BACKGROUND
People with hyperthyroidism often lose weight before treatment because the thyroid gland makes too much thyroid hormone, which speeds up metabolism. This is not a healthy weight loss since it also involves losing muscle and bone. After treatment, many patients regain the lost weight, and some may gain more than the weight they had lost and become overweight or develop obesity. Past studies reported possible risk factors for weight gain, such as having more severe hyperthyroidism with higher thyroid hormone levels, having Graves’ disease (the most common cause of hyperthyroidism), getting treatment with radioactive iodine or thyroid surgery, and having low thyroid hormone levels for some time during or after treatment. However, the results were not always similar in different studies. Earlier research also focused mainly on weight at diagnosis and final weight after treatment.

This study was done to better understand weight changes after treatment and find out which factors make some people more likely to gain a lot of weight after treatment of hyperthyroidism.

THE FULL ARTICLE TITLE
Kyriacou A et al. Severity of thyrotoxicosis is a risk factor for excessive weight gain in treated hyperthyroidism. Eur Thyroid J 2025;14(3):e240373; doi: 10.1530/ETJ-24- 0373. PMID: 40238086.

SUMMARY OF THE STUDY
Researchers reviewed patient information from three hospitals in Cyprus. The study included adults who were treated for hyperthyroidism, had at least 6 months of follow-up, and had at least one weight recorded between 6 and 36 months after diagnosis. People who had very mild hyperthyroidism, thyroid cancer, or reversible causes of hyperthyroidism like thyroiditis, pregnancy, weight loss surgery, or conditions or medicines that can affect the weight were excluded.

The researchers looked for factors linked to gaining too much weight after treatment for hyperthyroidism. The factors they studied were age, sex, ethnicity, smoking, disease-related weight loss, body mass index (BMI), thyroid hormone levels, hypothyroidism episodes, treatment type (antithyroid drugs, surgery, or radioactive iodine therapy), cause of hyperthyroidism (Graves’ disease or other), and timing of peak weight.

Weight at diagnosis was measured at the first clinic visit. Patients also reported how much weight they had lost since their symptoms began. Adding this to the diagnosis weight gave an estimate of their baseline weight. Peak weight was the highest recorded weight after treatment and during follow-up. Peak percentage weight gain (PWG) was calculated to show how much weight a person gained at their highest point compared to their weight at diagnosis. Excessive weight gain meant a PWG of 10% or more. Patients were split into two groups based on PWG. Group A had a PWG of 10% or more, and Group B had less than 10%. The 10% cutoff was based on earlier studies showing that about half of the patients gained at least this much weight.

The study included 110 patients with an average age of 49 years and an average follow-up of 24 months. About two-thirds were women, and 84% were Cypriot. Most patients (86%) were treated with medications alone, 11% had surgery after medications, and 3% had radioactive iodine treatment with medications. About 30% had hypothyroidism before reaching their peak weight. Overall, 53% of patients gained at least 10% more weight than at diagnosis. Patients with higher free T4 levels and greater weight loss before treatment were more likely to gain more weight. On average, patients gained about 8.4 kg at their highest weight and 7.3 kg by their last follow-up. Graves’ disease was more common in the group with higher weight gain. Men lost and regained more weight than women, but their percentage weight gain was similar.

WHAT ARE THE IMPLICATIONS OF THIS STUDY?
This study showed that many people gain weight after treatment for hyperthyroidism, especially if they lost a lot of weight before treatment, had more severe thyroid disease, or had Graves’ disease. While the risk of weight gain can seem discouraging, treating hyperthyroidism is very important to prevent serious complications. These findings give patients and physicians the chance to plan. The best way to stay in control is to be aware of the risk and take early steps. Talking about ways to prevent weight gain, healthy eating, physical activity, and regular monitoring can help manage weight changes and should be part of the treatment plan from the start.

— Ebru Sulanc, MD

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