When you eat a lot of sodium, your body holds on to extra water to dilute it, so blood volume and the pressure on your vessel walls go up. Potassium sits on the other side of the scale and helps the kidneys clear the excess. The chapter on how sodium and potassium affect blood pressure walks through that chain.
Sodium itself is an essential electrolyte: water balance inside and outside cells, nerve signals, and muscle contraction all depend on it, and with no sodium at all you could not survive (mechanism in Potassium & Sodium). The problem is the amount. The body needs very little, and the average person worldwide eats about twice the recommended limit. Salt is not the enemy, but for most people, moderate means less than now.
Mechanism · In table salt, the body tracks sodium
Table salt is sodium chloride (NaCl), and the part the body tracks is the sodium ion. Sodium sits mostly outside cells and potassium mostly inside; the gap between them lets nerves carry signals and muscles contract, and how much water sits outside your cells is set mainly by sodium. With no sodium at all, all of this would stop (mechanism in Potassium & Sodium).
The body needs very little sodium. In 2019 the US National Academies of Sciences, Engineering, and Medicine (NASEM) updated the dietary reference intakes for sodium and potassium together: the two are a pair and belong side by side, rather than a salt shaker to stare at. So the real questions about salt are three: how much you eat, whether you get enough potassium, and where the salt comes from.
Chapter 2
Sodium, potassium and blood pressure
Water follows sodium. When you eat a lot of sodium, the sodium level in your blood rises, and to dilute it back down your body holds on to more water. Blood volume goes up, and so does the pressure on your vessel walls. Eating salty food for years pushes blood pressure up along this path.
Potassium sits on the other side of the scale: it helps the kidneys send extra sodium out in the urine, and it relaxes vessel walls. In population studies, the sodium-to-potassium ratio tracks blood pressure more closely than sodium alone; this is an observed association. Modern diets often carry too much sodium and too little potassium, so both sides of the scale are off at once. Potassium's side comes down to two concrete switches: the gates in the kidney tubules that take sodium back, and the voltage across the membranes of smooth-muscle cells in vessel walls.
A CLOSER LOOK
Water follows sodium, affecting pressure
This is one sodium pathway from the article, not a prediction of an individual's blood pressure. The article also explains potassium's effects on kidney tubules and vessel walls.
1Essential, but amount matters
Sodium is essential. This pathway concerns excessive long-term intake, rather than eliminating sodium.
2Volume and pressure
Holding more water increases blood volume and changes pressure on vessel walls. Individual responses differ.
Illustration for understanding; not to scale. Saved figures include explanations and sources.
Mechanism · The two switches potassium turns
Potassium's side comes down to two switches, one in the kidney and one in the vessel wall.
In the kidney, potassium governs whether sodium gets to stay.
As blood flows through the kidney, a large volume of fluid is first filtered out, and the sodium in it then has to be picked back up along a long, thin tubule. The pickup is done by transporter proteins set in the membranes of the tubule cells, which work like a row of gates, pulling sodium from the tubule back into the body. Here is the point that is easy to miss: how much sodium you finally excrete depends less on how much was filtered out than on how wide this row of gates is open.
Potassium acts on that opening. When you eat more potassium, blood potassium rises slightly. Cells in the far end of the tubule sense the change, and a set of potassium-sensing switches inside them shifts state, turning down the transporters that pull sodium back. With the gates narrowed, less sodium is picked up along that stretch, and more of it keeps moving downstream and leaves in the urine.
So the first link of sodium's chain is weakened at the source: less sodium stays in the body, so less water has to be held to dilute it, and blood volume does not have to rise. This is not a vague claim like drink more water to flush it out; it is a specific switch in a specific place.
On the vessel wall, potassium governs whether it is loose or tight.
The vessel wall is wrapped in a layer of smooth muscle. When it contracts, the channel narrows, and the same blood flow has to be pushed through at higher pressure; when it relaxes, the channel widens and the pressure drops. Whether this muscle contracts depends on how much calcium gets into the muscle cells, and whether calcium can get in depends on the voltage across the cell membrane.
