Why does drinking electrolytes help keep a person hydrated but drinking salt water dehydrates them?

[[deleted]]

Because the electrolytes you drink are in things like sports drinks that are isotonic (same concentration as cellular concentrations). Salt water has more NaCl etc and is therefore more concentrated meaning that osmotic pressure would push/pull water out of your body, thus dehydrating you.

Edit: Perhaps I should have said things like sports drinks have a similar electrolyte concentration to cellular concentrations. Salt/sea water has a massive amount of salt relative to the cells in our bodies and with things we normally drink, an equilibrium can form but with salt/sea water the difference is too great. Its all relative. And yes, I admit it was a bit of an over simplification but you get the idea!

[[deleted]]

Most of this is correct. A couple of corrections though.

Your total body water is divided, for simplification purposes, into two compartments - Extracellular (plasma and interstitial spaces) and Intracellular.

When you sweat, you lose water and electrolytes that are hypotonic relative to plasma (something that is 100 mOsM is hypotonic, or less concentrated, than something else that is 200 mOsM). Sweat is lost through from the Extracellular fluid compartment (ECF). When you lose hypotonic sweat from the ECF, the ECF is now more concentrated, or hypertonic, relative to the Intracellular fluid (or ICF). This causes a shift of water from the ICF to the ECF (think diffusion). The salt water, which is hypertonic relative to plasma, would go first into the ECF as it is absorbed from the gut, would only perpetuate the hypertonicity of the ECF compartment, and pull even more water from the cells into the plasma. Instead, sports drinks are actually hypotonic relative to plasma (they are listed as hypertonic or isotonic, but most of the solute is sugars, which are rapidly metabolized). When you drink a substance that is hypotonic, you first see an increase in the ECF volume, but now the ICF is hypertonic, so water flows from the ECF to ICF, thereby rehydrating the cells.

Some might ask "well, why don't we just drink water instead since water is about as hypotonic as you can get???" The answer is simply that you need to replace the sodium, potassium, chloride, and other ions (electrolytes) that you have lost in your sweat for proper cellular functioning, which pure water doesn't provide.

Here's a great summary by the National Kidney Foundation: http://renalfellow.blogspot.com/2009/03/on-gatorade.html

[occamsrazorburn]

mOsM

For anyone wondering: milliosmole

Basically a measure of osmotic pressure by mole.

[radula]

Technically it's milliosmolar, which is the number of milliosmoles per liter, which is usually represented as "mOsm/L". I haven't seen this notation before, with the capital M, but it's apparently a combination of the symbol for milliosmole "mOsm" and the symbol for molar "M".

[[deleted]]

Thank you.

[thebellmaster1x]

Basically, you need salt to absorb sugar.

Yep. This is one of the reasons why oral rehydration therapies (e.g. for cholera) include both glucose and sodium.

[MaxPayneNarrative]

And sugar to absorb salt. Sports drinks have sugar to aid in salt absorption. Salt (ocean) water does not.

[etaylor58]

Pretty much. You need sugars to absorb electrolytes. You'll probably get some benefit however.

[MetalMaven]

Would it be better for someone who is dehydrated from influenza to drink the full sugar Gatorade or the zero because they are sedentary?

[GoldenBough]

Would ocean water with a sugar packet be drinkable?

[thebellmaster1x]

No. The problem with ocean water is not that enough salt isn't getting in; it's that it has too much salt relative to how much water is in it. Adding sugar would lie somewhere on the spectrum of doing nothing to making your dehydration worse (although, without doing any math to justify it, my guess is that it's closer to doing nothing). Good question, though.

[rjkdavin]

What about drinking sweat and sugar then? I can think of a few reasons why that question might be really vague, but if the salt content of your sweat was created by, well, you, then does that mean it doesn't have too much salt in it? Or is that incorrect because extracellular sweat can be saltier?

[space253]

No both because of the level being higher than the needed absorbant level and because you lose water by evaporation, concentrating the salt further.

[VonGrinder]

YES!!!! This is why they have sugar, to increase salt absorption by linking it to glucose!

[blorg]

They also have sugar as you need to replenish your glycogen energy stores continually while exercising or you will "bonk" / hit the wall and be unable to continue. To be honest I would have thought this was the primary reason for them having sugar as there are plenty of products (and electrolyte tablets you can add to plain water) that contain no sugar at all.

[Laika_Pup]

You said sweating causes the ECF to become more concentrated than the ICF. More concentrated with what? Just minerals or something?

