A novel caged Cookson-type reagent toward a practical vitamin D derivatization method for mass spectrometric analyses.

RATIONALE: 25-Hydroxylated vitamin D is the best marker for vitamin D (VD). Due to its low ionization efficiency, a Cookson-type reagent, 1,2,4-triazoline-3,5-dione (TAD), is used to improve the detection/quantification of VD metabolites by liquid chromatography/tandem mass spectrometry (LC/MS/MS). However, the high reactivity of TAD makes its solution stability low and inconvenient for practical use. We here describe the development of a novel caged Cookson-type reagent, and we assess its performances in the quantitative and differential detection of four VD metabolites in serum using LC/MS/MS. METHODS: Caged 4-(4'-dimethylaminophenyl)-1,2,4-triazoline-3,5-dione (DAPTAD) analogues were prepared from 4-(4'-dimethylaminophenyl)-1,2,4-triazolidine-3,5-dione. Their stability and reactivity were examined. The optimized caged DAPTAD (14-(4-(dimethylamino)phenyl)-9-phenyl-9,10-dihydro-9,10-[1,2]epitriazoloanthracene-13,15-dione, DAP-PA) was used for LC/MS/MS analyses of VD metabolites. RESULTS: The solution stability of DAP-PA in ethyl acetate dramatically improved compared with that of the non-caged one. We measured the thermal retro-Diels-Alder reaction enabling the release of DAPTAD and found that the derivatization reaction was temperature-dependent. We also determined the detection limit and the lower limit of quantifications for four VD metabolites with DAPTAD derivatization. CONCLUSIONS: DAP-PA was stable enough for mid- to long-term storage in solution. This advantage shall contribute to the detection and quantification of VD in clinical laboratories, and as such to the broader use of clinical mass spectrometry.

Half the Genetic Variance in Vitamin D Concentration is Shared with Skin Colour and Sun Exposure Genes.

This study assessed the heritability of 25 hydroxyvitamin D3 (25(OH)D3) in a large twin cohort and the shared effect of sun exposure and skin colour on 25(OH)D3 variance. Study participants included 1604 twin pairs and their siblings (n = 4020). Twin correlations for 25(OH)D3 concentration were rMZ=0.79 (584 pairs) and rDZ = 0.52 (1020 pairs) consistent with an average h2 = 0.50 throughout the year. Significant phenotypic and genetic seasonal fluctuation was observed in 25(OH)D3 concentrations with heritability decreasing during the winter (h2 = 0.37) compared to summer (h2 = 0.62). Skin colour (measured both ordinally and quantitatively) and self-reported sun exposure were found to significantly affect 25(OH)D3 concentration. Twins with olive/dark skin had significantly lower 25(OH)D3 concentrations than those with fair/pale skin and multivariate genetic analysis showed that approximately half of the total additive genetic variation in 25(OH)D3 results from genes whose primary influence is on skin colour and sun exposure. Additionally, 37% of the total variance was attributed to shared environmental effects on vitamin D, skin colour and sun exposure measures. These results support a moderate estimate of vitamin D heritability and suggest significant influence of season, skin colour and sun exposure on the genetic variance.

Metabolic and bone profile in postmenopausal women with and without type 2 diabetes: a cross-sectional study.

INTRODUCTION: Current studies support the implication of metabolic changes associated with type 2 diabetes in altering bone metabolism, structure and resistance. OBJECTIVE: We conducted a cross-sectional study on postmenopausal women aimed to analyze the differences in metabolic and bone profile in patients with and without type 2 diabetes Methods. We analyzed the metabolic and bone profile in postmenopausal women with and without type 2 diabetes (T2DM). Clinical, metabolic, hormonal parameters, along with lumbar, hip and femoral bone mineral density (BMD) and trabecular bone score (TBS) were evaluated. RESULTS: 56 women with T2DM(63.57±8.97 years) and 83 non-T2DM (60.21±8.77 years) were included. T2DM patients presented a higher value of body mass index (BMI) and BMD vs. control group (p = 0.001; p = 0.03-lumbar level, p = 0.07-femoral neck and p = 0.001-total hip). Also, BMI correlated positively with lumbar-BMD and glycated hemoglobin (HbA1c) (r = 0.348, p = 0.01; r = 0.269, p = 0.04), correlation maintained even after age and estimated glomerular filtration rate (eGFR) adjustment (r = 0.383, p = 0.005; r = 0.237, p = 0.08). Diabetic patients recorded lower levels of 25(OH)D(p = 0.05), bone markers (p ≤ 0.05) and TBS(p = 0.07). For the entire patient group we found a negative correlation between HbA1c level and bone markers: r = -0.358, p = 0.0005-osteocalcin, r = -0.40, p = 0.0005-P1NP, r = -0.258, p = 0.005-crosslaps. CONCLUSIONS: Our results indicate the presence of altered bone microarchitecture in T2DZ patients according to the TBS score, combined with lower levels of bone markers, with a statistically significant negative correlation between HbA1c level and bone markers.

