Background. Disturbed thyroid function is accompanied with weight changes in most of patients. Less
is known how the therapy of hyperthyroidism and hypothyroidism influences their body composition.
Methods and Results. We investigated 18 persons with newly diagnosed hyperthyroidism (group I), 15
persons with newly diagnosed hypothyroidism (group II), 22 persons with long-lasting well-controlled
primary hypothyroidism (group II) and 17 persons with history of cured hyperthyroidism (group IV). Body
composition, including percentage of body fat, was examined with Dual energy absorptiometry method
(DXA; GE Lunar prodigy). There was no significant difference in age, BMI, and % of body fat between
groups. Group I had mean levels of free T4: 43.1±20.1 pmol/L, and TSH 0.03±0.05 mU/L. Mean values of
TSH 28.55±20.64 mU/L and free T4 5.94±2.27 pmol/L were in accordance with the diagnosis of untreated
hypothyroidism in group II. Thyroid function in groups III and IV was within normal limits. The mean weight
gain in group I was 3.9 kg and their BMI increased from 25.78±3.73 kg/m2 to 27.36±4.03 kg/m2 after the
therapy (p=0.023). BMI has not changed significantly in group II after the normalization of thyroid function,
nor in group II and III. A significant parallel increase in the total body fat (26737±6993 g vs. 31277±8735 g),
(p=0.0078) as well as in lean mass (43936±9886 g vs 51065±9501 g) (p= 0.0156) was observed only in group
I after therapy. There was no increase in percentage of body fat (38.04±8.6% vs.38.0±9.8%) (NS). The body
composition did not changed in the other patients treated during the follow-up.
Conclusions. Normalization of thyroid function of newly diagnosed hyperthyroid patients caused the
parallel increase in their fat mass and lean body mass, assed with DXA. Percentage of fat mass did not
change significantly after the treatment. Correction of hypothyroidism did not lead to the body
composition changes; patients did not show any weight loss either.
body composition, DXA, percentage of body fat, thyroid function.