Sodium

What it is

Sodium is a mineral element; table salt is sodium chloride, and the FDA notes the two words are often used interchangeably although they do not mean the same thing. Sodium also reaches the diet through additives such as monosodium glutamate, sodium bicarbonate, sodium nitrite and sodium benzoate. Electrolyte supplements deliver sodium as tablets, capsules, powders or drinks, usually alongside potassium, chloride and magnesium. Sodium is an essential nutrient the body needs in relatively small amounts to keep fluid balance and nerve and muscle function working.

What the research says

The state of the evidence: how much sodium people eat is one of the most heavily trialled questions in nutrition, and reducing it lowers blood pressure by a small but reproducible amount. What is far weaker is the case for taking extra sodium as a supplement. The largest observational study of sodium supplement use in ultra-endurance runners found no difference in supplement intake between runners who became hyponatraemic and those who did not, and a systematic review found the sodium-cramp link is not documented. Acute overdose of salt has killed both adults and children, and exercise-associated hyponatraemia from over-drinking still causes deaths.

Evidence grade: Disputed.

What goes wrong

A systematic review of case reports documented 35 deaths from acute salt ingestion, with estimated lethal doses below 10 g sodium in two children. (Source 1)

• Systematic review, Low certainty.
• Size: 35 fatalities in 27 reports (19 adults, 16 children)
• Who: adults and children who acutely ingested salt.
• How long: acute single ingestions.
• Result: lethal dose estimated at less than 10 g sodium in two children and less than 25 g sodium in four adults; frequency could not be determined.
• Funding: not stated.

In 27 reports, there were 35 fatalities documented (19 in adults and 16 in children). The lethal dose was estimated to be less than 10 g of sodium (<5 teaspoons of salt) in two children, and less than 25 g sodium in four adults (<4 tablespoons of salt).

Exercise-associated hyponatraemia still causes neurological injury and deaths, with reported incidence of 7 to 15% in two large marathon studies. (Source 2)

• Expert review, not systematic, Low certainty.
• Size: 135 articles considered.
• Who: marathon runners.
• How long: single endurance events.
• Result: incidence 7 to 15% for symptomatic and asymptomatic exercise-associated hyponatraemia in two major studies; risk factors included high temperatures and female sex.
• Funding: not stated.

However, despite progressive research, neurological disorders and even deaths due to hyponatremic encephalopathy continue to occur.

The US Food and Drug Administration states average intake is about 3,400 mg/day against a Dietary Guidelines limit of less than 2,300 mg/day for adults. (Source 3)

• Official position, Certainty not rated.
• Size: population-level.
• Who: adults in the United States.
• How long: habitual intake.
• Result: average intake about 3,400 mg/day; recommended limit less than 2,300 mg/day; lower limits for children under 14.
• Funding: government body.

Americans eat on average about 3,400 mg of sodium per day. However, the Dietary Guidelines for Americans recommends adults limit sodium intake to less than 2,300 mg per day

What the evidence supports

Cutting salt intake by about 4.4 g/day for four weeks or more lowered blood pressure in a pooled analysis of 34 randomised trials. (Source 4)

• Meta-analysis, Moderate certainty.
• Size: 3,230 participants across 34 trials.
• Who: adults with and without hypertension.
• How long: four weeks or longer.
• Result: systolic −4.18 mm Hg (95% CI −5.18 to −3.18, I2=75%); diastolic −2.06 mm Hg (−2.67 to −1.45, I2=68%); urinary sodium fell 75 mmol/24 h.
• Funding: independent (the authors state the research received no specific grant from any funding agency)

Thirty four trials (3230 participants) were included. Meta-analysis showed that the mean change in urinary sodium (reduced salt v usual salt) was −75 mmol/24 h (equivalent to a reduction of 4.4 g/day salt), and with this reduction in salt intake, the mean change in blood pressure was −4.18 mm Hg (95% confidence interval −5.18 to −3.18, I2=75%) for systolic blood pressure and −2.06 mm Hg (−2.67 to −1.45, I2=68%) for diastolic blood pressure.

