The 25-hydroxyvitamin D3 C-3 epimer: distribution, correlates, and reclassification of 25-hydroxyvitamin D status in the population-based Atherosclerosis Risk in Communities Study (ARIC)

Seasonal changes in free 25-(OH)D and vitamin D metabolite ratios and their relationship with psychophysical stress markers in male professional football players

Introduction: Novel markers of vitamin D status are currently being investigated, including free 25-(OH)D (25-(OH)DF) and the vitamin D metabolite ratio (24,25-(OH)2D3:25-(OH)D3; VMR). The VMR may provide additional functional information on vitamin D metabolism in athletes. Therefore, the main objective of the current study was to evaluate 25-(OH)DF, bioavailable 25-(OH)D (25-(OH)DB), VMR, and psychophysical stress markers during different training periods over a half-season. The second aim was to assess the association between vitamin D binding protein (VDBP), total and free 25-(OH)D, VMRs, and psychophysical stress markers in professional football players. Moreover, we examined the relationship between 25-(OH)D3 and vitamin D metabolites (24,25-(OH)2D3, 3-epi-25-(OH)D3) to determine if training loads in different training periods influenced the vitamin D metabolome. Methods: Twenty professional football players were tested at six different time points across half a year (V1-June; V2-July; V3-August; V4-October; V5-December; V6-January). Results: Analyses indicated a significant seasonal rhythm for VDBP, and total 25-(OH)D (25-(OH)DT), 25-(OH)DB, 24,25-(OH)2D3, 3-epi-25-(OH)D3, 25-(OH)D3:24,25-(OH)2D3, and 24,25-(OH)2D3:25-(OH)D3 VMRs throughout the training period. No correlation was detected between 25-(OH)DT, 25-(OH)DB, 25-(OH)DF, vitamin D metabolites, VMRs, VDBP, and ferritin, liver enzymes (aspartate transaminase [AST] and alanine transaminase [ALT]), creatine kinase (CK), cortisol, testosterone, and testosterone-to-cortisol ratio (T/C) in each period (V1-V6). However, there was a strong statistically significant correlation between 25-(OH)D3 and 24,25-(OH)D3 in each training period. Conclusion: In conclusion, a seasonal rhythm was present for VDBP, 25-(OH)DT, 25-(OH)DB, vitamin D metabolites (24,25-(OH)2D3, 3-epi-25-(OH)D3), and VMRs (25-(OH)D3:24,25-(OH)2D3, 25-(OH)D3:3-epi-25-(OH)D3). However, no rhythm was detected for 25-(OH)DF and markers of psychophysical stress (ferritin, liver enzymes, CK, testosterone, cortisol, and T/C ratio). Moreover, the relationships between free and total 25-(OH)D with psychophysical stress markers did not demonstrate the superiority of free over total measurements. Furthermore, training loads in different training periods did not affect resting vitamin D metabolite concentrations in football players.

Vitamin D and Its Metabolites Status before and during Chemotherapy in Caucasian Breast Cancer Patients

BACKGROUND

The predictive role of vitamin D (VD) in breast cancer (BC) patients' survival is still being investigated. This paper aims to evaluate the changes in VD metabolites during chemotherapy (CTH) and the predictive role of VD status in Caucasian BC patients treated with CTH.

METHODS

Vitamin D and its metabolites were assessed with reference LC-MS/MS methodology in 98 consecutive BC patients starting CHT, after 3 and 6 months, and compared to the control group.

RESULTS

The frequency of VD deficiency in BC patients was greater than in the control group (56.1% vs. 37.2%). After 6 months of CTH, the number of VD-deficient BC patients slightly increased to 60%. The concentrations of VD active forms [25(OH)D2, 25(OH)D3], and catabolites [24,25(OH)2D3 and 3-epi-25(OH)D3] decreased after 3 and 6 months of CTH compared to the baseline values. Strong positive correlations between concentrations of 3-epi-25(OH)D3 and 25(OH)D in both groups were found. Similar correlations were also observed between 24,25(OH)2D3 and 25(OH)D levels. Kaplan-Meier survival analysis showed significantly longer survival in BC patients without deficiency (>20 ng/mL) at baseline (HR = 2.44 (95% CI 1.07-5.59), p = 0.026).

CONCLUSIONS

(1) Our data provide further evidence that BC patients before CTH are more VD-deficient than the general population and this deficiency increases further during CTH treatment, as observed using the reference LC-MS methodology. (2) Presented results show that VD catabolism is not affected in BC patients. (3) The poorer survival in VD-deficient BP patients supports the importance of VD supplementation in BC patients with 25(OH)D levels below 20 ng/mL.

Relationship Between Metabolites of Vitamin D, Free 25-(OH)D, and Physical Performance in Indoor and Outdoor Athletes

The potential effects of vitamin D in athletes have received considerable attention in the literature. However, little is known about vitamin D metabolites and their association with physical performance in athletes. Therefore, the aim of our study was to determine the relationship between metabolites of vitamin D, vitamin D binding protein (VDBP), free, bioavailable 25-(OH)D, and physical fitness tests in athletes. A total of 40 indoor and outdoor players (16 judoists and 24 football players) participated in the study. Vitamin D metabolites (25-(OH)D, 24,25-(OH)₂D₃, 3-epi-25-(OH)D₃, and 1,25-(OH)₂D) were assessed using LM-MS/MS. Free 25-(OH)D concentration was evaluated by calculation using serum albumin and VDBP levels. Athletic performance was assessed using handgrip and vertical jump. Our study showed a significant correlation between vitamin D metabolites and handgrip strength and vertical jump variables in indoor players. It demonstrated a significant association between 3-epi-25-(OH)D₃ and vertical jump parameters in outdoor players. The results of our study showed relationship between free, bioavailable 25-(OH)D, and vertical jump variables in indoor players. In conclusion, we provide novel information on the vitamin D metabolites and athletic performance in athletes. Based on the results of our study, we concluded that vitamin D metabolites might be involved in skeletal muscle function in relation to athletic performance.

Bariatric Surgery Induced Changes in Blood Cholesterol Are Modulated by Vitamin D Status

The effect of metabolically active bariatric surgery treatment on lipid metabolism is inconclusive. The authors of this study presume that initial vitamin D status may play a regulating role in influencing the beneficial post-effects of bariatric surgery, especially the lipid profile. The biochemical data obtained from 24 patients who had undergone laparoscopic one-anastomosis gastric bypass (OAGB) at baseline, 3 months before the surgery, at the time of surgery, and 6 months later, demonstrate that vitamin D status influenced the postoperative lipid profile. The baseline established the partition line which divided patients into two groups according to the stated calcidiol initial concentration level of 32 ng/mL. The data shows that OAGB induces a decrease in TG and hsCRP while increasing HDL. Conversely, in patients whose 25(OH)D₃ was below 32 ng/mL TC significantly increased while those above this concentration remained in the normal physiological range. The changes induced by OAGB in TG, glucose, and hsCRP were similar in both groups. Unexpectedly, the surgery did not affect vitamin D metabolites. In conclusion, the results of the study suggest that a higher concentration of serum 25(OH)D₃ may enhance the protective effects of OAGB.

total and free vitamin D in type 2 diabetes mellitus patients in Baghdad city

Background: The free-form of vitamin D has been used by many researchers as an index of vitamin D status in health and disease. Several methods are there to estimate free, total, and even bioavailable vitamin D. Objective: The present work was carried out to measure free vitamin D using a special formula suggested by Bikle and Schwartz in 2019, which includes the vitamin D binding protein (VDBP). The results will be used to evaluate the vitamin D status in patients with type 2 diabetes mellitus (T2DM), and its relation to the disease progression. Methods: Sixty-four patients with T2DM and 73 healthy subjects, all from Baghdad city, were enrolled in the current study from March to October 2020. For each participant, fasting blood glucose, hemoglobin (HbA1c), insulin resistance HOMA-IR, and body mass index (BMI) were measured in addition to the total vitamin D and VDBP. Moreover, free vitamin D was calculated by the formula of Bikle & Schwartz. Results: There were highly significant correlations between total vitamin D and absolute values of free vitamin D or its percentage. The difference in total vitamin D was significant between patients and healthy controls with no significant change in VDBP, free and bio-available vitamin D, while free vitamin D% was higher in the patient’s group. Correlations between vitamin D and each of BMI, fasting glucose, HbA1c, and HOMA-IR were not significant; however, there was a negative correlation with BMI and fasting glucose in the healthy control subjects only. The Receiver Operating Characteristic (ROC) curve analysis of vitamin D in the diagnosis of diabetes mellitus was poor. Conclusion: Total vitamin D can represent vitamin D status, but it cannot be used as a factor for diagnosing T2DM. However, it could be of importance to change the glycemic status.

