Vitamin d binding protein and bone health

Vitamin D in patients with chronic kidney disease: a position statement of the Working Group "Trace Elements and Mineral Metabolism" of the Italian Society of Nephrology

In the late 1970s, calcitriol was introduced into clinical practice for the management of secondary renal hyperparathyroidism in chronic kidney disease (CKD). Since then, the use of calcifediol or other native forms of vitamin D was largely ignored until the publication of the 2009 Kidney Disease Improving Global Outcomes (KDIGO) recommendations. The guidelines suggested that measurement of circulating levels of 25(OH)D (calcifediol) and its supplementation were to be performed on the same basis as for the general population. This indication was based on the fact that the precursors of active vitamin D had provided to CKD patients considerable benefits in survival, mainly due to their pleiotropic effects on the cardiovascular system. However, despite the long-term use of various classes of vitamin D in CKD, a clear definition is still lacking concerning the most appropriate time for initiation of therapy, the best compound to prescribe (active metabolites or analogs), the proper dosage, and the most suitable duration of therapy. The aim of this position statement is to provide and critically appraise the current plentiful evidence on vitamin D in different clinical settings related to CKD, particularly focusing on outcomes, monitoring and treatment-associated risks. However, it should be taken in account that position statements are meant to provide guidance; therefore, they are not to be considered prescriptive for all patients and, importantly, they cannot replace the judgment of clinicians.

Hypovitaminosis D: a novel risk factor for coronary heart disease in type 2 diabetes?

Vitamin D (25(OH)D) levels have been associated with cardiovascular disease. Thus, the aim of our study was to investigate the association of 25(OH)D levels with coronary heart disease (CHD) in 698 consecutive type 2 diabetic outpatients. 698 consecutive type 2 diabetic outpatients (25.2 % men, age 66 ± 9 years) and 100 (90 % men, age 65 ± 13 years) age-matched non-diabetic volunteers were enrolled. 25(OH)D assay and the main cardiovascular risk factors were explored. 25(OH)D concentration was 22 ± 10 ng/ml in control subjects and 18.23 ± 10 ng/ml in diabetic patients (p < 0.01). The prevalence of hypovitaminosis D was higher in diabetic patients than in control subjects (90 vs. 83 %, p < 0.01). Diabetic subjects with hypovitaminosis D had higher prevalence of high values of A1C (p < 0.01), BMI (p < 0.01), LDL cholesterol (p < 0.01), triglycerides (p < 0.01), and glycemia (p < 0.01) than their vitamin D-sufficient counterparts. 25(OH)D and HDL cholesterol were lower (p < 0.01), while BMI (p < 0.01), age (p < 0.01), systolic (p < 0.01) and diastolic blood pressure (p < 0.01), diabetes duration (p < 0.01), A1C (p < 0.01), glycemia (p < 0.01), fibrinogen (p < 0.01), triglycerides (p < 0.01), and total (p < 0.01) and LDL cholesterol (p < 0.01) were higher in diabetic subjects with CHD than diabetic subjects without CHD. At the logistic regression analysis, the association of vitamin D with CHD was lost, while sex (p = 0.026), diabetes duration (p = 0.023), and age (p = 0.024) were the most powerful predictors of CHD. The current study demonstrates that 25(OH)D does not have a direct effect on CHD but may have an indirect effect mediated by cardiovascular risk factors such as diabetes duration, age, and sex.

Polymorphisms affecting vitamin D-binding protein modify the relationship between serum vitamin D (25[OH]D3) and food allergy

BACKGROUND

There is evolving evidence that vitamin D insufficiency may contribute to food allergy, but findings vary between populations. Lower vitamin D-binding protein (DBP) levels increase the biological availability of serum vitamin D. Genetic polymorphisms explain almost 80% of the variation in binding protein levels.

OBJECTIVE

We sought to investigate whether polymorphisms that lower the DBP could compensate for adverse effects of low serum vitamin D on food allergy risk.

METHODS

From a population-based cohort study (n = 5276) we investigated the association between serum 25-hydroxyvitamin D3 (25[OH]D3) levels and food allergy at age 1 year (338 challenge-proven food-allergic and 269 control participants) and age 2 years (55 participants with persistent and 50 participants with resolved food allergy). 25(OH)D3 levels were measured using liquid chromatography-tandem mass spectrometry and adjusted for season of blood draw. Analyses were stratified by genotype at rs7041 as a proxy marker of DBP levels (low, the GT/TT genotype; high, the GG genotype).

RESULTS

Low serum 25(OH)D3 level (≤50 nM/L) at age 1 years was associated with food allergy, particularly among infants with the GG genotype (odds ratio [OR], 6.0; 95% CI, 0.9-38.9) but not in those with GT/TT genotypes (OR, 0.7; 95% CI, 0.2-2.0; P interaction = .014). Maternal antenatal vitamin D supplementation was associated with less food allergy, particularly in infants with the GT/TT genotype (OR, 0.10; 95% CI, 0.03-0.41). Persistent vitamin D insufficiency increased the likelihood of persistent food allergy (OR, 12.6; 95% CI, 1.5-106.6), particularly in those with the GG genotype.

CONCLUSIONS

Polymorphisms associated with lower DBP level attenuated the association between low serum 25(OH)D3 level and food allergy, consistent with greater vitamin D bioavailability in those with a lower DBP level. This increases the biological plausibility of a role for vitamin D in the development of food allergy.

First 25-hydroxyvitamin D assay for general chemistry analyzers

25-Hydroxyvitamin D [25(OH)D], the predominant circulating form of vitamin D, is an accurate indicator of the general vitamin D status of an individual. Because vitamin D deficiencies have been linked to several pathologies (including osteoporosis and rickets), accurate monitoring of 25(OH)D levels is becoming increasingly important in clinical settings. Current 25(OH)D assays are either chromatographic or immunoassay-based assays. These assays include HPLC, liquid chromatography-tandem mass spectrometry (LC-MS/MS), enzyme-immunosorbent, immunochemiluminescence, immunofluorescence and radioimmunoassay. All these assays use heterogeneous formats that require phase separation and special instrumentations. In this article, we present an overview of these assays and introduce the first homogeneous assay of 25(OH)D for use on general chemistry analyzers. A special emphasis is put on the unique challenges posed by the 25(OH)D analyte. These challenges include a low detection limit, the dissociation of the analyte from its serum transporter and the inactivation of various binding proteins without phase separation steps.