Thyroid Hormone levels in Highlanders- A Comparison Between Residents of Two Altitudes in Nepal

Abstract

Background The endocrine changes related to altitude adaptation in human have attracted physiologists around the globe for long. A number of high altitude studies to detect the physiological changes have been performed now and then. But, the study to see the hormonal changes to compare populations residing at different high altitudes is a scarce. Hence, we have performed a study in native populations of different high altitude comparing changes in thyroid hormones in western Nepal. The Jharkot population included in this study is at altitude of 3760m and Jomsom population at 2800m height from sea bed. Objective The study is to compare changes in thyroid hormones at two different high altitude natives. Methods To compare thyroid status between high altitude natives at two different altitudes a cross sectional study is performed by random sampling method. The blood sample was collected in a vacutainer from fifty eight individuals after obtaining the informed consent of participants. The blood collected from antecubital vein was centrifuged in an hour and the serum obtained was used for biochemical analysis of free triiodothyronine, free thyroxine and thyroid stimulating hormone. Results Mean free thyroxine (fT4) of Jharkot population is significantly larger (p = 0.001) than Jomsom population. Mean thyroid stimulating hormone (TSH) with p = 0.597, does not indicate the difference between this two population. There is no significant difference between mean free triiodothyronine (fT3) of Jharkot and Jomsom population (p = 0.345). Conclusion The rise in free thyroid hormone at high altitude is not dependent on the thyroid stimulating hormone released from anterior pituitary. The rise in free thyroxine is found at higher altitude and no difference in fT3 level is detected in population studied at high altitudes. DOI: http://dx.doi.org/10.3126/kumj.v11i1.11017 Kathmandu University Medical Journal Vol.11(1) 2013: 18-21

Establishment of Reference Intervals for Thyroid-Associated Hormones Using refineR Algorithm in Chinese Population at High-Altitude Areas

“…Our results roughly concurred with previous studies which reported significant increases in thyroidassociated hormones for people following short-term or prolonged exposure to high-altitude environments (11,17,24,25). Elevated thyroid-associated hormones in high-altitude environments facilitate the resistance of the body to the harsh environment of high altitude and seem to be independent on pituitary gland secretion of TSH (24,26). Furthermore, altitudedependent FT3 rise may also be relevant to physiological changes caused by the relative lack of iodine, as studies have shown that Tibetan regions have lower urinary iodine levels and a higher risk of iodine deficiency compared with mainland China (27,28).…”

Adrenal, thyroid and gonadal axes are affected at high altitude

“…Thyroid function dysregulations are not clear according to previous studies. Nepal et al compared thyroid function in indigenous people at 2800 and 3750 m ( 9 ). fT4 was significantly elevated at 3750 m, but not fT3 and TSH.…”

“…Several studies have already investigated various hormone concentrations at high altitude ( 1 , 2 , 3 , 4 , 5 , 6 , 7 , 8 , 9 , 10 ).…”

Das Endokrinium auf bis zu 7000 Höhenmetern

“…Bei einer Höhe unter 5300 m scheint die Hypophysen-Schilddrüsen-Funktion hingegen weniger oder nicht supprimiert zu sein. So verglichen Nepal et al [21] die Schilddrüsenfunktion bei Einheimischen auf 2800 und 3750 Höhenmetern. Freies T4 war auf 3750 m erhöht, nicht jedoch freies T3 und TSH.…”