Potassium is the lead actor in that voltage: the difference in potassium concentration inside and outside the cell is what sets the resting membrane potential (the voltage across the membrane when the cell is not firing). When potassium outside the cell rises slightly, potassium channels in the membranes of smooth-muscle cells and of the cells lining the vessel let potassium out more readily, and the sodium-potassium pump in the membrane runs faster. The inside of the membrane becomes more negative, which is called hyperpolarization. As the membrane potential moves more negative, the voltage-operated calcium channels become harder to open, less calcium enters the muscle cells, the smooth muscle stays relaxed, the channel widens, and the pressure on the wall falls.
The two switches run in parallel, which is why the sodium-to-potassium ratio is not a slogan.
Cutting salt alone changes the entrance to sodium's chain: less sodium comes in, but the opening of the tubule gates and the tightness of the vessel wall stay as they were. Adding potassium-rich foods back turns both switches at once: the gates narrow, so sodium that has already come in leaves more easily, and the wall is pushed toward relaxation, so the same blood flow does not have to press against as much pressure. The two act on different links, so their effects can add up, which fits the DASH-Sodium feeding trial, where cutting sodium and eating more produce added together.
You can also work it the other way: someone who cuts salt hard but eats almost no vegetables, fruit, or legumes in a day has closed only one entrance, while the other two switches have not moved, so a limited effect is no surprise. That is also why eat less salt and eat more potassium-rich whole foods always come as a pair in advice on cutting salt, not as a choice of one.
Evidence · Do less sodium and more potassium add up
DASH-Sodium (Sacks 2001, published in the NEJM) was a randomized feeding trial in 412 people, in which the researchers supplied all the food. It pulled two moves apart and then stacked them: cutting sodium from high to low within the same diet, and a usual control diet versus the DASH diet (more produce, more potassium).
Within both the control diet and the DASH diet, going from high to low sodium lowered blood pressure further. The effects of cutting sodium and of DASH added together, and the largest drop came from low-sodium DASH. So cutting sodium and eating more potassium-rich food are two roads you can take at once, not a choice of one.
For the effect of cutting salt on its own, there is one pooled figure: He 2013 combined 34 randomized trials (3,230 people), and eating about 4.4 g less salt a day lowered systolic blood pressure (the higher number in a reading) by about 5.4 mmHg on average in people with high blood pressure and by about 2.4 mmHg in people with normal blood pressure. People whose blood pressure responds especially strongly to cutting sodium are called salt-sensitive. They are more common among people with high blood pressure, older adults, Black people, and people with diabetes or chronic kidney disease; how large a share of the population they make up varies widely, because studies measure it differently.
Where your salt comes from depends on where you live and how you eat. China's National Health Commission spells it out in its diet guideline for adults with hypertension: more than 75% of the sodium that Chinese residents eat comes from salt added in home cooking, followed by high-salt condiments such as soy sauce and other sauces, with processed food a growing third route. In Europe and the US it is the other way around: most sodium comes from processed food and restaurant meals.
So in China, the first switch for cutting salt is at your own stove: use less salt, and less soy sauce and other sauces. If you often eat takeout, snacks, or processed meat, add a second switch: read the sodium figure on the nutrition label.
In practice · Sodium in food that does not taste salty
Beyond the stove, sodium hides in these places:
Processed and ultra-processed foods (Ultra-processed Foods (UPF)): bread, crackers, instant noodles, sausages and deli meat (Processed Meat), canned soup, and all kinds of sauces. They do not always taste very salty, but in industry sodium adds flavor, preserves the food, and improves texture, so it adds upTakeout and restaurant food: for flavor, cooks usually use more salt and sauce than you would at homeFood that does not taste salty: sweet baked goods and breakfast cereals also carry plenty of sodium Sodium does not have to taste salty to pile into your daily total. So cut it at both ends: use less salt and sauce when you cook at home, and when you buy processed food, read the sodium on the nutrition label and swap part of it for whole ingredients.
Chapter 4
How much, cutting back, and cautions
For healthy adults, sodium should stay under 2 g a day, equal to 5 g of salt, about a level teaspoon. That is a strong recommendation from the World Health Organization (WHO), and China's diet guideline for adults with hypertension likewise says under 5 g of salt a day. The goal is not zero salt; it is pulling the excess back.
