Severity of thyrotoxicosis is a risk factor for excessive weight gain in treated hyperthyroidism

Hyperthyroidism is characterized by weight fluctuations and overshoot of weight regain following treatment. We aimed to identify parameters predicting peak percentage weight gain (PWG) in the post-treatment period.

We included 110 patients (73 (66.4%) women) with hyperthyroidism 6-36 months after treatment initiation. The primary outcome was PWG of ≥10% (group A) or <10% (group B). We performed adjusted analyses by logistic regression with age, sex, disease-related weight loss, hypothyroidism occurrence, free T4 at diagnosis (fT4-t0) and disease duration as independent variables.

Post-treatment mean (SD) weight gain was 7.4 (5.22) kg, whereas disease-related weight loss was 5.3 (5.15) kg. Group A (52.7% participants) compared to group B had significantly higher median (IQR) fT4-t0 at 47.4 (36.2, 97.2) vs 29.3 (22.8, 40.4) ng/dL (P < 0.001) and disease-related weight loss at 6.8 (3, 10) vs 2.5 (0, 4.8) kg (P < 0.001) and non-significantly higher presentation free triiodothyronine at 19.6 (10.4, 44.1) vs 11.8 (8.7, 22.9) pg/mL (P = 0.078) and TRAb at 6.3 (3, 16.1) vs 4.2 (2.4, 8.7) IU/L (P = 0.093), respectively. Significant predictor variables of post-treatment PWG in logistic regression were disease-related weight loss (OR = 1.23, P = 0.002) and fT4-t0 (OR = 1.04, P = 0.008).

More than half the patients with hyperthyroidism had ≥10% PWG post-treatment. Indicators of disease severity, namely disease-related weight loss and baseline thyroid hormones, were predictive of excessive weight gain post-treatment and could be utilized for risk stratification and early intervention.