Every year, an increasing number of people travel to high altitude and travellers with asthma are becoming more common in remote environments.1 It is well recognised that certain situations at high altitude, such as exercising in cold air, may provoke symptoms.2 However, the mountain environment offers a reduced pollutant and allergen load, potentially causing fewer exacerbations.3 Additionally, increased sympathetic tone and adrenocortical output caused by hypoxia counteract bronchospasm. Acetazolamide, used widely by trekkers for the prophylaxis of acute mountain sickness (AMS), has an additional benefit in patients with asthma of reducing airway hyperreactivity.4 To our knowledge, this is the first prospective study comparing lung function, physiology and success in mountain summiting among subjects with asthma and their non-asthmatic counterparts.

We studied altitude physiology and the incidence of AMS in tourist trekkers attempting the summit (Uhuru Peak) of Mount Kilimanjaro (5895 m) in August 2005. All subjects gave written informed consent and ethics approval was obtained from the Tanzanian Commission for Science and Technology (2005-261-NA-2005-62). Lake Louise Score for AMS and basic physiological measurements were taken on ascent. All subjects ascended the mountain over 4 or 5 days.

We compared 18 subjects with asthma (nine males, nine females, mean age 30 years (SD 6.2), mean body mass index 22.9 (1.9)) with 291 subjects without asthma (175 males, 116 females, mean age 34.5 (12.3) years, mean body mass index 22.9 (3.2)). Four were taking acetazolamide. Five subjects were controlled with occasional β agonists, six with regular β agonists, two with inhaled steroids and five were unsure of their medication. None declared any comorbidities and two were smokers.

No significant differences were found in any of the physiological parameters between subjects with and without asthma on ascent. There was an increase in peak expiratory flow rate (Micro Plus device; Micro Medical, Chatham, Kent, UK) in patients with asthma at higher altitude, but its significance (p = 0.123) was limited by underpowering and the fluctuation of readings that meters are subject to at different altitudes.

The incidence of AMS was not different between subjects with and without asthma at any altitude (2700 m: 0/18 vs 3/291, p = 0.665; 4700 m: 9/16 vs 141/224, p = 0.602) and there was no difference in summit success (50% of subjects with asthma vs 61% of subjects without asthma, p = 0.523). No subjects reported any asthma exacerbations.

This study shows that well controlled mild to moderate asthma should not preclude trekkers from attempting to reach high altitude, does not increase the risk of high altitude illness and does not decrease their chance of reaching the summit. This is similar to trekkers with other chronic diseases.5 However, we recognise that these individuals have self-selected; only those with well controlled disease participate in such physical exertion and we are relying on unverified diagnoses. We recommend optimal asthma control before travel, an awareness of the logistics and availability of health care at the destination (including adequate travel insurance), a stock of sufficient medication (including rescue therapy) and, as with all high altitude trips, adequate time for acclimatisation.