Determination of bone mass using multisite quantitative ultrasound and biochemical markers of bone turnover during residency at extreme altitude: a longitudinal study.

A group of 221 male healthy volunteers of Indian Army were the subjects of the study. The baseline parameters of skeletal health were measured during their residency at an altitude of 3542 m. These subjects were then taken to an extreme altitude (EA, 5400-6700 m) where they stayed for about 4 months. The study parameters were repeated following their de-induction (DI) to 3542 m. On random selection, a subgroup was constituted from the above mentioned volunteers for detailed investigations on various bone turnover markers. Results of this study indicate a loss of body weight after DI from EA. The bone impairment was detected at the proximal phalanx, which is known to undergo early morpho-structural changes associated with bone resorption. The intact parathyroid hormone (i-PTH) levels showed a significant increase, while alkaline phosphatase (ALP) and bone specific alkaline phosphatase (BAP) activities declined significantly after DI from EA. This elevation in i-PTH might be required for maintenance of blood Ca level. 25 (OH) Vitamin D3 (25VitD) and calcitonin (CT) also showed a significant decline, which may suggest a negative impact on bone formation during sojourn at EA. The causes of deterioration of skeletal health at EA although are poorly understood but may be due to acute hypoxemia arising from extreme hypobaric hypoxia prevalent at extreme altitude.