Fasting and Exercise Induce Changes in Serum Vitamin D Metabolites in Healthy Men

Background: Vitamin D plays pleiotropic roles in the body and hence, changes in its metabolism and distribution during starvation could play an important role in the adaptive response to famine. We aimed to identify the responses of some vitamin D metabolites to 8 d of fasting and exercise. Methods: A repeated-measures design was implemented, in which 14 male volunteers fasted for 8 d and performed an exercise test before and after fasting. Serum samples were collected on day 1 after night fasting and after 8 d of complete food restriction, before and 1 h and 3 h after exercise. Results: After 8 d of fasting, compared with baseline values, serum 24,25(OH)₂D₃ and 3-epi-25(OH)D₃ levels significantly increased; those of 25(OH)D₃ and 1,25(OH)₂D₃ were unaffected; and those of 25(OH)D₂ decreased. Exercise on the first day of fasting induced an increase in serum 3-epi-25(OH)D₃ levels, while exercise performed after 8 d of fasting induced an increase in 25(OH)D₃, 24,25(OH)₂D₃, 25(OH)D₂, and 3-epi-25(OH)D₃ levels. Conclusion: Increases in 24,25(OH)₂D₃ and 3-epi-25(OH)D₃ levels imply that fasting stimulates vitamin D metabolism. The effects of exercise on serum vitamin D metabolites, which are most pronounced after fasting and in subjects with serum 25(OH)D₃ above 25 ng/mL, support the notion that fasting and exercise augment vitamin D metabolism.

25-hydroxyvitamin D, Fibroblast Growth Factor 23, and Risk of Acute Kidney Injury Over 20 Years of Follow-Up

INTRODUCTION

Low serum 25-hydroxyvitamin D levels have been identified as a risk factor for acute kidney injury (AKI) among critically ill patients. Whether low 25-hydroxyvitamin D levels are associated with long-term incidence of hospitalization with AKI in the general population is unknown.

METHODS

Among 12,380 participants (mean age, 57 years; 24% black) in the Atherosclerosis Risk in Communities (ARIC) Study who attended visit 2 (1990-1992), we explored the association of serum 25-hydroxyvitamin D with incident hospitalization with AKI. Multivariable Cox models were used to estimate hazard ratios (HRs). We also examined the association of serum fibroblast growth factor 23 (FGF23) with AKI.

RESULTS

During a median follow-up of 24.3 years, 2145 participants had incident hospitalization with AKI (crude incidence rate: 8.3; 95% confidence interval [CI]: 8.0-8.7, per 1,000 person-years). In multivariable Cox models (including adjustment for kidney function), lower 25-hydroxyvitamin D and higher FGF23 levels were each significantly associated with an increased risk of AKI (HR: 1.35; 95% CI: 1.17-1.54, for lowest vs. highest quartile for 25-hydroxyvitamin D, and HR: 1.19; 95% CI: 1.05-1.36, for highest vs. lowest quartile for FGF23). The association was consistent across demographic and clinical subgroups, regardless of whether AKI was the primary diagnosis for hospitalization, and when adjusting for incident chronic kidney disease (CKD) or cardiovascular disease (CVD) as a time-varying covariate.

CONCLUSION

Among middle- to older-age adults in the community, low 25-hydroxyvitamin D and high FGF23 levels were independently associated with an increased risk of AKI. Future studies should explore underlying mechanisms linking these bone mineral metabolism markers with kidney injury.

Measurement of plasma 25-hydroxyvitamin D2, 25-hydroxyvitamin D3 and 3-epi-25-hydroxyvitamin D3 in population of patients with cardiovascular disease by UPLC-MS/MS method

Vitamin D has a potential role in protecting against cardiovascular disease (CVD). Serum 25-hydroxyvitamin D (25D) is the most widely used indicator of vitamin D status in the human body. 25D is estimated as total of 25-hydroxyvitamin D2 (25D2) and 25-hydroxyvitamin D3 (25D3). However, the presence of 3-epi-25-hydroxyvitamin D3 (3epi25D3) can affect 25D measurement. In this research a novel validated UPLC-MS/MS technique was developed to measure three vitamin D metabolites, 25D2, 25D3 and 3epi25D3 in human plasma. A liquid-liquid extraction using hexane was applied for isolation of the analytes from the samples. A chromatographic separation was achieved in a Kinetex F5 analytical column with isocratic elution (water and methanol with 0.1% methanoic acid, 20:80 v/v). Mass spectrometry detection of the metabolites was performed in a triple-quadruple tandem mass spectrometer under positive ion mode. Concentrations of the analytes were estimated in plasma samples of 54 patients. Validation parameters of the UPLC-MS/MS method, including linearity, precision, accuracy, and stability, fulfilled the requirements for bioanalytical assays. The deficient concentration of 25D (<20 ng/mL) was stated in over 60% of patients. 3epi25D3 was present in 78% of samples and its relative amount ranged from 0 to 54.1% of 25D concentration. The analysis of 25D2, 25D3 and 3epi25D3 by the validated UPLC-MS/MS method in plasma of patients with CVD permitted the classification of the patients with insufficient levels of 25D. 3epi25D3 might be relevant in the classification of vitamin D status.

Ultra-Marathon-Induced Increase in Serum Levels of Vitamin D Metabolites: A Double-Blind Randomized Controlled Trial

Purpose: While an increasing number of studies demonstrate the importance of vitamin D for athletic performance, the effects of any type of exercise on vitamin D metabolism are poorly characterized. We aimed to identify the responses of some vitamin D metabolites to ultra-marathon runs. Methods: A repeated-measures design was implemented, in which 27 amateur runners were assigned into two groups: those who received a single dose of vitamin D₃ (150,000 IU) 24 h before the start of the marathon (n = 13) and those (n = 14) who received a placebo. Blood samples were collected 24 h before, immediately after, and 24 h after the run. Results: In both groups of runners, serum 25(OH)D₃, 24,25(OH)₂D₃, and 3-epi-25(OH)D₃ levels significantly increased by 83%, 63%, and 182% after the ultra-marathon, respectively. The increase was most pronounced in the vitamin D group. Body mass and fat mass significantly decreased after the run in both groups. Conclusions: Ultra-marathon induces the mobilization of vitamin D into the blood. Furthermore, the 24,25(OH)₂D₃ and 3-epi-25(OH)D₃ increases imply that the exercise stimulates vitamin D metabolism.

Vitamin D status in cats with cardiomyopathy

BACKGROUND

Low vitamin D concentrations have been associated with advanced heart disease and poorer outcomes in people and dogs. Vitamin D status typically is assessed by serum 25(OH)D concentration. However, cats also produce notable amounts of a C-3 epimer of 25(OH)D (3-epi).

HYPOTHESIS/OBJECTIVES

Determine if vitamin D status, estimated by 25(OH)D₃ alone or combined with 3-epi (summation vitD), is lower in cats with cardiomyopathy (CM) compared to clinically normal (N) cats and if indicators of disease severity are associated with vitamin D status.

ANIMALS

Privately owned cats, 44 with CM and 56 N.

METHODS

Cross-sectional observational study using clinical and echocardiographic findings, diet history, and serum 25(OH)D₃ and 3-epi measurements.

RESULTS

Cat age was negatively related to vitamin D status. Summation vitD was lower in CM cats (median = 47.1 ng/mL) compared to N cats (median = 58.65 ng/mL) both before (P = .03) and after (P = .04) accounting for age. However, 25(OH)D₃ became nonsignificant between CM and N cats after age was included. Summation vitD was related positively to survival time and fractional shortening (FS), but negatively to left atrial enlargement (LAE) severity, both before and after accounting for age. For 25(OH)D₃ alone, only survival time and FS remained significant after including age.

CONCLUSIONS AND CLINICAL IMPORTANCE

We report 25(OH)D₃ and 3-epi concentrations in CM and N cats. Age had an important (negative) relationship to vitamin D status. After accounting for age, summation vitD was lower in CM cats. Vitamin D status was related positively to survival time and FS, but negatively to LAE severity.

