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Background: Weight gain during treatment of hyperthyroidism is a frequent and for many patients unwanted outcome. With this repeated measurement study, we explored the timing of weight changes during the first year of antithyroid drug (ATD) treatment and assessed the correlation between body weight changes and changes in thyroid hormones, resting energy expenditure (REE), physical activity level, and energy efficiency. Methods: Patients with new onset hyperthyroidism were investigated every second month during the first year of ATD treatment. At each investigation, the following were measured: body weight, thyroid hormone concentrations, physical activity level, and daily number of steps, REE, and exercise performance. Results: Two men and eleven women, all sedentary, mean age 49(SD: 9.3) years were included. Significant changes after 1 year occurred for body weight (68.9–74.1 kg), thyroid hormones (free T3 [fT3] 17.5 to 4.42 pmol/L), REE (1,630–1,484 kcal/24 h), and energy efficiency at lower (50 W) workloads (16.0–17.6%). In individual patients, only REE and fT3 correlated to changes in body weight. Physical activity level did not change during treatment. Conclusion: In this study, treatment of hyperthyroidism was associated with marked increase in body weight in the patients. This increase correlated to a decrease in REE and only to a negligible extent to changes in energy efficiency and not at all to changes in physical activity level of daily living.

Objectives: In previous studies, around half of all hypothyroid patients preferred levo-thyroxine (L-T4) + levo-triiodothyronine (L-T3) combination therapy, 25% preferred T4, and 25% had no preference. The reason for this is yet to be explored. Methods: A total of 45 overtly autoimmune, hypothyroid patients – now euthyroid on ≥6 months’ L-T4 therapy – participated in a prospective, double-blind, cross-over study. The patients were randomized into 2 groups of either 3 continuous months’ L-T4 therapy followed by 3 months’ combination therapy or vice versa. In all periods, 50 μg L-T4 was blindly replaced by either (identical) 50 μg L-T4 or by 20 μg T3. L-T4 was hereafter adjusted to obtain normal serum TSH values. We investigated 3 single nucleotide polymorphisms (SNPs) on the type II iodothyronine deiodinase (DIO2) gene (rs225014 (Thr92Ala), rs225015, and rs12885300 (ORFa-Gly3Asp)) and 1 SNP on the cellular membrane transport-facilitating monocarboxylate transporter (MCT10) gene (rs17606253), and asked in which of the 2 treatment periods patients felt better (i.e., which treatment was preferred). Results: 27 out of 45 patients (60%) preferred the combination therapy. Two polymorphisms (rs225014 (DIO2, Thr92Ala) and rs17606253 (MCT10)) were combined yielding 3 groups: none vs. 1 of 2 vs. both SNPs present, and 42 vs. 63 vs. 100% of our patients in the 3 groups preferred the combined treatment (Jongheere-Terpstra trend test, p = 0.009). Conclusion: The present study indicates that the combination of polymorphisms in DIO2 (rs225014) and MCT10 (rs17606253) enhances hypothyroid patients’ preference for L-T4 + L-T3 replacement therapy. In the future, combination therapy may be restricted or may be even recommended to individuals harbouring certain polymorphisms.

Important interaction exists between thyroid function, weight control, and obesity. Several mechanisms seem to be involved, and in studies of groups of people the pattern of thyroid function tests depends on the balance of obesity and underlying thyroid disease in the cohort studied. Obese people with a normal thyroid gland tend to have activation of the hypothalamic-pituitary-thyroid axis with higher serum TSH and thyroid hormones in serum. On the other hand, small differences in thyroid function are associated with up to 5 kg difference in body weight. The weight loss after therapy of overt hypothyroidism is caused by excretion of water bound in tissues (myxoedema). Many patients treated for hyperthyroidism experience a gain of more weight than they lost during the active phase of the disease. The mechanism for this excessive weight gain has not been fully elucidated. New studies on the relation between L-T₃ therapy and weight control are discussed. The interaction between weight control and therapy of thyroid disease is important to many patients and it should be studied in more detail.

Objective: To investigate the association between reproductive history and later development of various nosological subtypes of overt hyperthyroidism. Study Design: From the Danish population, we included incident hyperthyroid women, and for each case we recruited 4 euthyroid age-sex-region-matched controls from the same sub-population. Hyperthyroid cases/controls were: Graves’ disease (GD, n = 232/928), multinodular toxic goitre (MNTG, n = 91/364), solitary toxic adenoma (STA, n = 21/84). Patients diagnosed with hyperthyroidism within 1 year after delivery including post-partum GD were excluded. In multivariate conditional regression models (reference: no reproductive events), we analysed the association between development of GD/MNTG/STA and reproductive factors such as age at menarche/menopause, reproductive span, number of pregnancies/childbirths/abortions, investigations for infertility, and years on oral contraceptives. We adjusted for possible confounders such as alcohol intake, smoking, co-morbidity, and education. Age was studied as a potential effect measure modifier. Results: GD patients diagnosed before the age of 40 years had given births more often than control subjects (OR [95% CI] for 1/2/3+ births [ref.: nulliparous] were 1.57 [0.80–3.11]/2.06 [1.001–4.22]/3.07 [1.50–6.26]), and they had induced abortions performed more often (OR for 1/2+ induced abortions [ref.: no: events] were 0.99 [0.54–1.84]/2.24 [1.12–4.45]). No associations were observed between any reproductive factor and the development of MNTG or STA. Conclusions: Childbirths and induced abortions may be followed by development of Graves’ hyperthyroidism after the post-partum period. This was not the case for the non-autoimmune subtypes of hyperthyroidism.