Weight gain after therapy for hyperthyroidism

Weight gain is a common complaint in patients who have been treated for hyperthyroidism. There were reports of up to 79% patient's increasing week after hyperthyroid treatment. Several studies show changes in body mass index, total fat mass, and totally mass after initiation of treatment for hyperthyroidism. Others have described an increase in muscle and bone mass. There are multiple factors that are implicated in the weight gain which include pre-existing obesity (BMI greater than 25 kg/m2), patients with Graves' disease, and in patient's younger than 30 years of age.into studies female sex had previously been identified as a risk factor for weight gain in some patients. these findings are relevant for patients since the likelihood of hypothyroidism developing after the initiation of treatment for hypothyroidism can be as high as 67%. Also, obesity is very common, with an estimated prevalence in the United States of approximately 33%, man and 35% among women.  Generally, if the patient reduces their caloric intake after the beginning of hyperthyroid treatment, waking will be much less noticeable.

A recent study by Dr. Safer*, was the first to report on a racial and ethnic differences and T3 levels at diagnosis as risk factors for weight gain after the treatment for hyperthyroidism with radioactive iodine.  there were 111 patient studied with an average age of 53, 79% of which were diagnosed with Graves' disease, and all were treated with radioactive iodine. On average all patients gain weight after treatment and the serum T3 level at the time of diagnosis of hyperthyroidism was the most significant predictor of this weight gain, with higher levels of T3 associated with higher weight gain. Male sex and African American or Hispanic raise are all found to be independent predictors of weight gain. The mean weight increase after reactive iodine therapy reached a maximum of 3.87 kg (5%) at 24 months after treatment. In comparison healthy young adults gained only a mean of 0.2 up to 0.8 kg per year. Weight seemed to stabilize in the long-term setting, with minimal increases between 8 and 12 months and at 24 months after radioactive iodine treatment. The clinical significance of weight gain from the time of diagnosis of hyperthyroidism to 2 years after radioactive iodine therapy is unclear. Limitations of the study were that it was a retrospective study, there is an inability to obtain all the weights and thyroid function values from all patients in the study, and sample sizes were small for the Hispanic and Asian patients. 

*Endocr Pract. 2010 Jul-Aug;16(4):609-16. Male sex, African American race or ethnicity, and triiodothyronine levels at diagnosis predict weight gain after antithyroid medication and radioiodine therapy for hyperthyroidism.