Towards harmonization of directly measured free 25-hydroxyvitamin D using an enzyme-linked immunosorbent assay.

The majority of circulating 25-hydroxyvitamin D (25(OH)D) is protein bound and perhaps less available than the free fraction of 25(OH)D; therefore, researchers have proposed that the measurement of free 25(OH)D in human serum may be a better indicator of vitamin D health status than total 25(OH)D. The availability of a new enzyme-linked immunosorbent assay (ELISA) for the determination of free 25(OH)D provides a method for direct measurement of the low levels of non-protein bound 25(OH)D. As an initial step towards harmonization of measurements of free 25(OH)D, the ELISA was used to measure free 25(OH)D in three existing Standard Reference Materials (SRMs): SRM 972a Vitamin D Metabolites in Frozen Human Serum, SRM 2973 Vitamin D Metabolites in Frozen Human Serum (High Level), and SRM 1949 Frozen Prenatal Human Serum. Target values for free 25(OH)D in the nine SRM serum pools, obtained by combining the results from two laboratories, ranged from 3.76 ± 0.36 to 10.0 ± 0.58 pg/mL. Of particular significance is the assignment of free 25(OH)D target values to SRM 1949, which consists of four serum pools from non-pregnant female donors of reproductive age and pregnant women in each of the three trimesters and which also has values assigned for vitamin D binding protein, which increases during pregnancy. The availability of target values for free 25(OH)D in these SRMs will allow researchers to validate new analytical methods and to compare their results with other researchers as an initial step towards harmonization of measurements among different studies and laboratories.

Interlaboratory comparison of 25-hydroxyvitamin D assays: Vitamin D Standardization Program (VDSP) Intercomparison Study 2 - Part 1 liquid chromatography - tandem mass spectrometry (LC-MS/MS) assays - impact of 3-epi-25-hydroxyvitamin D3 on assay performance.

An interlaboratory comparison study was conducted by the Vitamin D Standardization Program (VDSP) to assess the performance of liquid chromatography - tandem mass spectrometry (LC-MS/MS) assays used for the determination of serum total 25-hydroxyvitamin D (25(OH)D), which is the sum of 25-hydroxyvitamin D2 (25(OH)D2) and 25-hydroxyvitamin D3 (25(OH)D3). A set of 50 single-donor samples was assigned target values for concentrations of 25(OH)D2, 25(OH)D3, 3-epi-25-hydroxyvitamin D3 (3-epi-25(OH)D3), and 24R,25-dihydroxyvitamin D3 (24R,25(OH)2D3) using isotope dilution liquid chromatography - tandem mass spectrometry (ID LC-MS/MS). VDSP Intercomparison Study 2 Part 1 includes results from 14 laboratories using 14 custom LC-MS/MS assays. Assay performance was evaluated using mean % bias compared to the assigned target values and using linear regression analysis of the test assay mean results and the target values. Only 53% of the LC-MS/MS assays met the VDSP criterion of mean % bias ≤ |±5%|. For the LC-MS/MS assays not meeting the ≤ |±5%| criterion, four assays had mean % bias of between 12 and 21%. Based on multivariable regression analysis using the concentrations of the four individual vitamin D metabolites in the 50 single-donor samples, the performance of several LC-MS/MS assays was found to be influenced by the presence of 3-epi-25(OH)D3. The results of this interlaboratory study represent the most comprehensive comparison of LC-MS/MS assay performance for serum total 25(OH)D and document the significant impact of the lack of separation of 3-epi-25(OH)D3 and 25(OH)D3 on assay performance, particularly with regard to mean % bias.

Interlaboratory comparison of 25-hydroxyvitamin D assays: Vitamin D Standardization Program (VDSP) Intercomparison Study 2 - Part 2 ligand binding assays - impact of 25-hydroxyvitamin D2 and 24R,25-dihydroxyvitamin D3 on assay performance.