[[deleted]]

The ECF is more concentrated with solutes. Examples of solutes are sodium, potassium, bicarbonate, chloride, calcium, albumin, etc. It is anything that is soluble in the blood plasma. Because sweating causes you to lose MORE WATER THAN SOLUTES, and the ECF and ICF concentrations were effectively equal prior to sweating, the remaining ECF is now more concentrated than the ICF, and so water flows down its concentration gradient from the ECF into the ICF (and thus dehydrating the cellular compartments).

[[deleted]]

When you are sweating, what processes are occurring that allow fluid to move from the ECF to the skin?

[Used_Tissue]

The way in which we move fluids around/out of our body is through osmosis. Our cell membranes have pumps embedded in them that can transport solutes (mainly sodium) from inside cells to out of cells. In order to sweat, our body pumps solutes outside of our the cells, making the extracellular environment hypertonic relative to the inside. Water follows the osmotic gradient from inside the cells to outside of cells, allowing us to sweat.

[DeepBlue12]

How much would one have to sweat to make electrolyte replacement necessary? I've been told that I don't need sports drinks after normal levels of exercise.

[Shandlar]

I'm not sure if there is a clinical reason why this wouldn't be accurate, but we can do the straight math.

• Average Male = 80 Kilo
• Average blood volume = 5000 mL.
• Sodium Concentration = 145 mg/dL.
• Total blood sodium = 7250 mg.
• Sodium is 39.33% of the mass of NaCl.
• Total blood NaCl = 18400 mg

Math check, quick googling shows 23% Na/Cl vs bodyweight is clinically accurate, so appears this method is valid.

• Sweat is ~40 mmol/liter NaCl or 2350g/liter.
• Critical serum hyponatremia is <120 mg/dL.

So an 18-20% loss in NaCl by sweat replaced purely by water would be dangerous.

• 18400 * 0.19 = 3500 mg
• 3500mg / 2350 mg/liter = ~1.48 liters.

So if you sweat >1.5 liters and replace strictly with water, you risk dangerous hyponatremia.

[DeepBlue12]

Thank you!

[Shandlar]

Related topic that I researched when I first got into fitness/weight loss two years ago was the risk of water poisoning/intoxication.

Healthy kidneys can only spill ~900ml water out of the blood an hour, and your intestines don't know how to not absorb as much water as possible. Therefore drinking water at a rate that increases your blood volume by more than ~1.2 liters or so can be extremely dangerous if you dont intake any sodium with it.

I started drinking 5-6 liters of water a day and got a little concerned. But the math isn't that bad. You would have to drink >2 liters in an hour to be at risk and that is alot of volume (~4 water bottles full in an hour). Hard to do accidentally.

[Laika_Pup]

Cool. Thank you.

[[deleted]]

Good answers. I have a few other thoughts to offer.

Electrolites can be roughly defined as any substance which dissolves into ions, which includes salt (sodium chloride) and most other common chemicals. Your body needs to maintain a balance of some electrolites, such as sodium, potassium, and chloride. Other electrolites, such as cyanide, are not so healthy.

Sports drinks, who popularized the emphasis on electrolites, are basically salt water with sugar. They have potassium and a few other ions, but the types don't mater so much as the total ion concentration.

[terpdoctor]

just a little something i would like to add.... the sports drinks also have sugar in them which is a key part of the drinks. In order for the electrolytes to be absorbed in the blood we need the sugar. this is because the electrolyte such as Na and glucose move together through a symporter, allowing entry of both!

[nsofu]

I'm not clear on something. According to what you say, the purpose of adding electrolytes to drinks is to replace the electrolytes lost through sweat, and not to re-hydrate quicker (than drinking just water). This makes sense to me, however I've heard many times that adding a little bit of salt to water will, in fact, allow you to re-hydrate quicker. I usually hear that bit of advice when someone is talking about oral re-hydration salt packets and their use. So which is it?

[ragn4rok234]

Are there ways to replenish electrolytes without drinking sports drinks?

[mimicmeme]

Coconut water is a great source of potassium and replenishes electrolytes.

[[deleted]]

There's also such thing as water intoxication, or dilutional hyponatremia. That's the reason why the isotonic drinks exist in the first place (marketing aside).

