Does Salt Raise Blood Pressure? What the DASH Trial Evidence Shows

The relationship between salt and blood pressure has been understood since the early 20th century, and the clinical trial evidence is now quite strong. But the story gets misread in both directions. Some people claim salt has no effect on blood pressure, citing individual variation. Others imply everyone should radically cut their sodium intake. Neither extreme is accurate.

The DASH-Sodium Trial

The clearest experimental evidence comes from the DASH-Sodium trial, published in the New England Journal of Medicine in 2001 (Sacks et al., PMID: 11136953). This was a randomized controlled trial, not an observational study.

Participants were assigned to either a typical American diet or the DASH diet (rich in fruits, vegetables, and low-fat dairy), then fed sodium at three levels: high (3,450mg/day), intermediate (2,300mg/day), and low (1,150mg/day). Each participant rotated through all three sodium levels.

The result: among participants with hypertension eating the DASH diet, reducing sodium from 3,450 to 1,150mg/day cut systolic blood pressure by 11.5 mmHg. For context, that’s the magnitude of effect you’d expect from a first-line blood pressure medication.

Even participants on the typical American diet (not the DASH diet) showed systolic reductions of 8.3 mmHg with the same sodium cut. The combination of DASH diet plus low sodium produced the largest effect.

Why the Response Varies

That 11.5 mmHg average conceals real individual variation, and that variation is not random.

Salt sensitivity is a documented physiological phenomenon. Weinberger (1996, Hypertension) defined it as a blood pressure change of at least 10 mmHg in response to sodium loading or depletion. Using this definition, roughly 50% of people with hypertension are salt-sensitive. For people with normal blood pressure, the figure is closer to 25%.

Think of it like two pipes under pressure. Some pipes are sensitive to volume changes. Add more fluid, pressure spikes. Others have more flexibility and buffer the volume without much pressure change. Salt sensitivity works similarly through kidney handling of sodium and fluid volume.

Salt sensitivity is more common in Black Americans, older adults, people with diabetes, and people with chronic kidney disease. For these populations, the blood pressure response to sodium reduction is often larger and more consistent.

For a young, normotensive person with healthy kidneys, the same sodium reduction may produce very little measurable effect. That doesn’t mean sodium is irrelevant. It means their particular physiology buffers the change.

The Population vs. Individual Distinction

This is where the debate gets muddled.

Population-level guidance is designed to benefit the largest number of people, including those who are most salt-sensitive and most at risk. The AHA recommendation to stay under 2,300mg/day is appropriate guidance for a population that includes millions of salt-sensitive hypertensives. Processed foods, restaurant meals, and packaged breads are the dominant sources of that sodium, and reducing them helps those people.

But that same guidance applied rigidly to an individual with normal blood pressure, healthy kidneys, and no family history of hypertension may not produce any meaningful health benefit. The Cochrane review by Graudal et al. (2017) found that sodium reduction in normotensive individuals produces small blood pressure reductions (less than 2 mmHg systolic on average) and also raises renin, aldosterone, and cholesterol in compensatory responses.

Population guidance and individual clinical guidance are different things. Your doctor can assess which situation you’re in.

Where Sodium Actually Comes From

Most Americans don’t add much salt at the table. The sodium problem is in packaged and restaurant food.

Roughly 70% of sodium intake in American diets comes from processed foods and food service, not from a salt shaker. Bread, canned soups, deli meats, pizza, and fast food are the dominant contributors. Salt added during cooking at home is a minor fraction.

This matters for the policy discussion. Telling people to put down the salt shaker addresses about 5-10% of the problem. Reformulating packaged foods addresses the bulk of it.

What the Evidence Doesn’t Say

A few points worth being direct about.

The DASH-Sodium trial doesn’t prove that reducing sodium to 1,150mg/day is practical or optimal for everyone long-term. That’s below the levels most researchers consider advisable for healthy adults, and very low sodium intake has its own risks, particularly for people on certain medications.

The trial also combined sodium reduction with a specific diet. You can’t cleanly separate the sodium effect from the full DASH dietary pattern in the real world.

And the trial population was adults with prehypertension or stage 1 hypertension. The results are most directly applicable to people who already have elevated blood pressure.

This article is for educational purposes only. It’s not medical advice. Talk to your doctor or a registered dietitian before making significant changes to your diet.