People with diagnosed high blood pressure, heart failure, or chronic kidney disease face stricter limits, often coordinated with medication; follow your doctor's and dietitian's advice rather than making big changes on your own. Potassium-containing low-sodium salt is not for everyone either: if your kidney function is poor, or you take a drug that raises blood potassium, ask your doctor before using it.
Numbers · How much salt adults should eat
The World Health Organization's 2012 strong recommendation: adults should eat under 2 g of sodium a day, equal to 5 g of salt. Children do not get a separate rule; the adult limit is scaled down by their energy needs. China's National Health Commission, in its 2023 diet guideline for adults with hypertension, likewise says to bring salt down step by step to under 5 g per person per day.
Keep sodium and salt apart: 1 g of sodium is roughly 2.5 g of salt, and food labels usually list sodium. The average person worldwide eats about twice this limit.
In practice · Less salt, more potassium, some umami
How to cut back:
Start at the stove: use less salt when you cook, use less of high-salt condiments such as soy sauce, oyster sauce, and bean paste, add salt at the end of cooking, and serve dipping sauces on the sideEat less takeout and ultra-processed food: for people who often eat out, this step cuts the mostEat more potassium-rich whole foods: vegetables, fruit, legumes, potatoes (potato), bananas (banana), and the like help tip the sodium-potassium balance backLet umami stand in for some of the salt: tomato, mushrooms, kelp, and the glutamate in (MSG / Glutamate) keep food tasty with less saltGive your taste buds time: after a few weeks of cutting salt gradually, you taste the food itself again, and the old saltiness starts to feel heavy You can also swap the salt itself: low-sodium salt, or salt substitute, in which potassium chloride replaces part of the sodium chloride. SSaSS was a cluster-randomized trial in rural China (20,995 people, mostly older adults, most of whom had had a stroke). In the villages assigned to the substitute, strokes and cardiovascular events were both less frequent. But salt substitute contains potassium: people with chronic kidney disease, and people taking drugs that raise blood potassium (potassium-sparing diuretics, ACE inhibitors, or sartan-type blood pressure drugs), should ask their doctor before using it, because of the risk of high blood potassium.
People with diagnosed high blood pressure, heart failure, or chronic kidney disease face stricter sodium limits and often need them coordinated with medication; follow your doctor's and dietitian's specific advice rather than making big changes on your own. A rare few situations (heavy-sweating endurance exercise, certain illnesses) actually call for more sodium; these are individual cases for a professional to judge. This is general education for healthy adults and does not replace medical advice.
Chapter 5
Iodized salt and pricey specialty salts
Your thyroid needs iodine to make its hormones. Iodizing salt puts that trace ingredient into something almost everyone eats, which made it one of the most successful public-health measures of the twentieth century (the iodine mechanism is in iodine).
Himalayan pink salt, sea salt, and rock salt are almost no different from ordinary salt where sodium is concerned; the trace minerals they carry are nutritionally negligible, and most of them are not iodized. When you cut salt, do not cut out your iodine with it, and do not pay extra for a healthier-sounding label.
In practice · Keep your iodine; skip pricey salts
In many regions, iodizing salt is cheap and reaches almost everyone, and it has nearly wiped out goiter and childhood intellectual harm caused by iodine deficiency (the iodine mechanism is in iodine). Keep an eye on iodine when you cut salt: if you sharply reduce iodized salt and rarely eat seafood, check that you have another source of iodine.
Premium salts are often marketed as healthier, but their sodium content is about the same as ordinary salt. The 84 trace minerals on the label come in amounts so tiny they are nutritionally negligible, and most of these salts are not iodized. Which salt to buy is mainly a matter of taste and texture; do not pay extra for a healthier-sounding label, and certainly do not eat more because of it.
What matters far more than which salt is fancier is the total amount and the balance of sodium and potassium: cut salt starting at the stove and with processed food, let umami help, and keep your iodine.
