A preliminary study of the effect of menstruation on the incidence of acute mountain sickness

Over 50% of those engaging in high altitude activities are women. Nonetheless, women have historically been neglected in scientific literature regarding backcountry environments. Acute mountain sickness (AMS), a condition triggered by hypoxia, is common at altitudes >2500 m above sea level, and prior studies suggest that women are particularly vulnerable to it due to hormonal changes associated with menstruation. Therefore, this study assessed the association of menstruation and AMS incidence during a highaltitude expedition to Mount Kilimanjaro. This retrospective study involved a review of records from the Equal Playing Field expedition, in which 48 female athletes trekked to the summit of Mount Kilimanjaro via the Shira route (5895 m) to set a world record for the highest altitude soccer match. One emergency medicine physician with altitude experience served as Chief Medical Officer along with two wilderness emergency medical technicians. The medical team conducted ‘rounds’ in the mountain camp every evening, determining if anyone had any AMS or other nonAMS symptoms. AMS was defined by the Lake Louise Consensus Scale and the physician’s clinical judgement. Moreover, formal physiological assessments of every participant were conducted throughout the expedition and detailed records were kept. The incidence of AMS was recorded and compared between women who were and were not menstruating during the expedition as well as those women taking and not taking acetazolamide. Relative risk (RR) was used to compare AMS incidence by menstruation status, prophylaxis status, and menstruation and prophylaxis status combined. All analyses were conducted in R Studio V.1.4.1717 with an alpha level of 0.05. Two women were excluded from analyses as one was postmenopausal and one had prior highaltitude exposure, which may have decreased her odds of developing AMS compared to those without exposure. Of the 46 women, 13 (28.3%) developed AMS. Among the 17 menstruating, 6 developed AMS (35.3%) vs 7 of the 29 not menstruating (24.1%), RR 1.5, 95% CI 0.6 to 3.6 (table 1). For the 37 (80.4%) women that took prophylactic acetazolamide therapy, 11 developed AMS (29.7%) vs 2 of the 9 (22.2%) that did not take acetazolamide, RR 1.3, 95% CI 0.4 to 5.0. Of women taking acetazolamide, AMS incidence was 38.5% in those menstruating vs 25.0% of those not menstruating, RR 1.6, 95% CI 0.6 to 4.1. There was no significant difference in AMS incidence between women who were and were not menstruating or any effect of prophylaxis on this relationship. While the sample size is small, this provides evidence against menstruation having a large effect on the development of AMS, mostly contradicting prior literature. Although participants menstruating versus not menstruating were not matched in terms of age, medical history or medication use, we still believe this is an important preliminary study on this topic. It has been suggested that the hormones involved in menstruation may account for women’s susceptibility to developing AMS. Richalet et al observed that womens’ physiological responses to high altitude were related to menstrual cycle phase, with the luteal/midluteal phase being protective against AMS. This is supported by Takase et al, who similarly found that women in the luteal phase at high altitude had an enhanced ventilatory response in hypoxic conditions than those in the follicular phase. Contrastingly, Riboni et al found no difference in AMS incidence, symptom scores or oxygen saturation between women at midfollicular versus midluteal phase in a hyperbaric chamber simulating 15000 ft of altitude. Future research should focus on investigating specific hormonal influences on AMS incidence and performing a larger, similar study with more rigorous controls. Such research may add to the paucity of information on the topic and address discrimination against female athletes in extreme conditions. Megan Elizabeth Paul , Thomas D Wagner, Connor A Tukel, Dana R Levin Medical Education, Icahn School of Medicine at Mount Sinai, New York, New York, USA Medical Education, Columbia University Vagelos College of Physicians and Surgeons, New York, New York, USA Aerospace Medicine, The University of Texas Medical Branch at Galveston, Galveston, Texas, USA Emergency Medicine, University of Colorado— Anschutz Medical Campus, Aurora, Colorado, USA