I am a 38-year old that loves hiking as a hobby. I usually do 10-20km hikes with up to 2km altitude change. This year I started tours with a new crew and two people talked to me independently that my walking regime is unusual if not straightforward harmful. Basically, I feel the best if I'm warm and sweating. That means, I'll be more clothed and will drink more water than the most; but I'm not extreme - maybe one layer of clothes more than the next hiker. If anyone has its jacket zipped, it will be me. And a hat or hoodie - always. On a last hike (18km, 1km+,18°) hike, I drank cca 4.5 liters of water, with my urination somewhat less than usual. But these guys warned me about potential, but unspecified kidney (water) and heart (heat) problems. The probable reason for my routine is that I hate being cold or even cooled. The whole water thing is kinda necessary consequence of being warm.

So, do these guys have a point and should I push to adapt to lower temperature?

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    I don't think it is anywhere near "harmful", just less practical. – Tomas By Nov 29 '20 at 10:38
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    @TomasBy As in extra water to haul? I mean, I wouldn't care a bit because I'm comfortable in my hiking setting but just wanted to be sure there are no health down-side to it. – i_prob_should_know_this Nov 29 '20 at 10:47
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    Well maybe that also, but mainly sweaty clothes need to dry, and they get very cold very quickly if you need to stop. – Tomas By Nov 29 '20 at 10:56
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    Is this day hikes, or multiple days back to back? I wouldn't be in the least concerned in the former case, but would be a little cautious in the latter, especially if the weather is changeable.I wonder what your friends would say about someone who wore less and drank/sweated that much in warmer weather - they'd probably think it was perfectly normal – Chris H Nov 29 '20 at 13:28
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    I am not sure where your companions are coming from, but it sounds like you might be running a risk of overheating! Our core temperature rises quite significantly when we exercise. Drinking will allow you to sweat and thus cool you down if the sweat can evaporate. But the scenario you are describing sounds like your sweat cannot evaporate and you are creating a microclimate. That can lead to hyperthermia etc. – user2705196 Nov 30 '20 at 14:13

There are a couple of concerns to worry about, though neither is quite what your friends are saying:

First is electrolytes - depending on how much/what you eat you might end up short. Electrolyte tablets to add to some of your water might be a good idea. I'm the opposite to you and don't like to be too hot, but I use them in the summer; I've been known to drink (and mostly sweat out) 9 litres in a day cycling in the mountains. This is more likely to be an issue if you're going hiking on consecutive days, but one tablet in every other bottle will provide a bit of a top-up. The most important here is sodium (Na), i.e. common salt. If you like salty foods while hiking, they'll go a long way to meeting your needs.

Second - cooling off. If you feel the cold that much, you probably carry an extra layer, and that's a good idea. If you have an unplanned or longer-than-planned stop, sweaty clothes cool you down quickly (even with a windproof outer layer, though that helps). If an accident, navigational mishap, or other delay keeps you out as the temperature drops at the end of the day, that can get serious - so carry a bit of spare clothing.

Most people would try to minimise the amount of sweat in their clothes by adjusting their layers. You have more reason than some of us to choose good base and mid layers that have decent insulation while damp.

To try to get to the bottom of where your friends are coming from, I assumed they were worried about you getting seriously dehydrated. It doesn't sound like you are - you're just doing extra work carrying more water. I might carry a similar weight in camera gear on a wildlife hike - the extra weight is your choice, no big deal. Dehydration does increase blood viscosity, and thicker blood is a risk for heart attacks. A lot has been written, not all trustworthy, so here's a link to a scientific paper on the subject. Similarly the kidneys are affected by dehydration, particularly chronic dehydration - another paper.

Again though, unless your risk is already elevated, and you're getting dehydrated, these aren't significant - I don't know (or want to know) if you're at high risk, and it doesn't sound like you're getting badly dehydrated. If this was a significant risk in general, people would be dropping like flies on every mountain in the summer, and we'd hear about it.

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    @i_prob_should_know_this While this answer is true, I would like to point out that lack of electrolyte generally has acute symptoms and no long term damage. That is: If you feel fine, then there is no problem with them. Second point, the most important "electrolyte" is just table salt. Might seem strange, but adding just a little table salt to your water can help (for me personally, this tastes delicious when I need it and disgusting at every other time, so it's easy to get it right). Some others like Magnesium and Potassium are contained in bananas and other common food. – Nobody Nov 29 '20 at 17:52
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    Regarding electrolyte imbalance from drinking too much water, see en.wikipedia.org/wiki/Water_intoxication . There are apparently documented cases of this happening to hikers: wemjournal.org/article/S0953-9859(93)71207-3/pdf -- but 3/4 of the cases there were in over-100F weather conditions. So warming yourself up a bit is probably not going to get you there. And drinking sufficient electrolytes with your water will help too. – Glenn Willen Nov 30 '20 at 0:21
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    @GlennWillen: that paper actually contains a lot of relevant information from which we can calcluate a rough guesstimate of OP loosing 225 mmol Na⁺ which would lower their serum Na⁺ about 4 % (154 -> 148 mmol/l). Hyponatremia starts at 130 mmol/l or 12 % below normal. Since OP is apparently a trained sweater, their sweat is likely to be on the low end of Na⁺ losses. Yes, they'll need to replace the Na⁺ loss, but 225 mmol ≈ 5.2 g Na⁺ or 13 g of NaCl. Typical daily intake with normal nutrition is 3 - 6 g Na⁺ or 7.5 - 15 g NaCl.... – cbeleites unhappy with SX Nov 30 '20 at 12:10
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    ... 100 g of dried salami-type sausage or hard cheese contain 1 - 1.5 g Na⁺. => The Na⁺ losses here can be managed well with rather normal nutrition (i.e. no particular need for electrolytes/salted drinks - though they are of course an option) assuming that OP listens to their "salt hunger" (yes, humans do have a so-called specific appetite according to Na⁺ status) and isn't doing multi-day trips on a vegetable + water diet. (I've been going through 10 l of water a day no salt added, but eating bread, salami + cheese and a "mountaineer meal" in the evening - they tend to be salty as well) – cbeleites unhappy with SX Nov 30 '20 at 12:19
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    @cbeleitesunhappywithSX that's a good option, and why I tend to only worry about electrolyte drinks in summer (as well as sweating far more, my appetite tends towards fruit and away from dry, portable salty foods). I do always carry one or two tablets on the bike - I've had days when for some reason I couldn't eat without feeling very sick but the only way home was several hours more riding. Bread also has worthwhile amounts of salt, as do most potato products. – Chris H Nov 30 '20 at 12:33

