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PHILADELPHIA -- A decline in blood pressure (BP) going from a high- to a low-sodium diet was confirmed regardless of hypertension status and antihypertensive medications used, a crossover trial found.

At the end of the first week on a high-sodium versus a low-sodium diet, systolic BP differed by 8 mm Hg on 24-hour ambulatory monitoring (P<0.001) among study participants. This was consistent across subgroups by age, sex, race, diabetes, hypertension status, and antihypertensive medications, reported Deepak Gupta, MD, MSCI, of Vanderbilt University Medical Center in Nashville, Tennessee.

He reported that with the addition of a sodium supplement, going from usual diet to a high-sodium diet did not significantly increase median systolic BP (126 vs 125 mm Hg, P=0.14), whereas the low-sodium diet intervention did lower BP (119 vs 125 mm Hg, P<0.0001). About three-quarters of people experienced some reduction in systolic BP between the low- and high-sodium diets.

"For most middle-aged to elderly adults, dietary sodium reduction resulted in clinically meaningful BP lowering which was safely achieved within 1 week. The effect of dietary sodium reduction in BP is comparable to a commonly utilized first-line antihypertensive medication [such as] hydrochlorothiazide 12.5 mg daily," Gupta reported at the annual conference of the American Heart Association (AHA).

A full manuscript of the CARDIA-SSBP crossover study was published simultaneously in .

Having cemented the role of dietary sodium in BP across key populations, the next question is how a low-sodium diet can be implemented and sustained in the real world.

With 24-hour urine sodium excretion analysis, Gupta's group found that usual diet was already very high in sodium at 4.6 g per day. Sodium intake reached 5.5 g daily with the high-sodium diet and 1.7 g daily with the low-sodium diet -- the latter still higher than the intended intake of 500 mg daily from standardized low-sodium meals that are commercially available at grocery stores.

"We need to make it simple for participants to be successful with their diet," Gupta said during an AHA press conference. He cited structural barriers to lowering dietary sodium, which is added in high levels during industrial and commercial food preparation. One estimate puts roughly 70% of dietary sodium as coming from packaged, processed, and restaurant foods.

The FDA currently estimates that Americans eat on average about 3,400 mg of sodium per day.

Two years ago, the agency advised industry on voluntary sodium reduction goals with the purpose of reducing average sodium intake in the U.S. to 3,000 mg/day, or 12% over 2.5 years. The had gone further to recommend a limit of 2,300 mg of sodium daily for men and women 14 years and older.

During the AHA press conference, George Bakris, MD, of UChicago Medicine, called salt the "four-letter word." He recalled recently being referred two patients, both said to be resistant on three drugs, who turned out to have sodium intake of 10 g a day. "They worked with me and the dietitian, and within 2 months they were off all their medicines."

"Now, they didn't have kidney disease, they were not obese, they didn't have heart disease," acknowledged Bakris, who was not involved with the present study. Still, he maintained: "Do not underestimate the power of salt."

CARDIA-SSBP included 213 people who completed both high- and low-sodium intervention diets in either order (median age 61 years, 65% women, 64% Black).

Investigators had enrolled some participants from CARDIA, a prospective observational cohort study that is following individuals enrolled in 1985-1986 in four U.S. cities. Non-CARDIA participants were also enrolled in Chicago and Birmingham, Alabama, following a 2022 amendment to the study protocol.

The final cohort had a 25% prevalence of normal BP, 20% prevalence of controlled hypertension, 25% untreated hypertension, and the rest uncontrolled hypertension based on the BP threshold of 130/80 mm Hg.

Gupta noted that the effects of dietary sodium on systolic BP were consistent across these four groups.

There was a 4 mm Hg median within-individual change in mean arterial pressure between high- and low-sodium diets was 4 mm Hg (P<0.001), which did not significantly differ by hypertension status.

Compared with the high-sodium diet, the low-sodium diet induced a drop in mean arterial pressure in 73.4% of individuals. Nearly half of individuals were classified as "salt sensitive" based on ≥5 mm Hg declines in mean arterial pressure between a high-sodium and a low-sodium diet.

Adverse events were mild and similarly likely during the high- (9.9%) and low-sodium diet phases (8.0%). These were most commonly headaches, gastrointestinal side effects, and edema with the high-sodium diet, and cramping and weakness with the low-sodium diet.

CARDIA-SSBP investigators were unable to completely control what participants ate, so there was room for dietary nonadherence. Gupta also acknowledged the limited generalizability of the study to other populations.

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