If drinking salt water further dehydrates the body, why is saline used to treated dehydration?
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Salt water is too salty and saline is just right.
When you are dehydrated you also lose salts/electrolytes which are not exactly the same as sea water, for example.
https://ispyphysiology.com/2019/07/10/sea-water-vs-saline-why-not-all-salty-water-is-created-equal/
Amount of sodium is the biggest factor. Saline is purified water with a small amount of sodium chloride. Sea water is a high amount of sodium.
False premise. Drinking salt water doesn’t *necessarily* dehydrate the body. It’s just that to avoid that particular effect, you have to drink much smaller quantities *at a time*, more consistently over long periods of time.
Normal saline is 0.9% sodium chloride.
That’s 9 grams of NaCl in one liter of water. This is isotonic to your blood.
Sea water has ~35 grams per liter, almost 4 times as much.
Its all about concentration. Saline is meant to match the body’s natural level of electrolytes. It’s the same reason sport drinks like Gatorade contain electrolytes. They can replenish fluid levels without disrupting the electrolytes balance.
Just to add on what other people have said, route of administration matters. Saline to treat dehydration is given intravenously not orally which is an important difference.
I read thing a few years back, people at sea on a liferaft survived by seawater enemas.
Your body requires salts to function. Without salts your neurons would cease to signal each other and the cells in your body would stop working.
If you just drunk ultra pure water you would die as it would flush the salts from your body.
The difference between a medicine and a poison is dosage. While sea water is saline and hydration fluids is saline, hydration fluids are 0.9% saline sea water sits around 35%.
Sea water is waaaaaaay salter than saline. We need enough salt(electrolytes) to be able to conduct bio-electrical signals, but too much salt causes water to be sucked out of our cells, as it equalizes the salinity across the water content of our body.
There are recommended daily intakes of everything things your body needs including water, sodium, chloride, potassium, glucose, protein, vitamins etc. If you become dehydrated you have been losing mainly sodium and water, therefore both need replacing. Sea water has too much salt, too much salt damages your kidneys among other things.
When enough salt (sodium) is given, other intravenous fluids such as dextrose saline (sugar water) is given, the limits for sugar are much higher than salt so it doesn’t matter so much.
Additionally, giving pure water intravenously is not a good idea because if it doesn’t have enough electrolytes or molecules like sodium or dextrose it can have an osmotic effect i.e. Water will move into the cells rather than stay in the veins where it is needed. This can swell and damage organs. Drinking pure water can cause this too but its less likely.
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