Relevance of vitamin D deficiency in patients with chronic autoimmune atrophic gastritis: a prospective study.

BACKGROUND: Chronic autoimmune atrophic gastritis (CAAG) is an autoimmune disease characterized by hypo/achlorhydria. A role of CAAG in the pathogenesis of nutritional deficiencies has been reported, therefore we hypothesized a possible association between CAAG and 25-OH-Vitamin D [25(OH)D] deficiency. Aim of the present study is to evaluate the prevalence of 25(OH)D deficiency in CAAG patients. METHODS: 87 CAAG patients (71 females; mean age 63.5 ± 12.8 years) followed at our Centre from January 2012 to July 2015 were consecutively evaluated. 25(OH)D, vitamin B12, parathormone, and calcium were measured in all the CAAG patients. The results were compared with a control group of 1232 healthy subjects. RESULTS: In the CAAG group the mean 25(OH)D levels were significantly lower than in the control group (18.8 vs. 27.0 ng/ml, p < 0.0001). 25(OH)D levels < 20 ng/ml was observed in 57 patients, while levels < 12.5 ng/ml in 27 patients. A significant correlation between vitamin B12 values at diagnosis and 25(OH)D levels was observed (rs = 0.25, p = 0.01). Interestingly, the CAAG patients with moderate/severe gastric atrophy had lower 25(OH)D values as compared to those with mild atrophy (11.8 vs. 20 ng/ml; p = 0.0047). Moreover, the 25(OH)D levels were significantly lower in CAAG patients with gastric carcinoid as compared to those without gastric carcinoid (11.8 vs. 19.8 ng/ml; p = 0,0041). CONCLUSION: Data from the present study showed a significant reduction of 25(OH)D levels in CAAG patients and a possible impairment of vitamin D absorption in CAAG may be postulated. Any implication to the genesis of gastric carcinoids remains to be elucidated.

Maternal vitamin D and markers of glycaemia during pregnancy in the Belfast centre of the Hyperglycaemia and Adverse Pregnancy Outcome study.

AIMS: To measure total 25-hydroxyvitamin D levels in women in mid-pregnancy who participated in the Belfast centre of the Hyperglycaemia and Adverse Pregnancy Outcome (HAPO) observational study, and to investigate the associations between levels of 25-hydroxyvitamin D and markers of gestational diabetes mellitus and lipid biomarkers. METHODS: A total of 1585 pregnant women had serum samples available for measurement. Participants were recruited from the Royal Jubilee Maternity Hospital, Belfast, Northern Ireland, at 24-32 weeks' gestation, as part of the HAPO study. 25-hydroxyvitamin D concentrations were measured using liquid chromatography tandem mass spectrometry. Glucose, C-peptide and lipid levels were previously analysed in a central laboratory. Statistical analysis was performed. RESULTS: The median (interquartile range) 25-hydroxyvitamin D concentration during pregnancy was 38.6 (24.1-60.7) nmol/l, with 65.8% of women being vitamin D-deficient (≤50 nmol/l). In regression analysis, the association between maternal 25-hydroxyvitamin D and fasting plasma glucose levels approached significance [regression coefficient -0.017 (95% CI -0.034 to 0.001); P=0.06], and a significant positive association was observed between maternal 25-hydroxyvitamin D and ß-cell function [1.013 (95% CI 1.001 to 1.024); P=0.031]. Maternal 25-hydroxyvitamin D level was positively associated with HDL [0.047 (95% CI 0.021 to 0.073) P≤ 0.001] and total cholesterol [0.085 (95% CI 0.002 to 0.167); P=0.044] in regression analysis. CONCLUSIONS: These results indicate a high prevalence of vitamin D deficiency during pregnancy, which requires identification and treatment; however, only weak associations were observed between 25-hydroxyvitamin D level and markers of glucose and insulin metabolism. This would suggest that these are of doubtful clinical significance.

Vitamin D levels and atopic eczema in infancy and early childhood in Norway: a cohort study.

