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Preoperative Thyroid Function Does Not Affect Postoperative Normalization of TSH Levels or Weight Loss After Bariatric Surgery
Sayantan Deb, Lindsey Voller*, Wes Turner, Chase Palisch, Rachel Dwinal, Homero Rivas, Dan Azagury, John M. Morton
General Surgery, Stanford University, Stanford, CA
BACKGROUND: Morbid obesity is a prevalent public health concern in the U.S. Studies have demonstrated an association between obesity and elevated thyroid-stimulating hormone (TSH, thyrotropin) levels; however, no study to date has evaluated the relationship between preoperative thyroid function and its effects on weight loss and reduction of TSH levels after bariatric surgery.
METHODS: 1,671 individuals from a single academic institution undergoing bariatric surgery were included in this retrospective study. Anthropometric and demographic data, as well as TSH levels, were collected from patient charts preoperatively and at 3, 6, and 12 months following surgery. Body mass index (BMI) and percentage of excess weight loss (%EWL) were calculated at all time points. Thyroid function was defined by average TSH levels and subjects were divided into 3 groups preoperatively: normal (0-2.5 mU/L, n=1,318, 78.9%), subclinical (>2.5-4.0 mU/L, n=270, 16.2%), and abnormal (>4.0 mU/L, n=83, 4.9%) TSH levels. Subjects undergoing thyroid hormone replacement therapy were excluded from the study. Data were analyzed using Student’s t-test, ANOVA, Pearson correlation, or their non-parametric equivalent as appropriate using GraphPad Prism v6.01.
RESULTS: All three TSH level-groups experienced significant reductions in BMI at each postoperative time point, with improvements at one year as follows: normal, 46.0 preoperatively to 32.3 kg/m2 at 12 months; subclinical, 46.8 preoperatively to 32.2 kg/m2 at 12 months; abnormal, 48.9 preoperatively to 33.4 kg/m2 at 12 months (all p<.0001). There were no significant differences in %EWL between the three groups. Mean TSH levels normalized from preop to one year among subclinical (3.1 to 2.4 mU/L, p=.0006) and abnormal (5.3 to 2.8 mU/L, p<.0001) TSH-level groups. Additionally, while average TSH levels significantly differed between the three groups preoperatively (p<.0001), this effect disappeared at one year after surgery (p=.9557) and overall mean TSH levels were 2.3 mU/L ± 0.45. These changes in TSH levels did not correlate with BMI at any postoperative time point among the three groups (all p>.05).
CONCLUSION: This study is the first of its kind to report equivalent weight loss and improvement in thyroid function after bariatric surgery based on preoperative TSH classification. Moreover, decreases in BMI did not significantly correlate with postoperative TSH levels, suggesting further regulatory pathways modulating TSH levels after bariatric surgery beyond weight loss alone. This warrants further exploration and may highlight an additional benefit of bariatric surgery.
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