References · 6
National Academies of Sciences, Engineering, and Medicine. (2019). Dietary Reference Intakes for Sodium and Potassium. National Academies Press. The PubMed book abstract (PMID 30844154) gives no reference values; it says the report updates the sodium and potassium DRIs with an expanded model that adds chronic-disease endpoints (the Chronic Disease Risk Reduction Intake). The numeric AIs and CDRRs were not re-read for this note (abstract). www.ncbi.nlm.nih.gov/books/NBK538102
Sacks, F. M., Svetkey, L. P., Vollmer, W. M., Appel, L. J., Bray, G. A., Harsha, D., Obarzanek, E., Conlin, P. R., Miller, E. R., Simons-Morton, D. G., Karanja, N., & Lin, P.-H. (DASH-Sodium Collaborative Research Group). (2001). Effects on blood pressure of reduced dietary sodium and the Dietary Approaches to Stop Hypertension (DASH) diet. New England Journal of Medicine, 344(1), 3-10. Randomized feeding trial (n=412): within both a control diet and the DASH diet, reducing sodium from high to low further lowered blood pressure; the effects of sodium reduction and of the DASH diet were additive, with the largest reduction from combining a low-sodium DASH diet. 10.1056/NEJM200101043440101
World Health Organization. (2012). Guideline: Sodium intake for adults and children. World Health Organization. Recommends a reduction to less than 2 g/day of sodium (5 g/day of salt) in adults - a strong recommendation. For children, the recommended maximum adult level of 2 g/day sodium should be adjusted downward based on the energy requirements of children relative to those of adults. www.who.int/publications/i/item/9789241504836
He, F. J., Li, J., & MacGregor, G. A. (2013). Effect of longer term modest salt reduction on blood pressure: Cochrane systematic review and meta-analysis of randomised trials. BMJ, 346, f1325. 34 randomised trials (3,230 participants), at least 4 weeks. Mean urinary sodium fell 75 mmol/24 h (about 4.4 g/day less salt); systolic pressure fell 4.18 mmHg (95% CI 5.18 to 3.18) and diastolic 2.06 mmHg overall. In people with hypertension, systolic −5.39 mmHg (−6.62 to −4.15), diastolic −2.82; in normotensive people, systolic −2.42 mmHg (−3.56 to −1.29), diastolic −1.00. A 6 g/day salt reduction was associated with a 5.8 mmHg fall in systolic pressure after adjustment (abstract, PMID 23558162). 10.1136/bmj.f1325
General Office of the National Health Commission of China. (2023). Dietary guidelines for adults with hypertension (2023 edition). Issued January 2023. Five food-and-nourishment principles: cut sodium and raise potassium with a light diet; reasonable balanced diet; balance eating with activity for a healthy weight; stop smoking and limit alcohol; monitor blood pressure and self-manage. Verified specifics: salt intake should be brought down step by step to under 5 g per person per day; more than 75 percent of dietary sodium among Chinese residents comes from salt used in home cooking, followed by high-salt condiments, with processed food a growing third route; potassium should be raised through potassium-rich foods and, for people with good renal function, potassium-enriched low-sodium salt - but potassium SUPPLEMENTS (including drugs) are explicitly NOT recommended for lowering blood pressure, and anyone with impaired renal function must consult a doctor before supplementing potassium; inadequate dietary calcium is described as a widespread problem among Chinese residents; whole grains or mixed beans should make up one quarter to one half of the grain portion. www.nhc.gov.cn/sps/c100088/202301/f01895a06c5349ef999f25da833c166d/files/1732844468193_68545.pdf
Neal, B., Wu, Y., Feng, X., Zhang, R., Zhang, Y., Shi, J., et al. (2021). Effect of salt substitution on cardiovascular events and death (SSaSS). New England Journal of Medicine, 385(12), 1067-1077. Open-label cluster-randomised trial in 600 rural Chinese villages. Verbatim: "A total of 20,995 persons were enrolled in the trial"; mean age 65.4, 72.6% with prior stroke, mean follow-up 4.74 years. Stroke rate ratio 0.86 (95% CI 0.77-0.96, P=0.006); major cardiovascular events also lower. 10.1056/NEJMoa2105675