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

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.