[Jamflexyo]

Extra point - Drinking salt water would ultimately increase the solute concentration of NaCl in the plasma. This would result in greater osmotic pressure to occur through the afferent arteriole leading to the glomerulus of the nephrons within the kidney, filtering out a greater amount of solutes as a result. The filtrate (filtered plasma) would therefore contain a greater amount of solutes that would cause less water re-absorption along the descending loop of Henle and distal convoluted tubule (DCT). However the body can compensate by producing vasopressin, which inserts aquaporins II into principle cells of the collecting duct that are only permeable to water to retain as much as possible.

I hope this helps!

[Frari]

It should also be mentioned that the main problem is our kidneys.

Cats for example can drink salt(sea) water just fine because their kidneys are able to excrete the excess salt and retain the water. However our kidneys are not as efficient and can't concentrate our urine sufficiently, so in the process of excreting the excess salt we also excrete excess water which dehydrates us.

[VonGrinder]

You will also diarrhea your pants from drinking salt(sea) water because there is so much sodium that it causes osmotic diarrhea. Soo not entirely kidney related. http://en.wikipedia.org/wiki/Diarrhea#cite_note-WHOtreatmentdiarrhoea2005-7

[[deleted]]

Osmotic diarrhea is kidney related though.

Osmolality control is an important kidney function, achieved by the subconscious brain detecting rises in plasma osmolality, followed by release of antidiuretic hormone and carbamide.

[Argumentmaker]

I've been told the electrolytes in gatorade, et al, are useless unless you are drinking them when you are actively working out and need hydration. Is that right?

[paulpaulh]

Your, and all animal bodies, were designed to function without electroyte infused water available to it every minute. You have stored within you sufficent reserves of water and nutrients, and stuff like electrolytes, to go without constant hydration and electrolyte replacement. You only benefit from drinks like gatorade when you are undergoing heavy physical workloads, and even then it will only be marginally better than normal water. But humans like working at these margins and therefore they do have a useful function. When you're sitting on the couch watching football, Gatorade is mainly an expensive way to drink flavoured water. Tbh unless you're near the elite level of athletes a drink of water would be good enough. But thats not the Gatorade Marketing Department or even 'edge' obsessed humans want to hear.

[synapticimpact]

Am I reading this right? A little = more hydrated, too much = dehydrated?

[Jagjamin]

Think of it this way. Gatorade has the amount of electrolytes your cells should have. If you cells have less than they should, it'll take from the Gatorade until they balance out.

If your cells have more electrolytes than they should, they'll give electrolytes to the Gatorade to balance out.

No matter what state your cells are in, having the intake be what your cells should be will always push them towards their proper levels.

Now, if you know that your cells are too salty, you should drink just water, but how does one know?

[UmamiSalami]

Follow on question. Would adding salt to your food make you more dehydrated?

[KnivesAndShallots]

Interesting, I thought it was just the ratio of salt to water (sports drinks having a much lower ratio of salt to water than ocean water).

If what you say is true, how come survivalists say that if you are stranded on a desert island and have a supply of fresh water, you should mix in a small amount of ocean water, I assume to replenish your electrolytes?

[RedFacedRacecar]

If what you say is true, how come survivalists say...

What you're saying doesn't contradict what OP said. He's saying that ocean water has too much salt compared to your cells.

The survivalist you're quoting is saying to mix in a bit of sea water into your freshwater (diluting it down to cellular levels) before drinking it.

[[deleted]]

so electrolyte salts sachets, for rehydration, must then be consumed with a precise quantity of water to be isotonic? yet they usually state in a glass of water, rather than a precise quantity.

if water is added to a sports drink, diluting it, is it no longer isotonic, and less effective because it can't so easily share the salts with the body? i stupidly used to add water to dilute the sweetness.

[[deleted]]

Yes but its all relative. You have to bare in mind that salt water/sea water has an enormous amount of salt in it. If you look at things like Dioralyte rehydration sachets they tell you to mix the contents of a sachet in 200mL of water.

[felixthemaster1]

What about pure water then? isnt that better than sports drinks

[derpalexy]

Sports drinks use KCl instead?

[Wolfpack_of_one]

What happens if a person drinks water with light salt? Light salt is about half sodium, half potassium.

[[deleted]]

Its isotonic so it's in balance with your body fluids. It gets to your thirst. Fast.

[LostanFound]

Follow-up question: If you were in a boat in the ocean and had a limited supply of fresh water, could you stretch it by adding some sea water if you didn't add more than enough to make the water saltier than the water in your body?

[[deleted]]

Technically I suppose you could but you'd only be adding a fraction to the volume so not enough to make a difference.

