Relationships of serum 25-hydroxyvitamin D, ionized calcium and parathyroid hormone after obesity surgery.

ObjectiveThe high prevalence of secondary hyperparathyroidism (SHPT) after obesity surgery is a concern for long-term bone health. Limited knowledge exists about optimal vitamin D and suppression of parathyroid hormone (PTH) after these procedures. The aim of this study was to investigate the prevalence of SHPT and its relation to vitamin D status. DesignA cross-sectional study at Oslo University Hospital, Norway. PatientsA total of 502 consecutive patients, age 22-64years, attending 2-year follow-up after Roux-en-Y gastric bypass. MeasurementsA serum intact PTH >7.0pmol/L in the absence of elevated serum ionized calcium (iCa) was considered as SHPT. Vitamin D status was defined by serum concentrations of 25-hydroxyvitamin D (S-25(OH)D). ResultsAltogether, 171 patients (34%) had SHPT. The prevalence of SHPT varied across the range of S-25(OH)D (P<0.001), being highest (71%) with S-25(OH)D<25nmol/L. Compared with S-25(OH)D<50nmol/L, the prevalence of SHPT was lower with S-25(OH)D50nmol/L (29.0%; RR=0.64 (95%-CI:0.50-0.81)) and S-25(OH)D75nmol/L (27.7%; RR=0.61 (95%-CI:0.44-0.84)). S-25(OH)D 100nmol/L was associated with the lowest PTH and the lowest prevalence of SHPT (16.0%; RR=0.35 (95%-CI:0.14-0.88) compared with S-25(OH)D<50nmol/L) and the most normal calcium distribution. These associations were most pronounced with iCa in the lower range. A synergistic association was found for S-25(OH)D and iCa on SHPT. ConclusionsVitamin D deficient patients had the highest prevalence of SHPT 2years after gastric bypass. PTH and the prevalence of SHPT were notably lower with S-25(OH)D100nmol/L, compared with lower target levels.