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

Summary: Objective: The 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. Design: A cross‐sectional study at Oslo University Hospital, Norway. Patients: A total of 502 consecutive patients, age 22‐64 years, attending 2‐year follow‐up after Roux‐en‐Y gastric bypass. Measurements: A serum intact PTH >7.0 pmol/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). Results: Altogether, 171 patients (34%) had SHPT. The prevalence of SHPT varied across the range of S‐25(OH)D (<italic>P</italic> < 0.001), being highest (71%) with S‐25(OH)D < 25 nmol/L. Compared with S‐25(OH)D < 50 nmol/L, the prevalence of SHPT was lower with S‐25(OH)D ≥ 50 nmol/L (29.0%; RR = 0.64 (95%‐CI:0.50‐0.81)) and S‐25(OH)D ≥ 75 nmol/L (27.7%; RR = 0.61 (95%‐CI:0.44‐0.84)). S‐25(OH)D ≥ 100 nmol/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 < 50 nmol/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. Conclusions: Vitamin D deficient patients had the highest prevalence of SHPT 2 years after gastric bypass. PTH and the prevalence of SHPT were notably lower with S‐25(OH)D ≥ 100 nmol/L, compared with lower target levels. [ABSTRACT FROM AUTHOR]