ObjectiveVitamin D insufficiency is common in primary hyperparathyroidism (pHPT). Patients with pHPT frequently have a reduced health-related quality of life (HRQoL). Our objectives were to evaluate whether HRQoL in pHPT is associated with vitamin D insufficiency and whether vitamin D supplementation after parathyroidectomy (PTX) could improve HRQoL.DesignA randomized, double-blind study (ClinicalTrials.gov identifier: NCT00982722).MethodsThe study included 150 pHPT patients randomized, 6 weeks after PTX, to daily treatment with either cholecalciferol 1600 IU and calcium carbonate 1000 mg (D+) or calcium carbonate alone (D−). HRQoL was estimated with SF-36 before and after PTX and after 12 months of study medication.ResultsThree-quarters (77%) of the pHPT patients had vitamin D insufficiency, defined as 25OHD <50 nmol/l. The pHPT patients scored lower than a reference population in all domains of SF-36. A total of 135 patients completed the entire study period. Improvements in nearly all domains were registered at the follow-up 6 weeks after PTX. At the end of the study medication period, the D+ group had a significantly higher median serum (s-) 25OHD concentration (76 (65; 93) (lower; upper interquartile ranges) vs 48 (40; 62) nmol/l, P<0.001) and a lower plasma (p-) parathyroid hormone concentration (40 (34; 52) vs 49 (38; 66) ng/l, P=0.01) than the D− group. The improvements in HRQoL remained unchanged at the follow-up 1 year after PTX. Postoperative vitamin D supplementation had no obvious effect on HRQoL.ConclusionPTX resulted in significant improvements in HRQoL. Despite a high prevalence of vitamin D insufficiency, 1 year of postoperative vitamin D supplementation had no obvious beneficial effect on HRQoL.