DEFINITION
A short yet comprehensive description
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ANALYTICAL METHOD
ANALYTICAL TRICKS AND TIPS
THE BIOLOGICAL CONTEXT
DIAGNOSTIC USE
Issues
Specificity, sensitivity etc.
Diagnostic Algorithms
PROs and CONTROs
Open Questions
J Bone Miner Res. 2011 Mar 17. doi: 10.1002/jbmr.387. [Epub ahead of print]
Vitamin D binding protein modifies the vitamin D-bone mineral density relationship. 2011
Powe CE, Ricciardi C, Berg AH, Erdenesanaa D, Collerone G, Ankers E, Wenger J, Karumanchi SA, Thadhani R, Bhan I.
Division of Nephrology, Department of Medicine, Massachusetts General Hospital and Harvard Medical School, Boston, MA.
Abstract
BACKGROUND: Studies examining the relationship between total circulating 25-hydroxyvitamin D (25(OH)D) levels and bone mineral density (BMD) have yielded mixed results. Vitamin D binding protein (DBP), the major carrier protein for 25(OH)D, may alter the biologic activity of circulating vitamin D. We hypothesized that free and bioavailable 25(OH)D, calculated from total 25(OH)D, DBP and serum albumin levels, would be more strongly associated with BMD than levels of total 25(OH)D.
METHODS: We measured total 25(OH)D, DBP, and serum albumin levels in 49 healthy young adults enrolled in the Metabolic Abnormalities in College-Aged Students (MACS) study. Lumbar spine BMD was measured in all subjects using dual X-ray absorptiometry. Clinical, diet, and laboratory information was also gathered at this time. We determined free and bioavailable (free + albumin bound) 25(OH)D using previously validated formulae and examined their associations with BMD.
RESULTS: BMD was not associated with total 25(OH)D levels (r=0.172 p=0.236). In contrast, free and bioavailable 25(OH)D levels were positively correlated with BMD (r=0.413 p=0.003 for free, r=0.441 p=0.002 for bioavailable). Bioavailable 25(OH)D levels remained independently associated with BMD in multivariate regression models adjusting for age, sex, body mass index, and race (p=0.03).
CONCLUSION: Free and bioavailable 25(OH)D are more strongly correlated with BMD than total 25(OH)D. These findings have important implications for vitamin D supplementation in vitamin D deficient states. Future studies should continue to explore the relationship between free and bioavailable 25(OH)D and health outcomes. © 2011 American Society for Bone and Mineral Research.
Working Hypothesis
Bassi livelli di vitamina D incidono negativamente anche sul metabolismo del glucosio
Coloro che presentano bassi livelli di vitamina D hanno maggiore probabilità di essere diabetici, indipendentemente dal peso corporeo. È quanto emerso da uno studio pubblicato online prima della stampa su Journal of Clinical Endocrinology & Metabolism.
I risultati aiutano a chiarire la connessione fra vitamina D, obesità e diabete. Secondo lo Scientific Statement on the non-skeletal effects of vitamin D (Endocrine Rev 2012; 33 (3)), diverse evidenze hanno mostrato come i soggetti con bassi livelli di vitamina D siano più probabilmente obesi, con diabete di tipo 2, prediabete o sindrome metabolica rispetto a coloro che ne presentano livelli normali.
Il nuovo studio ha confrontato i biomarker della vitamina D in 158 soggetti, classificati in base al loro BMI e alla presenza di diabete o prediabete o all’assenza di disordini glicemici. I ricercatori hanno misurato i livelli di vitamina D nel sangue e l’espressione del gene per il recettore della vitamina D nel tessuto adiposo. Le analisi hanno mostrato che gli obesi che non hanno disordini del metabolismo del glucosio presentano più elevati livelli di vitamina D rispetto ai diabetici e che i soggetti magri con diabete o altri disordini del metabolismo glicemico hanno più probabilità di avere bassi livelli di vitamina D.
La vitamina D risulta direttamente correlata coi livelli glicemici, ma non con il BMI, suggerendo come i livelli di questa vitamina siano associati più fortemente con il metabolismo del glucosio che con l’obesità. Lo studio suggerisce inoltre che la deficienza di vitamina D e l’obesità interagiscono sinergicamente ad aumentare il rischio di diabete e altri disturbi del metabolismo.
Serum 25-Hydroxyvitamin D and Adipose Tissue Vitamin D Receptor Gene Expression: Relationship with Obesity and Type 2 Diabetes. 2015
- Context: The relationship between 25-hydroxyvitamin D [25(OH)D] and obesity and type 2 diabetes is not completely understood. Vitamin D receptor (VDR) expression in adipose tissue (AT) is related to obesity and might be regulated by 1,25-dihydroxyvitamin D3 [1,25(OH)2D3]. Objective: To analyze serum 25(OH)D and VDR gene expression in AT according to body mass index (BMI) and glycemic status and the effect of 1,25(OH)2D3 on AT according to BMI. Design and Patients: Two cohorts were studied: 1) 118 subjects classified according to their BMI (lean, overweight, obese, or morbidly obese [MO]) and their glycemic status (normoglycemic [NG] and prediabetic and diabetic [P&D]); and 2) 30 obese subjects (BMI > 30 kg/m2) classified as NG and P&D. VDR gene expression was analyzed during preadipocyte differentiation and in vitro stimulation with 1,25(OH)2D3 of AT explants from donors with different BMI values. Setting: University Hospital. Main Outcome Measures: Serum 25(OH)D, PTH, and AT VDR gene expression. Results: 25(OH)D levels were lower in P&D than NG subjects, significantly so in the lean and MO groups (P < .05). 25(OH)D levels correlated negatively with homeostasis model of assessment for insulin resistance (r = -0.200; P = .032) and glucose (r = -0.295; P = .001), but not with BMI. VDR gene expression was higher in MO than in the other BMI groups (P < .05). 1,25(OH)2D3 increased VDR gene expression in AT from obese patients (P < .05) but not from lean subjects. Conclusions: 25(OH)D levels are diminished in P&D compared to NG subjects, independently of BMI, and are closely related to glucose metabolism variables, suggesting that vitamin D deficiency is associated more with carbohydrate metabolism than with obesity. Moreover, AT has a different response to 1,25(OH)2D3 depending on the degree of obesity.
