Context: It is known that hypothalamic amenorrhea (HA) is associated with low bone turnover due to low gonadal hormone levels. Estrogens are critical for activation of bone remodeling, suppression of bone reabsorption, increase of 1-25(OH) Vitamin D receptors expression. Other mechanisms include improper diet and unbalanced exercise, influencing the peripheral conversion of Thyroxine to active Triiodothyronine (low-T3). On the other hand, hormonal influences on antioxidant systems could affect Vitamin D metabolism. Objective: To evaluate the impact of hormonal alterations and antioxidant systems on bone turnover. Patients: 37 female patients with a history of secondary amenorrhea, lasting at least six months, aged 17– 33 years, with a BMI range 17.4–23.4 kg/mq. Intervention: Morning blood sample collection for: FSH, LH, estradiol, fT3, fT4, TSH, IGF-1, osteocalcin, Total Antioxidant Capacity (TAC). Patients were divided in three groups according to fT3 levels; group A (n=18): low T3 (<1.4 pg/ml according to laboratory range); group B (low-normal fT3) and group C (normal fT3) were divided according to the median obtained in patients with fT3 level in the normal range, group B (n=10) with fT3 range of 2.4-2.6 pg/ml and group C (n=9) with fT3 values>2.6 pg/ml. Methods: Hormones were assayed by chemiluminescence; osteocalcin by electrochemiluminescence. TAC was evaluated as latency time (LAG, sec) in the appearance of chromogen ABTS, whose radical species are spectroscopically detectable, using the system H2O2-metmioglobin. Results: Patients of group A showed significantly lower mean±SEM levels of IGF-1 (167,47±22,73 ng/mL vs group B 191,44±7,11 and group C 256,78±25,22) and osteocalcin (17,27±1,55 ng/mL vs group B 18,29±2,22 and group C 26,11±2,27); on the contrary LAG values were significantly higher in group A 63,08±6,68 vs group B 55,71±2,71, group C 46,67±6,21. Moreover a significant direct correlation was found between both IGF-1 and fT3 with osteocalcin (r² = 0,204, p=0,0052 and r² = 0,4384, p=0,00013, respectively) and an inverse correlation between LAG and fT3 (r² = 0,114, p=0,0492) Conclusions: These data confirm high prevalence of low T3 syndrome in HA. Hormonal derangement are more frequent in patients with low fT3 and low normal fT3. Oxidative stress could be the link underlying different bone turnover pattern and endocrine dysfunction in HA.