Key Points:
- Daily sodium intake remains high (on average ~3,500 mg/day), despite recommendations from the AHA and WHO to limit sodium intake to around 2,000 mg/day.
- Salt-sensitivity to BP (SSBP) is an emerging concept supporting the notion that both normotensive and hypertensive individuals can have BP responses to their dietary sodium concentration.
- The CARDIA-SSBP trial was a prospective, multicenter, randomized cross-over study that enrolled 228 participants to 1 week of either a high sodium diet (with up to 2,200 mg of sodium added/day) or a low sodium diet (with standardized meals containing 500 mg of sodium added/day), followed by another week crossing over to the other diet. At baseline and at the end of each week of diet, 24-hr ABPM and 24-hr urine collections were performed.
- The low-sodium diet resulted in a significant reduction in median SBP of 6 mm Hg, which was similar to the average effect that would be observed with 12.5 mg of hydrochlorothiazide. On the other hand, further increases in daily sodium intake did not result in any significant increase in BP in this cohort – most likely as the baseline diets were already saturated in sodium.
- In conclusion, these data support that clinically meaningful lowering of BP through dietary sodium reduction can be achieved safely and rapidly within 1 week, with a magnitude comparable with that of a common first-line antihypertensive medication.
Since the publication of the DASH-SODIUM trial, dietary sodium has been known to significantly influence blood pressure (BP): in this trial for example, the transition from a high (~3500 mg/day) to a low (~1,150 mg/day) salt diet caused a significant systolic BP (SBP) reduction of 6.7 mm Hg (1). Despite this established evidence, the average diet in high-income countries, and progressively more in low- to middle-income countries as well, remains elevated in sodium content, on average around 3,500 mg/day (2), despite several recommendations from organizations like AHA and WHO to limit sodium intake to around 2,000 mg/day.
Salt-sensitivity to BP (SSBP) is an emerging concept supporting the notion that both normotensive and hypertensive individuals can have BP responses to their dietary sodium concentration. To date, however SSBP remains an incompletely understood concept, and several unanswered questions remain, such as understanding how BP changes in relation to higher or lower dietary sodium concentrations compared to an individual’s own usual diet, or understanding the association between anti-hypertensive pharmacotherapies and changes in an individual salt sensitivity.
Some of these questions were finally addressed through the CARDIA-SSBP trial (Effects of Dietary Sodium on Systolic Blood Pressure in Middle-Aged Individuals: A Randomized Order Cross-Over Trial), which was presented by the principal investigator, Dr. Deepak Gupta (Vanderbilt University Medical Center, Nashville, Tennessee) as a late-breaking clinical trial at the annual American Heart Association (AHA) Scientific Session, held this year on November 10-13th in Philadelphia, PA.
This was a prospective, multicenter, randomized cross-over study that enrolled 228 participants between April 2021 and February 2023 through 2 sources: the CARDIA year 35 core examination as well as non-CARDIA participants from Chicago and Birmingham (NCT04258332) (3). The study included patients aged 50 to 75 years who were willing to adhere to the diet of the study protocol. Key exclusion criteria were SBP of 90-160 mm Hg or diastolic BP (DBP) outside 50-100 mm Hg at the enrollment visit, respectively, resistant hypertension, or contraindications to high- or low-sodium diets (for example due to heart, renal or liver failure). Each participant completed 1 week of either a high sodium diet (with up to 2,200 mg of sodium added/day) or a low sodium diet (with standardized meals containing 500 mg of sodium added/day), followed by another week crossing over to the other diet. Participants attended 4 study visits: enrollment, baseline, end of the first diet week, and end of the second diet week, with 24-hr ABPM and 24-hr urine collections performed at the beginning of the day during the latter 3 visits.
Enrolled participants had mean age 61 years, 65% female and 65% of black race, with about 50% on no BP medications at baseline, 30% on 1 BP medication and the rest on 2 or more BP medications, with average baseline SBP 128 mm Hg and DBP 78 mm Hg. Based on the 24-hour urine sodium excretion, the low-sodium diet resulted in a median reduction of about 1 teaspoon of table salt (i.e. 2.3 g of sodium) per day compared to the usual diet. Notably, this corresponded to a significant reduction in median SBP of 6 mm Hg. This mean reduction was
similar to the average effect that would be observed with 12.5 mg of hydrochlorothiazide. On the other hand, further increases in daily sodium intake did achieve a significant increase of approximately 0.5 teaspoons of table salt (i.e. approximately 1.1 g of sodium), but did not result in any significant increase in BP in this cohort. In terms of safety, both diets were well tolerated, with 8% of individuals reporting any adverse event in the low sodium vs 9.9% in the high-sodium diet – most of which were minor (headaches, GI upset in both arms, and edema in the high-sodium diet phase).
Commenting the study results, Dr. Gupta explained that the lack of incremental BP increase after 1 week of the high-sodium diet suggests that usual diets in this population may have been sodium-saturated already – and not that added sodium beyond usual diet does not adversely contribute to health. As a matter of fact, once a low-sodium diet was attained for 1 week among study participants, returning to a higher-sodium diet afterward did raise BP. In conclusion, these data support that clinically meaningful lowering of BP through dietary sodium reduction can be achieved safely and rapidly within 1 week, with a magnitude comparable with that of a common first-line antihypertensive medication. For further information, the study is available for review as a simultaneous publication on JAMA (4).
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