An interlaboratory comparison study was conducted by the Vitamin D Standardization Program (VDSP) to assess the performance of ligand binding assays (Part 2) for the determination of serum total 25-hydroxyvitamin D [25(OH)D]. Fifty single-donor samples were assigned target values for concentrations of 25-hydroxyvitamin D2 [25(OH)D2], 25-hydroxyvitamin D3 [25(OH)D3], 3-epi-25-hydroxyvitamin D3 [3-epi-25(OH)D3], and 24R,25-dihydroxyvitamin D3 [24R,25(OH)2D3] using isotope dilution liquid chromatography-tandem mass spectrometry (ID LC-MS/MS). VDSP Intercomparison Study 2 Part 2 includes results from 17 laboratories using 32 ligand binding assays. Assay performance was evaluated using mean % bias compared to the assigned target values and using linear regression analysis of the test assay mean results and the target values. Only 50% of the ligand binding assays achieved the VDSP criterion of mean % bias ≤ |± 5%|. For the 13 unique ligand binding assays evaluated in this study, only 4 assays were consistently within ± 5% mean bias and 4 assays were consistently outside ± 5% mean bias regardless of the laboratory performing the assay. Based on multivariable regression analysis using the concentrations of individual vitamin D metabolites in the 50 single-donor samples, most assays underestimate 25(OH)D2 and several assays (Abbott, bioMérieux, DiaSorin, IDS-EIA, and IDS-iSYS) may have cross-reactivity from 24R,25(OH)2D3. The results of this interlaboratory study represent the most comprehensive comparison of 25(OH)D ligand binding assays published to date and is the only study to assess the impact of 24R,25(OH)2D3 content using results from a reference measurement procedure.

Assessment of serum total 25-hydroxyvitamin D assays for Vitamin D External Quality Assessment Scheme (DEQAS) materials distributed at ambient and frozen conditions.

The Vitamin D External Quality Assessment Scheme (DEQAS) distributes human serum samples four times per year to over 1000 participants worldwide for the determination of total serum 25-hydroxyvitamin D [25(OH)D)]. These samples are stored at -40 °C prior to distribution and the participants are instructed to store the samples frozen at -20 °C or lower after receipt; however, the samples are shipped to participants at ambient conditions (i.e., no temperature control). To address the question of whether shipment at ambient conditions is sufficient for reliable performance of various 25(OH)D assays, the equivalence of DEQAS human serum samples shipped under frozen and ambient conditions was assessed. As part of a Vitamin D Standardization Program (VDSP) commutability study, two sets of the same nine DEQAS samples were shipped to participants at ambient temperature and frozen on dry ice. Twenty-eight laboratories participated in this study and provided 34 sets of results for the measurement of 25(OH)D using 20 ligand binding assays and 14 liquid chromatography-tandem mass spectrometry (LC-MS/MS) methods. Equivalence of the assay response for the frozen versus ambient DEQAS samples for each assay was evaluated using multi-level modeling, paired t-tests including a false discovery rate (FDR) approach, and ordinary least squares linear regression analysis of frozen versus ambient results. Using the paired t-test and confirmed by FDR testing, differences in the results for the ambient and frozen samples were found to be statistically significant at p < 0.05 for four assays (DiaSorin, DIAsource, Siemens, and SNIBE prototype). For all 14 LC-MS/MS assays, the differences in the results for the ambient- and frozen-shipped samples were not found to be significant at p < 0.05 indicating that these analytes were stable during shipment at ambient conditions. Even though assay results have been shown to vary considerably among different 25(OH)D assays in other studies, the results of this study also indicate that sample handling/transport conditions may influence 25(OH)D assay response for several assays.

Adjusting Coronavirus Prevalence Estimates for Laboratory Test Kit Error.

Testing representative populations to determine the prevalence or the percentage of the population with active severe acute respiratory syndrome coronavirus 2 infection and/or antibodies to infection is being recommended as essential for making public policy decisions to ease restrictions or to continue enforcing national, state, and local government rules to shelter in place. However, all laboratory tests are imperfect and have estimates of sensitivity and specificity less than 100%-in some cases, considerably less than 100%. That error will lead to biased prevalence estimates. If the true prevalence is low, possibly in the range of 1%-5%, then testing error will lead to a constant background of bias that most likely will be larger, and possibly much larger, than the true prevalence itself. As a result, what is needed is a method for adjusting prevalence estimates for testing error. Methods are outlined in this article for adjusting prevalence estimates for testing error both prospectively in studies being planned and retrospectively in studies that have been conducted. If used, these methods also would help harmonize study results within countries and worldwide. Adjustment can lead to more accurate prevalence estimates and to better policy decisions. However, adjustment will not improve the accuracy of an individual test.

