Long-term weight changes in treated hyperthyroid and hypothyroid patients.

To compare the effect of three treatments for thyrotoxicosis on subsequent body weight, a retrospective survey of 65 patients was performed. The effect of thyroxine replacement on body weight in 25 patients with primary hypothyroidism was also examined. In one year after starting therapy 21 patients treated with carbimazole gained a mean of 5.4kg (95% confidence interval 3.6 to 7.2kg); 20 patients after thyroidectomy gained a mean of 6.3kg (95% c.i. 3.4 to 9.2kg); and 24 patients given radioiodine gained a mean of 7.4kg (95% c.i. 5.2 to 9.6kg), p less than 0.001 in all three groups. The weight gain in the three groups was not significantly different. 54-67% of the weight gain occurred in the first three months. The patients treated for hypothyroidism had lost an insignificant amount of weight 12 months after starting therapy--mean change was -0.6kg (95% c.i. -2.2 to +1.1kg) p greater than 0.1. This data suggests that all patients treated for thyrotoxicosis will gain body weight irrespective of the treatment used, but patients treated for primary hypothyroidism will not lose an appreciable amount of weight. Therefore dietary advice should be given, where appropriate, at the onset of any treatment of thyroid dysfunction.