Climbers scaling Africa’s highest peak need to be more aware of the risks associated with high altitude, researchers warn.
More than 25,000 climbers attempt to summit Mount Kilimanjaro each year, which has become an increasingly popular destination.
University researchers tested altitude sickness levels among more than 200 climbers making the ascent.
They found that many of the climbers were taking unnecessary risks at high altitude by failing to acclimatise.
This can lead to altitude sickness, which is potentially fatal.
Almost half of the climbers studied were suffering from altitude sickness, which can occur above 2,500 metres and is caused by climbing too fast.
Symptoms can include headaches, fatigue, and sleep disturbance.
Mount Kilimanjaro, at 5,895 metres, is the world’s highest free-standing mountain.
It is popular among novice climbers, and its profile was also raised last year with a celebrity Comic Relief charity climb.
Most people have no exposure to high altitude before making their ascent because the mountain’s base is only 1,860 metres above sea level.
Scientists camped at 4,730 metres on the mountain for three weeks and studied climbers for symptoms of altitude sickness.
Their study, published in the journal High Altitude Medicine and Biology, found that during the steep ascent, neither altitude sickness drugs nor a rest day during the climb had a major effect against altitude sickness.
They concluded that climbers were going up so steeply that drugs could not protect against the harmful effects of the altitude.
However, the research found that climbers who had managed to acclimatise prior to the climb were less likely to suffer from altitude sickness.
Opportunities for such acclimatisation can be found on Mount Meru, which is 4,566 metres high and located conveniently close to Mount Kilimanjaro.
The researchers have also published advice about how to climb safely and avoid altitude sickness.
In severe instances altitude sickness can lead to potentially fatal conditions.
This includes high altitude pulmonary oedema - fluid accumulating in the lungs - and high altitude cerebral oedema - fluid build-up in the brain.