Development and application of a LC-MS/MS assay for simultaneous analysis of 25-hydroxyvitamin-D and 3-epi-25-hydroxyvitamin-D metabolites in canine serum

Hypovitaminosis D and hypervitaminosis D are well recognised disorders in dogs. Hypovitaminosis D can occur following consumption of a diet inadequately supplemented with vitamin D or as a sequelae of severe intestinal disease. Hypervitaminosis D may occur as a result of consuming proprietary dog foods over-supplemented with vitamin D or through ingestion of vitamin D containing medicinal products or rodenticides. Consequently, there is a clear need to establish a methodology that can accurately quantify vitamin D metabolites across a broad dynamic range in dogs. The existence of C3-epimers of vitamin D metabolites has yet to be elucidated in dogs, yet are known to interfere with the analysis of vitamin D and have unknown biological activity in other species. Here, we describe the development and validation of a sensitive, specific and robust analytical liquid chromatography tandem mass spectrometry (LC-MS/MS) assay capable of separating and accurately measuring 25-hydroxyvitamin-D_2/3 (25(OH)D_2/3) and 3-epi-25-hydroxyvitamin-D_2/3 (3-epi-25(OH)D_2/3). We describe a simplified workflow utilising supported liquid extraction (SLE) without derivatization that provides good linearity (mean r > 0.996) and accuracy across a broad dynamic range of 4-500 nmol/L for D₃ metabolites and 7.8-500 nmol/L for D₂ metabolites. Upon application of this assay to 117 canine serum samples, 25(OH)D₃ was detectable in all samples with a median concentration of 82.1 nmol/L (inter-quartile range (IQR) 59.7-101.8 nmol/L). 3-epi-25(OH)D₃ could be detected in 87.2 % of the study population, with a median concentration of 5.2 nmol/L (2.4-8.1 nmol/L). However, 3-epi-25(OH)D₃ was quantified below the LLOQ in 40.2 % of these samples. 3-epi-25(OH)D₃ contributed on average 6.3 % to 25(OH)D₃ status (contribution ranges from 0 to 23.8%) and a positive correlation was detected between 25(OH)D₃ and 3-epi-25(OH)D₃ concentrations. Free 25(OH)D was also measured using an immunoassay with a median concentration of 15.2 pmol/L (12.5-23.2 pmol/L), and this metabolite was also positively correlated to both 3-epi-25(OH)D₃ and 25(OH)D₃ concentrations. D₂ metabolites were not detected in canine serum as expected. Vitamin D metabolite concentrations were variable between individuals, and research into the causes of this variation should include factors such as breed, age, sex and neuter status to determine the impact of genetic and hormonal factors. Given the clinical importance of vitamin D in dogs, and the immense potential for utilising this species as a model for human disease, further elucidation of the vitamin D pathway in this species would provide immense clinical and research benefit.

Non-linear associations of 25-hydroxyvitamin D concentrations with risk of cardiovascular disease and all-cause mortality: Results from The Health Improvement Network (THIN) database

BACKGROUND

There is increasing evidence that vitamin D supplementation may only be beneficial in people with vitamin D deficiency, and the lack of sufficient people with very low vitamin D levels could explain the lack of protection against cardiovascular disease (CVD) reported in recent clinical trials of vitamin D supplementation. The aim of this study was to assess associations of low to moderate circulating concentrations of 25-hydroxyvitamin D (25(OH)D with risk of incident CVD and all-cause mortality, as well as the risk of ischaemic heart disease (IHD), cerebrovascular disease, and heart failure separately.

METHODS AND RESULTS

Longitudinal analysis of electronic health records in The Health Improvement Network (THIN), a UK primary care database. The analysis included 180,263 patients age 18 years and older without a history of CVD and with circulating concentrations of 25(OH)D. After a mean follow-up of 2.2 (SD 1.7) years, there were 3747 patients diagnosed with CVD and 3912 patients died. Compared to patients in the highest quintile of 25(OHD) (≥ 67.5 nmol/L), those in the lowest 25(OH)D quintile (<23.1 nmol/L) had a hazard ratio (HR) of 1.24 (95% CI 1.12-1.38, P <  0.001) for CVD and 1.71 (1.55-1.88, P <  0.001) for mortality. The HR for both outcomes associated with 25(OH)D concentration was non-linear, being significantly increased in patients with 25(OH)D <35 nmol/L, and highest in those with 25(OH)D <25 nmol/L, although increased for mortality at 25(OH)D ≥100 nmol/L. The increased CVD HR in the lowest 25(OH)D quintile was more from IHD (1.35, 95% CI 1.13-1.60) and heart failure (1.38, 95% CI 1.08-1.77), than from cerebrovascular disease (1.13, 95% CI 0.97-1.31).

CONCLUSION

Low 25(OH)D are associated with highest risk of CVD and mortality, and are consistent with accumulating evidence that increased risk of these diseases occurs primarily in people with vitamin D deficiency.

Serum 25-Hydroxyvitamin D Concentrations and Incidence of Age-Related Macular Degeneration: The Atherosclerosis Risk in Communities Study

Purpose

To investigate the association between serum 25-hydroxyvitamin D (25[OH]D) concentrations at visit 2 (1990–1992) and the 18-year incidence of age-related macular degeneration (AMD) between visit 3 (1993–1995) and visit 5 (2011–2013).

Methods

This prospective analysis was conducted in a subset of participants (n = 1225) from the Atherosclerosis Risk in Communities Study. We evaluated the incidence of any, early, and late AMD from visit 3 to 5. The 25(OH)D concentrations were assessed in 2012–2013 by using stored serum from visit 2. Retinal fundus photographs taken at both visits were graded side by side to determine the incidence of AMD. Logistic regression was used to estimate the odds ratios (ORs) and 95% confidence intervals (CIs) for incident AMD outcomes during 18 years of follow-up (1993–1995 to 2011–2013) by tertile of 25(OH)D adjusted for age, race, and smoking status. P for linear trend was estimated by using continuous 25(OH)D concentrations. Sensitivity analyses applied inverse probability weights to account for selection to have eye photographs, death, and loss to follow-up.

Results

There was a decreased odds of any incident AMD (n = 139) and large, soft drusen (n = 80) in 25(OH)D tertile 3 versus 1, with OR (95% CI) = 0.57 (0.36–0.90), P trend = 0.11 and with 0.52 (0.28–0.93), P trend = 0.18, respectively. Applying sampling weights attenuated these results to 0.66 (0.38–1.16), P trend = 0.32 (any incident AMD) and 0.54 (0.27–1.09), P trend = 0.36 (large, soft drusen), respectively, suggesting these associations may be biased by loss to follow-up and sampling for retinal photographs at visit 5. No statistically significant results were observed with pigmentary abnormalities (n = 46) or incident late AMD (n = 26).

Conclusions

High 25(OH)D concentrations, approximately >70 nM, may be associated with decreased odds of incident early AMD.

The vitamin D metabolome: An update on analysis and function

Current understanding of vitamin D tends to be focussed on the measurement of the major circulating form 25-hydroxyvitamin D3 (25OHD3) and its conversion to the active hormonal form, 1α,25-dihydroxyvitamin D3 (1α,25(OH)₂ D3) via the enzyme 25-hydroxyvitamin D-1α-hydroxylase (CYP27B1). However, whilst these metabolites form the endocrine backbone of vitamin D physiology, it is important to recognise that there are other metabolic and catabolic pathways that are now recognised as being crucially important to vitamin D function. These pathways include C3-epimerization, CYP24A1 hydroxylase, CYP11A1 alternative metabolism of vitamin D3, and phase II metabolism. Endogenous metabolites beyond 25OHD3 are usually present at low endogenous levels and may only be functional in specific target tissues rather than in the general circulation. However, the technologies available to measure these metabolites have also improved, so that measurement of alternative vitamin D metabolic pathways may become more routine in the near future. The aim of this review is to provide a comprehensive overview of the various pathways of vitamin D metabolism, as well as describe the analytical techniques currently available to measure these vitamin D metabolites.

Temporal increases in 25-hydroxyvitamin D in midlife women: Longitudinal results from the Study of Women's Health Across the Nation

OBJECTIVE

25-hydroxyvitamin D (25(OH)D) is critical for bone mineralization and may prevent fractures. Understanding vitamin D deficiency trends in midlife women is particularly important given their concurrent menopausal changes that increase risk for fracture. We aimed to evaluate changes in mean 25(OH)D over time and their determinants in a racially, ethnically and socioeconomically diverse cohort of midlife women.

DESIGN

A multi-centre prospective cohort study.

PATIENTS

1585 women ages 42-52 years at baseline.

