Effect of one year residence in Antarctica on bone mineral metabolism and body composition

Objective: To evaluate the changes of the biochemical parameters of mineral metabolism and to assess the effect of these changes on the bone mass of y oung healthy men who voluntarily lived in the Antarctic Continent for one y ear. Design: Lumbar spine and whole body bone mineral density (BMD) were measure d pre- and post-campaign (14 months later). Serum and urinary biochemical p arameters were measured every two months. Serum levels of calcium. phosphat e, total alkaline phosphatase, parathormone (PTH) and 25-hydroxyvitamin D ( 250HD) were determined in blood fasting samples; and hydroxyproline, calciu m and creatinine in 2 h fasting urine. The subjects received a dose of 100 IU/d of vitamin D during May after obtaining the samples and then an averag e of 125 IU/d from July to January. Subjects: Seventeen healthy volunteers. who left Buenos Aires during the 19 92 summer: ten arrived in the Belgrano II Base at the end of January and th e other seven arrived in San Martin in March and stayed there up to summer 1993. Results: BMD increased in lumbar spine (L2-L4), total body and the subarea of the legs but there were no differences between the pre- and post-campaig n values in arms and pelvis. The percentage of fat mass decreased significa ntly after 1 y of residence in Antarctica, in comparison to the basal value s. Most biochemical parameters remained unaltered and within the normal ran ge during the whole study. PTH showed a nadir in March tend of the summer) when compared to initial levels (73.0 +/- 28.2 vs 39.9 +/- 32.7 pg/ml, P < 0.05, and recovered its initial value in spring. Calcium levels showed a si gnificant decrease in March (9.5 +/- 00.4 vs 8.5 +/- 1.0 mg%, P < 0.01). 25 0HD levels began to decrease in March (24.7 +/- 6.4 vs 18.7 +/- 5.3 ng/ml), reaching a minimum value whose difference approached statistical significa nce during the winter period (July: 16.4 +/- 8.2 mi, 0.05 < P < 0.06). No s ignificant changes in serum phosphate, total alkaline phosphatase, urinary hydroxyproline/creatinine and calcium/creatinine ratios were found through the year. Conclusions: 250HD levels decreased in autumn and winter (nadir in July) an d recovered the initial levels by the end of the campaign. An unexplained m arked diminution in PTH and serum calcium was found at the beginning of the campaign. In spite of the low vitamin D levels, bone mass in this group of young healthy men increased, probably because of their intense physical ac tivity. Sponsorship: Fundacion Argentina de Osteologia e Institute Antartico Argent ino.