The total 25-hydoxy-vitamin-D (t-25OHD) level reflects the supply of vitamin D, but is also influenced by the levels of 25OHD binding proteins (DBP). We aimed studying t-25OHD and bioavailable 25OHD (bio-25OHD) levels in healthy females with different reproductive ages.
Methods: t-25OHD, bio-intact parathormone (PTHi-184) (ECLIA, cobas e411, Roche), DBP (turbidimetry, Dako), calcium and albumin (Alb) levels were measured by routine methods (Modular, Roche). Bio-25OHD and albumin corrected Ca (AlbCa) were calculated in 126 healthy young women (age: 35.3±15.9 years) of whom 41 took oral contraceptives (OC); 45 were without pills (C1) and 40 were pregnant (PRG). An older control group of 21 postmenopausal women was also included (C2: age: 68.5±14.5 years).
Results: The highest levels of DBG were found in the PRG and OC groups. Based on the t-25OHD levels, only 12% of women in the OC, but 36% of women in the C1 group had suboptimal (<75 nmol/l) vitamin D supply. Bio25-OHD values reflecting suboptimal (<6.4 nmol/l) vitamin supply occurred most frequently (51%) in the OC and least frequently in the C1 group (15%). Levels of t-25OHD were highest (P<0.001) in the OC (100 (88 117) nmol/l) and the lowest (P<0.001) in PRG group (41 (28 57) nmol/l). However, bio-25OHD levels were lower in the OC (6.3 (5.6 8.1) nmol/l) than in the C1 group (8.1 (6.6 9.7) nmol/l P=0.06). Associations were observed between t-25OHD and PTH-184 levels in all groups (C1: β=−0.29 P<0.05; C2: β=−0.62 P<0.01; OC: β=−0.36 P<0.05) except the PRG group. There was no association between t-25OHD and CaAlb levels, while a correlation was detected between bio-25OHD vitamin and CaAlb levels (β=0.53 P<0.05) in the C2 group only.
Conclusions: t-25OHD and DBP levels may dysproportionally change. The estimates of vitamin D supply are influenced by the 25OHD fraction assessed especially in case of estrogen excess.
27 Apr - 01 May 2013
European Society of Endocrinology