Assessment of serum total 25-hydroxyvitamin D assay commutability of Standard Reference Materials and College of American Pathologists Accuracy-Based Vitamin D (ABVD) Scheme and Vitamin D External Quality Assessment Scheme (DEQAS) materials: Vitamin D Standardization Program (VDSP) Commutability Study 2.

An interlaboratory study was conducted through the Vitamin D Standardization Program (VDSP) to assess commutability of Standard Reference Materials® (SRMs) and proficiency testing/external quality assessment (PT/EQA) samples for determination of serum total 25-hydroxyvitamin D [25(OH)D] using ligand binding assays and liquid chromatography-tandem mass spectrometry (LC-MS/MS). A set of 50 single-donor serum samples were assigned target values for 25-hydroxyvitamin D2 [25(OH)D2] and 25-hydroxyvitamin D3 [25(OH)D3] using reference measurement procedures (RMPs). SRM and PT/EQA samples evaluated included SRM 972a (four levels), SRM 2973, six College of American Pathologists (CAP) Accuracy-Based Vitamin D (ABVD) samples, and nine Vitamin D External Quality Assessment Scheme (DEQAS) samples. Results were received from 28 different laboratories using 20 ligand binding assays and 14 LC-MS/MS methods. Using the test assay results for total serum 25(OH)D (i.e., the sum of 25(OH)D2 and 25(OH)D3) determined for the single-donor samples and the RMP target values, the linear regression and 95% prediction intervals (PIs) were calculated. Using a subset of 42 samples that had concentrations of 25(OH)D2 below 30 nmol/L, one or more of the SRM and PT/EQA samples with high concentrations of 25(OH)D2 were deemed non-commutable using 5 of 11 unique ligand binding assays. SRM 972a (level 4), which has high exogenous concentration of 3-epi-25(OH)D3, was deemed non-commutable for 50% of the LC-MS/MS assays.

Prevalence and Determinants of QuantiFERON-Diagnosed Tuberculosis Infection in 9810 Mongolian Schoolchildren.

BACKGROUND: There is controversy regarding the potential influence of vitamin D deficiency, exposure to environmental tobacco smoke, BCG vaccination, season, and body habitus on susceptibility to Mycobacterium tuberculosis (MTB) infection. METHODS: We conducted a cross-sectional analysis to identify determinants of a positive QuantiFERON-TB Gold (QFT) assay result in children aged 6-13 years attending 18 schools in Ulaanbaatar, Mongolia. Data relating to potential risk factors for MTB infection were collected by questionnaire, physical examination, and determination of serum 25-hydroxyvitamin D (25[OH]D) concentrations. Risk ratios (RRs) were calculated with adjustment for potential confounders, and population attributable fractions (PAFs) were calculated for modifiable risk factors identified. RESULTS: Nine hundred forty-six of 9810 (9.6%) participants had a positive QFT result. QFT positivity was independently associated with household exposure to pulmonary tuberculosis (adjusted RR [aRR], 4.75 [95% confidence interval {CI}, 4.13-5.46, P < .001]; PAF, 13.1% [95% CI, 11.1%-15.0%]), vitamin D deficiency (aRR, 1.23 [95% CI, 1.08-1.40], P = .002; PAF, 5.7% [95% CI, 1.9%-9.3%]), exposure to environmental tobacco smoke (1 indoor smoker, aRR, 1.19 [95% CI, 1.04-1.35]; ≥2 indoor smokers, aRR, 1.30 [95% CI, 1.02-1.64]; P for trend = .006; PAF, 7.2% [95% CI, 2.2%-12.0%]), and increasing age (aRR per additional year, 1.14 [95% CI, 1.10-1.19], P < .001). No statistically significant independent association was seen for presence of a BCG scar, season of sampling, or body mass index. CONCLUSIONS: Vitamin D deficiency and exposure to environmental tobacco smoke are potentially modifiable risk factors for MTB infection.