BACKGROUND: Epidemiological data and the effect of sun exposure on atopic eczema (AE) suggest that vitamin D (vitD) may be involved in the pathogenesis. OBJECTIVES: To investigate if vitD levels were associated with the presence or severity of AE in the first 2 years of life in children living in south-east Norway. METHODS: Infants, recruited to a clinical trial on acute bronchiolitis (n = 404) and from the general population (n = 240), were examined at 1-13 months (first visit) and at 2 years of age (second visit). Caregivers were interviewed using a structured questionnaire. AE was diagnosed clinically, based on well-established criteria. Disease severity was assessed using the SCORing Atopic Dermatitis index. Blood samples were taken for vitD measurements, using liquid chromatography-tandem mass spectrometry and for common filaggrin mutation analyses. Complete data on AE and vitD were available in 596 and 449 children at the first and second visit, respectively. RESULTS: Atopic eczema was diagnosed in 67 children (11%) at the first visit and in 103 children (23%) at the second. Mean vitD levels were 58·2 nmol L(-1) at the first visit and 66·9 nmol L(-1) at the second. Using vitD level tertiles in multivariate regression analysis, there was no association between vitD levels and AE at either visit, regardless of filaggrin mutation. In children without AE at the first visit, vitD levels did not predict AE at the second. CONCLUSIONS: In this cohort of young children in Norway, we found no association between vitD levels and the presence or severity of AE.

Cholecalciferol v. ergocalciferol for 25-hydroxyvitamin D (25(OH)D) repletion in chronic kidney disease: a randomised clinical trial.

Patients with chronic kidney disease (CKD) demonstrate complex mineral metabolism derangements and a high prevalence of vitamin D deficiency. However, the optimal method of 25-hydroxyvitamin D (25(OH)D) repletion is unknown, and trials analysing the comparative efficacy of cholecalciferol and ergocalciferol in this population are lacking. We conducted a randomised clinical trial of cholecalciferol 1250µg (50 000 IU) weekly v. ergocalciferol 1250µg (50 000 IU) weekly for 12 weeks in forty-four non-dialysis-dependent patients with stage 3-5 CKD. The primary outcome was change in total 25(OH)D from baseline to week 12 (immediately after therapy). Secondary analyses included the change in 1,25-dihydroxyvitamin D (1,25(OH)2D), parathyroid hormone (PTH), D2 and D3 sub-fractions of 25(OH)D and 1,25(OH)2D and total 25(OH)D from baseline to week 18 (6 weeks after therapy). Cholecalciferol therapy yielded a greater change in total 25(OH)D (45·0 (sd 16·5) ng/ml) v. ergocalciferol (30·7 (sd 15·3) ng/ml) from baseline to week 12 (P<0·01); this observation partially resulted from a substantial reduction in the 25(OH)D3 sub-fraction with ergocalciferol. However, following cessation of therapy, no statistical difference was observed for total 25(OH)D change from baseline to week 18 between cholecalciferol and ergocalciferol groups (22·4 (sd 12·7) v. 17·6 (sd 8·9) ng/ml, respectively; P=0·17). We observed no significant difference between these therapies with regard to changes in serum PTH or 1,25(OH)2D. Therapy with cholecalciferol, compared with ergocalciferol, is more effective at raising serum 25(OH)D in non-dialysis-dependent CKD patients while active therapy is ongoing. However, levels of 25(OH)D declined substantially in both arms following cessation of therapy, suggesting the need for maintenance therapy to sustain levels.

Vitamin D activity of breast milk in women randomly assigned to vitamin D3 supplementation during pregnancy.