MEASUREMENTS

We measured serum 25(OH)D at 2 time points (1998-2000 and 2009-2011). Between-visit change was assessed in the whole cohort and in socioeconomic and demographic subgroups. Among those with vitamin D deficiency (25(OH)D <30 nmol/L) at baseline, we evaluated determinants of persistent deficiency at follow-up.

RESULTS

Mean 25(OH)D increased from 53.8 to 70.0 nmol/L (P < 0.001), and the prevalence of deficiency decreased from 20.4% to 9.7% (P < 0.001). While baseline 25(OH)D differed among subgroups, the changes in 25(OH)D were similar among groups. The proportion of women reporting dietary supplement use increased from 40.8% to 67.1% (P < 0.001), and the increase in 25(OH)D was significantly higher in supplement users. Among women with vitamin D deficiency at baseline, White women and supplement users were less likely to remain deficient at follow-up.

CONCLUSIONS

Among midlife women, temporal increases in 25(OH)D concentrations are driven largely by increases in supplement use. The proportion of women with 25(OH)D <30 nmol/L and thus at high risk for skeletal consequences remains substantial. Targeted screening for vitamin D deficiency in populations at risk for fragility fracture may be advisable.

Accuracy-Based Vitamin D Survey: Six Years of Quality Improvement Guided by Proficiency Testing

CONTEXT.—

The goal of the College of American Pathologists Accuracy-Based Proficiency Testing Program is to promote the quality, standardization, and harmonization of clinical laboratory results through proficiency testing specimens that are free from matrix effects, have target values that are traceable to reference methods, and that probe the limitations of current methods.

OBJECTIVE.—

To summarize the first 6 years of the Accuracy-Based Vitamin D Survey and highlight key insights from the data generated as it relates to assay performance.

DESIGN.—

Accuracy-based challenges were created by using pooled human serum samples. Certain samples were derived from participants in an institutional review board-approved protocol in which vitamin D-deficient participants were treated with ergocalciferol (vitamin D₂). Reference targets for the survey were set by the Centers for Disease Control and Prevention using isotope-dilution liquid chromatography-tandem mass spectrometry. Each method was compared with the reference method procedure over the course of the program (n = 43 proficiency testing samples).

RESULTS.—

Linear regression versus the reference method procedure revealed proportional biases across the methods, ranging from 0.0% to 16.7%. Pearson correlation coefficients (r²) ranged from 0.902 to 0.996. Results were influenced by the concentration of 25-hydroxyvitamin D₂ as well as the C-3 epimer of 25-hydroxyvitamin D₃. During the 6 years, 2 manufacturers altered their assays to match the reference method procedure more closely.

CONCLUSIONS.—

There is considerable bias, both proportional bias and sample-specific matrix effects, affecting many assays. This ongoing accuracy-based proficiency testing program for vitamin D will provide the data needed for laboratories and manufacturers to improve their assays and thereby patient care.

The DALI vitamin D randomized controlled trial for gestational diabetes mellitus prevention: No major benefit shown besides vitamin D sufficiency

BACKGROUND & AIMS

As vitamin D deficiency is associated with an increased risk of gestational diabetes mellitus (GDM), we aimed to test vitamin D supplementation as a strategy to reduce GDM risk (evaluated after fasting plasma glucose (FPG), insulin resistance and weight gain) in pregnant overweight/obese women.

METHODS

The DALI vitamin D multicenter study enrolled women with prepregnancy body mass index (BMI) ≥ 29 kg/m², ≤19 + 6 weeks of gestation and without GDM. Participants were randomized to receive 1600 IU/day vitamin D3 or placebo (each with or without lifestyle intervention) on top of (multi)vitamins supplements. Women were assessed for vitamin D status (sufficiency defined as serum 25-hydroxyvitamin D (25(OH)D) ≥ 50 nmol/l), FPG, insulin resistance and weight at baseline, 24-28 and 35-37 weeks. Linear or logistic regression analyses were performed to assess intervention effects.

RESULTS

Average baseline serum 25(OH)D was ≥50 nmol/l across all study sites. In the vitamin D intervention arm (n = 79), 97% of participants achieved target serum vitamin 25(OH)D (≥50 nmol/l) at 24-28 weeks and 98% at 35-37 weeks vs 74% and 78% respectively in the placebo arm (n = 75, p < 0.001). A small but significantly lower FPG (-0.14 mmol/l; CI95 -0.28, -0.00) was observed at 35-37 weeks with the vitamin D intervention without any additional difference in metabolic status, perinatal outcomes or adverse event rates.

CONCLUSION

In the DALI vitamin D trial, supplementation with 1600 IU vitamin D3/day achieved vitamin D sufficiency in virtually all pregnant women and a small effect in FPG at 35-37 weeks. The potential of vitamin D supplementation for GDM prevention in vitamin D sufficient populations appears to be limited.

TRIAL REGISTRATION NUMBER

ISRCTN70595832.

Association of Plasma Vitamin D Metabolites With Incident Type 2 Diabetes: EPIC-InterAct Case-Cohort Study

BACKGROUND

Existing evidence for the prospective association of vitamin D status with type 2 diabetes (T2D) is focused almost exclusively on circulating total 25-hydroxyvitamin D [25(OH)D] without distinction between its subtypes: nonepimeric and epimeric 25(OH)D3 stereoisomers, and 25(OH)D2, the minor component of 25(OH)D. We aimed to investigate the prospective associations of circulating levels of the sum and each of these three metabolites with incident T2D.

METHODS

This analysis in the European Prospective Investigation into Cancer and Nutrition (EPIC)-InterAct case-cohort study for T2D included 9671 incident T2D cases and 13,562 subcohort members. Plasma vitamin D metabolites were quantified by liquid chromatography-mass spectrometry. We used a multivariable Prentice-weighted Cox regression to estimate hazard ratios (HRs) of T2D for each metabolite. Analyses were performed separately within country, and estimates were combined across countries using random-effects meta-analysis.

RESULTS

The mean concentrations (SD) of total 25(OH)D, nonepimeric 25(OH)D3, epimeric 25(OH)D3, and 25(OH)D2 were 41.1 (17.2), 40.7 (17.3), 2.13 (1.31), and 8.16 (6.52) nmol/L, respectively. Plasma total 25(OH)D and nonepimeric 25(OH)D3 were inversely associated with incident T2D [multivariable-adjusted HR per 1 SD = 0.81 (95% CI, 0.77, 0.86) for both variables], whereas epimeric 25(OH)D3 was positively associated [per 1 SD HR = 1.16 (1.09, 1.25)]. There was no statistically significant association with T2D for 25(OH)D2 [per 1 SD HR = 0.94 (0.76, 1.18)].

CONCLUSIONS

Plasma nonepimeric 25(OH)D3 was inversely associated with incident T2D, consistent with it being the major metabolite contributing to total 25(OH)D. The positive association of the epimeric form of 25(OH)D3 with incident T2D provides novel information to assess the biological relevance of vitamin D epimerization and vitamin D subtypes in diabetes etiology.

25-Hydroxyvitamin D Measurement in Human Hair: Results from a Proof-of-Concept study

Vitamin D deficiency has been implicated in numerous human diseases leading to an increased interest in assessing vitamin D status. Consequentially, the number of requests for vitamin D measurement keeps dramatically increasing year-on-year. Currently, the recognised best marker of vitamin D status is the concentration of the 25-hydroxyvitamin D (25(OH)D₃) in the blood circulation. While providing an accurate estimate of vitamin D status at the point in time of sampling, it cannot account for the high variability of 25(OH)D₃ concentration. In this proof of concept study we set out to provide evidence that 25(OH)D₃ can be extracted from hair samples in a similar fashion to steroid hormones. Two of the authors (L.Z. and M.H.) provided hair samples harvested from the crown area of the scalp and the third author (E.L.) provided beard samples. These samples, cut into 1 cm lengths, were weighed, washed and dried. 25(OH)D was extracted using a previously published steroid hormones extraction procedure. Blood samples were taken from the subjects at the same time all tissue samples were analysed using liquid-chromatography mass spectrometry. Hair samples showed presence of quantifiable 25(OH)D₃ with concentrations ranging from 11.9–911 pg/mg. The beard sample had a concentration of 231 pg/mg. Serum levels of 25(OH)D₃ ranged from 72–78 nmol/L. The results presented here confirm the feasibility of measuring 25(OH)D₃ in hair samples. The findings warrant further validation and development and have the potential to yield valuable information relating to temporal trends in vitamin D physiology.