Vitamin D assays and the definition of hypovitaminosis D: results from the First International Conference on Controversies in Vitamin D.

The First International Conference on Controversies in Vitamin D was held in Pisa, Italy, 14-16 June 2017. The meeting's purpose was to address controversies in vitamin D research, review the data available, to help resolve them, and suggest a research agenda to clarify areas of uncertainty. The serum 25-hydroxyvitamin D [25(OH)D] concentration [i.e. the sum of 25(OH)D3 and 25(OH)D2 ] remains the critical measurement for defining vitamin D status. Assay variation for 25(OH)D has contributed to the current chaos surrounding efforts to define hypovitaminosis D. An essential requirement to develop a consensus on vitamin D status is that measurement of 25(OH)D and, in the future, other potential vitamin D biomarkers [e.g. 1α,25(OH)2 D3 , 3-epi-25(OH)D, 24,25(OH)2 D3, vitamin D-binding protein, free/bioavailable 25(OH)D and parathyroid hormone] be standardized/harmonized, to allow pooling of research data. Vitamin D Standardization Program tools are described and recommended for standardizing 25(OH)D measurement in research. In the future, similar methodology, based on National Institute for Standards and Technology standard reference materials, must be developed for other candidate markers of vitamin D status. Failure to standardize/harmonize vitamin D metabolite measurements is destined to promulgate continued chaos. At this time, 25(OH)D values below 12 ng ml-1 (30 nmol l-1 ) should be considered to be associated with an increased risk of rickets/osteomalacia, whereas 25(OH)D concentrations between 20 ng ml-1 and 50 ng ml-1 (50-125 nmol l-1 ) appear to be safe and sufficient in the general population for skeletal health. In an effort to bridge knowledge gaps in defining hypovitaminosis D, an international study on rickets as a multifactorial disease is proposed.

Implications of standardization of serum 25-hydroxyvitamin D data for the evaluation of vitamin D status in Germany, including a temporal analysis.

BACKGROUND: Comparability of 25-hydroxyvitamin D (25(OH)D) measurements is hampered by method-related differences in measurement values. International standardization of laboratory assays has been suggested to solve this problem. METHODS: As part of the European Commission-funded project 'Food-based solutions for optimal vitamin D nutrition and health through the life cycle' (ODIN), original measurements of serum 25(OH)D of three German national health surveys conducted between 1998 and 2011 have been standardized retrospectively. In these representative population-based samples including persons aged between 1 and 79 years, the original 25(OH)D values were compared with those after standardization. Mean values and prevalences of vitamin D deficiency, insufficiency, and sufficiency (25(OH)D levels < 30, 30- < 50, and > =50 nmol/l, respectively) were calculated by sex and age groups based on original and standardized 25(OH)D data. RESULTS: In comparison to the original 25(OH)D levels, the standardized levels showed higher means overall and in age- and sex-specific analyses. After standardization, the prevalence of vitamin D deficiency was lower in all surveys while the prevalence of vitamin D sufficiency was higher. Nevertheless, even after standardization ~ 15% of adults and 12.5% of children had serum 25(OH)D levels < 30 nmol/l. Thus, the proportion of deficient vitamin D levels in the German population is still considerable. CONCLUSIONS: The use of standardization of 25(OH)D levels has a substantial impact on estimates of the vitamin D status in Germany. Since clinical diagnostic, therapeutic and public health decision-making require valid and comparable data, standardization and calibration of commercial, clinical and research laboratory assays for 25(OH)D measurement should become common practice. Until then, researchers, health practitioners and policy makers should be aware of the peculiarities of the measurement methods when comparing and interpreting 25(OH)D levels.

The Reverse J-Shaped Association Between Serum Total 25-Hydroxyvitamin D Concentration and All-Cause Mortality: The Impact of Assay Standardization.

