Weight gain following treatment of hyperthyroidism

OBJECTIVE Patients frequently express concern that treating hyperthyroidism will lead to excessive weight gain. This study aimed to determine the exte nt of, and risk factors for, weight gain in an unselected group of hyperthy roid patients. DESIGN and SUBJECTS We investigated 162 consecutive hyperthyroid patients f ollowed for at least 6 months. Height, weight, clinical features, biochemis try and management were recorded at each clinic visit. RESULTS Documented weight gain was 5.42 +/- 0.46 kg (mean +/- SE) and incre ase in BMI was 8.49 +/- 0.71%, over a mean 24.2 +/- 1.6 months. Preexisting obesity, Graves' disease causing hyperthyroidism, weight loss before prese ntation and length of follow-up each independently predicted weight gain. P atients treated with thionamides or radioiodine gained a similar amount of weight (thionamides n = 87, 5.16 +/- 0.63 kg vs. radioiodine, n = 62: 4.75 +/- 0.57 kg, P = 0.645), but patients who underwent thyroidectomy (n = 13) gained more weight (10.27 +/- 2.56 kg vs. others, P = 0.007). Development o f hypothyroidism (even transiently) was associated with weight gain (never hypothyroid, n = 1.02, 4.57 +/- 0.52 kg, transiently hypothyroid, n = 29, 5 .37 +/- 0.85 kg, on T4, n = 31, 8.06 +/- 1.42 kg, P = 0.014). This differen ce remained after correcting for length of follow-up. In the whole cohort, weight increased by 3.95 +/- 0.40 kg at 1 year (n = 144) to 9.91 +/- 1.62 k g after 4 years (n = 27) (P = 0.008), representing a mean weight gain of 3. 66 +/- 0.44 kg/year. CONCLUSION We have demonstrated marked weight gain after treatment of hyper thyroidism. Pre-existing obesity, a diagnosis of Graves' disease and prior weight loss independently predicted weight gain and weight continued to ris e with time. Patients who became hypothyroid, despite T4 replacement, gaine d most weight.