The relative influence of serum ionized calcium and 25-hydroxyvitamin D in regulating PTH secretion in healthy subjects

Abstract Background While the inverse relationship between serum ionized calcium (Ca 2+ ) and PTH is well-established, the relationship between 25(OH)D and PTH showed conflicting results. The study aimed to evaluate the relative contributions of age, sex, serum Ca 2+ , ionized magnesium (Mg 2+ ), 25(OH)D and 1,25(OH) 2 D in regulating PTH secretion in healthy subjects. Methods This is a secondary analysis of an observational study performed from March 2014 to July 2015 carried out in 2259 blood donors (1652 men and 607 women, age range 18–68 years). Subjects with parathyroid disorders and taking drugs that affect mineral metabolism were excluded. Results Significant correlations [between Ca 2+ and PTH ( r  = −0.223, p r  = −0.178, p r  = 0.322, p 2+ , Mg 2+ , 25(OH)D, 1,25(OH) 2 D and sex as explanatory variables to determine the effect of each covariate on the response variable. For subjects 2+ levels regulated PTH secretion. Subjects with 25(OH)D  2+  ≥ 1.30 mmol/L had average lower PTH compared to subjects with Ca 2+ p 2+ accounted for 18% of the total variance, BMI for 14.3%, and 1,25(OH) 2 D for 11.1%. The remaining percentage was attributable to age and sex. This was confirmed by the regression tree approach, where 25(OH)D and Ca 2+ accounted for the largest variation in the average levels of PTH. Discussion Under stable conditions 25(OH)D plays a significant role in regulating PTH secretion. Under conditions of relative vitamin D sufficiency, Ca 2+ also plays an important role.