Claims review

Salt, Standing, and Why Ankles Swell by Evening

The salt explanation is the one everybody repeats. It is also the one nobody has tested. Here is what has actually been measured about swelling that arrives at the end of the day, and the one class of supplement with real trials behind it.

The shoe that fit this morning

By six in the evening the shoes are tight, there is a ring around each ankle where the sock sat, and a thumb pressed into the shin leaves a dent that takes a second to fill. By the next morning it has gone. Fine on waking, swollen by evening, fine again by morning: the pattern is common enough that most people stop mentioning it.

The explanation that circulates for it is salt. Eat less salt and the swelling goes. It is repeated in every comment thread on the subject, and it is why a lot of people spend a month measuring soy sauce. So this page starts there, because the salt explanation turns out to be the claim on this subject that almost nobody has checked.

What the salt explanation is missing

A search of the medical literature for sodium restriction against leg or ankle swelling returns fifteen records. Every one of them is in people who already have kidney disease, heart disease, liver disease or a drug reaction. In people without any of those, the number of trials testing whether eating less salt reduces evening ankle swelling is zero.

The large sodium reviews do exist, and they are excellent. They measure something else. The Cochrane review of sodium reduction covers one hundred and ninety-five randomised studies, and its outcomes are blood pressure, renin, aldosterone, catecholamines and lipids — Cochrane Database of Systematic Reviews, 2020, DOI 10.1002/14651858.CD004022.pub5. Leg swelling is not among them. What the review does report is that during sodium reduction renin rose by 1.56 nanograms per millilitre per hour and aldosterone by 104 picograms per millilitre. Those two hormones are the body's fluid-holding system, and the review measured them going up when salt went down.

That is not the same as saying less salt makes swelling worse. Nobody measured that either, and the honest sentence is the boring one: on this particular question, in people who are otherwise well, there is no trial to cite in either direction.

It is worth noticing what the clinical reviews of ordinary, unexplained swelling recommend instead. One puts the first-line treatment as spironolactone and never mentions salt at all — Journal of the American Board of Family Medicine, 2006, DOI 10.3122/jabfm.19.2.148. An earlier review lists weight counselling, elastic stockings and several drugs, and sodium is absent from that list too — American Journal of Kidney Diseases, 1999, DOI 10.1016/s0272-6386(99)70067-3.

What has been measured is gravity

The physiology of evening swelling has been measured properly, and the numbers are unglamorous. Standing still raises the pressure inside the small vessels of the leg until fluid is pushed out into the tissue around them, at a rate of about 0.17 per cent of leg volume per minute standing and 0.12 per cent sitting — European Journal of Applied Physiology, 1989, DOI 10.1007/BF02396578. In a second study from the same group, ten minutes of standing increased calf volume by 1.6 to 2.0 per cent — European Journal of Applied Physiology, 1993, DOI 10.1007/BF00599616.

The clearest version of it comes from a flight experiment. Twelve healthy volunteers sat through four simulated twelve-hour flights, and an average of 1,150 millilitres of fluid was retained; the increase in lower leg volume was significant but, in the authors' words, not pathological. That paper is from 1994 and predates digital identifiers, so the reference here is its PubMed number, 7832736 — which is the exception this site normally does not make, and is made because the alternative is leaving the measurement out.

Read together, those three papers say that a healthy leg fills up when it hangs down and empties when it does not. The swelling that arrives by evening is, for most people, that and nothing more mysterious.

The one class of product with trials behind it

There is a category of supplement for this, and it has a name older than the marketing around it: phlebotonics. It covers rutosides, diosmin, horse chestnut and French maritime pine bark extract, and unlike most supplement categories it has been reviewed as a class, properly, against placebo.

The verdict is real and it is small. Moderate-certainty evidence suggests that phlebotonics probably reduce oedema slightly in the lower legs, compared with placebo — a risk ratio of 0.70 across thirteen studies and 1,245 participants, Cochrane Database of Systematic Reviews, 2020, DOI 10.1002/14651858.CD003229.pub4. The same review adds that phlebotonics probably increase side effects slightly as well, at a risk ratio of 1.14. Slightly is the reviewers' word in both sentences, and it is worth keeping.

Within that class, one ingredient is sold harder than the others to people with evening swelling: French maritime pine bark extract. It is also the ingredient in the class with the thinnest evidence of its own. The same review is explicit about it: Based on very low-certainty evidence, it is uncertain whether French maritime pine bark extract reduces pain, heaviness and swelling.

Why this page carries an advertising link

Readers asked about one of those products by name often enough that saying nothing would have been its own kind of answer. So we did the work: read the trials, read the refund policy, opened the checkout, and wrote down what each one actually says, including the price, which most pages on this subject manage to leave out entirely.

That page is linked below. It carries an advertising link and so does this one, and if a reader follows it and buys something, this publication is paid a commission by the seller. Everything above was true before the link existed and stays true whether or not anybody follows it.

What we still don't know

Three questions, all open, and each one would change the practical answer if somebody settled it.

• Whether reducing sodium does anything at all for evening swelling in people without kidney, heart or liver disease. No trial has asked.
• Whether the small class effect the phlebotonic review found holds for pine bark extract specifically, which would take a trial larger than the two that exist.
• Whether swelling that follows the fine-in-the-morning pattern needs treating at all, as opposed to being what a leg does at the end of a day spent upright.

Swelling that does not settle overnight, that affects one leg and not the other, or that arrives with breathlessness or chest pain is a different subject from this page and belongs with a clinician the same week, not with a supplement.

General information about a common complaint and the published research on it. Not medical advice, and no substitute for asking somebody qualified who knows the rest of the picture. Nothing here is a reason to begin, stop or alter a prescription.