Effect of Weight Loss after Bariatric Surgery on Thyroid-Stimulating Hormone Levels in Euthyroid Patients with Morbid Obesity

Abstract

Obesity is associated with several endocrine abnormalities, including thyroid dysfunction. The objective of this study was to investigate the effect of weight loss after bariatric surgery on thyroid-stimulating hormone (TSH) levels in euthyroid patients with morbid obesity. We performed an observational study, evaluating patients with morbid obesity submitted to bariatric surgery. We included 129 patients (92 women) and 31 controls (21 women). Clinical, anthropometric, biochemical, and hormonal parameters were evaluated. The primary endpoint was circulating TSH (µU/mL). Fasting TSH levels were higher in the obese group (3.3 ± 0.2) than in the control group (2.1 ± 0.2). The mean excessive body mass index (BMI) loss (EBMIL) 12 months after bariatric surgery was 72.7 ± 2.1%. TSH levels significantly decreased in the obese patients after surgery; 3.3 ± 0.2 vs. 2.1 ± 0.2 before and 12 months after surgery, respectively. Free thyroxine (T4) (ng/dL) levels significantly decreased in the obese patients after surgery; 1.47 ± 0.02 vs. 1.12 ± 0.02 before and 12 months after surgery, respectively. TSH decreased significantly over time, and the decrement was associated with the EBMIL. In euthyroid patients with morbid obesity, weight loss induced by bariatric surgery promotes a significant decline of the increased TSH levels. This decrement of TSH is progressive over time after surgery and significantly associated with excess BMI loss.

Central Resistance to Thyroid Hormones in Morbidly Obese Subjects Is Reversed after Bariatric Surgery-Induced Weight Loss

“…This decrease is not due to an intrinsic effect of BS. A decrease in TSH has been found in obese patients after non-surgical induced weight loss [36] and the decrease in circulating TSH has been found to be associated with excess body weight loss after BS [17,19]. The present results show a decrease in the indices of central resistance to TH that is statistically significant 3 months after BS, and there was no further significant decrement, maybe due in part to the faster excess BMI loss in the first months after BS.…”

“…Serum TSH (mIU/L) was measured by a two-site chemiluminescent immunoassay (ADVIA Centaur, Siemens, Deerfield, IL, USA) with a sensitivity of 0.01 mIU/L and with intra-assay coefficients of variation of 2.5%, 2.4%, and 2.4% for low, medium, and high serum TSH levels, respectively; and with inter-assay coefficients of variation of 5.3%, 3.4%, and 2.1% for low, medium, and high TSH levels, respectively; as previously published [19]. Serum FT4 (ng/dL) was measured by a direct chemiluminescent immunoassay (ADVIA Centaur, Siemens) with a sensitivity of 0.1 ng/dL and with intra-assay coefficients of variation of 3.3%, 2.2%, and 2.5% for low, medium, and high plasma FT4 levels, respectively; and with inter-assay coefficients of variation of 2.5%, 4.0%, and 2.3% for low, medium, and high FT4 levels, respectively; as previously published [19]. Insulin (µU/mL) was determined with a chemiluminescent immunometric assay (Immulite 2000 Insulin, DPC, Los Angeles, CA, USA) and with an intra-assay CV of 5.5%, 3.3%, and 3.7% for low, medium, and high plasma insulin levels, respectively; and with an inter-assay CV of 7.3%, 4.1%, and 5.3% for low, medium, and high insulin levels, respectively.…”

“…Insulin (µU/mL) was determined with a chemiluminescent immunometric assay (Immulite 2000 Insulin, DPC, Los Angeles, CA, USA) and with an intra-assay CV of 5.5%, 3.3%, and 3.7% for low, medium, and high plasma insulin levels, respectively; and with an inter-assay CV of 7.3%, 4.1%, and 5.3% for low, medium, and high insulin levels, respectively. Serum GH (µg/L) and IGF-1 (ng/mL) were determined by a chemiluminescent assay (Immulite, EURO/DPC) as previously published [19]. Plasma glucose (mg/dL) was measured with an automatic glucose oxidase method (Roche Diagnostics, Mannheim, Germany).…”

“…The alteration of thyroid function and the effect of BS on thyroid function is not fully understood. There are previous studies showing different results regarding the variation of thyroid stimulating hormone (TSH) after weight loss surgery [15][16][17][18][19]. The free thyroxine (FT4) values in obesity and the variation after surgery are even more conflicting [15].…”

Altered GH-IGF-1 Axis in Severe Obese Subjects is Reversed after Bariatric Surgery-Induced Weight Loss and Related with Low-Grade Chronic Inflammation

“…Excess body fat is associated with endocrine alterations, including thyroid dysfunction, central resistance to thyroid hormones [ 7 , 8 ] and decreased growth hormone (GH) secretion [ 9 , 10 , 11 ]. The altered GH secretion of obesity can be reversed by body weight normalization [ 12 ].…”