BACKGROUND: Human milk is typically low in vitamin D activity (VDA). Whether the vitamin D content of breast milk at birth can be increased by supplementing the mother during pregnancy has not been reported to the best of our knowledge. OBJECTIVE: We examined the effect of vitamin D supplementation during pregnancy on breast-milk VDA in the first 2 mo of lactation. DESIGN: Breast-milk samples were obtained from women who were enrolled in a randomized, double-blinded, placebo-controlled trial of vitamin D supplementation during pregnancy. Pregnant women were enrolled at 27 wk of gestation and randomly assigned to the following 3 groups: a placebo group, a group who received one dosage of daily oral vitamin D3 (1000 IU), or a group who received 2 dosages of daily oral vitamin D3 (2000 IU). Serum 25-hydroxyvitamin D [25(OH)D] was measured at enrollment, at 36 wk of gestation, and in cord blood at birth. Study participants who were breastfeeding were invited to provide breast-milk samples for VDA measurement [concentration of vitamin D2, vitamin D3, 25(OH)D2, and 25(OH)D3] at 2 wk and 2 mo postpartum. A linear mixed model was used to compare breast-milk VDA between the 3 study groups. RESULTS: A total of 75 women provided breast-milk samples (44 women provided breast-milk samples at both 2 wk and 2 mo postpartum). The mean (95% CI) VDA at age 2 wk was 52 IU/L (12, 217 IU/L) in the placebo group, 51 IU/L (17, 151 IU/L) in the 1000-IU group, and 74 IU/L (25, 221 IU/L) in the 2000-IU group; and at age 2 mo, the mean (95% CI) VDA was 45 IU/L (16, 124 IU/L), 43 IU/L (18, 103 IU/L), and 58 IU/L (15, 224 IU/L), respectively. There was no significant interaction in VDA between the sample-collection time and treatment (P = 0.61), but there was a difference between lower- and higher-dosage treatment groups (P = 0.04). CONCLUSION: Maternal vitamin D supplementation during pregnancy of 2000 IU/d (compared with 1000 IU/d and with a placebo) results in a higher VDA of breast milk ≥2 mo postpartum. This trial was registered at the Australian New Zealand Clinical Trials Registry as ACTRN12610000483055.

An Integrated Predictive Model of Population Serum 25-Hydroxyvitamin D for Application in Strategy Development for Vitamin D Deficiency Prevention.

BACKGROUND: To enable food-based strategies for the prevention of vitamin D deficiency to be evidence-based, there is a need to develop integrated predictive models of population serum 25-hydroxyvitamin D [25(OH)D] that are responsive to both solar and dietary inputs of vitamin D. OBJECTIVES: The objectives of this work were to develop and validate an integrated mathematical model with the use of data on UVB availability, exposure, and dietary intake to predict serum 25(OH)D concentrations in a nationally representative sample of adults, and then test the model's performance with the use of 3 hypothetical fortification scenarios as exemplars. METHODS: Data on UVB availability and hours of sunlight in Ireland were used in a mathematical model to predict serum 25(OH)D in Irish adults aged 18-64 y. An equation from our dose-related vitamin D supplementation trial in adults was developed and integrated into the model, which allowed us to predict the impact of changes in dietary vitamin D on the contribution to annual serum 25(OH)D concentrations, accounting for seasonality of UVB availability. Recently published estimates of the impact of 3 vitamin D food fortification scenarios on vitamin D intake in a representative sample of Irish adults were used in the model as a test. RESULTS: The UVB- and vitamin D intake-serum 25(OH)D components of the integrated model were both validated with the use of independent data. The model predicted that the percentage of vitamin D deficiency [serum 25(OH)D <30 nmol/L] in the adult population during an extended winter period was 18.1% (vs. 18.6% measured), which could be reduced in a stepwise manner with the incorporation of an increased number of vitamin D-fortified foods, down to 6.6% with the inclusion of enhanced fortified dairy-related products, fat spreads, fruit juice and drinks, and cereal products. CONCLUSION: Mathematical models have the ability to inform how vitamin D food fortification in various constructs may affect population serum 25(OH)D concentrations and the prevalence of vitamin D deficiency.

Vitamin D deficiency contributes to the reduction and impaired function of naïve CD45RA⁺ regulatory T cell in chronic heart failure.

The effect of vitamin D pertinent to cardiovascular health on the heart itself is considered to shift toward an anti-inflammatory response in chronic heart failure (CHF); however, its underlying mechanism is not completely understood. In this study, we demonstrated that plasma 25(OH)D level, negatively associated with NT-ProBNP, correlated with the decreased Treg in CHF compared to the patients with other cardiovascular diseases and healthy and older donors. Naïve Treg cell (CD4(+)CD45RA(+)Foxp3(lo)T) subset, rather than whole Treg cells, contributes to the reduction of Treg in CHF. 1,25(OH)2D treatment maintained partial expression of CD45RA on CD4(+)T cell after αCD3/CD28 monoclonal antibodies activation and ameliorated the impaired CD4(+)CD45RA(+)T cell function from CHF patients through upregulating Foxp3 expression and IL-10 secretion in vitro. Low level of vitamin D receptor (VDR) was detected in CD4(+)CD45RA(+)T cell of CHF than control, while 1,25(OH)2D treatment increased the VDR expression to exert its immunosuppression on T cell. The results of this study might provide tangible evidence to our knowledge of the impact of vitamin D supplementation on naïve Tregs, which may offer new means of preventing and treating CHF.

