Dietary sodium intake significantly impacts blood pressure, reveals comprehensive study

In a recent study published in JAMA, researchers evaluate individual blood pressure (BP) responses to dietary sodium variations and account for baseline BP and antihypertensive medication use in a diverse population.

Study: Effect of Dietary Sodium on Blood Pressure: A Crossover Trial. Image Credit: Brainslav Nenin / Shutterstock.com

Background 

In the United States, adults, especially the middle-aged and elderly, often consume an average of 3.5 grams of sodium daily, which exceeds the U.S. Department of Health and Human Services, World Health Organization (WHO), and American Heart Association recommendations.

This habit, associated with increased sodium-related deaths, affects blood pressure variably, thus making personalized dietary sodium management challenging. Furthermore, many studies often exclude those on antihypertensive medications, further complicating understanding.

Additional research is needed to understand individual variability in BP responses to dietary sodium, especially among those on antihypertensive medications. Refining the definition and impact of salt sensitivity in diverse populations with varying hypertension statuses is also crucial.

About the study 

The Coronary Artery Risk Development in Young Adults (CARDIA) study was designed to explore the effects of dietary sodium on blood pressure. All participants who were part of this community-based, prospective, multicenter observational cohort provided their informed consent and were compensated for their participation.

The study, conducted between 2021 and 2023, included a diverse group of participants from various U.S. cities, balanced across sex, race, age, and education. The cohort included individuals between 50 and 75 years of age and included both CARDIA and non-CARDIA participants from Birmingham, Alabama, and Chicago, Illinois. 

Participants adhered to a high- and low-sodium diet for one week and were monitored through 24-hour ambulatory blood pressure and urine collections. The diets, customized to each participant’s caloric needs, followed U.S. dietary guidelines focusing on potassium and calcium. The study protocol required four visits to the University of Alabama at Birmingham or Northwestern University field centers, each one week apart.

A comprehensive analysis of subgroups based on various demographic and clinical factors was performed. The researchers also sought to identify any adverse events participants might experience during the dietary intervention.

Study findings 

In the present study, 281 individuals consented to participate, with 232 meeting the eligibility criteria. Of these individuals, 228 attended the initial baseline visit, and 213 completed both phases of the study involving low- and high-sodium diets.

Participants’ daily diets were high in sodium, which was further increased by the high-sodium diet and reduced by the low-sodium diet. The high-sodium diet increased sodium intake compared to the low-sodium and usual diets. This aspect of the study underscored the typical dietary patterns and their modification potential.

The study’s primary outcome, the salt sensitivity for BP (SSBP) for mean arterial pressure, revealed a median increase of four mm Hg when comparing the effects of low- to high-sodium diets. This response remained consistent across various participant subgroups, regardless of differences in baseline diastolic blood pressure. Interestingly, the SSBP did not vary according to the sequence in which the diets were administered.

SSBP across individuals with different hypertension statuses was also explored, including those with normotension, controlled hypertension, untreated hypertension, and uncontrolled hypertension. The response to dietary sodium alterations remained similar across these groups, thus indicating a universal effect of sodium intake on blood pressure.

Investigation into the relationship between different classes of antihypertensive drugs and SSBP found no significant associations. This observation suggests that the impact of dietary sodium on blood pressure is not significantly influenced by these medications.

A significant finding of the study was that the majority of the cohort experienced a decline in mean arterial pressure when switching from a high- to low-sodium diet. Using established criteria for salt sensitivity, about 46% of participants were categorized as salt sensitive, whereas a smaller portion of the cohort exhibited inverse salt sensitivity.

Upon comparing the participants’ usual diet with the low-sodium diet, there was a notable reduction in daily sodium intake. This reduction was associated with a decrease in systolic blood pressure in most participants. Comparatively, while increasing sodium intake, the high-sodium diet did not result in significant changes in blood pressure.

A parallel-group analysis revealed that individuals who began with a low-sodium diet exhibited significantly lower systolic blood pressure by the end of the first week compared to those who started with a high-sodium diet. This effect remained consistent across different subgroups, including sex, age, race, baseline blood pressure, and diabetes status.

The high-sodium diet was associated with symptoms such as headaches, gastrointestinal discomfort, and edema, whereas the low-sodium diet was associated with cramping and weakness. However, these events were relatively infrequent, as they affected less than 10% of participants on either diet. This suggests that dietary changes in sodium intake, both high and low, were generally well-tolerated by the study’s diverse cohort.