What happened to blood pressure when adults switched from a high- to a low-sodium diet?

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Dietary sodium recommendations are debated partly because blood pressure responses vary, and its effect in people taking antihypertensive medication has been understudied. Researchers examined the distribution of individual blood pressure responses, differences between people allocated to the high- or low-sodium diet first, and whether these varied with baseline blood pressure and medication use.

In this prospectively allocated crossover study, community-based participants were enrolled between April 2021 and February 2023 in two US cities. The 213 participants, aged 50–75, included people with normal blood pressure (25%), controlled hypertension (20%), uncontrolled hypertension (31%), and untreated hypertension (25%). They attended a baseline visit while eating their usual diet, then completed one week each on high- and low-sodium diets. The high-sodium diet added approximately 2,200 mg of sodium daily to the usual diet; the low-sodium diet contained approximately 500 mg daily in total. Outcomes included average 24-hour ambulatory systolic and diastolic blood pressure, mean arterial pressure, and pulse pressure.

All 213 completed both diet visits; their median age was 61, 65% were female, and 64% were Black. Median systolic blood pressure was 125 mm Hg on the usual diet, 126 mm Hg on the high-sodium diet, and 119 mm Hg on the low-sodium diet. The median within-person change in mean arterial pressure between the high- and low-sodium diets was 4 mm Hg (IQR, 0–8 mm Hg; P < .001), with no significant difference by hypertension status. Mean arterial pressure fell in 73.4% of participants on the low-sodium diet compared with the high-sodium diet. Using the commonly used threshold of a decline of at least 5 mm Hg, 46% were classified as salt sensitive.

At the end of the first intervention week, the mean systolic blood pressure difference between those allocated to the high- versus low-sodium diet was 8 mm Hg (95% CI, 4–11 mm Hg; P < .001). This difference was mostly similar across subgroups of age, sex, race, hypertension, baseline blood pressure, diabetes, and body mass index. Adverse events were mild and were reported by 9.9% on the high-sodium diet and 8.0% on the low-sodium diet.

The authors concluded that sodium reduction significantly lowered blood pressure in most middle-aged to older adults. The decline from the high- to low-sodium diet was independent of hypertension status and antihypertensive medication use, generally consistent across subgroups, and did not result in excess adverse events. The trial was registered at ClinicalTrials.gov (NCT04258332).