Objective: Surprisingly few studies have examined weight change in hypothyroid patients after initiation of levothyroxine (LT4) therapy. Our study aimed to investigate weight change after initiation of LT4 treatment for primary hypothyroidism.
Methods: Using electronic medical records from Boston Medical Center, Boston, Massachusetts, we performed a retrospective cohort study between January 1, 2003, and February 1, 2011. Adults ≥18 years of age with newly diagnosed primary hypothyroidism with an initial thyroid-stimulating hormone (TSH) level ≥10 mIU/L were identified. Patients with postsurgical hypothyroidism, thyroid cancer, and a history of radioactive iodine or head/neck irradiation, congestive heart failure, anorexia nervosa, end-stage renal disease, cirrhosis, pregnancy, or use of prescription weight-loss medications were excluded. TSH and weight at diagnosis and up to 24 months after LT4 initiation were collected. Weight change was assessed at the first posttreatment serum TSH level <5 mIU/L.
Results: A total of 101 patients (mean age, 48 ± 15 years; 71% women) were included. Initial median TSH was 18.3 mIU/L (range, 10.1 to 710.5 mIU/L) and initial median weight was 79.6 kg (range 41.5 to 167.5 kg). Posttreatment median TSH level was 2.3 mIU/L (range, 0.04 to 5 mIU/L), and weight change at a median of 5 months (range, 1.1 to 25.6 months) was -0.1 kg (range, -20.6 to 7.7 kg). Initial median body mass index (BMI) of 95 of the patients was 29.3 kg/m2 (range, 19.5 to 56.1 kg/m2), and the median change in BMI was -0.1 kg/m2 (range, -7.1 to 3.3 kg/m2). Only 52% of patients lost weight, with a mean weight loss of 3.8 ± 4.4 kg. Gender, race, education, insurance type, age, initial TSH level, time to normalization of TSH, and initial weight were not associated with changes in weight or BMI.
Conclusion: Contrary to popular belief, our study of 101 patients with primary hypothyroidism showed that no significant weight change occurs after initiation of LT4 treatment.