Functional Changes in the Thyroid Gland Following Bariatric Surgery

Introduction: Bariatric surgery, also known as metabolic surgery, is known to improve the metabolic profile of morbidly obese patients in many aspects, thereby improving their quality of life. Obesity is typically associated with subtle changes in thyroid homeostasis. Bariatric procedures, particularly sleeve gastrectomy and Roux-en-Y gastric bypass, are associated with reductions in thyroid-stimulating hormone (TSH), free triiodothyronine (FT3), and total triiodothyronine (TT3) levels during the first postoperative year. This study aimed to evaluate the impact of bariatric surgery on thyroid function and thyroxine requirements in patients with and without pre-existing hypothyroidism. Methods: This retrospective cross-sectional study was conducted at the Department of General Surgery, Dubai Health, United Arab Emirates. All patients who underwent bariatric surgery between September 2017 and December 2023 were included. Patients were divided into two groups: (1) those with preoperative hypothyroidism controlled on thyroxine therapy and (2) those with normal thyroid function. Patients with hyperthyroidism or a history of total thyroidectomy were excluded. Thyroid function tests and thyroxine requirements were evaluated preoperatively and at one- and two-year follow-up. Results: A total of 853 patients were included (mean age: 34.4 ± 11.0 years; 71.1% female). Sleeve gastrectomy accounted for 35.3% of procedures, Roux-en-Y gastric bypass for 55.9%, and redo-/mini-gastric bypass for 8.8%. All procedures resulted in significant weight loss at one and two years postoperatively (p < 0.001). Baseline thyroid function was within reference ranges, and postoperative TSH and free T4 levels remained stable. Among the 46 hypothyroid patients receiving thyroxine therapy, only a small proportion required dose adjustments, with no significant association with the type of surgery (χ²(6) = 3.35, p = 0.763). No correlation was found between BMI reduction and changes in thyroid hormone levels. Conclusion: This study found no significant association between weight loss following bariatric surgery and changes in thyroid hormone function. No significant alterations in thyroxine requirements were observed. Larger multicenter studies with follow-up beyond two years are needed to further evaluate these findings.