Dehydration: why water alone isn't enough
Story context (click to hide this block) (click to show this block)
This paragraph may contain plot information.
Under intense heat, Jinshi collapses, burning up, after staying bundled up and going without food all day. Maomao doesn’t just make him drink, she makes a precise diagnosis: he’s short on salt, and she regrets having lost her flask of water mixed with soybean and sugar. Lacking that, she pulls butterbur from her satchel to make up for the salt deficiency. The remedy isn’t water alone, it’s water, salt, and a little sugar.
The subject in depth
The human body is made up largely of water, but that water is never pure: it contains dissolved salts, foremost among them sodium, one of the components of table salt. Sodium governs how water is distributed between blood and cells, as well as how nerves and muscles function. When you sweat heavily, from heat or exertion, you don’t just lose water, you lose salt too
This is what explains the episode’s counterintuitive insight. Drinking large amounts of plain water after heavy sweating isn’t enough, and can even make things worse: the water further dilutes blood that’s already depleted in salt, throwing the balance further off. The signs of this kind of deficiency are exactly Jinshi’s, headache, weakness, feeling unwell in the heat. Maomao’s remark, “you’re short on salt,” is therefore an accurate diagnosis, not just a turn of phrase.
The solution she proposes, water with added salt and sugar, is remarkable, because it rests on a mechanism that medicine only formalized in the 20th century. In the intestine, water doesn’t cross the wall on its own, it follows the substances being absorbed. There is a transporter that brings sodium and glucose (sugar) in together. In the presence of sugar, salt is therefore absorbed more efficiently, and water is pulled in along with them. Adding a little sugar to salt water isn’t a matter of taste, it’s what makes rehydration fast and complete
Going further
Sources
Published on
Keep investigating
Auto-suggested from shared concepts, disciplines, episodes, or characters.
Carbon Monoxide
In The Apothecary Diaries, embers bring guests down at a party. We explain carbon monoxide, why it suffocates without warning, and the right thing to do.
Hypothermia
In The Apothecary Diaries, cold threatens lives. We explain hypothermia, why cold-water immersion is so dangerous, and how to rewarm safely.
Drinking Water and Waterborne Diseases
Why does boiling water make it safe to drink? Cholera, dysentery, typhoid: we explain waterborne diseases and the story of John Snow.
Induced Vomiting
Making someone vomit to clear a poison: an old intuition that modern medicine has largely abandoned. Risks, contraindications, the history of ipecac.
Salting and Brining
In The Apothecary Diaries, Maomao dates a batch of seaweed using her knowledge of brining. We explain how salt preserves food, and why it eventually fails.