Standardizing serum 25-hydroxyvitamin D data from four Nordic population samples using theVitamin D Standardization Programprotocols: Shedding new light on vitamin D status in Nordic individuals

Abstract

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.

Non-skeletal health effects of vitamin D supplementation: A systematic review on findings from meta-analyses summarizing trial data

“…Development of new methods or reliance on the Bradford Hill criteria may be necessary to refind our understanding of vitamin D [300]. A major limitation to the interpretation of prior longitudinal studies is lack of standardization of 25OHD measurements [301]. It has been documented that use of different methods for measuring 25OHD levels may cause huge variations in levels measured and thereby affect the classification of vitamin D status [302–305].…”

Vitamin D deficiency in Europe: pandemic?

“…We also had vitamin D deficiency prevalence data from 4 additional European studies, on which we had previously standardized serum 25(OH)D data by using the same VDSP approach (14, 37), and we combined these data with data from the 14 new studies in generating a pooled estimate in the present work. The descriptions of these other 4 studies [National Adult Nutrition Survey, Ireland; Health 2011, Finland; HUBRO (Oslo Health Study), Oslo, Norway; and Health2006, Copenhagen, Denmark] have been reported in detail elsewhere (14, 37). None of the 18 studies included pregnant women or older adults in care homes.…”

The positive impact of general vitamin D food fortification policy on vitamin D status in a representative adult Finnish population: evidence from an 11-y follow-up based on standardized 25-hydroxyvitamin D data

“…The S-25(OH)D data, which arose from the 2 different assays used, were standardized with the use of the VDSP protocols, allowing for more valid comparisons of changes over time (24). If the S-25(OH)D data sets had not been standardized, the mean increase in S-25(OH)D concentration over the 11-y period would have been 10 nmol/L higher, leading to a biased interpretation of the results (24).…”

“…As a consequence of the widely accepted method-related differences in S-25(OH)D estimates (18), S-25(OH)D concentrations from both surveys were standardized with the use of VDSP protocol for standardizing S-25(OH)D values from past surveys, as described in detail elsewhere (18,23), allowing for a more valid comparison of vitamin D status over the 11-y period. The S-25(OH)D concentrations from H2011 were previously standardized (24), and the existing S-25(OH)D concentrations from H2000 (25) were standardized as part of this study according to VDSP protocol. The CDC-certified liquid chromatography-tandem mass spectrometry method was used to reanalyze the specific subsets of both overall survey samples per VDSP protocol (18,23).…”