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 ( iC a) 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 ( P  < 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 iC a in the lower range. A synergistic association was found for S‐25( OH )D and iC a 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.