We evaluated the impact of standardizing the originally measured serum total 25-hydroxyvitamin D (25(OH)D) values from Third National Health and Nutrition Examination Survey (NHANES III, 1988-1994) on the association between 25(OH)D and rate of all-cause mortality. Values were standardized to the gold-standard laboratory method. Follow-up from 1990-2006 consisted of 15,099 participants aged at least 20 years at baseline, among whom there were 3,784 deaths. Relative risk of death was adjusted for age, sex, race/ethnicity, and season using Poisson regression. Results were obtained for eight 25(OH)D (nmol/L) categories: <20 nmol/L, 20-29 nmol/L, 30-39 nmol/L, 40-49 nmol/L, 50-59 nmol/L, 60-74 nmol/L, 75-99 nmol/L (reference), and ≥100 nmol/L. Assay standardization dramatically shifted original 25(OH)D values toward zero. Accordingly, risk ≥120 nmol/L could not be evaluated (i.e., n = 7 and ndeaths = 2). Relative risk (95% confidence interval (CI)) <40 nmol/L remained significant (30-39 nmol/L: relative risk (RR) = 1.4 (95% CI: 1.1, 1.6); 20-29 nmol/L: RR = 1.6 (95% CI: 1.3, 1.9), and <20 nmol/L: RR = 2.1 (95% CI: 1.6, 2.7). However, adjusted relative risk estimates for 25(OH)D levels ≥40 nmol/L were no longer significant (40-49 nmol/L: RR = 1.2 (95% CI: 0.99, 1.4); 50-59 nmol/L: RR = 1.2 (95% CI: 1.04, 1.4); 60-74 nmol/L: RR = 1.1 (95% CI: 0.94, 1.2); 75-99 nmol/L: RR = 1.0 (referent), and ≥100 nmol/L: RR = 1.1 (95% CI: 0.6, 2.1). In summary, after standardization, risk of death from all causes increased with decreasing 25(OH)D <40 nmol/L, while there was no association with values in categories between 40 nmol/L and 120 nmol/L.

Development of an Improved Standard Reference Material for Vitamin D Metabolites in Human Serum.

The National Institute of Standards and Technology (NIST) has developed Standard Reference Material (SRM) 972a Vitamin D Metabolites in Frozen Human Serum as a replacement for SRM 972, which is no longer available. SRM 972a was developed in collaboration with the National Institutes of Health's Office of Dietary Supplements. In contrast to the previous reference material, three of the four levels of SRM 972a are composed of unmodified human serum. This SRM has certified and reference values for the following 25-hydroxyvitamin D [25(OH)D] species: 25(OH)D2, 25(OH)D3, and 3-epi-25(OH)D3. The value assignment and certification process included three isotope-dilution mass spectrometry approaches, with measurements performed at NIST and at the Centers for Disease Control and Prevention (CDC). The value assignment methods employed have been modified from those utilized for the previous SRM, and all three approaches now incorporate chromatographic resolution of the stereoisomers, 25(OH)D3 and 3-epi-25(OH)D3.

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.

Significance of serum 24,25-dihydroxyvitamin D in the assessment of vitamin D status: a double-edged sword?

BACKGROUND: 24,25-Dihydroxyvitamin D [24,25(OH)2D] in serum may be both a nuisance and nutritionally valuable. METHODS: We investigated the impact of 24,25(OH)2D3 on the performance of commercially available immunoassays for serum total 25-hydroxyvitamin D [25(OH)D] using (a) serum from a nationally representative sample of adults, (b) serum from a spiking experiment, and (c) data from the UK Vitamin D External Quality Assurance Scheme (DEQAS). We also investigated the utility of the serum ratio of 24,25(OH)2D3 to 25(OH)D as an index of inactivation and of response to vitamin D supplementation using randomized controlled trial (RCT) data. Measurement of 24,25(OH)2D in sera by a LC-MS/MS method allowed for an investigation of its impact on immunoassay-derived serum 25(OH)D values as well as its clinical utility. We report data from a nationally representative sample of adults, a recent vitamin D RCT in older adults, and DEQAS. RESULTS: 24,25(OH)2D3 contributed to the positive bias observed in some immunoassays relative to LC-MS/MS-derived estimates for total 25(OH)D. A spiking experiment showed that the degree of cross-reactivity with 24,25(OH)2D was high and may underpin this positive bias. Adjustment for 24,25(OH)2D3 concentration brought estimates closer to true values. Data from the vitamin D RCT showed that the ratio of 24,25(OH)2D3 to 25(OH)D was associated with serum 25(OH)D3 and with response of serum 25(OH)D to vitamin D supplementation. CONCLUSIONS: Our findings highlight that the effect of 24,25(OH)2D3 in serum is a double-edged sword-an interferent for some immunoassays, yet potentially informative of nutritional status.

