The headache that turns out to be dehydration — the long version posts 31–60
This is a continuation of a long topic, addressed by post number rather than by page. Start at post 1.
Vomiting and diarrhoea lose fluid and electrolytes together, and replacing only fluid is what turns a short illness into a longer problem.
Two things can be true about headache at once: the mechanism is plausible and the evidence for the size of the effect is thin. Most of the argument here is people defending the first against attacks on the second.
Post #33 is the version of this I will quote in future. One addition.
I keep a log for headache specifically because my memory of it turned out to be systematically wrong in one direction. Six weeks of notes cost nothing and settled it.
Everything in post #33 holds. The case it does not cover is the one I have.
Cramping is the symptom most confidently attributed to electrolytes and has the weakest evidence linking it to them.
The confident version of this sentence would be wrong, so here is the hedged one.
Symptoms attributed to electrolytes here are non-specific and overlap with dehydration, low intake and poor sleep. Attribution from symptoms alone is unreliable.
That is one dataset and I would not build a rule on it.
Before the thread moves on from headache — what is the sample size behind the claim? I am not being difficult; I have seen the same figure quoted from an n of four and from an n of four hundred.
What would change my mind on headache is a second dataset collected by someone with no stake in the first. Until then I hold it loosely and I would rather say so than pretend to more.
Adding salt to food is the intervention most consistently reported as helping and is also the one least likely to cause harm.
I am not the right person to answer the follow-up to this.
Orthostatic symptoms: dizziness on standing after lying down can indicate dehydration or electrolyte depletion. Increasing fluids, salt, and potassium usually resolves it.
What I want from this headache thread is the list of things that would need to be true for the claim to hold. If we can write that list, we can check it.
The thing about headache that took me longest to accept is that a plausible mechanism is not evidence of an effect. It is a reason to look, not a result.
The most useful posts here describe what was measured, what was changed, and what happened, in that order.
The uncertainty is in the assumption, not in the calculation.
Careful with the language on headache. "Not detected" and "not present" are different findings and the first is a statement about the method.
Post #46 is right about the mechanism and I think understates the practical bit.
Two questions I would want answered before drawing anything from the headache data above: how were the cases selected, and what happened to the ones that dropped out.
Narrowing post #46, because the general version has more than one answer.
The number people quote for headache is a central estimate presented without its interval, and the interval is wide enough that the estimate is nearly uninformative on its own.
Everything in post #48 holds. The case it does not cover is the one I have.
Reading this headache thread as someone who came in with a fixed view: the third and seventh replies moved me and the confident ones did not.
Coming back to post #51, because the follow-up matters more than the original answer.
I read the earlier replies on headache twice before writing this, because I had assumed the opposite and wanted to be sure I was disagreeing with what was said rather than what I expected.
Post #51 is right about the mechanism and I think understates the practical bit.
The honest answer on headache is that it depends, and the useful part is the list of what it depends on. Four items, in rough order of how much they matter.
Most people get the first two right and then argue about the fourth.
Rapid correction of a genuine abnormality can be more dangerous than the abnormality, which is another reason this belongs in clinical hands.
Adding a source would improve this post and I do not have one to hand.
Orthostatic symptoms: dizziness on standing after lying down can indicate dehydration or electrolyte depletion. Increasing fluids, salt, and potassium usually resolves it.
The short version is the first sentence; the rest is why.
Post #55 answers the question as asked. The question underneath it is different.
Worth stating the null on headache before we explain it: the observation may be nothing. That possibility deserves a sentence and usually does not get one.
Reading back through, this was answered upthread and I missed it. My fault.
Adding the measurement that post #58 says would settle it.
Since headache keeps coming up, it should probably be a maintained page rather than a recurring thread. I am happy to draft it if someone with more direct experience will review it.