You're doing extremely physically challenging hikes, and whatever you're doing seems to be working for you. Ignore your friends and do what you like.

The only problem with bringing 4.5 liters of water is that it's a huge amount of weight. But if you feel thirsty for that much water, and it makes you happy, then presumably you've just consciously chosen to carry all that weight.

Drinking too much or too little water is not normally a big problem. There is a very wide range that's OK. There is a myth that "thirst is too late," or that you have to drink some huge amount of water every day in order to avoid becoming "dehydrated." This is nonsense. You will feel extremely thirsty long before you get anywhere near medical dehydration.

You're posting this on Nov. 30, which is northern hemisphere winter, and you describe wearing lots of layers because you don't want to get too cold. Furthermore, you're going up to high elevations in the mountains. So evidently you're in cold conditions, and this further reduces the danger of dehydration. I'll often do a long day hike in winter and only drink 500 ml of water.

It's true that drinking very large amounts of water in a short time can cause hyponatremia, which can be deadly and comes on without any sensation to give your brain a recognizable danger sign. The amount you're drinking, spread out over a long and strenuous day of hiking, is nowhere near that level.

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    +1, though I'd like to point out that cold conditions reduce the risk of dehydration works only for what I'd call moderately cold/cool conditions (say, around 0°C). When T drops substantially below 0°C, one actually looses a whole lot of water via exhaled air, and there is risk of dehydration because people tend to not be aware of this as they are of sweating. Again, thirst will take care of this unless one ignores it. – cbeleites unhappy with SX Dec 1 '20 at 2:56
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    While they're posting in late November, the example hike in the question was at 18 degrees. I think we can take that to be Celsius - we'd all be wrapped up a lot in it was Fahrenheit. So that's nearly room temperature, not winter conditions. Short sleeves weather for me. That's not to disagree with your conclusion though. – Chris H Dec 1 '20 at 6:41
  • I generally agree. One other problem/disadvantage of too warm clothing: It’s exhausting and reduces your maximum power output. And unlike hot weather, sweating under clothing is very inefficient. – Michael Dec 1 '20 at 7:38
  • @ChrisH: I took 18 degrees to be the slope angle of the climbing. I'll post a comment on the question asking for clarification. – Ben Crowell Dec 1 '20 at 16:55
  • Fair enough - I assumed it couldn't be given that we also have a distance and ascent that work out to 1:18 which is a few degrees (still less than 10 if you assume the distance includes an equal descent) – Chris H Dec 1 '20 at 21:04

Your co-hikers probably read or heard something somewhere about hyponatremia, without remembering the term or the concept. Four and a half liters is a lot so it might be a valid concern. Hydration is NOT a contest. Thirsty trumps dead every trip of the train.

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    4.5l would be quite normal (or even on the low side) on a warm or hot day. So that by itself is not cause for concern. – Michael Nov 30 '20 at 7:43
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    Dead of heatstroke/dehydration is just as dead as dead of hyponatremia. The proper solution to the problem here is as light as ≈10 - 15 g of table salt - and according to the paper @GlennWillen linked in another comment, 4.5 l of sweat correspond to a Na⁺ loss of ≈225 mmol. Without any replacement of Na⁺ (but all of the water), this would lower the serum Na⁺ from normal 154 mmol/l to about 148 mmol/l for a 70 kg standard human (or about -4 %). Hyponatremia starts at 130 mmol/l (≈ -12 %). OP has a comfortable safety margin even without eating salt. – cbeleites unhappy with SX Nov 30 '20 at 12:28
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    I routinely drink 6l of water a day, sitting in front of my computer. Should I be dead? I didn't get the memo. – Eric Duminil Nov 30 '20 at 13:26
  • @Michael: The OP is talking about wearing lots of layers because they're too cold, and they're posting about something that happened in late November, i.e., northern hemisphere winter. So these are not warm or hot conditions. – Ben Crowell Nov 30 '20 at 23:20
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    @cbeleitesunhappywithSX: Heatstroke is completely unrelated to dehydration. People don't die of dehydration without getting extremely thirsty first. – Ben Crowell Nov 30 '20 at 23:21

The drinking isn't at a level I would regard as dangerous, but the overdressing is another matter.

Suppose you were injured--it need not be serious, just something that stops or greatly slows you. You're going to get quite cold, depending on the weather you could be in hypothermia territory. Sweating is ok if you can keep it up, it can go very badly if you can't.

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