Automated Competitive Protein-Binding Assay for Total 25-OH Vitamin D, Multicenter Evaluation and Practical Performance.

BACKGROUND: The Roche Elecsys Vitamin D Total competitive protein-binding assay uses recombinant vitamin D binding protein for measuring 25-hydroxyvitamin D (25-OHD), which is different from commonly used antibody assays. METHODS: The assay, standardized against LC-MS/MS, was tested at four sites. Evaluation included precision; between-laboratory variability; functional sensitivity; correlation to LC-MS/MS, HPLC, and immunoassays; as well as robustness, traceability, and EQAS performance. RESULTS: Precision testing showed within-run coefficient of variations (CVs) of ≤ 7%, within-laboratory CVs of <9.5%, between-laboratory precision CVs of ≤ 10.1%, and a functional sensitivity below 9.8 nmol/l (at CV 12.9%). The assay showed equivalent 25-OHD levels for matched serum and plasma samples, good reagent lot-to-lot consistency in pooled sera over time, and good agreement with HPLC (relative bias -8.8%). Comparison with LC-MS/MS methods yielded relative biases of -15.4, -13.5, -10.2, and 3.2%. Comparison against immunoassays showed a relative bias of 14.5% (DiaSorin Liaison) and -58.2% (IDS-iSYS). The overall mean results in 2 years DEQAS was 102% of the ALTM. In a certified reference patient panel, the average bias was < 4% for the sum of 25-OHD2 and 25-OHD3. CONCLUSION: The Elecsys Vitamin D Total assay demonstrated good overall performance and is, according to present standards, very suitable for automated measurement of 25-OHD.

Concentrations of the vitamin D metabolite 1,25(OH)2D and odds of metabolic syndrome and its components.

AIM: Few epidemiological studies have investigated the association between circulating concentrations of the active vitamin D metabolite 1,25(OH)2D and metabolic syndrome. We sought to determine whether blood levels of 1,25(OH)2D are associated with metabolic syndrome and its individual components, including waist circumference, triglycerides, blood pressure, and glucose, and high-density lipoprotein. We also investigated these associations for the more abundant precursor vitamin D metabolite, 25(OH)D. METHODS: Participants from two completed clinical trials of colorectal neoplasia with available metabolic syndrome data and blood samples for measurement of 1,25(OH)2D (n=1048) and 25(OH)D (n=2096) were included. Cross-sectional analyses of the association between concentrations of 1,25(OH)2D, 25(OH)D, metabolic syndrome, and its components were conducted. RESULTS: A statistically significant inverse association was observed for circulating concentrations of 1,25(OH)2D and metabolic syndrome, with adjusted ORs (95% CIs) of 0.73 (0.52-1.04) and 0.52 (0.36-0.75) for the second and third tertiles of 1,25(OH)2D, respectively (p-trend <0.001). Significant inverse relationships were also observed between 1,25(OH)2D and high triglycerides (p-trend <0.001), and low high-density lipoprotein (p-trend <0.001). For 25(OH)D concentrations, significant inverse associations were found for metabolic syndrome (p-trend <0.01), high waist circumference (p-trend <0.04) and triglyceride levels (p-trend <0.01). Participants with 25(OH)D ≥30 ng/ml and in the highest tertile of 1,25(OH)2D demonstrated significantly lower odds of metabolic syndrome, with an OR (95% CI) of 0.38 (0.19-0.75) compared to those in the lowest category for both metabolites. CONCLUSION: These results provide new evidence that the relatively rarely-studied active hormonal form of vitamin D, 1,25(OH)2D, is associated with metabolic syndrome and its components, and confirm prior findings for 25(OH)D. The finding that 1,25(OH)2D is related to high-density lipoprotein, while 25(OH)D is not, suggests that there may be an independent mechanism of action for 1,25(OH)2D in relation to metabolic dysregulation.

Overestimation of 25-hydroxyvitamin D3 by increased ionisation efficiency of 3-epi-25-hydroxyvitamin D3 in LC-MS/MS methods not separating both metabolites as determined by an LC-MS/MS method for separate quantification of 25-hydroxyvitamin D3, 3-epi-25-hydroxyvitamin D3 and 25-hydroxyvitamin D2 in human serum.