Replacing ordinary salt with a potassium-enriched salt substitute lowered blood pressure and reduced death and cardiovascular events across 21 randomised trials. (Source 5)

• Meta-analysis, Certainty not rated.
• Size: 31,949 participants across 21 trials.
• Who: adults in multiple countries, 19 trials reporting blood pressure and 5 reporting clinical outcomes.
• How long: varies by trial.
• Result: SBP −4.61 mm Hg (95% CI −6.07 to −3.14); total mortality RR 0.89 (0.85 to 0.94); cardiovascular mortality RR 0.87 (0.81 to 0.94); cardiovascular events RR 0.89 (0.85 to 0.94)
• Funding: not stated.

Limit of this finding: The published abstract prints one of these confidence intervals with a stray space - the interval for cardiovascular mortality appears as "0. 81 to 0.94" - and the quote keeps the paper's printing exactly as it stands. Read it as 0.81 to 0.94. The same passage also spells sodium chloride as "sodium choloride". Neither is our error and neither changes any of the results.

There were clear protective effects of salt substitute on total mortality (risk ratio (RR) 0.89, 95% CI 0.85 to 0.94), cardiovascular mortality (RR 0.87, 95% CI 0. 81 to 0.94) and cardiovascular events (RR 0.89, 95% CI 0.85 to 0.94).

What the evidence does not support

A Cochrane review of low versus high sodium diets reported the blood pressure fall in people with normal blood pressure was about 0.3%, while renin and aldosterone rose substantially. (Source 6)

• Systematic review, Certainty not rated.
• Size: not stated in the plain-language summary.
• Who: people with normal blood pressure and people with hypertension.
• How long: varies by included trial.
• Result: normotensive SBP/DBP fell 1.1/0 mm Hg (about 0.3%); hypertensive 5.7/2.9 mm Hg (about 3%); renin +55%, aldosterone +127%, adrenalin +14%, noradrenalin +27%, cholesterol +2.9%, triglyceride +6.3%.
• Funding: not stated.

The reduction in SBP/DBP in people with normal blood pressure was 1.1/0 mmHg (about 0.3%) , and in people with hypertension 5.7/2.9 mmHg (about 3%).

In a 161-km ultramarathon, rate of sodium intake from supplements did not differ between runners who finished hyponatraemic and those who did not; overhydration distinguished them. (Source 7)

• Survey study, Low certainty.
• Size: 376 starters, 296 finishers; 53.0% of finishers gave both a survey and a blood sample.
• Who: runners in the Western States Endurance Run, of whom 93.9% used sodium supplements.
• How long: a single race of up to 30 hours.
• Result: hyponatraemia incidence 6.6% of finishers; postrace serum sodium correlated with supplement sodium intake rate (r = 0.24, P = 0.0027) and inversely with body weight change (r = −0.19, P = 0.010), but no group difference in supplement intake.
• Funding: not stated.

There was no difference in rate of sodium intake in supplements between the hyponatremic and normonatremic finishers, and none of the hyponatremic finishers lost >4.3% body weight.

Where the evidence is mixed

The blood pressure benefit of salt reduction was several times larger in people with hypertension than in people with normal blood pressure. (Source 8)

• Meta-analysis, Moderate certainty.
• Size: 3,230 participants across 34 trials.
• Who: hypertensive and normotensive adults analysed separately.
• How long: four weeks or longer.
• Result: hypertensive systolic −5.39 mm Hg (−6.62 to −4.15); normotensive systolic −2.42 mm Hg (−3.56 to −1.29) and diastolic −1.00 mm Hg (−1.85 to −0.15)
• Funding: independent.

In normotensive people, the figures were −2.42 mm Hg (−3.56 to −1.29, I2=66%) and −1.00 mm Hg (−1.85 to −0.15, I2=66%), respectively.

A systematic review of sodium in endurance sport concluded that both high and low sodium intakes are linked to health and performance problems in athletes, and that the sodium-cramp link is theory rather than established. (Source 9)

• Systematic review, Low certainty.
• Size: not stated (literature 2000-2021 from PubMed and Scopus)
• Who: endurance and ultra-endurance athletes.
• How long: varies.
• Result: no pooled estimate reported; the review reports associations in both directions and attributes the cramp link to theory.
• Funding: not stated.

Sodium intake, both at high and low doses, has been found to be associated with health and performance issues in athletes. Besides, there have been theories that an electrolyte imbalance, specifically sodium, contributes to the development of muscle cramps (EAMC) and hyponatremia (EAH).