Vitamin D C3-epimer levels are proportionally higher with oral vitamin D supplementation compared to ultraviolet irradiation of skin in mice but not humans

A proportion of circulating 25-hydroxy vitamin D₃ (25(OH)D₃₎) undergoes epimerization to form C3-epi 25(OH)D₃ and C3-epi 1,25(OH)₂D₃. These epimers have less calcaemic activity than non-epimerized metabolites and are not differentiated by many immunoassays when reporting total 25(OH)D₃ levels. This study aimed to compare the effect of exposure to ultraviolet radiation (UVR) and oral vitamin D₃ supplementation on vitamin D C3-epimer levels. C57Bl/6 female mice were fed either vitamin D-sufficient (vitamin D₃ 2000 IU/kg) or -deficient diets (no vitamin D₃) for 4 weeks. Among the vitamin D-deficient group, the shaved backs of half were irradiated daily for 4 days with 1 kJ/m² UVR, followed by twice weekly irradiation for 4 weeks. Despite similar 25(OH)D₃ levels, the UV-irradiated group had a lower proportion of C3-epi 25(OH)D₃ at week 7 (p < 0.05) and week 9 (p < 0.01). C3-epimer concentrations and %C3-epi 25(OH)D₃ were also analysed in serum samples from two human clinical trials. These trials investigated the effect of high dose oral vitamin D₃ supplementation and narrowband UVB phototherapy, respectively. Serum 25(OH)D₃ and the %C3-epi 25(OH)D₃ levels measured at 12 months after oral vitamin D₃ supplementation were not significantly different to those measured at the time of maximal effect of phototherapy (2 months). Thus, the proportion of 25(OH)D₃ that undergoes epimerization is greater with oral vitamin D₃ supplementation than exposure to UVR in mice, but not in humans. This important difference between human and murine vitamin D metabolism warrants consideration when interpreting animal studies.

Serum Vitamin D Concentrations and Cognitive Change Over 20 Years: The Atherosclerosis Risk in Communities Neurocognitive Study

BACKGROUND/AIMS

25-hydroxyvitamin D (25[OH]D) concentrations have been associated with cognitive decline and incident dementia in elderly populations; however, these relationships are susceptible to reverse causation. Less is known about the association of midlife 25(OH)D with long-term cognitive decline.

METHODS

This was a prospective cohort study of 13,044 participants (mean age 57 years at baseline) in the Atherosclerosis Risk in Communities Study. 25(OH)D was measured from serum collected at baseline (1990-1992) using liquid chromatography tandem high-sensitivity mass spectrometry. Cognition was assessed using 3 neuropsychological tests at 3 time points, which were combined into a composite cognitive Z-score. Multivariable-adjusted linear mixed-effects models with random intercepts and slopes were used to estimate associations between 25(OH)D and cognitive change over 20 years.

RESULTS

Compared to persons with sufficient 25(OH)D (≥30 ng/mL), those with deficient (< 20 ng/mL) and intermediate (20-< 30 ng/mL) 25(OH)D concentrations had similar cognitive decline in composite cognitive Z-scores (deficient versus sufficient: -0.035 [95% CI -0.104 to 0.033] and intermediate versus sufficient: -0.029 [95% CI -0.080 to 0.023]).

CONCLUSIONS

Lower concentrations of 25(OH)D measured in midlife were not significantly associated with more rapid cognitive decline over a 20-year follow-up period. The results of this prospective study are less susceptible to reverse causation than prior studies.

Simultaneous determination of 25-hydroxyvitamin D2 and 25-hydroxyvitamin D3 in human serum by ultra performance liquid chromatography: An economical and validated method with bovine serum albumin

A simple and economical method has been developed for simultaneous determination of human serum 25-hydroxyvitamin D₂ (25OHD₂) and 25-hydroxyvitamin D₃ (25OHD₃) using Ultra Performance Liquid Chromatography (UPLC). Non-human matrix of 4% BSA was used to construct the calibration curve and in quality control samples' preparation to avoid interference of the endogenous 25-hydroxyvitamin D (25OHD) present in the human serum. 25OHD₂, 25OHD₃ and dodecanophenone (internal standard, IS) were separated on a CORTECS solid-core particle column and monitored by photodiode array detector at wavelength of 265 nm within five min run time. The relationship between 25OHD concentration and peak area ratio (25OHD:IS) was linear over the range of 12.5 - 200 nM with mean correlation coefficients (r²) >0.998. The limit of detection (LOD) for 25OHD₂ and 25OHD₃ was 3.00 nM and 3.79 nM, while the lower limit of quantification (LLOQ) was 9.11 nM and 11.48 nM, respectively. High repeatability was obtained for both isomers with intra-day CV% <5.6% and <5.3% for inter-day assay. This method was further tested with a commercial lyophilized serum control with an accuracy of 92.87-108.31% and applied on 214 human serum samples. In summary, this validated method with BSA can be reliably applied for routine quantification of 25OHD in adults.

Markers of vitamin D metabolism and incidence of clinically diagnosed abdominal aortic aneurysm: The Atherosclerosis Risk in Communities Study

Little is known about whether markers of vitamin D metabolism are associated with the development of abdominal aortic aneurysm (AAA), though these markers have been linked to other cardiovascular diseases. We tested the hypotheses that risk of AAA is higher among individuals with low serum concentrations of 25-hydroxy vitamin D [25(OH)D], and among those with elevated concentrations of calcium, fibroblast growth factor 23 (FGF23), phosphorus, and parathyroid hormone (PTH) using data from a cohort of black and white individuals with long-term follow-up. Markers of vitamin D metabolism were measured using serum collected in 1990-1992 from ARIC study participants (mean ± SD age 56.9 ± 5.7 years, 43.2% male, 23.9% black). A total of 12,770 participants were followed until 2011 for incident AAA. Multivariable-adjusted Cox regression models were used. A total of 449 incident AAA events occurred over a median follow-up of 19.7 years. For the association between serum calcium and risk of incident AAA there was evidence of interaction by sex ( p-interaction 0.02). Among women, in the fully adjusted model, the hazard ratio (95% confidence interval) comparing the highest to lowest quartile was 2.43 (1.25-4.73), whereas in men it was 1.01 (0.72-1.43). Not associated with risk of incident AAA were 25(OH)D, FGF23, phosphorus, and PTH. In this large prospective cohort, there was little evidence that markers of vitamin D metabolism are associated with risk of incident AAA. The positive association of calcium with AAA among women may warrant further investigation and replication in other populations.

Measurement of Vitamin D for Epidemiologic and Clinical Research: Shining Light on a Complex Decision

Vitamin D is a fat-soluble vitamin that is synthesized in the skin with exposure to sunlight or is ingested from dietary supplements or food. There has been a dramatic increase in research on vitamin D, linking it with health outcomes as varied as reproductive function, infection, cardiovascular disease, and cancer. The study of vitamin D has generated much excitement, partly because there is an ideal intervention: Low levels may be common and can be remedied with widely available supplements. Determination of vitamin D status is complex and has advanced dramatically in the past 5 years. In this paper, we begin by describing important considerations for measurement of total 25-hydroxyvitamin D (25(OH)D), the biomarker traditionally assessed in epidemiologic studies. While 25(OH)D remains the most commonly measured biomarker, emerging evidence suggests that other related analytes may contribute to the characterization of an individual's vitamin D status (e.g., vitamin D-binding protein, bioavailable and free 25(OH)D, the C-3 epimer of 25(OH)D, 1,25-dihydroxyvitamin D, and 24,25-dihydroxyvitamin D). The measurement of these analytes is also complex, and there are important considerations for deciding whether their measurement is warranted in new research studies. Herein we discuss these issues and provide the reader with an up-to-date synthesis of research on vitamin D measurement options and considerations.

