Sodium

Children with gastroenteritis, which is nobody in a gym. The trials were graded poor to moderate quality and mostly unblinded, since a drink cannot be disguised as a drip. Each route carries its own complication: vein inflammation with the drip, a stalled gut with drinking, roughly one in 50 and one in 33. The death counts, six against two across four trials, are far too small to read anything into.

Hospitalised children with acute diarrhoea, compared against another rehydration solution rather than against water, so nothing here reaches a well person drinking one. This is the 2002 version of a review since updated, cited for the finding that changed the formulation. The trials were mostly unblinded and largely in low- and middle-income hospital settings. Low blood sodium was looked for in only six trials with events in three, so that reassurance rests on thin data.

A position stand is expert consensus with no stated search and no risk-of-bias grading, and panels in this field have included researchers with sports-drink funding. It was written before the 2015 consensus on exercise-related low blood sodium and before the field studies that found sodium supplements did not prevent it. Advising people to individualise because sweat varies is not evidence that individualising improves any outcome, which is the step the personalised-hydration industry takes.

These are general-population reference values, not sport nutrition, and they describe what a healthy adult is thought to need over a day rather than what anyone should drink during exercise. The salt equivalent is arithmetic from the sodium figure, not a separately measured value. The report's own opening observation is that what you eat does not usually move your blood electrolyte levels, because the kidneys and hormones hold them steady.

One real exception sits inside the largest of these studies: among American footballers alone, sweat measurements did carry a weak signal, and in the other ten sports none did. Beyond that, cramping was self-reported throughout, and serum electrolytes were sampled before and after a race rather than inside the muscle at the moment a cramp struck, which is where the theory actually locates the problem. Forty-three crampers is enough to rule out a dominant effect, not a small one.

Twenty crampers is a small group, and the finish-line enzyme gap is borderline at p = 0.034 with spreads wide enough to swallow it. The blood was drawn after the cramp, so muscle damage could as easily follow a cramp as cause one. Crampers and non-crampers only diverged in pace from 25 kilometres onward, which points back at effort. The paper's own abstract calls 20 of 88 a rate of 24 percent; it is 22.7 percent.

Five desert stage races, which is what extreme heat does across six days, not what a hot afternoon does. Only 174 of the 266 runners enrolled gave a post-race sample. The link between hot races and low blood sodium is not statistically reliable, its interval running from 0.9 to 25.9; the link with high blood sodium is much firmer. And the 4.7 kilogram average carries a standard deviation twice its own size.

Both are narrative reviews with no stated search and no risk-of-bias grading, so which literature they cite is at the authors' discretion. The lead author of one chaired the consensus conferences on this condition, which makes the summary authoritative and not independent of the position it summarises. 'Conclusively identified' is their own confidence wording, not a graded rating.

One race, one temperate day in 2002, and a blood sample at the finish line rather than an experiment. Only 488 of the 766 runners who signed up gave a usable sample, so the 13 percent could sit either side of the truth. What people drank was reconstructed from a questionnaire they filled in after four hours of running.

These are the cases somebody wrote up. Severe and unusual presentations get published and mild ones do not, so this describes the case record rather than everyone it happened to. The search was a manual sweep of two databases, not a registered protocol. Women appear more often as a share of participants, not in greater numbers, a distinction the review itself insists on.

This is a reference-intake document for the general population, not exercise guidance, and it says nothing about what to drink during a race. The 2,300 milligram figure is a chronic-disease risk-reduction value introduced in the same 2019 report, not a toxicity threshold, and the child and adolescent versions were extrapolated from the adult one rather than measured. Anyone whose kidneys or medication affect how they handle potassium sits outside all of it.

This is transport physiology rather than a trial, and the two-to-one ratio is standard textbook mechanism restated by the review, not a new finding of it. The review was written to argue for developing drugs that improve on rehydration therapy, which frames how generously that therapy is described. Its own authors note the treatment reverses dehydration without shortening the illness or reducing stool output.

A survey of what runners believe; nothing in it tests whether the capsules work. Participants opted into a longitudinal tracking study, so they are more engaged with the sport than average, which makes the belief's persistence more striking rather than less. One country dominates the sample, one sport, 2018 data. The authors' verdict that the evidence is settled rests partly on their own earlier studies.

A chemical identity record, not a study: it says what these compounds weigh and nothing about what they do in a body. Both percentages were calculated from the retrieved molecular weights rather than read off the record, so they carry that rounding.

The men were fully hydrated and fasted when they drank, which is nobody's state when they reach for one of these, and retention behaves differently in someone already short of fluid. All 72 were male. The outcome is urine volume over four hours, a stand-in for retention rather than for feeling or performing better. The drinks were not matched for sodium, so this ranks these particular products, not electrolytes as an idea.

The analysis came out of a sports-drink manufacturer's own sweat-testing database, which cuts against the simplest commercial reading but travels with the finding either way. The people tested had chosen to come for sweat testing, so they skew athletic. Two of the three models used forearm patches, an indirect estimate; the whole-body method covered 48 tests. Unexplained variance includes measurement error, so this shows these variables do not predict sweat sodium, not that nothing could.

Weak discrimination is not a screening test, and the authors do not offer it as one. Cramp history was self-reported, and sweat was collected during ordinary training, never during a cramp. Forearm patches estimate whole-body sweat sodium indirectly and carry real measurement error. One other significant result among roughly fourteen comparisons, potassium content in women, is what chance produces at that many tests.

Nobody was randomised: runners chose their own salt and their own drinking, so everything else they did differently comes along with the comparison. Intake was reconstructed from a questionnaire filled in after the race. Almost everyone supplemented, 94 in 100, which leaves barely any unsupplemented group at all, so this says more salt did not protect rather than that salt does nothing. Self-selected ultramarathon fields, single races.

Whether deliberately taking salt changes the risk of low blood sodium in endurance races is untested. Nobody has randomised runners to salt or none, because in these races almost everyone already takes it.

The finish-time result is a single p-value of 0.04 among eight reported outcomes, the shape of finding that most often fails to repeat. The abstract never says how many minutes faster, so the size of the advantage is not on the record anywhere. The trial's registry entry declared 40 participants against the 26 analysed, unexplained. Four to six hours of racing by trained triathletes says nothing about an hour in a gym.

One randomised trial found salt capsules got triathletes to the finish sooner, on a single borderline result in 26 people. Whether that holds up is open, because nobody has repeated it.