Where the research disagrees

whether population salt intake should be pushed down to about 3 g/day

• He, Li and MacGregor (BMJ meta-analysis of 34 trials), meta-analysis: The current recommendations to reduce salt intake from 9-12 to 5-6 g/day will have a major effect on blood pressure, but a further reduction to 3 g/day will have a greater effect and should become the long term target for population salt intake. (Source 10)
• Graudal and colleagues (Cochrane review of low versus high sodium diets), systematic-review: Furthermore, several studies have shown that salt reduction activates the salt conserving hormonal system (renin and aldosterone), the stress hormones (adrenalin and noradrenalin) and increases fatty substances (cholesterol and triglyceride) in the blood. (Source 11)

How much

• Reference intake: The FDA describes sodium as an essential nutrient needed in relatively small amounts, with a caveat about heavy sweating. We could not capture the National Academies 2019 Adequate Intake figure verbatim from a primary page, so no numeric reference intake is asserted here. (Source 3)
• Upper limit: The Dietary Guidelines for Americans limit quoted by FDA is less than 2,300 mg/day for adults, with lower limits for children under 14. This is a recommended limit, not a Tolerable Upper Intake Level. (Source 3)
• Studied: Trials pooled by He and colleagues reduced salt intake by about 4.4 g/day, measured as a 75 mmol/24 h fall in urinary sodium. (Source 4)
• Studied: The Cochrane low-sodium review compared a mean intake reduced from 11.5 g/day salt to 3.8 g/day salt. (Source 6)

A common belief, and what the research shows

The belief: Taking salt or electrolyte tablets during long exercise prevents low blood sodium and stops cramps.

What the research shows: In the largest field study of the question, supplement sodium intake did not separate runners who ended up hyponatraemic from those who did not: "There was no difference in rate of sodium intake in supplements between the hyponatremic and normonatremic finishers, and none of the hyponatremic finishers lost >4.3% body weight." A systematic review of sodium in endurance sport frames the cramp link as unproven theory: "Besides, there have been theories that an electrolyte imbalance, specifically sodium, contributes to the development of muscle cramps (EAMC) and hyponatremia (EAH)."

Questions and answers

What is it?

Sodium is a mineral element and one of the two elements in table salt, whose chemical name is sodium chloride. The FDA points out that "table salt" and "sodium" are often treated as the same thing but are not. Sodium also enters food through additives such as monosodium glutamate, baking soda, sodium nitrite and sodium benzoate. Electrolyte supplements package sodium as tablets, capsules, powders or drinks. (Source 12)

What does it do in the body?

Sodium is the main ion in the fluid outside cells, and the FDA describes it as an essential nutrient needed in relatively small amounts to keep body fluids in balance and nerves and muscles working. Because sodium attracts water, higher intakes draw water into the bloodstream and raise blood volume, which is the route by which intake affects blood pressure. The FDA adds a qualifier about substantial sweating, which is the context in which electrolyte supplements are marketed. (Source 3)

Is it good or bad for you?

Both, depending on amount and setting. Sodium is essential, but trial evidence shows lowering habitual intake lowers blood pressure, and the effect is much larger in people with hypertension than in people with normal blood pressure. The Cochrane review put the fall in normotensive people at about 0.3% while finding large rises in renin and aldosterone, which is why the optimal level is genuinely contested. At the other extreme, acute salt overdose has been fatal. (Source 6)

How do you get more of it?

Most sodium in a typical Western diet already comes from packaged and prepared foods rather than the salt shaker, according to the FDA, which puts that share at over 70%. Trials of electrolyte supplements deliver sodium as tablets, capsules or drinks. This describes what was studied and what the food supply contains, not a recommendation. (Source 13)

If it is harmful, what reduces it?

Sodium is cleared by the kidneys in urine, which is why 24-hour urinary sodium is used to measure intake. In the trials pooled by He and colleagues, participants cut salt by about 4.4 g/day, seen as a 75 mmol/24 h fall in urinary sodium, and blood pressure fell accordingly. Reducing packaged and prepared foods is the route those trials used. (Source 4)

Why might someone be low in it or missing it?

Frank sodium deficiency is rare on a normal diet. Low blood sodium in athletes is mostly a dilution problem rather than a shortfall of intake: the marathon literature attributes it to a mix of event factors such as high temperatures and person factors such as female sex, with excess fluid intake the dominant driver. Losses in sweat, vomiting, diarrhoea and some diuretic medicines can also lower body sodium. (Source 14)

Which whole foods contain it or feed it?