BACKGROUND: An LC-MS/MS method was developed for simultaneous quantification of 25-hydroxyvitamin D3 (25(OH)D3), 3-epi-25(OH)D3, and 25(OH)D2 in human serum. METHODS: Sample preparation consisted of protein precipitation followed by off-line SPE. Calibration curves for each vitamin D metabolite were constructed in phosphate-buffered saline with 60 g/L albumin including its corresponding stable isotope labelled (SIL) internal standard. A pentafluorophenyl (PFP) analytical column was used to resolve 25(OH)D3 from 25(OH)D2 and 3-epi-25(OH)D3, followed by SRM registration using positive ESI-MS/MS. Accuracy was assessed from measurement of samples with NIST reference method procedure (RMP) assigned values. The PFP LC-MS/MS method was compared to an in-house C18 column LC-MS/MS method, not resolving 25(OH)D3 from 3-epi-25(OH)D3, using adult and newborn samples. RESULTS: Intra-assay and inter-assay coefficients of variation were less than 4% and 7.5%, respectively for all three vitamin D metabolites; lower limits of quantification were 1, 1 and 2 nmol/L and linearity of methods were 1-500, 1-200 and 2-500 nmol/L for 25(OH)D3, 3-epi-25(OH)D3 and 25(OH)D2, respectively. The PFP LC-MS/MS method showed minimal bias to the NIST RMP. Method comparison revealed that in the C18 LC-MS/MS method, the 3-epi-25(OH)D3 concentration is overestimated inadvertently not only from co-elution of both analytes, but also by an additional 30-40% higher ionisation efficiency of 3-epi-25(OH)D3 when compared to 25(OH)D3. CONCLUSION: This accurate LC-MS/MS method allows the simultaneous measurement of 25(OH)D3, 3-epi-25(OH)D3, and 25(OH)D2 in human serum. Due to increased ionisation efficiency, the contribution of the 3-epi-25(OH)D3 metabolite to the total 25(OH)D3 concentration is significantly overestimated in MS methods that do not resolve 3-epi-25(OH)D3 from 25(OH)D3 and may compromise its use in infant samples known to have significant amounts of 3-epi-25(OH)D3.

25-Hydroxyvitamin D in African-origin populations at varying latitudes challenges the construct of a physiologic norm.

BACKGROUND: The vitamin D-endocrine system is thought to play a role in physiologic processes that range from mineral metabolism to immune function. Serum 25-hydroxyvitamin D [25(OH)D] is the accepted biomarker for vitamin D status. Skin color is a key determinant of circulating 25(OH)D concentrations, and genes responsible for melanin content have been shown to be under strong evolutionary selection in populations living in temperate zones. Little is known about the effect of latitude on mean concentrations of 25(OH)D in dark-skinned populations. OBJECTIVE: The objective was to describe the distribution of 25(OH)D and its subcomponents in 5 population samples of African origin from the United States, Jamaica, Ghana, South Africa, and the Seychelles. DESIGN: Participants were drawn from the Modeling of the Epidemiologic Transition Study, a cross-sectional observational study in 2500 adults, ages 25-45 y, enrolled between January 2010 and December 2011. Five hundred participants, ∼50% of whom were female, were enrolled in each of 5 study sites: Chicago, IL (latitude: 41°N); Kingston, Jamaica (17°N); Kumasi, Ghana (6°N); Victoria, Seychelles (4°S); and Cape Town, South Africa (34°S). All participants had an ancestry primarily of African origin; participants from the Seychelles trace their history to East Africa. RESULTS: A negative correlation between 25(OH)D and distance from the equator was observed across population samples. The frequency distribution of 25(OH)D in Ghana was almost perfectly normal (Gaussian), with progressively lower means and increasing skewness observed at higher latitudes. CONCLUSIONS: It is widely assumed that lighter skin color in populations outside the tropics resulted from positive selection, driven in part by the relation between sun exposure, skin melanin content, and 25(OH)D production. Our findings show that robust compensatory mechanisms exist that create tolerance for wide variation in circulating concentrations of 25(OH)D across populations, suggesting a more complex evolutionary relation between skin color and the vitamin D pathway.

No effect of high-dose vitamin D supplementation on glycemic status or cardiovascular risk factors in subjects with prediabetes.

