Mountain genetics part 2: Reaching the summit

My friends and I, along with an inflatable elephant called Paula, climbed Kilimanjaro and fundraised for Tsavo Trust – an elephant conservation project. Thank you very much to everyone who supported us!

Emily and Paula at Big Tree Camp:


In Mountain Genetics part 1, I wrote about the ACE gene, and the genetic test that all 4 of us took as part of our Kilimanjaro preparations. There were 3 genetic possibilities: super resistant to altitude (II genotype), medium resistant (ID) and sensitive (DD). And out of our group, 2 people tested as II, and my partner and I tested as ID. We were all very curious to see how the genetic tests will play out in practice when we actually climbed the mountain. This post is a breakdown of the differences and challenges we encountered during the trek.


How the trek went

First of all: we all reached the top. Not only that, but we all reached the top together at the same time, which is something we really wanted to do. You’re only allowed to spend up to 15 minutes on the summit because after that the lack of oxygen can make you ill. While we were prepared to split up if need be during the final night, the whole thing was a joint adventure, and we did really want that photo together. We weren’t particularly fast (it took us 12 hours to get to the summit: 1am to 1pm), but we made it.


Secondly: we all found it difficult. On the 4th day when altitude sickness first hit me properly, I joked “No problem – this is still easier than finishing a PhD”. On the 7th day, with the lack of oxygen and the endless shifting sand, I made no such proclamations. I would now put it on par with that PhD final year (in difficulty if not in length), while everyone else in the group said that reaching the summit was the most difficult thing they’d ever done. I would now even recommend summit day to prospective PhD students as a quick simulation of the experience, which might help them make a more informed decision about future career plans :)


Those things being said – I don’t think everyone found it equally difficult, and also, all of us hit difficulties at different times. So while it was a challenge for everyone, I was incredibly impressed with people who found it particularly hard and encountered a lot of difficulties, and still somehow managed to keep going. I felt like it was a real triumph of determination and will, and found it really admirable.


Mountain genetics in practice

In terms of how the genotypes and the difficulties played out: from the results, we expected that the IIs would breeze through it, while my partner and I would struggle with our ID genotypes. The reality turned out to be a bit more complicated than that.

The genotypes played out to the letter in the sense that my partner and I did get symptoms of altitude sickness at various points, like headaches and nausea, whereas the IIs barely even had a mild headache. Luckily noone experienced anything actually medically serious, only things that are in the “normal” range of unpleasant responses to altitude. But it’s true that the genotypes accurately predicted the occurrence of these. However, altitude sickness is just one of a number of factors that determine how well you cope on the mountain.


In terms of relative difficulty – two of us, me and one of the IIs, got off comparatively easy. I felt that I really breezed through it up until about 4500m altitude, with basically no symptoms and even quite a lot of excess energy. After that, the altitude did start getting to me, but the difficulty was manageable. The II in question did struggle and freeze with the rest of us, and found sleeping during the cold nights particularly difficult. However, they managed not to get too sick, and were the only person on summit night to manage to carry their daypack all the way to the top (for the rest of us, the guides took them off us when we started getting particularly exhausted). The people who found it more difficult were the other ID, and surprisingly, one of the IIs.


Hitting altitude

If you haven’t been at that altitude, it might be a bit unspecific what I mean by “difficulty”. The more active altitude sickness symptoms like headaches and nausea are something that only happened occasionally to two of us, they weren’t a persistent thing. Instead, the difficult thing was just how exhausted we were all the way through, more so the further up we went. And it’s not really physical exhaustion I’m talking about – for example, my muscles weren’t sore in the slightest at any point during the trek. Instead, the lack of oxygen just makes everything really tiring and difficult, and the further up you get, the worse it gets.


After a point you will realise that taking more than one sip of water at the time will make you breathless – you will need to hyperventilate for a minute to catch up on the oxygen that you’ve missed out on. From about day 5, I pay attention to only take a sip at a time, followed by a few deep breaths, followed by another sip. Hyperventilation in fact becomes a sort of habit, because it’s required to recover from so many different everyday activities. A few days after reaching sea level, I still found myself slipping back into it occasionally, and also waking up breathing fast. In fact, as I write this paragraph, I can’t help but do it again from just thinking about the altitude. Altitude is this tiring, out of breath, uncomfortable, slightly queasy feeling that doesn’t go away.