Investigation of the C-3-epi-25(OH)D3 of 25-hydroxyvitamin D3 in urban schoolchildren

The physiological relevance C-3 epimer of 25-hydroxyvitamin D (3-epi-25(OH)D) is not well understood among youth. The objective of this study was to assess whether demographic/physiologic characteristics were associated with 3-epi-25(OH)D3 concentrations in youth. Associations between 3-epi-25(OH)D3 and demographics and between 3-epi-25(OH)D3, total 25-hydroxyvitamin (25(OH)D) (25(OH)D2 + 25(OH)D3), total cholesterol, high-density lipoprotein, low-density lipoprotein, and triglycerides were examined in racially/ethnically diverse schoolchildren (n = 682; age, 8-15 years) at Boston-area urban schools. Approximately 50% of participants had detectable 3-epi-25(OH)D3 (range 0.95-3.95 ng/mL). The percentage of 3-epi-25(OH)D3 of total 25(OH)D ranged from 2.5% to 17.0% (median 5.5%). Males were 38% more likely than females to have detectable 3-epi-25(OH)D3 concentrations. Both Asian and black race/ethnicity were associated with lower odds of having detectable 3-epi-25(OH)D3 compared with non-Hispanic white children (Asian vs. white, odds ratio (OR) 0.28, 95% confidence interval (CI) 0.14-0.53; black vs. white, OR 0.38, 95%CI 0.23-0.63, p < 0.001). Having an adequate (20-29 ng/mL) or optimal (>30 ng/mL) 25(OH)D concentration was associated with higher odds of having detectable 3-epi-25(OH)D3 than having an inadequate (<20 ng/mL) concentration (OR 4.78, 95%CI 3.23-6.94 or OR 14.10, 95%CI 7.10-28.0, respectively). There was no association between 3-epi-25(OH)D3 and blood lipids. However, when considering 3-epi-25(OH)D3 as a percentage of total 25(OH)D, total cholesterol was lower in children with percent 3-epi-25(OH)D3 above the median (mean difference -7.1 mg/dL, p = 0.01). In conclusion, among schoolchildren, sex, race/ethnicity, and total serum 25(OH)D concentration is differentially associated with 3-epi-25(OH)D. The physiological relevance of 3-epi-25(OH)D3 may be related to the 3-epi-25(OH)D3 as a percentage of total 25(OH)D and should be considered in future investigations.

Biomarkers of Mineral and Bone Metabolism and 20-Year Risk of Hospitalization With Infection: The Atherosclerosis Risk in Communities Study

CONTEXT

Mineral and bone disorders (MBDs) might be relevant in the etiology of infection.

OBJECTIVE

To determine whether MBD biomarkers were associated with the incidence of hospitalization with infection. We also assessed the cross-sectional association between MBD biomarker levels and kidney function.

DESIGN, SETTING, PARTICIPANTS

Community-based cohort study of 11,218 participants with an estimated glomerular filtration rate (eGFR) ≥30 mL/min/1.73m2 in the Atherosclerosis Risk in Communities study. We assessed the cross-sectional associations of five MBD markers-fibroblast growth factor 23 (FGF23), 25-hydroxyvitamin D [25(OH)D], parathyroid hormone (PTH), calcium corrected for hypoalbuminemia, and phosphorus-with eGFR from 1990 to 1992 and their longitudinal associations with incident hospitalization with infection in 1990 to 2013.

MAIN OUTCOME

Incident hospitalization with infection.

RESULTS

In age-, sex-, and race-adjusted models, lower eGFRs were significantly associated with greater levels of FGF23, PTH, and corrected calcium but not 25(OH)D or phosphorus. During follow-up, 5078 hospitalizations with infection occurred. In fully adjusted Cox models, with the second quartile as the reference, the hazard ratio (HR) was significantly greater in the highest quartile of FGF23 [HR, 1.12; 95% confidence interval (CI), 1.03 to 1.21], PTH (HR, 1.09; 95% CI, 1.01 to 1.18), and corrected calcium (HR, 1.11; 95% CI, 1.03 to 1.20), and lowest quartile for 25(OH)D (HR, 1.11; 95% CI, 1.03 to 1.21). The association with phosphorus was significant only when the outcome was restricted to primary diagnosis of infection. These findings were consistent across subgroups of age, sex, race, and eGFR (<60 vs ≥60 mL/min/1.73 m2).

CONCLUSIONS

MBD biomarkers were associated with eGFR and the subsequent risk of infection, supporting MBD involvement in the etiology of infection.

Impact of a single oral dose of 100,000 IU vitamin D3 on profiles of serum 25(OH)D3 and its metabolites 24,25(OH)2D3, 3-epi-25(OH)D3, and 1,25(OH)2D3 in adults with vitamin D insufficiency

BACKGROUND

We investigate the effect of a high dose of vitamin D3 on circulating concentrations of 25(OH)D3 and its metabolites 24,25(OH)2D3, 3-epi-25(OH)D3, and 1,25(OH)2D3 in healthy individuals with self-perceived fatigue and vitamin D insufficiency [25(OH)D3<50 nmol/L].

METHODS

One hundred and seven study participants (age 20-50 years) were randomized to receive a single 100,000 IU dose of vitamin D3 (n=52) or placebo (n=55). Vitamin D metabolite concentrations in serum were measured before, and 4 weeks after, supplementation.

RESULTS

Overall, 52% of participants receiving vitamin D3 attained a serum 25(OH)D3 level >75 nmol/L. Among individuals who received vitamin D3, there were significant increases in serum concentrations of 25(OH)D3 and its metabolites 24,25(OH)2D3, 3-epi-25(OH)D3, and 1,25(OH)2D3 at 4 weeks; however, inter-individual variability in these changes was substantial. Positive correlations between serum 25(OH)D3 and 24,25(OH)2D3 and 3-epi-25(OH)D3, and a significant negative correlation between serum 1,25(OH)2D3 and 3-epi-25(OH)D3, were found 4 weeks after supplementation. The 24,25(OH)2D3/25(OH)D3 and 24,25(OH)2D3/1,25(OH)2D3 ratios were significantly increased, compared with baseline, in participants receiving vitamin D3. Baseline 25(OH)D3 concentration was the only factor predictive of the change in 25(OH)D3 after supplementation.

CONCLUSIONS

Administration of a single high dose of vitamin D3 leads to a significant increase in concentrations of 25(OH)D3, 24,25(OH)2D3, 3-epi-25(OH)D3 and 1,25(OH)2D3; induction of the catabolic pathway predominates over the production of 1,25(OH)2D3. Due to the high inter-individual variation in the 25(OH)D3 response to supplementation, any given dose of vitamin D is unlikely to achieve optimal vitamin D status in all treated individuals.

Serum 25-hydroxyvitamin D is associated with incident peripheral artery disease among white and black adults in the ARIC study cohort

BACKGROUND AND AIMS

Low 25-hydroxyvitamin D [25(OH)D] concentrations have been associated with peripheral artery disease (PAD). Prevalence of low 25(OH)D and PAD differ between whites and blacks. However, these associations have not been studied prospectively or in a population based cohort. We tested the hypothesis that low 25(OH)D is associated with greater risk of incident PAD in white and black adults.

METHODS

25(OH)D was measured in serum collected at ARIC visit 2 (1990-1992). We followed 11,789 ARIC participants free of PAD at visit 2 through 2011 for incident PAD events. 25(OH)D (ng/mL) was categorized as deficient (<20), insufficient (20 to <30) or sufficient (≥30). PAD was defined by an ankle brachial index (ABI) of <0.9 at ARIC visits 3 or 4 or a hospital diagnosis with an ICD-9 code indicating PAD during follow-up. Analysis used multivariable-adjusted Cox proportional hazards regressions.

RESULTS

Over a mean follow-up of 17.1 years, 1250 incident PAD events were identified. 22% of whites and 61% of blacks were 25(OH)D deficient. After adjustment for demographic characteristics, the hazard ratio (95% CI) of PAD in participants with deficient versus sufficient 25(OH)D was 1.49 (1.26, 1.76). Inclusion of BMI, physical activity, and smoking status attenuated the association [1.25 (1.06, 1.48)]. The association between 25(OH)D and PAD was qualitatively stronger in blacks (p for interaction = 0.20).

CONCLUSIONS

Deficient 25(OH)D was associated with increased risk of PAD in black and white participants. Whether treatment of low vitamin D through supplementation or modest sunlight exposure prevents PAD is unknown.

The Road Not So Travelled: Should Measurement of Vitamin D Epimers during Pregnancy Affect Our Clinical Decisions?

Observational studies suggest an adverse effect of maternal hypovitaminosis D during pregnancy. However, intervention studies failed to show convincing benefit from vitamin D supplementation during pregnancy. With analytical advances, vitamin D can now be measured in ten forms—including as epimers—which were thought to be biologically inactive, but can critically impair immunoassays. The aim of this commentary is to highlight the potential clinical and analytical significance of vitamin D epimers in the interpretation of vitamin D roles in pregnancy. Epimers may contribute a considerable proportion of total vitamin D—especially in the neonate—which renders the majority of common assays questionable. Furthermore, epimers have been suggested to have activity in laboratory studies, and evidence suggests that the fetus contributes significantly to epimer production. Maternal epimer levels contribute significantly to predict neonate circulating 25-hydroxyvitamin D concentrations. In conclusion, the existence of various vitamin D forms (such as epimers) has been established, and their clinical significance remains obscure. These results underscore the need for accurate measurements to appraise vitamin D status, in order to understand the current gap between observational and supplementation studies on the field.

