The Effect of Different Types of Bariatric Surgery on Levothyroxine Requirement in Hypothyroid Bariatric Patients.

Background Bariatric surgeries are carried out to improve a patient's quality of life, and to reduce respiratory, cardiac, endocrine, and metabolic complications encountered by those with high body mass index (BMI). A complication associated with high hypothyroidism is weight gain, which may lead to obesity. Here, we explore the effect of different bariatric procedures on thyroid function and levothyroxine dosage.  Methods This is a retrospective review of 887 patients referred to a tertiary bariatric service between 2008 and 2020 and treated for hypothyroidism at the time of referral. The study identified 57 patients on thyroxine replacement. Of these, 22 underwent restrictive bariatric procedures, 16 underwent restrictive/malabsorptive procedures, and 19 did not undergo operative intervention. Comparisons were made among each group throughout the timeline of interest. Results Out of 57 patients, 50 (87.7%) were female. The average age for patients was 47.26+/- 8.89 years. The average BMI at baseline was 48.72+/- 8.68 kg/m2. The mean dose of levothyroxine in controls was 115.8+/- 53.5 mcg while that of surgical patients was 149.8+/- 68.4 mcg. There were no statistically significant differences in levothyroxine doses between surgical and control at T0 (baseline), T1 (one-year post-op in surgical patient, or two-year post referral in control patient), T2 (two-year post-op in surgical patient, or three-year post referral in control patient), and T3 (most recent result available). The surgical group was then categorized further into restrictive and restrictive/malabsorptive. When they were compared with the control group, there were no statistically significant differences in doses. A generalized linear mixed model was applied to assess differences in levothyroxine dose with time as a random variable. This was adjusted for age, sex, BMI, T4 level, and hypothyroid cause. Through this assessment, there were several statistically significant differences in levothyroxine dosage between the groups. Control group required on average 28.06 mcg less levothyroxine than the restrictive/malabsorptive group (p=0.015). Also, the restrictive group required on average 23.57 mcg less levothyroxine than the restrictive/malabsorptive group (p=0.033). There were no statistically significant differences observed between the control group and the restrictive group (p=0.67) Conclusion Patients who have bariatric surgery have changes to their anatomy and physiology which may affect both their thyroid hormone homeostasis and levothyroxine pharmacokinetics. Thus, hypothyroid bariatric patients requiring levothyroxine must have their thyroid function monitored regularly. In this study, it was found that hypothyroid patients who underwent restrictive surgery had an overall statistically significant lower levothyroxine requirement to remain euthyroid as compared to the restrictive/malabsorptive group (p=0.033). Additionally, the control group required statistically significantly less levothyroxine than the restrictive/malabsorptive group (p=0.015). These factors may determine the type of surgery chosen by hypothyroid bariatric patients. However, further studies that are randomized, controlled, and multi-center with a higher population are required.