Background  The low-pressure and low-oxygen environment at high altitude leads to changes in the levels of various endocrine hormones. However, the results of previous studies are inconsistent.

  Objective  To investigate the effects of high altitude on endocrine hormone levels in healthy adults.

  Methods  The blood samples were collected from 98 healthy soldiers (59 males, 31.07 ± 7.50 years old; 39 females, 36.05 ± 5.56 years old) who entered from Lanzhou (1500 m) to Ngari (4300 m) for one year. Radioimmunoassay and chemiluminescence were used to detect the levels of aldosterone, cortisol, thyroid hormone, sex hormone and biochemical indicators in soldiers.

  Results  Totally 98 healthy soldiers were enrolled, including 59 males aged 31.07 ± 7.50 years old and 39 females aged 36.05 ± 5.56 years old. There were no significant changes in serum aldosterone and cortisol levels in subjects of different genders after one year in Ngari. The level of free triiodothyronine (FT3) significantly decreased (P<0.05), while the level of anti-triiodothyronine (RT3) significantly increased (P<0.05) comparing with that before entering to the plateau. In addition, the level of total triiodothyronine (TT3) in male was higher than that in control subjects (P<0.05). Moreover, the levels of follicle stimulating hormone (FSH), luteinizing hormone (LH) and prolactin (PRL) in healthy men increased obviously after one year of stationing at high altitude (P<0.05). In contrast, blood testosterone (T) levels reduced significantly (P<0.05). For women, T level increased significantly (P<0.05), and estradiol (E2) level showed a downward trend after one year in Ngari, but the difference was not statistically significant (P=0.067). Furthermore, the levels of alanine aminotransferase (ALT) and glutamyl transpeptidase (GGT) decreased (P<0.05), and the level of bilirubin increased significantly (P<0.05) in male. Under the same condition, ALT, total bilirubin (T-BIL), indirect bilirubin (I-BIL) and their abnormal rates increased significantly in female subjects (P<0.05), and the levels of blood urea nitrogen (BUN) and creatinine (CREA) also significantly increased (P<0.05). The correlation analysis between biochemical indexes and hormone levels in male showed that the LH level was positively correlated with the changes of T-BIL (r=0.315, P<0.05) and I-BIL (r=0.336, P<0.05). RT3 level was also positively correlated with direct bilirubin (D-BIL) (r=0.330, P<0.05), while FT3 was negatively correlated with BUN/CREA (r=-0.382, P<0.05). In female, the T level was positively correlated with T-BIL (r=0.490, P<0.05 ), D-BIL (r=0.389, P<0.05) and I-BIL (r=0.495, P<0.05). E2 level was negatively correlated with T-BIL (r=-0.452, P<0.05) and I-BIL (r=-0.449, P<0.05).

  Conclusion  Living at high altitude for one year has a certain degree of influence on the levels of thyroid hormone and sex hormone in healthy adults. In addition, there is a correlation between the change of hormone levels and liver renal function. The above changes are adaptive mechanism of the body to maintain the relative balance of internal environment to adapt to the plateau environment.