Serum calcium and incident type 2 diabetes: the Atherosclerosis Risk in Communities (ARIC) study

BACKGROUND

Elevated serum calcium has been associated with a variety of metabolic abnormalities and may be associated with a greater risk of diabetes.

OBJECTIVE

The purpose of this study was to test the hypothesis that serum calcium concentration is positively and independently associated with the incidence of diabetes and to evaluate the association of calcium-sensing receptor (CaSR) gene single nucleotide polymorphism (SNP) rs1801725 with incident diabetes.

DESIGN

Atherosclerosis Risk in Communities study participants free of diabetes at baseline (n = 12,800; mean age: 53.9 y; 22.6% black) were studied for incident diabetes. Serum calcium was measured at baseline and corrected for serum albumin. Diabetes was defined by use of glucose concentrations, self-report, or medication use. Cox proportional hazards regression was used.

RESULTS

During a mean 8.8 y of follow-up, 1516 cases of diabetes were reported. Participants in the highest compared with lowest calcium quintile were at greater risk of incident diabetes after adjustment for demographic and lifestyle factors [HR (95% CI): 1.34 (1.14, 1.57); P-trend across quintiles <0.0001] and with further adjustment for waist circumference and body mass index [1.26 (1.07, 1.48); P-trend = 0.004]. Additional adjustment for biomarkers on the metabolic pathway (e.g., 25-hydroxyvitamin D, parathyroid hormone, phosphorus) had little impact. The calcium-diabetes association was statistically significant in blacks [1.48 (1.11, 1.98); P-trend = 0.002] but not whites [1.17 (0.96, 1.43); P-trend = 0.17] after adjustment for adiposity. In whites, CaSR gene SNP rs1801725 was associated with serum calcium but not with risk of diabetes.

CONCLUSIONS

Consistent with 3 previous cohort studies, elevated serum calcium was found to be associated with a greater risk of type 2 diabetes. Further research is needed to understand the role, if any, that calcium plays in the pathogenesis of diabetes.

Short-term Variability of Vitamin D-Related Biomarkers

BACKGROUND

Quantifying the variability of biomarkers is important, as high within-person variability can lead to misclassification of individuals. Short-term variability of important markers of vitamin D metabolism is relatively unknown.

METHODS

A repeatability study was conducted in 160 Atherosclerosis Risk in Communities study participants (60% female, 28% black, mean age 76 years). Fasting serum was drawn at 2 time points, a median of 6 (range 3-13) weeks apart. Vitamin D binding protein (VDBP) and 25-hydroxyvitamin D [25(OH)D] were measured by LC-MS, fibroblast growth factor (FGF23) and parathyroid hormone (PTH) by enzyme-linked immunoassay, and calcium and phosphorus by Roche Cobas 6000. Free and bioavailable 25(OH)D were calculated. We calculated the within-person CV (CV_W), intraclass correlation coefficient (ICC), Spearman rank correlation coefficient (r), and percent reclassified.

RESULTS

The CV_W was lowest for calcium (2.0%), albumin (3.6%), 25(OH)D (6.9%), VDBP (7.0%) and phosphorus (7.6%); intermediate for free 25(OH)D (9.0%) and bioavailable 25(OH)D (9.9%); and highest for PTH (16.7%) and FGF23 (17.8%). Reclassification was highest for PTH, VDBP, and phosphorus (all 7.5%). The ICC and r were highest (≥0.80) for 25(OH)D, free 25(OH)D, bioavailable 25(OH)D and PTH, but somewhat lower (approximately 0.60-0.75) for the other biomarkers.

CONCLUSIONS

Six-week short-term variability, as assessed by CV_W, was quite low for VDBP, calcium and phosphorus, but fairly high for FGF23 and PTH. As such, multiple measurements of FGF23 and PTH may be needed to minimize misclassification. These results provide insight into the extent of potential misclassification of vitamin D markers in research and clinical settings.

Vitamin D supplementation: less controversy, more guidance needed

Vitamin D is a secosteroid hormone with multiple functions that extend beyond the regulation of intestinal calcium absorption. In recent years, the publication of research articles investigating associations between vitamin D status and health has reached an all-time high, and an increase in supplementation studies has followed. Given the pleiotropic effects of vitamin D, the scientific focus has gone beyond its known classic benefits on skeletal health to include diabetes and cardiovascular, neurological, respiratory, renal, and liver diseases, yet numerous conflicting findings continue to emerge. This review presents some examples of recent work within the context of controversies surrounding vitamin D and highlights key factors that should be considered when designing vitamin D supplementation regimens.

National Estimates of Serum Total 25-Hydroxyvitamin D and Metabolite Concentrations Measured by Liquid Chromatography-Tandem Mass Spectrometry in the US Population during 2007-2010

BACKGROUND

The 2007-2010 NHANES provides the first US nationally representative serum 25-hydroxyvitamin D [25(OH)D] concentrations measured by standardized liquid chromatography-tandem mass spectrometry.

OBJECTIVE

We describe patterns for total 25(OH)D and individual metabolites in persons aged ≥1 y stratified by race-ethnicity and grouped by demographic, intake, physiologic, and lifestyle variables.

METHODS

We measured 25-hydroxycholecalciferol [25(OH)D3], 25-hydroxyergocalciferol [25(OH)D2], and C3-epimer of 25(OH)D3 [C3-epi-25(OH)D3] in serum samples (n = 15,652) from the 2007-2010 cross-sectional NHANES [total 25(OH)D = 25(OH)D3 + 25(OH)D2].

RESULTS

Concentrations (median, detection rate) of 25(OH)D3 (63.6 nmol/L, 100%) and C3-epi-25(OH)D3 (3.40 nmol/L, 86%) were generally detectable; 25(OH)D2 was detectable in 19% of the population. Total 25(OH)D, 25(OH)D3, and C3-epi-25(OH)D3 displayed similar demographic patterns and were strongly correlated (Spearman's r > 0.70). Concentrations of 25(OH)D2 (90th percentile) were much higher in persons aged ≥60 y (17.3 nmol/L) than in younger age groups (≤4.88 nmol/L). We noted significant race-ethnicity differences in mean total 25(OH)D [non-Hispanic blacks (NHBs), Hispanics, and non-Hispanic whites (NHWs): 46.6, 57.2, and 75.2 nmol/L, respectively] and in the prevalence of total 25(OH)D <30 nmol/L overall (24% of NHBs, 6.4% of Hispanics, and 2.3% of NHWs) as well as stratified by season (winter months: 30% of NHBs, 7.5% of Hispanics, and 3.8% of NHWs; summer months: 17% of NHBs, 4.4% of Hispanics, and 1.6% of NHWs). Persons with higher vitamin D intakes (diet, supplements, or both) and those examined during May-October had significantly higher total 25(OH)D. Significant race-ethnicity interactions in a multiple linear regression model confirmed the necessity of providing race-ethnicity-specific estimates of total 25(OH)D.

CONCLUSIONS

Race-ethnicity differences in the prevalence of low total 25(OH)D remained strong even after adjustment for season to account for the NHANES design imbalance between season, latitude, and race-ethnicity. The strong correlation between C3-epi-25(OH)D3 and 25(OH)D3 may be because the epimer is a metabolite of 25(OH)D3. The presence of 25(OH)D2 mainly in older persons is likely a result of high-dose prescription vitamin D2.

Serum 25-hydroxyvitamin D concentrations in Mid-adulthood and Parkinson's disease risk

BACKGROUND

Low vitamin D levels are common among patients with Parkinson's disease (PD). Experimental evidence further suggests that vitamin D may be protective against PD. The objective of this study was to prospectively assess the association between serum 25-hydroxyvitamin D and PD among 12,762 participants of the Atherosclerosis Risk in Communities Study cohort.