Estimating the population distribution of usual 24-hour sodium excretion from timed urine void specimens using a statistical approach accounting for correlated measurement errors.

BACKGROUND: High US sodium intake and national reduction efforts necessitate developing a feasible and valid monitoring method across the distribution of low-to-high sodium intake. OBJECTIVE: We examined a statistical approach using timed urine voids to estimate the population distribution of usual 24-h sodium excretion. METHODS: A sample of 407 adults, aged 18-39 y (54% female, 48% black), collected each void in a separate container for 24 h; 133 repeated the procedure 4-11 d later. Four timed voids (morning, afternoon, evening, overnight) were selected from each 24-h collection. We developed gender-specific equations to calibrate total sodium excreted in each of the one-void (e.g., morning) and combined two-void (e.g., morning + afternoon) urines to 24-h sodium excretion. The calibrated sodium excretions were used to estimate the population distribution of usual 24-h sodium excretion. Participants were then randomly assigned to modeling (n = 160) or validation (n = 247) groups to examine the bias in estimated population percentiles. RESULTS: Median bias in predicting selected percentiles (5th, 25th, 50th, 75th, 95th) of usual 24-h sodium excretion with one-void urines ranged from -367 to 284 mg (-7.7 to 12.2% of the observed usual excretions) for men and -604 to 486 mg (-14.6 to 23.7%) for women, and with two-void urines from -338 to 263 mg (-6.9 to 10.4%) and -166 to 153 mg (-4.1 to 8.1%), respectively. Four of the 6 two-void urine combinations produced no significant bias in predicting selected percentiles. CONCLUSIONS: Our approach to estimate the population usual 24-h sodium excretion, which uses calibrated timed-void sodium to account for day-to-day variation and covariance between measurement errors, produced percentile estimates with relatively low biases across low-to-high sodium excretions. This may provide a low-burden, low-cost alternative to 24-h collections in monitoring population sodium intake among healthy young adults and merits further investigation in other population subgroups.

Multivitamin-mineral use is associated with reduced risk of cardiovascular disease mortality among women in the United States.

BACKGROUND: Multivitamin-mineral (MVM) products are the most commonly used supplements in the United States, followed by multivitamin (MV) products. Two randomized clinical trials (RCTs) did not show an effect of MVMs or MVs on cardiovascular disease (CVD) mortality; however, no clinical trial data are available for women with MVM supplement use and CVD mortality. OBJECTIVE: The objective of this research was to examine the association between MVM and MV use and CVD-specific mortality among US adults without CVD. METHODS: A nationally representative sample of adults from the restricted data NHANES III (1988-1994; n = 8678; age ≥40 y) were matched with mortality data reported by the National Death Index through 2011 to examine associations between MVM and MV use and CVD mortality by using Cox proportional hazards models, adjusting for multiple potential confounders. RESULTS: We observed no significant association between CVD mortality and users of MVMs or MVs compared with nonusers; however, when users were classified by the reported length of time products were used, a significant association was found with MVM use of >3 y compared with nonusers (HR: 0.65; 95% CI: 0.49, 0.85). This finding was largely driven by the significant association among women (HR: 0.56; 95% CI: 0.37, 0.85) but not men (HR: 0.79; 95% CI: 0.44, 1.42). No significant association was observed for MV products and CVD mortality in fully adjusted models. CONCLUSIONS: In this nationally representative data set with detailed information on supplement use and CVD mortality data ∼20 y later, we found an association between MVM use of >3 y and reduced CVD mortality risk for women when models controlled for age, race, education, body mass index, alcohol, aspirin use, serum lipids, blood pressure, and blood glucose/glycated hemoglobin. Our results are consistent with the 1 available RCT in men, indicating no relation with MVM use and CVD mortality.

