Seasonal Differences in Postoperative Hypocalcemia Following Total Thyroidectomy

ABSTRACT Objective To evaluate whether seasonal differences contribute to the development of post‐thyroidectomy hypocalcemia. Methods A total of 8731 patients who underwent total thyroidectomy between December 1, 2022, and November 20, 2023, were identified. Patients were grouped into seasonal cohorts based on the meteorological definition of seasons (Winter: December–February; Spring: March–May; Summer: June–August; Fall: September–November). Cohorts were controlled for age, sex, and race. Those with a history of calcium or vitamin D supplementation, chronic kidney disease, or related comorbidities were excluded. Hypocalcemia was defined as serum levels less than 8.5 mg/dL. PTH, vitamin D, and phosphorous levels were also assessed. Results When comparing the spring cohort to the winter cohort ( n = 1911), the risk of hypocalcemia was 18.7% versus 15.5%, respectively ( p < 0.01). No significant differences in hypocalcemia risk were observed between other seasonal groups. Differences in levels of 25‐Hydroxy‐vitamin D, PTH, and phosphorus were also not significant between groups. Conclusion Seasonal variation was observed in laboratory‐defined hypocalcemia following total thyroidectomy, with patients undergoing surgery in the spring demonstrating a higher risk compared with those undergoing surgery in the winter. These findings challenge the hypothesis that postoperative hypocalcemia risk is highest during colder months because of reduced sun exposure and suggest that seasonal influences on postoperative calcium homeostasis may be more complex than vitamin D status alone. Further prospective studies with standardized perioperative calcium, vitamin D, and PTH measurements are warranted to clarify the mechanisms underlying these seasonal differences. Level of Evidence 3.