OBJECTIVE: In observational studies, low serum 25-hydroxyvitamin D [25(OH)D] concentrations have been associated with insulin resistance and other risk factors for cardiovascular disease. RESEARCH DESIGN AND METHODS: We present 1-year data from an ongoing 5-year trial in 511 individuals with impaired fasting glucose (IFG) and/or impaired glucose tolerance (IGT) randomly assigned to 20,000 IU/week vitamin D3 or placebo. An oral glucose tolerance test was performed at baseline and after 1 year. RESULTS: Mean baseline serum 25(OH)D was 59.9 nmol/L and 61.1 nmol/L in the vitamin D and placebo groups, respectively, and increased by 45.8 nmol/L and 3.4 nmol/L, respectively. With adjustment for baseline concentrations, no differences in measures of glucose metabolism, insulin secretion or sensitivity, blood pressure, or hs-CRP were found after 1 year. There was a slight, but significant decrease in total and LDL cholesterol in the vitamin D group compared with the placebo group, but as there was also a decrease in HDL cholesterol, the change in the total/HDL cholesterol ratio did not differ significantly. Only analyzing subjects with 25(OH)D <50 nmol/L did not change the results. CONCLUSIONS: This study shows that vitamin D supplementation does not improve glycemic indices, blood pressure, or lipid status in subjects with IFG and/or IGT.

The 3 epimer of 25-hydroxycholecalciferol is present in the circulation of the majority of adults in a nationally representative sample and has endogenous origins.

Fundamental knowledge gaps in relation to the 3 epimer of 25-hydroxycholecalciferol [3-epi-25(OH)D3] limit our understanding of its relevance for vitamin D nutrition and health. The aims of this study were to characterize the 3-epi-25(OH)D3 concentrations in a nationally representative sample of adults and explore its determinants. We also used data from a recent randomized controlled trial (RCT) of supplemental cholecalciferol (vitamin D3) conducted in winter in older adults to directly test the impact of changes in vitamin D status on serum 3-epi-25(OH)D3 concentrations. Serum 25-hydroxycholecalciferol [25(OH)D3] and 3-epi-25(OH)D3 concentrations (via LC-tandem mass spectrometry) from our vitamin D3 RCT in adults (aged ≥50 y) and data on dietary, lifestyle, and biochemical characteristics of participants of the recent National Adult Nutrition Survey in Ireland (aged 18-84 y; n = 1122) were used in the present work. In the subsample of participants who had serum 3-epi-25(OH)D3 concentrations greater than the limit of quantification (n = 1082; 96.4%), the mean, 10th, 50th (median), and 90th percentile concentrations were 2.50, 1.05, 2.18, and 4.30 nmol/L, respectively, whereas the maximum 3-epi-25(OH)D3 concentration was 15.0 nmol/L. A regression model [explaining 29.9% of the variability in serum 3-epi-25(OH)D3] showed that age >50 y, vitamin D supplement use, dietary vitamin D, meat intake, season of blood sampling, and sun exposure habits were significant positive determinants, whereas increasing waist circumference and serum 25-hydroxyergocalciferol concentration were significant negative determinants. The RCT data showed that mean serum 25(OH)D3 and 3-epi-25(OH)D3 concentrations increased (49.3% and 42.1%, respectively) and decreased (-28.0% and -29.1%, respectively) significantly (P < 0.0001) with vitamin D3 (20 µg/d) and placebo supplementation, respectively, over 15 wk of winter. In conclusion, we provide data on serum 3-epi-25(OH)D3 in a nationally representative sample of adults. Our combined observational and RCT data might suggest that both dietary supply and dermal synthesis of vitamin D3 contribute to serum 3-epi-25(OH)D3 concentration.

Dietary vitamin D2--a potentially underestimated contributor to vitamin D nutritional status of adults?

It has been suggested that vitamin D2 is not very prevalent in the human food chain. However, data from a number of recent intervention studies suggest that the majority of subjects had measurable serum 25-hydroxyvitamin D2 (25(OH)D2) concentrations. Serum 25(OH)D2, unlike 25(OH)D3, is not directly influenced by exposure of skin to sun and thus has dietary origins; however, quantifying dietary vitamin D2 is difficult due to the limitations of food composition data. Therefore, the present study aimed to characterise serum 25(OH)D2 concentrations in the participants of the National Adult Nutrition Survey (NANS) in Ireland, and to use these serum concentrations to estimate the intake of vitamin D2 using a mathematical modelling approach. Serum 25(OH)D2 concentration was measured by a liquid chromatography-tandem MS method, and information on diet as well as subject characteristics was obtained from the NANS. Of these participants, 78.7 % (n 884) had serum 25(OH)D2 concentrations above the limit of quantification, and the mean, maximum, 10th, 50th (median) and 90th percentile values of serum 25(OH)D2 concentrations were 3.69, 27.6, 1.71, 2.96 and 6.36 nmol/l, respectively. To approximate the intake of vitamin D2 from these serum 25(OH)D2 concentrations, we used recently published data on the relationship between vitamin D intake and the responses of serum 25(OH)D concentrations. The projected 5th to 95th percentile intakes of vitamin D2 for adults were in the range of 0.9-1.2 and 5-6 µg/d, respectively, and the median intake ranged from 1.7 to 2.3 µg/d. In conclusion, the present data demonstrate that 25(OH)D2 concentrations are present in the sera of adults from this nationally representative sample. Vitamin D2 may have an impact on nutritional adequacy at a population level and thus warrants further investigation.