A select review reporting the quality of studies measuring endothelial dysfunction in randomised diet intervention trials.

A quality assessment of the primary studies reported in the literature carried out using select dietary ingredients (DI) purported to affect vascular endothelial function was conducted through a systematic PubMed search from January 2000 to August 2012. A total of seventy randomised controlled trials with defined DI (folic acid (fifteen), n-3 fatty acids (twenty), cocoa (fifteen) and isoflavones (twenty)) and standardised measures of vascular endothelial function were evaluated. Jadad scores, quality scoring parameters for DI and flow-mediated dilation (FMD) methodology used were ascertained. A total of 3959 randomised subjects, mean age 51 (se 0·21) years (range 9-79 years), were represented in the dataset. The mean Jadad scores did not differ statistically among the DI studies, with the majority of the studies being of good quality. Higher DI quality scores were achieved by studies using the botanical ingredients cocoa and isoflavones than by those using the nutrient ingredients folic acid and n-3 fatty acids. The mean DI quality scores were 4·13 (se 0·34), 5·20 (se 0·47), 6·13 (se 0·41) and 6·00 (se 0·59) for the folic acid, n-3 fatty acid, cocoa and isoflavone intervention studies, respectively (and significantly different). The mean Corretti FMD scores were 7·27 (se 0·56), 7·46 (se 0·79), 6·29 (se 0·61) and 7·11 (se 0·56) for the folic acid, n-3 fatty acid, cocoa and isoflavone intervention studies, respectively (NS). FMD studies failed to adequately describe the equipment used and more than half failed to provide an adequate description of the procedures used for vascular image acquisition and measurement. DI can be utilised for dietary intervention studies; however, the methodology should be clearly reported using the guidelines for assessment for both DI and FMD.

Standardizing serum 25-hydroxyvitamin D data from four Nordic population samples using the Vitamin D Standardization Program protocols: Shedding new light on vitamin D status in Nordic individuals.

Knowledge about the distributions of serum 25-hydroxyvitamin D (25(OH)D) concentrations in representative population samples is critical for the quantification of vitamin D deficiency as well as for setting dietary reference values and food-based strategies for its prevention. Such data for the European Union are of variable quality making it difficult to estimate the prevalence of vitamin D deficiency across member states. As a consequence of the widespread, method-related differences in measurements of serum 25(OH)D concentrations, the Vitamin D Standardization Program (VDSP) developed protocols for standardizing existing serum 25(OH)D data from national surveys around the world. The objective of the present work was to apply the VDSP protocols to existing serum 25(OH)D data from a Danish, a Norwegian, and a Finnish population-based health survey and from a Danish randomized controlled trial. A specifically-selected subset (n 100-150) of bio-banked serum samples from each of the studies were reanalyzed for 25(OH)D by LC-MS/MS and a calibration equation developed between old and new 25(OH)D data, and this equation was applied to the entire data-sets from each study. Compared to estimates based on the original serum 25(OH)D data, the percentage vitamin D deficiency (< 30 nmol/L) decreased by 21.5% in the Danish health survey but by only 1.4% in the Norwegian health survey; but was relatively unchanged (0% and 0.2%) in the Finish survey or Danish RCT, respectively, following VDSP standardization. In conclusion, standardization of serum 25(OH)D concentrations is absolutely necessary in order to compare serum 25(OH)D concentrations across different study populations, which is needed to quantify and prevent vitamin D deficiency.

The estimation of calibration equations for variables with heteroscedastic measurement errors.

