## 4 Discussion
This should serve as a reminder to routinely check for both TSH/free T4 and also T3 in patients receiving thyroxine replacement therapy to elucidate the risk of sarcopenia. As an indicator of nutritional status, GNRI has been shown to be a predictor of sarcopenia in generally healthy older people [33], older cardiac patients [34], older patients with chronic obstructive pulmonary disease [35], patients under hemodialysis [36], and patients with early-stage non-small cell lung cancer [37]. However, to the best of our knowledge, this is the first study to prove this relationship in patients with total thyroidectomy. Other determinants of sarcopenia in this study were low femoral neck BMD with low muscle mass, low ASM/ht2 and long duration of menopause with weak handgrip strength, and young age with low gait speed. Except for the last factor, the other relationships are intuitive and have been reported in previous studies [38; 39; 40; 41]. It is unclear why our older patients had higher gait speeds. However, this result should serve as a reminder to evaluate dynapenia in female patients post-thyroidectomy, even if they are relatively young, as they may have sufficient muscle quantity but poor quality. Moreover, poor muscle quality has been associated with hard outcomes such as all-cause mortality and hospitalization [42]. Furthermore, sarcopenia has also been shown to increase the incidence of falls and fractures, metabolic impairment, chemotherapy-related toxicity, depression, and decreasing quality of life [4; 43]. Patients who undergo total thyroidectomy require lifelong levothyroxine therapy. In addition, if they are diagnosed with differentiated thyroid carcinoma and classified as being at high risk of recurrence or a structurally incomplete response, TSH over-suppression is recommended for longer relapse-free survival [44]. Current guidelines already emphasize the adverse effects of TSH suppression, including cardiovascular complications, osteoporosis, and cognitive dysfunction; however, they do not mention sarcopenia [44; 45]. Nevertheless, greater attention should be paid to muscle health because proteolysis or muscle breakdown has been observed in early hyperthyroidism, along with an increased heart rate, with resolution of the abnormality after the resolution of hyperthyroidism [46]. For patients who need to keep taking levothyroxine over-replacement, aerobic activity training [23], resistance training [47], and additional protein supplements [48] have been shown to partially improve muscle health. In our study population, the prevalence of ASM/ht2\(\leq\) 5.4 was 8%, which is similar to the 10% reported sarcopenia in healthy older women in previous studies [49]. Therefore, clinicians need to be aware of this common comorbidity in postmenopausal women with total thyroidectomy and try to prevent or manage it, as not doing do may result in a worse prognosis. In this study, there are some limitations. First, we cannot assess longitudinal relationships between these parameters and ASM/height2 or physiological performance because it is a cross-sectional study. Second, we were not able to include a control group of healthy postmenopausal women of the same group as potential confounders because several parameters used in this study were age dependent. Lastly, it is not possible to use statistical tests to draw reliable conclusions because of the relatively small number of enrolled patients. Therefore, to confirm our results, we need follow-up large-scale studies.