Warren Sun, BS, Jerry T Dang, MD, Noah J Switzer, MD, MPH, Daniel Ta, Chunhong Tian, PhD, Christopher de Gara, MBBS, Daniel W Birch, MD, MSc, Shahzeer Karmali, MD, MPH. University of Alberta
INTRODUCTION: We aimed to systematically review the literature to study the relationship between thyroid hormone levels and weight loss for patients undergoing bariatric surgery. Thyroid hormones are major regulators of the basal metabolic rate. The imbalance of energy expenditure and energy storage regulated by these hormones play an integral role in metabolic disorders, such as obesity. Several studies have tried to identify the relationship between thyroid hormone levels, obesity, and weight loss.
METHODS AND PROCEDURES: A comprehensive search of MEDLINE, EMBASE, SCOPUS, the Cochrane Library, and Web of Science prior to May 2017 was completed. Title searching was restricted to the following keywords/terms: sleeve gastrectomy/gastric bypass AND thyroid. After removing duplicate titles, 148 primary studies and abstracts were reviewed for inclusion into the systematic review. Inclusion criteria included English studies with five or more patients, age 16 or older, patients undergoing primary bariatric surgery, and outcome reporting of pre- or post-operative weight, TSH, free T4, or free T3. Exclusion criteria included patients diagnosed with overt hyper- or hypothyroidism, and patients on thyroid replacement therapy.
RESULTS: Sixteen primary studies (N=1556) were included in the systematic review. The average pre-operative BMI was 46.6 ± 3.8 kg/m2, which decreased to 32.7 ± 2.4 kg/m2 post-operatively (ten studies, n=798). All studies with documented pre- and post-operative TSH levels reported a decrease in TSH following bariatric surgery. The average pre-operative TSH was 2.6 ± 1.1 mU/L, which decreased to 1.8 ± 0.4 mU/L post-operatively (nine studies, n=736). Free T4 levels increased on average by 0.62 pmol/L (five studies, n=246), and free T3 levels decreased on average by 0.57 pmol/L (two studies, n=34). Two studies identified 79 patients with subclinical hypothyroidism (SH) pre-operatively with an average pre-operative TSH of 5.69 mU/L and pre-operative free T4 of 14.79 pmol/L. Following RYGB, TSH levels decreased on average by 2.94 mU/L into euthyroid range. Four studies found a statistically significant positive correlation between TSH and BMI at baseline. None of the studies found that lower TSH was correlated with greater weight loss.
CONCLUSION: There is a positive correlation between TSH and BMI at baseline, but no predictors of weight loss were identified. Bariatric surgery leads to a decrease in TSH levels. Subclinical hypothyroidism improved or resolved after RYGB. Further research is needed to try to identify potential hormonal predictors of weight loss associated with bariatric surgery.
Presented at the SAGES 2017 Annual Meeting in Houston, TX.
Abstract ID: 86926
Program Number: P607
Presentation Session: iPoster Session (Non CME)
Presentation Type: Poster