Sodium is not optional. You would die without it. That is worth stating first, because almost everything written about salt is about having too much, and it leaves people with the impression that the ideal amount would be none.
What sodium does when it is doing its job
Sodium is an electrolyte — a mineral that carries an electrical charge when dissolved. Your body uses that charge for three jobs it cannot do any other way.
- Nerve signalling. A nerve impulse is, physically, a wave of sodium ions rushing across a cell membrane. Every thought, every sensation and every instruction to a muscle travels this way.
- Muscle contraction. Including the heart. Cardiac muscle depends on the movement of sodium, potassium and calcium across cell membranes in a precise sequence.
- Fluid balance. This is the one that matters for blood pressure. Water follows sodium. Where sodium concentrates, water is drawn after it by osmosis — and your body uses that relationship to control how much fluid sits inside cells, between them, and in the bloodstream.
Your kidneys manage the whole system. They filter your entire blood volume many times a day, and decide continuously how much sodium to return to the bloodstream and how much to send out in urine. When you eat more sodium, healthy kidneys excrete more. That is the design.
How excess sodium raises blood pressure
The classic explanation is a volume argument, and it is the easiest to picture. More sodium in the blood means more water retained in the blood to keep the concentration steady. More water means greater blood volume. More volume inside a fixed set of vessels means greater pressure against the vessel walls — the same as pushing more water through a hose.
That is real, but the current understanding is that it is not the whole story. Research also points to effects on the blood vessels themselves: a high-sodium environment appears to reduce the ability of the endothelium — the artery’s inner lining — to relax the vessel, and stiffer, less responsive vessels raise pressure independently of how much fluid is present.
Sodium also interacts with your kidneys’ hormonal control of pressure over the long term, which is part of why the effect accumulates over years rather than showing up after a salty dinner.
Why some people are affected far more than others
This is where population advice and individual experience diverge, and it is worth knowing. People differ in salt sensitivity — how much their blood pressure moves in response to sodium intake. Salt sensitivity tends to be higher in older adults, in people who already have high blood pressure, in people with diabetes or chronic kidney disease, and it varies between individuals for reasons that are still being worked out.
So two people can eat the same meal and see genuinely different responses. That is not a reason to disregard the guidance; it is a reason your own doctor’s advice may differ from a general recommendation.
The potassium half of the equation
Sodium and potassium work against each other, and most sodium advice omits this. Potassium helps the kidneys excrete sodium, and it helps blood vessel walls relax. In broad terms the ratio of sodium to potassium in the diet appears to matter, not sodium alone.
Modern diets tend to be high in sodium and low in potassium — largely because sodium arrives via packaged food while potassium arrives via vegetables, fruit, beans and dairy. Which is one reason the dietary patterns that lower blood pressure, such as the DASH pattern developed through NIH-funded research, emphasise adding produce rather than only subtracting salt.
⚠️ One caution that matters: if you have kidney disease or take certain blood pressure medications, potassium is something to discuss with your doctor before increasing it, including salt substitutes based on potassium chloride. This is a genuine exception to otherwise general advice.
The numbers, and where the salt actually comes from
| Figure | Amount | Source |
|---|---|---|
| General daily limit for adults | no more than 2,300 mg | American Heart Association / Dietary Guidelines |
| Ideal limit, especially with high blood pressure | 1,500 mg | American Heart Association |
| Threshold to label a product “low sodium” | 140 mg or less per serving | FDA labelling rules |
| One teaspoon of table salt | about 2,300 mg of sodium | — |
The figure that changes behaviour most, though, is this one: according to the CDC and the American Heart Association, roughly 70% of the sodium people consume comes from packaged and restaurant food — not from the salt shaker on the table.
That reframes the whole problem. Putting the shaker away is a small adjustment to a small share of your intake. Reading labels on bread, sauces, deli meat, soup and crackers reaches the part that actually dominates the total. It is also why so much of this site is about labels and packaged goods rather than about cooking without salt.
Salt and sodium are also not interchangeable on a label. Table salt is sodium chloride, and only about 40% of it by weight is sodium. A label reporting sodium is already doing that conversion for you.
Where to go next
- What cholesterol is and how your body uses it — the other headline number, and a different mechanism entirely.
- Low-sodium heart-healthy eating — the practical guide.
- Our low-sodium guides — label-by-label and aisle-by-aisle.
- Blood pressure guides.
Sources for this page: American Heart Association, CDC, National Heart, Lung and Blood Institute (NIH), FDA labelling regulations, Harvard Health Publishing and Mayo Clinic. General educational information, not medical advice — see our editorial policy.