Genome-wide association study of circulating vitamin D-binding protein.

BACKGROUND: Vitamin D status may influence a spectrum of health outcomes, including osteoporosis, arthritis, cardiovascular disease, and cancer. Vitamin D-binding protein (DBP) is the primary carrier of vitamin D in the circulation and regulates the bioavailability of 25-hydroxyvitamin D. Epidemiologic studies have shown direct DBP-risk relations and modification by DBP of vitamin D-disease associations. OBJECTIVE: We aimed to characterize common genetic variants that influence the DBP biochemical phenotype. DESIGN: We conducted a genome-wide association study (GWAS) of 1380 men through linear regression of single-nucleotide polymorphisms (SNPs) in the Illumina HumanHap500/550/610 array on fasting serum DBP, assuming an additive genetic model, with adjustment for age at blood collection. RESULTS: We identified 2 independent SNPs located in the gene encoding DBP, GC, that were highly associated with serum DBP: rs7041 (P = 1.42 × 10⁻²46) and rs705117 (P = 4.7 × 10⁻9¹). For both SNPs, mean serum DBP decreased with increasing copies of the minor allele: mean DBP concentrations (nmol/L) were 7335, 5149, and 3152 for 0, 1, and 2 copies of rs7041 (T), respectively, and 6339, 4280, and 2341, respectively, for rs705117 (G). DBP was also associated with rs12144344 (P = 5.9 × 10⁻7) in ST6GALNAC3. CONCLUSIONS: In this GWAS analysis, to our knowledge the first to examine this biochemical phenotype, 2 variants in GC--one exonic and one intronic--were associated with serum DBP concentrations at the genome-wide level of significance. Understanding the genetic contributions to circulating DBP may provide greater insights into the vitamin D binding, transport, and other functions of DBP and the effect of vitamin D status on health outcomes.

Dietary calcium does not interact with vitamin D3 in terms of determining the response and catabolism of serum 25-hydroxyvitamin D during winter in older adults.

BACKGROUND: Interactions between calcium and vitamin D may have implications for the regulation of serum 25-hydroxyvitamin D [25(OH)D] and its catabolism and, consequently, the vitamin D dietary requirement. OBJECTIVE: We investigated whether different calcium intakes influenced serum 25(OH)D and indexes of vitamin D activation and catabolism during winter and in the context of both adequate and inadequate vitamin D intakes. DESIGN: A 15-wk winter-based, randomized, placebo-controlled, double-blind vitamin D3 intervention (20 µg/d) study was carried out in free-living men and women aged ≥50 y (n = 125) who were stratified according to calcium intakes [moderate-low (<700 mg/d) or high (>1000 mg/d) intake]. The serum 25(OH)D concentration was the primary outcome, and serum calcium, parathyroid hormone (PTH), 1,25-dihydroxyvitamin D [1,25(OH)2D], 24,25-dihydroxyvitamin D [24,25(OH)2D], the ratio of 24,25(OH)2D to 25(OH)D, vitamin D-binding protein, and free 25(OH)D were exploratory outcomes. RESULTS: A repeated-measures ANOVA showed there was no significant (P = 0.2) time × vitamin D treatment × calcium intake grouping interaction effect on the mean serum 25(OH)D concentration over the 15-wk intervention period. Serum 25(OH)D concentrations increased (P ≤ 0.005) and decreased (P ≤ 0.002) in vitamin D3 and placebo groups, respectively, and were of similar magnitudes in subjects with calcium intakes <700 mg/d (and even <550 mg/d) compared with >1000 mg/d. The response of serum PTH, 1,25(OH)2D, 24,25(OH)2D, the ratio of 24,25(OH)2D to 25(OH)D, and free 25(OH)D significantly differed in vitamin D3 and placebo groups but not by calcium intake grouping. CONCLUSIONS: We found no evidence of a vitamin D sparing effect of high calcium intake, which has been referred to by some authors as "vitamin D economy." Thus, recent dietary vitamin D requirement estimates will cover the vitamin D needs of even those individuals who have inadequate calcium intakes.