Residence at 1200 m Induces a Threefold Reduction in the Risk of Acute Mountain Sickness After Rapid Ascent to 3600 m.

UNLABELLED: Moderate-altitude residence (1600-2400 m) elicits altitude acclimatization and reduces acute mountain sickness (AMS) after rapid ascent to higher altitude (HA). Cross-sectional studies suggest lower-altitude residence (800-1200 m) provides similar benefits, but conclusions are unclear due to a lack of control.

PURPOSE: Determine whether moderate-altitude residents (MAR, 1200 m) experience less AMS than low-altitude residents (LAR) after active or passive ascent to HA (3600 m).

METHODS

Seventy-eight soldiers (mean ± standard deviation; age = 26 ± 5 yr; women = 8) were tested at their baseline residence at 331 m (LAR; n = 41) or 1200 m (MAR; n = 37), transported to Taos, NM (2845 m), hiked ( n = 39) or were driven ( n = 39) to 3600 m and stayed for 4 d. AMS was assessed using the Environmental Symptoms Questionnaire twice on day 1 (HA1), five times on days 2 and 3 (HA2, HA3), and once on day 4 (HA4). Daily peak cerebral factor score (AMS-C) was recorded; if AMS-C was ≥0.7, individuals were considered sick that day.

RESULTS

Ascent condition (active vs passive) did not demonstrate a significant main or interaction effect on AMS. The MAR versus LAR experienced lower AMS incidence on HA1 (16% vs 44%, P = 0.008) and HA2 (19% vs 39%, P = 0.05), similar incidence on HA3 (14% vs 29%, P = 0.08), and lower incidence on HA4 (0% vs. 17%, P = 0.007). AMS-C was lower in MAR versus LAR on HA1 (0.40 ± 0.49 vs 0.74 ± 0.86, P = 0.04), HA2 (0.30 ± 0.34 vs 0.86 ± 0.88, P = 0.001), HA3 (0.30 ± 0.36 vs 0.56 ± 0.69, P = 0.03), and HA4 (0.09 ± 0.14 vs 0.35 ± 0.58, P = 0.01). MAR exhibited an approximately threefold reduction in the odds of developing AMS at HA1 (odds ratio [OR] = 0.25, P = 0.01), HA2 (OR = 0.37, P = 0.05), and HA3 (OR = 0.38, P = 0.09) compared with LAR.

CONCLUSIONS

Residence at 1200 m induces a threefold reduction in the odds of developing AMS after rapid ascent to 3600 m.