Any kind of deviation from the “pole pole” slow and steady tempo also requires hyperventilation and recovery breaks. The activities include but are not limited to, for example, getting into your tent, or walking to the bathroom. I think a bit about illness and disability, and how different my life would be if this was a daily reality rather than a consequence of altitude. Energy becomes a scarce resource, more and more so the further up the mountain we go. My bits of spare energy for the first part of the trek feel like a real luxury at the time, and descending the mountain again is amazing.


Genotypes, environment and other factors

So, back to the genotypes. One of the IIs got off comparatively lightly (i.e. they only suffered a moderate amount), as predicted by their genotype, and their main ambition if they were to do the climb again would be to do it faster. One of the IDs experienced the sort of altitude difficulties that would be expected based on the genotype – they felt sick and exhausted from quite early on in the trek, and the symptoms and the exhaustion got worse as the altitude increased. They even lost their appetite completely, which is to the best of my knowledge, the first time that’s ever happened. You need to know my partner to truly grasp how weird and disturbing this really was! As soon as we were back at sea level, he went back to ordering two main meals at a time, and I breathed a big sigh of relief :p Though he still cringes at sentences containing the words “mountain” and “climb” – I hope a temporary side effect.


So, since one of the IDs and one of the IIs passed pretty much as predicted, the interesting question is why it was the other II struggled, and also why it was that I got off easy. And the truth is that there are many different factors that go into how well you do at climbing a mountain. For example, how much water you drink, how much you manage to eat (the more, the better), and how much sleep you manage to get. There’s also the issue of cold, which gets worse as you go further up. While we were there at a warm time of year, night time temperature was still at -15?C or so, which isn’t exactly a friendly camping temperature. In fact, the nights were one of the hardest things about the trek. During daytime, you would warm up from the walking, but during the night, it was hard to fall asleep in the freezing cold, even while wearing 7 layers and being inside a 4-season sleeping bag (for the last few nights, I really wore everything I could possibly put on).


So, anyway – in the case of the II, one of the huge things was the cold. They don’t respond particularly well to it and struggle to produce heat at the best of times, so parts of Kilimanjaro were really a trial. They also lost their appetite due to getting sick while travelling before Kilimanjaro, and consequently found it difficult to eat, and that makes a huge difference to energy levels. And the additional thing was that they felt breathless quite early on – like their lungs just weren’t taking in enough oxygen, despite best efforts (likely at least in part because of having a cold at the time). Between all of these things, while the lack of altitude sickness was certainly a bonus and quite beneficial, there were other significant difficulties that still made the trek a very challenging one.


As for why I got easy, well, we did have one theory. Here’s a weird anatomical fact: I have  disproportionately large lungs. It’s not a thing that comes up day to day – the only reason I know at all is because I went to some paid experiment or other where they measured my lung capacity. It was notable at the time because I was absolutely off the charts for women, and I was on the “extremely high lung capacity” side of the graph for men, even when height is taken into account. Before going to Kilimanjaro, the only advantage I’d ever found for this was that I could dive across almost the whole length of an Olympic swimming pool, not because I’m a super fast swimmer, but because holding my breath for a long time wasn’t that hard.

This wasn’t something I thought about in advance, and it only came up in a discussion around day 3, when we were sleeping at 3800m altitude, and I was unusually chirpy and energetic. I had spare energy to climb extra rocks, lift up heavy things, all sorts. It was weird. So as far as my genotype goes, we concluded that, yes, I do get altitude sickness when I’m low on oxygen. However, thanks to an unlikely physiological luck of the draw, I was actually receiving perfectly adequate quantities of oxygen for a remarkably long time during the trek, which wasn’t the case for people with lower lung capacity.



Despite the difficulties, ultimately it is really remarkable how well our bodies acclimatised to the strange new heights that we took them to. The first night at 3800m was difficult and we were all out of breath, but only a few days later we would find this exact height easy and a bit of a relief. The first time I hit 4600m, I felt super sick, but that feeling didn’t hit me again for the rest of the trek, despite going much higher.

Our amazing and super experienced guides also made a huge difference. This was both because they knew how to acclimatise us well, and because they somehow had a knack of coaxing us to carry on, even when all we wanted to do was give up. Sometimes this literally involved holding our hands and dragging us up the slope. So even with the whole genotype/phenotype discussion, I think ultimately the real credit should go to our guides Raymond and Dennis.

In terms of conclusions, well – the trek is hard for everyone, and our genetics play just one part in a complex puzzle that includes all sorts of physiological and psychological factors, and the help we get along the way. But remarkably, we all adapt too. And finally – you can make it. Whatever your genes are – keep going. You can make it.


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