Researchers from UK’s Edinburgh University who examined climbers attempting to scale the summit of Africa’s highest peak Mount Kilimanjaro, a destination that attracts more than 25,000 people every year, found that many of them were failing to acclimatize to the high altitude, leaving themselves open to high risk of of altitude sickness, a potentially fatal condition.

The study was the work of lead author Stewart J. Jackson and colleagues, and was published online in the journal High Altitude Medicine and Biology on 4 October.

Jackson, who has degree in in neuroscience, is a medical student at the Royal Infirmary of Edinburgh, University of Edinburgh, Scotland. Like several of his co-authors, he is an experienced climber with a long-standing interest in altitude physiology and medicine. He led the Edinburgh Altitude Research Expedition 2009 to Mount Kilimanjaro after being appointed President of the University of Edinburgh Wilderness Medicine Society.

Jackson and colleagues found that almost half of the 200-plus climbers they examined were suffering from altitude sickness, a potentially fatal illness that can start developing at 2500m above sea level, and is caused by climbing too fast.

There are three types of altitude sickness. Mild altitude sickness (also called AMS acute mountain sickness), is very common, and feels like a hangover with symptoms such as headache, nausea and fatigue. Some people are only slightly affected, while others can feel really ill.

If you have AMS you should take it as a warning sign, say Jackson and some of his team on a website they set up, and stop climbing.

The best treatment for AMS is descent, they urge, because having AMS means you are at risk of developing one, or more likely both, of the more serious types of altitude sickness, HAPE (high altitude pulmonary edema or excess fluid on the lungs) and HACE (high altitude cerebral edema, or fluid on the brain), both of which can kill within hours.

HAPE makes you feel breathless not just when you are climbing but also when you are resting, which is not normal, even if you are resting at the top of Mount Everest; if this happens, death is almost inevitable. HAPE can also cause fever, and a cough where you bring up frothy spit.

HACE makes you feel clumsy and confused, and you stumble. At first you may just feel lethargic and lazy, and you can also feel very violent or emotional. Death soon follows a period of drowsiness that ends in loss of consciousness.

Altitude sickness is most likely caused by two things: ascending faster than 500m per day, and vigorous physical exertion. It can affect even extremely fit people: Olympic athletes have been known to get altitude sickness, which happens because of the lower concentration of oxygen in the air at high altitude.

With a summit at 5895m or 19341ft above sea level, Mount Kilimanjaro, situated in north-eastern Tanzania in central East Africa, is the world’s highest free-standing mountain and the fourth most prominent mountain in the world.

It has become a popular destination among novice climbers, with many from the UK spurred by the well publicized celebrity Comic Relief charity climb that took place in 2009.

However, because the base of Mount Kilimanjaro is only at 1860m above sea level, most climbers have had no exposure to high altitude before they ascend toward the summit.

For their study, Jackson and colleagues got climbers to complete questionnaires based on the “Lake Louise consensus scoring system” (LLS), and they also examined the effect of the drug acetazolamide and different ascent profiles.

The LLS is a self-administered questionnaire that assesses the severity of symptoms like headache, gastrointestinal symptoms, fatigue and weakness, dizziness and lightheadedness, and sleep. It also assesses the extent to which the symptoms hamper activities and normal functioning.

The researchers recruited climbers on 3 different ascent itineraries. At 2743m they recruited 177 climbers, aged from 18 to 71 and average age 31, and got them to fill in the LLS and another epidemiological questionnaire.

Then at 4730m they got 189 participants (108 men and 68 women of average age 33, also in the range 18 to 71) to fill in the LLS, most of whom had been followed up from the lower level.

They found that 3 per cent of the climbers were positive for AMS at 2743m, and 47 per cent of all the climbers were positive for AMS at 4730m.

Of 136 climbers on one itinerary, 45 (33 per cent) were taking acetazolamide, a drug used to reduce mountain sickness; however, they had a similar rate of AMS and no statistical difference in symptom severity as measured by LLS compared to those not taking AMS prevention drugs.

The researchers also found no difference in AMS incidence between climbers who did and those who did not take a rest day at 3700m.

However, they found a significant reduction in AMS incidence among climbers who had pre-acclimatized themselves before starting the ascent.

They concluded that:

“Consistent with previous work, we found that the rate of AMS on Mount Kilimanjaro is high.”

“Furthermore, at these fast ascent rates, there was no evidence of a protective effect of acetazolamide or a single rest day,” they added, urging that there was a need to “increase public awareness of the risks of altitude sickness and we advocate a pragmatic ‘golden rules’ approach”.

There are three “golden rules”:

  1. If you feel unwell, assume you have altitude sickness until proven otherwise.
  2. Do not ascend further if you have symptoms of altitude sickness.
  3. If you are getting worse then descend immediately.

There are opportunities to acclimatize on Mount Meru, which is 4,566m high and situated close to Mount Kilimanjaro, the researchers said in a statement.

For more information on and advice on acclimatizing and the Golden Rules, and how to avoid AMS, HAPE and HACE, see the authors’ website at

On their website they write:

“Every year, people die of altitude sickness. All of these deaths are preventable. If you are travelling above 2500m (8000ft), read this information and tell your companions about it – it could save your life.”

“Incidence and predictors of acute mountain sickness among trekkers on Mount Kilimanjaro.”
Stewart J. Jackson, James Varley, Claudia Sellers, Katherine Josephs, Lucy Codrington, Georgina Duke, Marina A. Njelekela, Gordon Drummond, Andrew I. Sutherland, A. A. Roger Thompson, J. Kenneth Baillie.
High Altitude Medicine & Biology. Fall 2010, 11(3): 217-222.

Sources: Edinburgh University,

Written by: Catharine Paddock, PhD