Variability and Reproducibility of Circulating Vitamin D in a Nationwide U.S. Population
ABSTRACT Context:Most studies examining associations between circulating vitamin D and disease are based on a single measure of vitamin D, which may not reflect levels over time, particularly because vitamin D concentrations vary by season. Few studies evaluated how well multiple 25-hydroxyvitamin D [25(OH)D] measures track within the same individual over time.Objective:This study examined variability and reproducibility of vitamin D by evaluating repeat measurements of plasma 25(OH)D concentrations while accounting for determinants of circulating concentrations including dietary supplement use and latitude of residence from a population of U.S. radiologic technologists.Design and Participants:We analyzed circulating 25(OH)D in blood samples taken from 538 men and women from a prospective, nationwide study at two time points within a 1-yr period, most measured in different seasons. Inter- and intra-individual variability, reliability coefficients, and measurement error were examined.Results:The spearman rank correlation between two measurements of 25(OH)D concentrations was moderate (r = 0.75, P < 0.001) and did not vary significantly by participant characteristics including age, race, or latitude. The intraclass correlation coefficient was 0.72 (95% confidence interval = 0.68-0.76). The deattenuation factor of plasma 25(OH)D levels was 1.39, suggesting that a single measure of vitamin D on a continuous scale in regression analyses may result in attenuated relationships of about 40%.Conclusion:Our results suggest that a single blood sample obtained in spring or fall provides a reasonable average for 25(OH)D over a 1-yr period, but additional studies are needed to estimate variability and agreement in plasma 25(OH)D measurements over longer intervals and younger populations.
SourceAvailable from: Øivind Midttun[Show abstract] [Hide abstract]
ABSTRACT: Normal renal function is essential for vitamin D metabolism, but it is unclear whether circulating vitamin D is associated with risk of renal cell carcinoma (RCC). We assessed whether 25-hydroxyvitamin D3 (25(OH)D3) was associated with risk of RCC and death after RCC diagnosis in the European Prospective Investigation into Cancer and Nutrition (EPIC). EPIC recruited 385,747 participants with blood samples between 1992 and 2000. The current study included 560 RCC cases, 557 individually matched controls, and 553 additional controls. Circulating 25(OH)D3 was assessed by mass spectrometry. Conditional and unconditional logistic regression models were used to calculate odds ratios and 95% confidence intervals. Death after RCC diagnosis was assessed using Cox proportional hazards models and flexible parametric survival models. A doubling of 25(OH)D3 was associated with 28% lower odds of RCC after adjustment for season of and age at blood collection, sex, and country of recruitment (odds ratio = 0.72, 95% confidence interval: 0.60, 0.86; P = 0.0004). This estimate was attenuated somewhat after additional adjustment for smoking status at baseline, circulating cotinine, body mass index (weight (kg)/height (m)2), and alcohol intake (odds ratio = 0.82, 95% confidence interval: 0.68, 0.99; P = 0.038). There was also some indication that both low and high 25(OH)D3 levels were associated with higher risk of death from any cause among RCC cases.09/2014; DOI:10.1093/aje/kwu204
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ABSTRACT: Vitamin D deficiency is a global health problem. Epidemiological studies demonstrate that vitamin D is both cardioprotective and neuroprotective. Vitamin D also plays a substantial role in innate and acquired immunity. Our goal was to evaluate the association of serum vitamin D concentration on serious postoperative complications and death in noncardiac surgical patients.Anesthesia & Analgesia 08/2014; 119(3). DOI:10.1213/ANE.0000000000000096 · 3.42 Impact Factor
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ABSTRACT: Objective:To explore the associations between serum concentrations of vitamin D (25(OH)D) and all-cause mortality among US adults defined by lung function (LF) status, particularly among adults with obstructive LF (OLF).Methods:Data from 10 795 adults aged 20-79 years (685 with restrictive LF (RLF) and 1309 with OLF) who participated in the Third National Health and Nutrition Examination Survey (1988-1994), had a spirometric examination, and were followed through 2006 were included.Results:During 14.2 years of follow-up, 1792 participants died. Mean adjusted concentrations of 25(OH)D were 75.0 nmol/l (s.e. 0.7) for adults with normal LF (NLF), 70.4 nmol/l (s.e. 1.8) for adults with RLF, 75.5 nmol/l (s.e. 1.5) for adults with mild obstruction and 71.0 nmol/l (s.e. 1.9) among adults with moderate or worse obstruction (P=0.030). After adjustment for sociodemographic factors, lifestyle factors, clinical variables and prevalent chronic conditions, a concentration of <25 nmol/l compared with ⩾75 nmol//l was associated with mortality only among adults with NLF (hazard ratio (HR) 1.76; 95% confidence interval (CI) 1.03, 3.00). Among participants with OLF, adjusted HRs were 0.65 (95% CI 0.29, 1.48), 1.21 (95% CI 0.89, 1.66) and 0.97 (95% CI 0.78, 1.19) among those with concentrations <25, 25-<50 and 50-<75 nmol/l, respectively.Conclusions:Baseline concentrations of 25(OH)D did not significantly predict mortality among US adults with impaired LF.European Journal of Clinical Nutrition advance online publication, 13 August 2014; doi:10.1038/ejcn.2014.162.European Journal of Clinical Nutrition 08/2014; DOI:10.1038/ejcn.2014.162 · 2.95 Impact Factor