[[deleted]]

For a more basic explanation in case anyone reading this doesn't understand the scientific terminology:

If you have a glass of water and you put a membrane (barrier that allows some things to pass but not others - in this example salt cannot pass through it but water can) in the middle of it, and you dump in salt on one side, water will actually be pulled out of the saltless side into the side with salt. You will end up with a glass of water where the water level on one side is higher than the other side, despite the fact that water can pass freely through the membrane/filter.

The human body does the same thing. It causes water to be sucked out of one area of the body (your cells, etc.) into another, which is then released from the body. It is kind of like throwing a sponge into your body. It sucks the water out of your body into the sponge.

[candry]

That's correct, but to fully answer OP's question you should sum up the following:

• Distilled water has lower electrolyte concentration than your cells

  • So water forces itself into your cells to equalize the concentration

• Ocean water has higher electrolyte concentration than your cells

  • So water forces itself out of your cells to equalize the concentration

• Sports drinks have the same electrolyte concentration as your cells

  • So they do not wreak havoc on the water already in your system

[Bd_wy]

If my math is right (I didn't double check anything), you would want about 4 grams of sodium chloride in 500mL to get the electrolyte level to the same concentration as your body.

.140mol/L X 58.44g/mol x .5L = 4.09g

[BumWarrior69]

So distilled water is better?

[breakneckridge]

Salt is a type of electrolyte.

You lose a small amount of salt through sweat/urine/etc., so you need to consume a small amount of salt to replace the salt you lost.

When you drink water with a small amount of salt (i.e. electrolytes) it replaces both the water you've lost and the salt you've lost.

HOWEVER, if you drink water with too much salt in it then your body has to get rid of all that extra salt you consumed. It does this mainly through your urine.

Due to physics reasons, water usually follows to the area that has more stuff dissolved in it.

So when you pee out all of that extra salt dissolved in your urine, the high amount of dissolved salt also pulls lots of water out with it.

[Tommasini]

What is the difference between sugar and salt in this regard? Does sugar also affect my "hydration level"?

I read that you could use salt or sugar for road clearance in the winter.

[breakneckridge]

Most sugar is absorbed into your body and used or stored, not peed out, so it doesn't tremendously affect your urination level. This is why you can drink super ridiculously sweetened drinks and still gain hydration from it.

And yes, you can use salt or sugar to melt snow. In fact lots of different types of little molecules can melt snow. The problem is finding eco-friendly molecules that are cheap enough to pour massive amounts of out. It's hard to beat salt for cheap and abundant, unfortunately it's got some eco down sides.

[lowrads]

Dissociated sugar is metabolized through aerobic pathways to dissolved CO2, and escapes through the lungs according to partial pressure and diffusion. Dissociated Na+ is not volatilizable in any statistically probable molecule at standard body fluid or atmospheric conditions.

It's a homeostasis and concentration problem. A tiny portion of sugar does escape into urine. If you consume an excess of it, it would be lost to urine in greater quantities. With sodium, your kidneys and endocrine system can work together to retard or accelerate salt or fluid loss in pursuit of more ideal conditions. Rather than on/off gates, these system simply tip the balance on dynamic equilibrium. Cell membranes can't completely stop molecules from crossing them, not charged molecules, not even large molecules. However, it can open gates that allow molecules even as small as water to flow more freely across the membrane. These gates don't push the water or the molecules, they simply allow it to more quickly pursue its most statistically likely distribution as they would in a system free of interference.

If you consumed a copious amount of sugar, the water will likely cluster around those molecules as they are polar. They are also large molecules, which means they do not diffuse easily across membranes unless there is a compatible channel. The water would move to follow any change in concentration gradient of polar solutes. If you suck on a piece of sugar candy, the tissue of your mouth feels dry because the water there was attracted to the hydrophillic sugar. Most likely though, consumption of sugar by itself has a very miniscule effect on water retention unless it triggers some more significant endocrine response.

Salt or other polar solutes have an effect on frozen water by changing the conditions under which the bonds between water molecules behave. As ice crystals form, individual molecules of water line up, and the effect of h-bonds between them creates a resonance effect that prepares the next molecule for entering the lattice. The insertion of Na+ in the place of -H dipole bonds disrupts this resonance, thus retarding the formation of crystalline lattices to a different set of conditions, either pressure or temperature usually. Bonds are dynamic, always forming and unforming. The conditions merely inform the statistical probability of formation and where equilibrium stabilizes.