METHODS

Serum samples were collected in 1990-1992, and 25-hydroxyvitamin D was measured by liquid chromatography mass spectrometry. A total of 67 incident PD cases were identified through December 31, 2008. The median length of follow-up was 17 years. We used Cox proportional hazards models to obtain hazard ratios and 95% confidence intervals, adjusting for age, sex, and race. We did not find any association between serum 25-hydroxyvitamin D concentrations and PD risk, regardless of how serum 25-hydroxyvitamin D was modeled. Compared with participants with serum 25-hydroxyvitamin D < 20 ng/mL, the hazards ratio for PD was 1.05 (95% confidence interval, 0.58-1.90) for 20-30 ng/mL and 1.14 (95% confidence interval, 0.59- 2.23) for ≥30 ng/mL. Similar results were obtained in sensitivity analyses that included white participants only and that were stratified by the length of follow-up.

CONCLUSION

This prospective study lends no support to the hypothesis that vitamin D may reduce the risk of PD. © 2016 International Parkinson and Movement Disorder Society.

Dynamics of Vitamin D Metabolism in Maternal-Fetal Dyads

OBJECTIVES

Metabolites of vitamin D in maternal-neonatal dyads remain relatively unexplored. The goal of this study was to evaluate concentrations of 25(OH)D3, 24,25(OH)2D3, and 3-epi-25(OH)D3 in maternal-infant pairs at delivery.

METHODS

Serum samples of maternal and infant cord blood were collected on 131 mother-infant pairs at delivery. Vitamin D metabolites were analyzed in triplicate using liquid chromatography-tandem mass spectrometry. Statistical analysis was conducted using the Fisher exact test, Wilcoxon rank sum test, and Spearman correlation coefficients.

RESULTS

Mean 25(OH)D3 concentrations in maternal and cord blood were 32.9 and 18.5 ng/mL, respectively; mean maternal and cord 24,25(OH)2D3 were 2.0 versus 1.1 ng/mL, respectively. Absolute concentrations of 3-epi-25(OH)D3 were similar in maternal and cord samples (2.4 vs 2.2 ng/mL), whereas the proportion of the total 25(OH)D as the 3-epimer was 6.5% in maternal samples and 10.5% in cord samples. This suggests that the fetus contributes significantly to 3-epi-25(OH)D3 production. In contrast, the ratio of 25(OH)D3:24,25(OH)2D3 was identical in maternal and cord samples (18.5) suggesting equivalent CYP24A1 activity in mother and fetus. Maternal and cord metabolite levels were highly correlated (r = 0.78, 0.90, 0.89 for 25(OH)D3, 24,25(OH)2D3, and 3-epi-25(OH)D3, respectively, P = 0.001 for all). Serum concentrations of all metabolites were lower in nonwhite infants compared with white infants. Maternal and cord concentrations of 25(OH)D3 were positively associated with birth weight (r = 0.21, P = 0.02; r = 0.25, P = 0.003, respectively).

CONCLUSIONS

This data suggests that although maternal and cord concentrations of vitamin D metabolites are highly correlated, regulation of specific vitamin D metabolites in the mother and the neonate may be mediated independently.

High throughput LC-MS/MS method for the simultaneous analysis of multiple vitamin D analytes in serum

Recent studies suggest that vitamin D-deficiency is linked to increased risk of common human health problems. To define vitamin D 'status' most routine analytical methods quantify one particular vitamin D metabolite, 25-hydroxyvitamin D3 (25OHD3). However, vitamin D is characterized by complex metabolic pathways, and simultaneous measurement of multiple vitamin D metabolites may provide a more accurate interpretation of vitamin D status. To address this we developed a high-throughput liquid chromatography-tandem mass spectrometry (LC-MS/MS) method to analyse multiple vitamin D analytes, with particular emphasis on the separation of epimer metabolites. A supportive liquid-liquid extraction (SLE) and LC-MS/MS method was developed to quantify 10 vitamin D metabolites as well as separation of an interfering 7α-hydroxy-4-cholesten-3-one (7αC4) isobar (precursor of bile acid), and validated by analysis of human serum samples. In a cohort of 116 healthy subjects, circulating concentrations of 25-hydroxyvitamin D3 (25OHD3), 3-epi-25-hydroxyvitamin D3 (3-epi-25OHD3), 24,25-dihydroxyvitamin D3 (24R,25(OH)2D3), 1,25-dihydroxyvitamin D3 (1α,25(OH)2D3), and 25-hydroxyvitamin D2 (25OHD2) were quantifiable using 220μL of serum, with 25OHD3 and 24R,25(OH)2D3 showing significant seasonal variations. This high-throughput LC-MS/MS method provides a novel strategy for assessing the impact of vitamin D on human health and disease.

Factors Associated With Change in 25-Hydroxyvitamin D Levels Over Longitudinal Follow-Up in the ARIC Study

CONTEXT

A single measurement of 25-hydroxyvitamin D (25 [OH] D) may not accurately reflect long-term vitamin D status. Little is known about change in 25(OH)D levels over time, particularly among blacks.

OBJECTIVE

The objective of the study was to determine the longitudinal changes in 25(OH)D levels among Atherosclerosis Risk in Communities (ARIC) study participants.

DESIGN

This was a longitudinal study.

SETTING

The study was conducted in the general community.

PARTICIPANTS

A total of 9890 white and 3222 black participants at visit 2 (1990-1992), 888 whites and 876 blacks at visit 3 (1993-1994), and 472 blacks at the brain visit (2004-2006) participated in the study.

MAIN OUTCOME MEASURE

The 25(OH)D levels were measured, and regression models were used to assess the associations between clinical factors and longitudinal changes in 25(OH)D.

RESULTS

Vitamin D deficiency (<50 nmol/L [<20 ng/mL]) was seen in 23% and 25% of whites at visits 2 and 3, and in 61%, 70%, and 47% of blacks at visits 2, 3, and the brain visit, respectively. The 25(OH)D levels were correlated between visits 2 and 3 (3 y interval) among whites (r = 0.73) and blacks (r = 0.66). Among blacks, the correlation between visit 2 and the brain visit (14 y interval) was 0.33. Overall, increases in 25(OH)D levels over time was associated with male gender, use of vitamin D supplements, greater physical activity, and higher high-density lipoprotein-cholesterol (P < .001). Decreases in 25(OH)D levels over time were associated with current smoking, higher body mass index, higher education, diabetes, and hypertension (all P < .05).

CONCLUSIONS

Among US blacks and whites, 25(OH)D levels remained relatively stable over time. Certain modifiable lifestyle factors were associated with change in 25(OH)D levels over time.

Biomarkers of Vitamin D Status and Risk of ESRD

BACKGROUND

Disordered mineral metabolism is characteristic of decreased kidney function. However, the prospective associations between circulating levels of vitamin D binding protein, vitamin D, and end-stage renal disease (ESRD) have not been extensively evaluated in epidemiologic studies.

STUDY DESIGN

Nested case-control study.

SETTING & PARTICIPANTS

Middle-aged black and white men and women from 4 US communities.

PREDICTORS

Baseline levels of vitamin D binding protein, 25-hydroxyvitamin D (25[OH]D), and 1,25-dihydroxyvitamin D (1,25[OH]2D) were measured in blood samples collected at study visit 4 (1996-1998) of the ARIC (Atherosclerosis Risk in Communities) Study.

OUTCOME

ESRD cases (n=184) were identified through hospitalization diagnostic codes from 1996 to 2008 and were frequency matched to controls (n=251) on categories of estimated glomerular filtration rate, albuminuria, diabetes mellitus, sex, and race.

MEASUREMENTS

Logistic regression was used to estimate the association between mineral metabolism biomarkers (vitamin D binding protein, 25(OH)D, and 1,25(OH)2D) and incident ESRD, adjusting for age, sex, race, estimated glomerular filtration rate, albuminuria, diabetes mellitus, hypertension, education, specimen type, and serum levels of calcium, phosphate, and parathyroid hormone.

RESULTS

Higher vitamin D binding protein levels were associated with elevated risk for incident ESRD (OR, 1.76; 95% CI, 1.22-2.54; P=0.003). Higher free and bioavailable 25(OH)D levels were associated with reduced risk for incident ESRD (ORs of 0.65 [95% CI, 0.46-0.92; P=0.02] and 0.63 [95% CI, 0.43-0.91; P=0.02] for free and bioavailable 25[OH]D, respectively). There was no association between ESRD and overall levels of 25(OH)D (OR, 0.83; 95% CI, 0.58-1.19; P=0.3) or 1,25(OH)2D (OR, 0.73; 95% CI, 0.48-1.13; P=0.2).

LIMITATIONS

Lack of direct measurement of free and bioavailable vitamin D.

CONCLUSIONS

In the general population, blood levels of vitamin D binding protein were positively associated and blood levels of free and bioavailable 25(OH)D were inversely associated with new-onset ESRD during follow-up.