Thyroid hormone changes and their associations with weight loss after laparoscopic sleeve gastrectomy: a 12-month cohort study

Introduction In patients with obesity, thyroid-stimulating hormone (TSH) and free triiodothyronine (fT3) concentrations and the ratio of fT3 to free thyroxine (fT4) are often higher than in normal-weight individuals. Although laparoscopic sleeve gastrectomy (LSG) alters thyroid function, the temporal trajectory of these changes and the factors associated with them remain incompletely characterized. We therefore examined, in 232 patients followed for 12 months after LSG, how thyroid hormone parameters changed over the first postoperative year and which clinical and iron-related factors were associated with these changes. Methods In this retrospective cohort, patients (including 25 with treated autoimmune hypothyroidism) were assessed before surgery and at 6 and 12 months, with thyroid hormone trajectories analyzed by repeated-measures testing and their correlates examined by multivariable regression. Results TSH, fT3, and the calculated fT3/fT4 ratio decreased significantly over 12 months while fT4 rose modestly; changes were evident at 6 months, with no statistically significant additional change detected between 6 and 12 months (TSH, p = 0.482). No statistically significant association was detected between the changes in TSH, fT3, and fT4 and weight-loss magnitude within the observed range of total weight loss (11.0%–48.3%), including in the 207 patients not receiving levothyroxine; in the adjusted model for the TSH change, a 10-percentage-point difference in total weight loss corresponded to −0.03 μIU/mL (95% CI −0.15 to +0.09). No statistically significant association was detected with the changes in inflammatory markers. Each change was most strongly associated with its own baseline value, but these associations partly reflect mathematical coupling, measurement error, and regression to the mean and are not interpreted as physiological effects. A weak, nominal association between the changes in TSH and ferritin was specification-dependent and is regarded as exploratory. Among levothyroxine-treated patients, the dose was reduced in 16 of 25 (64%; 95% CI 44.5–79.8), a descriptive observation that cannot be attributed to surgery alone. Discussion Within the observed range, these data do not show a detectable association between weight-loss magnitude and thyroid hormone changes after LSG, although they do not establish equivalence; the exploratory ferritin signal warrants confirmation in prospective studies with comprehensive iron indices.