Public health implications of standardized 25-hydroxyvitamin D levels: A decrease in the prevalence of vitamin D deficiency among older women in Germany

Abstract Objective. To compare the public health implications of using unstandardized immunoassay measurements of serum 25-hydroxyvitamin D [25(OH)D] concentrations versus using measurements standardized by liquid chromatography tandem–mass spectrometry (LC–MS/MS) when assessing the prevalence of 25(OH)D insufficiency and deficiency in various subgroups of individuals. Method. We standardized immunoassay-based measurements of 25(OH)D with LC–MS/MS in a population-based sample of 5386 women aged 50–74 recruited in 2000–2002 in Germany. We used multivariate regression to assess 25(OH)D determinants and the association of vitamin D deficiency with health status. Results. Prevalences of 25(OH)D levels < 50 nmol/L (insufficiency) and < 30 nmol/L (deficiency) decreased considerably by standardization. The decrease in vitamin D deficiency (from 64.4% to 17.9%) was particularly strong in March–May among women aged ≥ 65. Independent of season of blood draw and standardization, women ≥ 70 years, obese, or currently smoking had an increased risk of having 25(OH)D levels < 30 nmol/L. Conclusion. The proportion of older women with vitamin D deficiency in Germany is much lower than previously reported, but prevalence of vitamin D insufficiency is high. Standardization of 25(OH)D values by immunoassay methods to LC–MS/MS equivalent values or direct measurement by LC–MS/MS is indispensable in drawing valid conclusions about the health implications of vitamin D deficiency or insufficiency.