December 7, 2021

I, Science

The science magazine of Imperial College

The extreme dehydration that one race runner suffered after getting lost in a desert storm ...

sahara thirst

Every April, one thousand or so of the world’s toughest athletes gather in southern Morocco for a punishing six-day foot race through the Sahara desert – The Marathon des Sables. Running a total of 156 miles (five and a half marathons) in 50-degree heat, competitors are allocated a day’s supply of water every morning. Aside from this, they’re entirely self-sufficient, carrying on their backs everything they need for their gruelling week of desert adventure.

Water makes up about 60% of our total body weight. Amongst its many essential functions it maintains our blood pressure, nourishes our cells, lubricates our joints, eliminates waste, and regulates our body temperature. On a typical day in a moderate climate we each lose around 2.5 litres of fluid, mostly through urine, sweat and moisture exhaled in our breath. On a hot day this figure rises to 3.5 litres. We maintain a ‘water balance’ by drinking and eating to replace the lost fluid. Combine the sweltering temperatures of the Sahara with prolonged heavy exercise, and the average Marathon des Sables runner requires a fluid intake of over 9 litres per day.

Race organisers ensure that competitors remain hydrated throughout the event. But what happens when the organisers are nowhere to be seen? In 1994 39-year-old Italian police officer, Mauro Prosperi, found out the hard way.

A gifted and experienced runner, Prosperi was in seventh place as he set off on Day 4 – a leg that demanded a whopping 50 miles of progress in one day. At the 20-mile checkpoint, Prosperi grabbed a 2-litre bottle of water and taped up a blistering foot before setting off again. Soon after, the wind picked up. A storm blew over, and for the next six hours sand was dumped across the marked trail in high drifts. Disorientated, Prosperi began to run south instead of east. He was lost, and 1000 miles of empty desert lay ahead. A day later, a rescue helicopter flew over, but failed to spot him. By the fourth day, Prosperi was reduced to drinking urine he’d saved in a bottle.

Desperate times and desperate measures

So just how thirst-quenching can pee be? Perhaps surprisingly, there’s no simple answer. The US Army Field Manual advises against drinking urine in a survival situation as it contains harmful body wastes and has a high salt content. To get rid of these extra salts, the kidneys need to excrete even more water. But many individuals have attributed their survival to drinking their own urine: Aron Ralston, for example – the American adventurer whose extraordinary tale is told in Danny Boyle’s movie, 127 Hours. Ralston (played by James Franco) became trapped in a canyon in Utah when a dislodged boulder pinned his arm against a wall. After four days, he ran out of food and water, and resorted to drinking his urine. On Day 5, Ralston freed himself by breaking his trapped arm and cutting it off using a dull two-inch knife on his multi-tool… which makes drinking his own pee seem decidedly less gruesome!

Bear Grylls is another great proponent of urine-drinking, pointing out that it can also be a pleasant cooling agent in the hot, dry desert. I can’t imagine that a urine-dowsed Grylls was particularly pleasant in the eyes of his camera crew though.

So who is right? Well, urine may be a useful last-resort, perhaps giving the stranded desert wanderer an extra day or two. A healthy person’s urine contains 95% water and is sterile. The problem is that all the toxic chemicals excreted by the kidneys end up back in your stomach, where they are reabsorbed and then returned to the kidneys. After several rounds, the urine becomes dangerously concentrated with harmful chemicals, and drinking it can cause symptoms similar to those of kidney failure. It may be safe to drink urine once or twice in an extreme emergency, but after that, you’re asking for trouble.

Back to the desert

Prosperi had the foresight to store urine from the point when he first ran out of water, giving himself the best possible chance of rehydration when he resorted to tucking in on his fourth day of wandering. Later that day, he thought he saw someone on the horizon, but the shape turned out to be a stone shrine. Another plane flew over without spotting him. Figuring that, at the shrine his body would at least be found, Prosperi sunk into such despair that he cut his wrists with his penknife. However, his blood was so thick from dehydration that it didn’t flow. Taking this as a sign, he awoke the following morning with a renewed determination to survive. Following a breakfast of bats, which he crushed with his bare hands, Prosperi headed towards the clouds in the hope that they would guide him towards water.

He walked only in the morning and late afternoon, and snacked on lizards and snakes. Finally, on his ninth day alone in the desert, he stumbled across a pool of muddy water. Footprints led away from the pool, and he eventually caught up with a young shepherdess, who raised the alarm.

Dubbed the ‘Robinson Crusoe of the Sahara’, Prosperi lost 40 pounds during his ordeal, and strayed 183 miles off course, winding up in neighbouring Algeria. He returned to the Sahara to compete again in 1998, only to be halted mid-way through by a badly stubbed toe. Arguably an improvement on his first attempt though!


IMAGE: Guilherme