Determinants of plasma 25-hydroxyvitamin D levels in healthy adults in the Netherlands.

BACKGROUND: Vitamin D plays a key role in maintaining skeletal health, but is also related to various non-skeletal health issues. Several determinants have been identified that influence blood plasma levels of 25-hydroxyvitamin D (25(OH) D), often in specific patients or elderly populations. This paper aims to replicate these findings in a healthy population. METHODS: Plasma levels of 25(OH)D were measured using tandem mass spectrometry. We examined the cross-sectional association of sociodemographic, health, lifestyle and sampling characteristics with 25(OH)D in a group of 539 adults, who were healthy control subjects in the NESDA study in the Netherlands (latitude 52 °N). RESULTS: Mean 25(OH)D levels were 68.0 (± 27.2) nmol/l. Levels under 50 nmol/l occurred in 27% of the population; 40% reached levels above 75 nmol/l. Women had higher levels than men, and the use of oral contraceptives showed a significant positive association among females. Subjects with non-European ancestry had dramatically lower 25(OH) D levels. Other factors that were negatively associated were body mass index and the renal estimated glomerular filtration rate (eGFR). Meteorological data replaced season as a significant determinant. Moderate alcohol consumption and sports showed a positive association, while physical activity and the hepatic marker gamma-glutamyl transferase did not. Our results disconfirm the influence of age in this population of under 65 year olds. CONCLUSION: Insufficient 25(OH)D levels were common in a healthy population. The set of eight variables that were significant in a multiple regression model (sex, ancestry, oral contraceptives, eGFR, BMI, sports, alcohol, sunshine) explained 29.5% of the variance.

Prevalence of vitamin D deficiency and consequences for PTH reference values.

Reference values of PTH depend on vitamin D status of the reference population. This is often not described in package inserts. The aim of the present study was therefore to calculate assay specific PTH reference levels in EDTA plasma for the Architect (Abbott) in relation to 25-hydroxyvitamin D (25OHD) levels. The relation between PTH levels, 25OHD, BMI, age, gender and kidney function was determined in a cohort of older individuals from the Longitudinal Aging Study Amsterdam (LASA, n = 738, age 55-65 years) and in a cohort of healthy individuals from the Netherlands Study of Depression and Anxiety (NESDA, n = 633, 18-65 years). The LASA cohort is a representative sample of the Dutch older population. As expected, PTH reference values were significantly lower in 25OHD sufficient subjects (25OHD>50 nmol/L) than in 25OHD deficient and insufficient subjects. The 97.5th percentile of PTH in 25OHD sufficient subjects was 10 pmol/L (94.3 pg/mL), which was higher than the upper limit stated by the manufacturer (7.2 pmol/L or 68.3 pg/mL). The relation between vitamin D and PTH was independent of age, gender, BMI and kidney function. In conclusion, we have shown that it is important to establish PTH reference values in a local reference population taking 25OHD status into account.