In men, 25(OH)D (48.0±2.4 vs 56.4±2.0 nmol/L, P = 0.003), 25(OH)DFree (10.3±0.7 vs 12.5±0.6 pmol/L; P = 0.044) and 25(OH)DBio (4.2±0.3 vs 5.1±0.2 nmol/L; P = 0.032) were lower in obese. Similarly in all subjects, 25(OH)D, 25(OH)DFree and 25(OH)DBio were lower in obese (P<0.001). DBP (399±12 vs 356±7mg/L, P = 0.008) and PTH (62.2±3.0 vs 53.3±1.9 ng/L; P = 0.045) were higher in obese than in normal-weight women. In all subjects, PTH and DBP were higher in obese (P = 0.047and P = 0.004, respectively). In obese women, 25(OH)D was negatively associated with distal radius trabecular density (R2 = 0.089, P = 0.009) and tibial shaft cortical strength index (CSI) (R2 = 0.146, P = 0.004). 25(OH)DFree was negatively associated with distal radius CSI (R2 = 0.070, P = 0.049), radial shaft cortical density (CorD) (R2 = 0.050, P = 0.045), and tibial shaft CSI (R2 = 0.113, P = 0.012). 25(OH)DBio was negatively associated with distal radius CSI (R2 = 0.072, P = 0.045), radial shaft CorD (R2 = 0.059, P = 0.032), and tibial shaft CSI (R2 = 0.093, P = 0.024).The associations between BMI and 25(OH)D, 25(OH)DFree, and 25(OH)DBio, DBP, and PTH suggest that obese subjects may differ from normal-weight subjects in vitamin D metabolism. BMI associated positively with trabecular bone traits and CSI in our study, and slightly negatively with cortical bone traits. Surprisingly, there was a negative association of free and bioavailable 25(OH)D and some of the bone traits in obese women.

Project description:BackgroundConcentrations of 25-hydroxyvitamin D [25(OH)D] tend to be lower in African Americans than in non-Hispanic whites, but whether adding information on parathyroid hormone (PTH) can help explain the higher cardiometabolic risk among African Americans is unknown.ObjectivesThis study examined race (black/white)-specific independent and joint associations of 25(OH)D and PTH with cardiometabolic biomarkers including high-sensitivity C-reactive protein (hs-CRP), estimated glomerular filtration rate (eGFR), and homeostasis model assessment of insulin resistance (HOMA-IR) and β-cell function (HOMA-B).MethodsAmong 1500 white and 1300 black postmenopausal women without cardiovascular disease from the Women's Health Initiative Observational Study, a weighted linear regression analysis and a novel penalized spline-based semiparametric model with contour plots, accounting for possible nonlinear relations and interactions simultaneously, were used to investigate the race-specific independent and joint associations of 25(OH)D and PTH with each biomarker.ResultsBlack women had lower concentrations of 25(OH)D and higher PTH, HOMA-IR, HOMA-B, hs-CRP, and eGFR than white women (all P values < 0.0001). Lower 25(OH)D and higher PTH were each independently and jointly associated with higher HOMA-IR in both white and black women, whereas a similar joint relation with HOMA-B was observed in white women only. In contrast, PTH was nonlinearly associated with HOMA-B in black women and positively associated with hs-CRP in white women, independently of 25(OH)D. Whereas there was an inverse linear relation between PTH and eGFR in white women after accounting for 25(OH)D, PTH and 25(OH)D were jointly and nonlinearly associated with eGFR in black women.ConclusionsWe found that the joint association of 25(OH)D and PTH with β-cell function, systemic inflammation, and kidney function apparently differed between white and black women. Further studies are needed to determine whether differences in the vitamin D-PTH endocrine system contribute to racial disparities in cardiovascular health.

Project description:UnlabelledA comparison of the association of different forms of 25-hydroxyvitamin D [25(OH)D] with parathyroid hormone (PTH) and with areal and volumetric bone mineral density (BMD) demonstrated that bioavailable and free 25(OH)D do not provide a better index of vitamin D status in terms of bone health compared to total 25(OH)D.IntroductionThis study aims to compare measures of vitamin D-binding protein (DBP) using a monoclonal versus polyclonal ELISA and assess correlations of total versus estimated free and bioavailable 25(OH)D with BMD and PTH concentrations.MethodsDXA and peripheral quantitative CT (pQCT) scans were obtained in 304 adults (158 black, 146 white), ages 21-80 years. Free and bioavailable 25(OH)D were calculated from total 25(OH)D, DBP, and albumin concentrations. Multivariable linear regression with standardized beta coefficients was used to evaluate associations of bone measures and PTH with total, free, and bioavailable 25(OH)D.ResultsMeasures of DBP obtained using a monoclonal versus polyclonal ELISA were not correlated (r s = 0.02, p = 0.76). Free and bioavailable 25(OH)D based on the polyclonal assay were lower in black versus white participants (p < 0.0001); this race difference was not evident using the monoclonal assay. Adjusted for age, sex, calcium intake, and race, all forms of 25(OH)D were negatively associated with PTH, but the absolute coefficient was greatest for total 25(OH)D (-0.34, p < 0.001) versus free/bioavailable 25(OH)D (-0.18/-0.24 depending on DBP assay, p ≤ 0.003). In analyses stratified on race, none of the measures of 25(OH)D were associated with BMD across DXA and pQCT sites.ConclusionsThe monoclonal versus polyclonal ELISA yielded highly discrepant measures of DBP, particularly among black individuals, likely related to established race differences in DBP polymorphisms. Contrary to prior studies, our findings indicate that using DBP to estimate bioavailable and free 25(OH)D does not provide a better index of vitamin D status in terms of bone health.

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The association of 25 hydroxyvitamin D and parathyroid hormone with metabolic syndrome in two ethnic groups in South Africa.

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