Sodium

What it is

In the body, sodium exists as a dissolved, positively charged ion. Roughly 95 percent of it is in the fluid outside cells, and together with chloride it sets extracellular fluid volume and plasma osmolality, the measure of how concentrated the blood is.^[1] The kidneys hold the balance, adjusting how much is excreted. Sodium also moves in sweat, and how much is lost varies widely from person to person.^[3]

Most dietary sodium comes as sodium chloride, table salt, which food makers use for flavor, texture and preservation.^[4] In a study of 450 US adults cited by the National Academies, 70.9 percent of sodium intake came from sources outside the home, 14.2 percent was inherent in food, 5.6 percent came from home cooking and 4.9 percent from salt added at the table.^[4] Dietary supplements contributed less than 0.5 percent of total intake in the same analysis.^[4]

Supplements and drink mixes use other sodium salts as well. Replenish uses sodium as trisodium citrate, the sodium salt of citric acid. It sits beside potassium, magnesium and calcium in the formula.

How much adults need

Source: National Academies of Sciences, Engineering, and Medicine, Dietary Reference Intakes for Sodium and Potassium (2019), Table S-2.^[2] AI = Adequate Intake. CDRR = Chronic Disease Risk Reduction Intake: the National Academies advise reducing intake if it is above this level. UL = Tolerable Upper Intake Level; ND = not determined, because no toxicological indicator specific to excess sodium was found.

Amount in Replenish: confirmed at launch

Two numbers matter here, and they point in opposite directions. The Adequate Intake of 1,500 mg is set from the lowest intakes tested in randomized trials without signs of deficiency, plus a balance study in which roughly neutral balance was reached under daily heat stress at 1,525 mg a day.^[2] The CDRR of 2,300 mg is the level above which cutting back is expected to lower chronic disease risk.^[2] In practice, more than 90 percent of US and Canadian adults eat more sodium than the Adequate Intake, so falling short is rare.^[4] There is no UL: the committee found evidence that sodium in a concentrated form could cause harm, but not enough to put a number on it.^[2]

What the evidence says

Blood pressure. The 2019 National Academies review rated the evidence from randomized trials as high strength that reducing sodium intake lowers both systolic and diastolic blood pressure, and as moderate strength that reducing it lowers the risk of cardiovascular events.^[2] Larger effects were seen in adults with high blood pressure, but the committee applied the reduction threshold to adults with and without it.^[2]

Swapping sodium for potassium. The largest outcome trial of a salt substitute enrolled 20,995 people in 600 rural Chinese villages who had a history of stroke, or were 60 or older with high blood pressure. Villages were randomized to a salt of 75% sodium chloride and 25% potassium chloride, or to regular salt. Over a mean 4.74 years, stroke occurred at 29.14 versus 33.65 events per 1,000 person-years (rate ratio 0.86), and major cardiovascular events and deaths were also lower.^[5] That was a high-risk population with a very salty diet, so the result does not transfer directly to everyone.

Sweat losses. Sweat sodium concentration is hard to predict. In an analysis of 1,944 sweat tests, individual characteristics plus exercise, environmental and dietary factors together explained only 17% to 23% of the variation between people; energy expenditure and season, a proxy for heat acclimatization, mattered most.^[6]

Hyponatremia in endurance events. Hyponatremia means a blood sodium concentration below 135 mmol/L.^[3] Among 488 runners tested at the finish of the 2002 Boston Marathon, 13% had hyponatremia and 0.6% had a critical level of 120 mmol/L or less. It was linked to substantial weight gain during the race, a finishing time over 4 hours and body-mass-index extremes. The composition of the fluids runners drank was not associated with it.^[7] In other words, the main risk came from drinking more than was lost, and a sports drink was not protective in that study. Hyponatremia in older adults usually has different causes: mainly medicines, inappropriate secretion of antidiuretic hormone, or hormonal disorders.^[8]

None of this research was done in people taking GLP-1 medications. How fluid and electrolytes fit together when appetite and thirst are lower is covered in electrolytes on a GLP-1 and GLP-1 dehydration.

Safety and interactions

For most adults the practical concern is too much sodium, not too little. The National Academies set no UL, but advise reducing intake above 2,300 mg a day, and the 2019 report found insufficient evidence that low sodium intakes are linked to other harmful health effects.^[2] People who have been told to limit salt, including many with high blood pressure, heart failure or kidney disease, should count sodium from drink mixes along with food.

Thiazide diuretics and some antidepressants. In older adults, drugs are a leading cause of low blood sodium, most often thiazide diuretics and antidepressants.^[8] Anyone on these medicines whose prescriber monitors sodium should mention any new electrolyte product.

Lithium. The prescribing information for lithium tells patients to avoid sodium restriction, keep a normal diet with salt and stay hydrated, and lists changes in sodium concentration among factors that raise the risk of lithium toxicity.^[9] A sudden large change in sodium intake, in either direction, is something to discuss with the prescriber.

If you take prescription medicine, ask your pharmacist or prescriber before adding a supplement.

In Replenish

Replenish provides sodium as trisodium citrate, one of its 4 electrolyte minerals plus zinc, alongside potassium, magnesium and calcium. It is there because sodium is the main electrolyte of the fluid outside cells, and the formula as a whole supports hydration.^† The amount per serving is published with the Supplement Facts panel. See Replenish.