In clinical chemistry and medical research, there is often a need to calibrate the values obtained from an old or discontinued laboratory procedure to the values obtained from a new or currently used laboratory method. The objective of the calibration study is to identify a transformation that can be used to convert the test values of one laboratory measurement procedure into the values that would be obtained using another measurement procedure. However, in the presence of heteroscedastic measurement error, there is no good statistical method available for estimating the transformation. In this paper, we propose a set of statistical methods for a calibration study when the magnitude of the measurement error is proportional to the underlying true level. The corresponding sample size estimation method for conducting a calibration study is discussed as well. The proposed new method is theoretically justified and evaluated for its finite sample properties via an extensive numerical study. Two examples based on real data are used to illustrate the procedure.

Consensus Statement on Vitamin D Status Assessment and Supplementation: Whys, Whens, and Hows.

The 6th International Conference, "Controversies in Vitamin D," was convened to discuss controversial topics, such as vitamin D metabolism, assessment, actions, and supplementation. Novel insights into vitamin D mechanisms of action suggest links with conditions that do not depend only on reduced solar exposure or diet intake and that can be detected with distinctive noncanonical vitamin D metabolites. Optimal 25-hydroxyvitamin D (25(OH)D) levels remain debated. Varying recommendations from different societies arise from evaluating different clinical or public health approaches. The lack of assay standardization also poses challenges in interpreting data from available studies, hindering rational data pooling and meta-analyses. Beyond the well-known skeletal features, interest in vitamin D's extraskeletal effects has led to clinical trials on cancer, cardiovascular risk, respiratory effects, autoimmune diseases, diabetes, and mortality. The initial negative results are likely due to enrollment of vitamin D-replete individuals. Subsequent post hoc analyses have suggested, nevertheless, potential benefits in reducing cancer incidence, autoimmune diseases, cardiovascular events, and diabetes. Oral administration of vitamin D is the preferred route. Parenteral administration is reserved for specific clinical situations. Cholecalciferol is favored due to safety and minimal monitoring requirements. Calcifediol may be used in certain conditions, while calcitriol should be limited to specific disorders in which the active metabolite is not readily produced in vivo. Further studies are needed to investigate vitamin D effects in relation to the different recommended 25(OH)D levels and the efficacy of the different supplementary formulations in achieving biochemical and clinical outcomes within the multifaced skeletal and extraskeletal potential effects of vitamin D.

Urinary excretion of sodium, potassium, and chloride, but not iodine, varies by timing of collection in a 24-hour calibration study.

Because of the logistic complexity, excessive respondent burden, and high cost of conducting 24-h urine collections in a national survey, alternative strategies to monitor sodium intake at the population level need to be evaluated. We conducted a calibration study to assess the ability to characterize sodium intake from timed-spot urine samples calibrated to a 24-h urine collection. In this report, we described the overall design and basic results of the study. Adults aged 18-39 y were recruited to collect urine for a 24-h period, placing each void in a separate container. Four timed-spot specimens (morning, afternoon, evening, and overnight) and the 24-h collection were analyzed for sodium, potassium, chloride, creatinine, and iodine. Of 481 eligible persons, 407 (54% female, 48% black) completed a 24-h urine collection. A subsample (n = 133) collected a second 24-h urine 4-11 d later. Mean sodium excretion was 3.54 ± 1.51 g/d for males and 3.09 ± 1.26 g/d for females. Sensitivity analysis excluding those who did not meet the expected creatinine excretion criterion showed the same results. Day-to-day variability for sodium, potassium, chloride, and iodine was observed among those collecting two 24-h urine samples (CV = 16-29% for 24-h urine samples and 21-41% for timed-spot specimens). Among all race-gender groups, overnight specimens had larger volumes (P < 0.01) and lower sodium (P < 0.01 to P = 0.26), potassium (P < 0.01), and chloride (P < 0.01) concentrations compared with other timed-spot urine samples, although the differences were not always significant. Urine creatinine and iodine concentrations did not differ by the timing of collection. The observed day-to-day and diurnal variations in sodium excretion illustrate the importance of accounting for these factors when developing calibration equations from this study.