Different impact of sleeve gastrectomy and Roux-en-Y gastric bypass on thyroid function and levothyroxine requirements

Bariatric surgery might impact the thyroid function test and, in hypothyroid patients, the dose of levothyroxine (LT4), but data are not univocal. We evaluated changes in thyroid function during the first year following bariatric surgery in patients without pre-existing thyroid disease, as well as adjustments in LT4 dosage in those with thyroid disorders, comparing the effects of Roux-en-Y gastric bypass (RYGB) and sleeve gastrectomy (SG). A retrospective observational study including 69 patients on LT4 therapy (Tr) and 85 patients with normal thyroid function (Nt) at pre-surgical work-up and at regular follow-up at 45 days, 3–6 months and 1-year visits after surgery. The mean body weight reduction for the entire cohort was in 31.4 ± 0.7% 1 year after surgery. In the two Nt groups, TSH levels remained stable throughout the observation period, without differences for type of surgery and without relationship with body weight. After bariatric surgery, the patients treated with LT4, belonging to both Tr-RYGB and Tr-SG, needed to increase the dosage per kg body weight to achieve stable TSH. At 1 year, the increase of LT4/kg/die was higher in the Tr-RYGB group than Tr-SG group (0.44 vs 0.30 mcg/kg/die, p = 0.032). In patients with severe obesity and normal thyroid function, TSH levels are not related with body weight change. Patients treated with LT4, after bariatric surgery need to in-crease the dosage per kg of body weight of the LT4 especially after surgery with malabsorptive component (RYGB) compared to restrictive surgery (SG).