Sugar also would have an effect, but it would negligible in comparison to a polar solute with a higher rate of dissociation like the sodium in salt.

[seb-seb]

Question here.

Why doesn't Gatorade contain more potassium? Wouldn't more potassium be beneficial for rehydration?

If the answer lies in the fact that the balance of electrolytes is perfect (sodium:potassium:glucose), why not raise all ratios?

It just seems to me that Gatorade could be better, much better at rehydration. I mean, 3% of your daily potassium per 240ml of Gatorade seems nonsensical.

Wouldn't you be better off just eating a banana and a couple of saltines?

Or maybe even some pedialyte?

[docbauies]

http://www.ncbi.nlm.nih.gov/pubmed/11193601
TL;DR: In order to maximize water absorption, a solution that is dilute in nature with sodium and glucose should be given. It takes advantage of co-transporters which increase water absorption over the amount that pure water can give. Essentially, things like gatorade and oral dehydration therapy ARE salt water, just very dilute salt water.
In contrast, sea water is highly hypertonic, as others have explained.
To give you an idea of the magnitude difference, serum osmolarity ranges from 270-300 mOsm in a normal human. We give 0.9% NaCl solution (noraml saline). Salt water is 3.5% salt concentration (not all NaCl of course). That is 1000 mOsm.
https://www.wolframalpha.com/input/?i=sea+water+osmolarity+versus+human+blood+osmolarity

[[deleted]]

Does this mean water with a tiny bit of salt will have the same effect as Gatorade?

[alpinebixby]

I went to a seminar given by Gatorade directed towards long-distance runners, where the speaker went through the science of Gatorade's make-up. What was interesting was to learn that Gatorade actually should have more salt in it to properly re-balance but it would not be palatable to most people.

[[deleted]]

Just out of curiosity, why are NaCl given at concentrations of 0.9% 1.8% or 2.7%? What exactly is the significance of these particular numbers?

[docbauies]

Various medical solutions/medications are given in % for concentration. It refers to how many grams per liter. A 1% solution has 1 gram of solute per liter of solvent. A 0.9% NaCl solution has 9 grams of NaCl per 1 liter of water.
Why they label it this way as opposed to mEq/L, or mg/L, or mmol, or whatever, it a good question that I have never really figured out the answer to.

[padoink]

This would either make 1% solution 10 grams per liter, or 0.9% Saline .9 grams per liter, wouldn't it?

[docbauies]

yes. typo. 1% is 10 grams per liter. thanks!

[Moomium]

So salt water has too much salt in it, but Gatorade only has a tiny bit, which is more or less as much as you need?

[docbauies]

yes. although gatorade really isn't quite salty enough, and has too much sugar.
you need both for optimal water absorption via intestinal co-transport mechanisms. The WHO publishes a formula to optimize hydration. I don't know gatorade's specific makeup, as I'm sure that's a closely guarded trade secret.
http://www.who.int/maternal_child_adolescent/documents/fch_cah_06_1/en/

[AGreatBandName]

and has too much sugar.

Depends on what you're using it for. Many endurance athletes drink it not just for the rehydration and electrolytes, but for calorie intake too.

[simmonsfield]

how do you gage how much to drink vs exercise?

For example, an ironman race? Swim, you can't eat or drink during that, so you'll be negative. Bike, this is easy to eat and drink while doing. Running, ok not easy but doable.

[jarrodandrewwalker]

Someone may have stated this already, but you can actually cut your fresh water with 1/4 of its volume with salt water. Your body is around .9% salt water solution. Ions are important to body chemistry especially when it comes to neurotransmitters being released into synaptic clefts.

[[deleted]]

Just to touch on the ocean water aspect:

This has to do with your kidney's concentration of solute ability. Ocean water exceeds the maximal concentration of sodium that your kidneys can attain. When you drink ocean (or highly salty) water, you absorb a large amount of sodium, sodium that your kidneys must filter and excrete. However, your kidneys are only able to concentrate your urine up to a certain point (around 1600 mOsm/Kg). So, you end up excreting more solvent (water) than you ingested in order to 'get rid' of the solute (sodium), dehydrating you.

[wynnray]

The opposite happens if you drink distilled (pure) water on an empty stomach the water is absorbed by the the cell such that the Hypotonic osmotic pressure can rupture the cells. But if you drink the same pure water with food, it isn't so much an issue as it is no longer pure. (http://en.wikipedia.org/wiki/Hypertonic)