The FDA, citing CDC data, reports that about 40% of the sodium Americans eat comes from a short list of everyday foods: deli meat sandwiches, pizza, burritos and tacos, soups, savoury snacks, poultry, pasta mixed dishes, burgers, and egg dishes. Sodium content varies widely between similar products, and some high-sodium foods such as breads and cereals do not taste salty. (Source 15)

What happens if you do not have it?

Severely low blood sodium is dangerous. In endurance sport, hyponatraemic encephalopathy still causes neurological disorders and deaths, and reported incidence of exercise-associated hyponatraemia in two large marathon studies ranged from 7 to 15%. At the level of ordinary diet, outright sodium deficiency is not the usual concern; dilution from drinking too much fluid is. (Source 2)

How can you test for it?

Two different tests answer two different questions. Blood sodium concentration tells you whether the blood is dangerously dilute or concentrated, and is what the ultramarathon study measured after finishing. Intake is measured instead by 24-hour urinary sodium, the method used in the salt reduction trials. Neither is routinely done to check whether an electrolyte supplement is working. (Source 7)

References

1. Nutrients. A Systematic Review of Fatalities Related to Acute Ingestion of Salt. A Need for Warning Labels?. 2017. PMID 28644412, DOI 10.3390/nu9070648. Read the source
2. Journal of Clinical Medicine. Exercise-Associated Hyponatremia in Marathon Runners. 2022. PMID 36431252, DOI 10.3390/jcm11226775. Read the source
3. U.S. Food and Drug Administration. Sodium in Your Diet: Use the Nutrition Facts Label and Reduce Your Intake (Know Your Numbers). undated web page, accessed 2026-09-30. Read the source
4. BMJ. Effect of longer term modest salt reduction on blood pressure: Cochrane systematic review and meta-analysis of randomised trials. 2013. PMID 23558162, DOI 10.1136/bmj.f1325. Read the source
5. Heart. Effects of salt substitutes on clinical outcomes: a systematic review and meta-analysis. 2022. PMID 35945000, DOI 10.1136/heartjnl-2022-321332. Read the source
6. Cochrane Database of Systematic Reviews. Effects of low sodium diet versus high sodium diet on blood pressure, renin, aldosterone, catecholamines, cholesterol, and triglyceride (plain language summary, key results). 2020. DOI 10.1002/14651858.CD004022.pub5. Read the source
7. Medicine and Science in Sports and Exercise (record held by Gettysburg College Cupola). Sodium Supplementation and Exercise-Associated Hyponatremia during Prolonged Exercise. 2015. PMID 25551404, DOI 10.1249/MSS.0000000000000599. Read the source
8. BMJ. Effect of longer term modest salt reduction on blood pressure: Cochrane systematic review and meta-analysis of randomised trials (subgroup and hormone results). 2013. PMID 23558162, DOI 10.1136/bmj.f1325. Read the source
9. International Journal of Environmental Research and Public Health. Effects of Sodium Intake on Health and Performance in Endurance and Ultra-Endurance Sports. 2022. PMID 35329337, DOI 10.3390/ijerph19063651. Read the source
10. BMJ. Effect of longer term modest salt reduction on blood pressure: Cochrane systematic review and meta-analysis of randomised trials (conclusions). 2013. PMID 23558162, DOI 10.1136/bmj.f1325. Read the source
11. Cochrane Database of Systematic Reviews. Effects of low sodium diet versus high sodium diet on blood pressure, renin, aldosterone, catecholamines, cholesterol, and triglyceride (plain language summary, background). 2020. DOI 10.1002/14651858.CD004022.pub5. Read the source
12. U.S. Food and Drug Administration. Sodium in Your Diet: Use the Nutrition Facts Label and Reduce Your Intake (Table Salt and Sodium: Defined; Sodium as a Food Ingredient). 2024. Read the source
13. U.S. Food and Drug Administration. Sodium in Your Diet: Use the Nutrition Facts Label and Reduce Your Intake (where dietary sodium comes from). undated web page, accessed 2026-09-30. Read the source
14. Journal of Clinical Medicine. Exercise-Associated Hyponatremia in Marathon Runners (results section of abstract). 2022. PMID 36431252, DOI 10.3390/jcm11226775. Read the source
15. U.S. Food and Drug Administration. Sodium in Your Diet: Use the Nutrition Facts Label and Reduce Your Intake (Food Choices Matter). undated web page, accessed 2026-09-30. Read the source