Is there a difference between being thirsty and dehydrated? Like scientifically, biologically – by the time you notice that you are thirsty, are you already dehydrated?



Is there a difference between being thirsty and dehydrated? Like scientifically, biologically – by the time you notice that you are thirsty, are you already dehydrated?

In: Biology


Dehydration is a medical condition in which you have less than an adequate amount of water.

You can be thirsty without being dehydrated and if you weren’t you’d probably become dehydrated because you’d be unlikely to drink unless making a conscious effort to do so at regular intervals.

Thirst is just a sensation, like being tired or such. Obviously you’d be likely to be thirsty if dehydrated, but thirst also triggers regularly before dehdration to keep you drinking to *prevent* dehydration.

Think of it like this: you want to drive somewhere but you’re kind of low on gas. If you can make it there and not have to fill up, you might consider stopping anyways just to top off. This this thirst.

If you plan a drive and determain you don’t have enough gas to get there,that would be akin to dehydration. Its phydically not enough, vs just maintaining. Either way, you consider stopping for the gas, but if you’re low enough, you won’t make it. Thats the difference.

Edit: thanks for the ~~silver~~ awards!

Edit: jeez! This really blew up, i can’t believe how many awards it got! Glad I was able to help anyone!

The purpose of thirst is to prevent dehydration. Some may claim that it’s the first sign of dehydration, but I feel that makes the definition of dehydrated too broad to be useful.

The ‘if you feel thirsty you are already dehydrated’ thing is a myth spread by drill sergeants and gym teachers.

A number if things can trigger thirst, including but not limited to dehydration.

Signs of dehydration are nausea, headaches, dry mouth and throat, reduced blood pressure, dark urine.

The tl;dr is you should drink when you are thirsty- not force yourself to drink when you are not.

Edit: To clarify, if you have symptoms of dehydration other than thirst you totally should have a glass of water even if you don’t want it. Sometimes your body is weird like that.

Medications that cause dry mouth – I take some of these – make people feel very thirsty because the mouth does not have enough saliva. When I have these symptoms I could drink water non-stop and still feel thirsty.

Aiight so I don’t understand something here.

If the healthy thing for your body is to drink a lot of water (a gallon a day, which just seems absurd), but folks here are saying “don’t drink water just to drink water, only drink if you are thirsty”, those two things do not seem to work together.

I try to drink a lot of water. I can normally get close to drinking 3L of water per day, but often I am just finishing off a liter of water before a meal (to try to avoid overeating). I can say, though, I am definitely not “thirsty” every time I drink, and if I only drank while thirsty, there is no way I’d be able to drink a gallon (or not even) a day.

So … what is the proper move? Drink a lot of water each day OR only drink when thirsty?

Here’s the thing though. I’ve always thought millions of years of evolution wouldn’t leave me feeling ok and not thirsty if I was dehydrated.

But am pretty sure I drink a glass of water a day (at most) and the rest is coffee, tea and Diet Coke. This is hardly the 5 litres a day or whatever stupid amount am supposed to drink…

I’m pretty sure thirst is just when your mouth and throat feel dry but dehydration is when your body can’t perform normally due to lack of water

I read somewhere recently that while the two are separate, thirst is VERY easy to ignore. Thirst comes first, then dehydration. When you’re busy doing something and don’t want to go grab a glass of water or tell yourself you’ll grab some I’m 10 minutes, you’re essentially training yourself to ignore the “thirst” signal your body is sending.

Pretty soon you kind of just ignore the signal until you remember you needed a drink and you end up dehydrated. Similar to how you “forget” to eat or suddenly your not hungry anymore. You learn to ignore the signal for food your body is sending.

Thirst is regulated by two things: the volume of fluid in your body and the balance of salts/electrolytes in that fluid, mostly sodium. You have sensors/receptors in certain areas of your body specifically tuned to each. If the volume receptors sense that you have less fluid in your blood stream, they will release signals to other parts of your body to change how your body balances water and salts so that you retain more water and pee out less. If your sodium level is way out of balance, other signals will try to regulate your salt levels. Since water and salt really like to follow each around, it’s not super clean and regulating water levels oftentimes means some changes to salt levels, with a few exceptions. One of the responses to these signals is behavioral: thirst. You feel the behavioral urge to drink.

Side note: there are certain behavioral problems wherein a patient drinks and drinks and drinks if they have access to water, and can do so to the point that they can dangerously drop their salt levels and suffer bad consequences like seizures. The term for that is psychogenic polydipsia. (Poly roughly means many and dispsia roughly refers to drinking).

Dehydration refers to having less than the necessary amount of fluid volume in your body. You can be dehydrated with low sodium levels, normal sodium levels, or high sodium levels. Depending on how intact and functional your thirst regulators are, you may or may not feel thirsty, or if you’re unconscious or otherwise altered, you may not be able to drink anything despite your body trying to tell you too.

Your body goes through a certain amount of fluid every day just taking care of its basic functions. You get fluid from drinking but also from the foods you eat that have liquid. Healthy people with functioning kidneys should drink when they’re thirsty. If it’s hot outside or you’re doing something active, drink a little bit more. Trust your kidneys. If they’re healthy, they know what to do better than some arbitrary fluid goal.

Edited to add: since I didn’t say it outright, to get to the heart of your question. Thirst is a behavioral response/feeling that is most frequently driven by overall fluid balance, but which can also be driven by other factors, like salt balance. Dehydration is a physical state of low body fluid status compared to where it needs to be to support your body’s internal functions.

Supposedly when you get thirsty your already anywhere from hydrated to mild dehydrated depending on the person, with most of us being slightly de hydrated. Now this is not really a problem for most of us but if your exercising or in a really hot climate your not adjusted to then you can dehydrate before your body tells you your thirsty. For most of us it’s fine to drink water when we are thirsty though.

If you want an easy to digest summary of the research (with citations) this is good:

A lot of what people are claiming in either direction is not supported by science. 8 glasses a day is not supported. “If you are thirsty you are already dehydrated” isn’t either.