NephJC Shorts: Salt reduction still lowers BP

JAMA 2023 Dec 19;330(23):2258-2266

doi: 10.1001/jama.2023.23651.

Effect of Dietary Sodium on Blood Pressure: A Crossover Trial

Deepak K Gupta, Cora E Lewis, Krista A Varady, Yan Ru Su, Meena S Madhur, Daniel T Lackland, Jared P Reis, Thomas J Wang, Donald M Lloyd-Jones, Norrina B Allen

PMID: 37950918

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We know reducing sodium intake lowers blood pressure (BP), but what is truly the effect in those with normal BP versus high BP? Those taking BP meds versus those who do not? In the Coronary Artery Risk Development in Young Adults (CARDIA)–SSBP trial (Gupta et al, JAMA 2023), the investigators enrolled 213 individuals either with normal BP or not, and either on BP meds with controlled or uncontrolled hypertension. They crossed over from the usual diet to low sodium (diet with 500 mg i.e. ~ 25 mmol sodium) and high sodium (with 2 bouillon packets, each containing 1100 mg of sodium added to the usual diet). The low sodium diet did result in lower BP in all subgroups, by about 5 - 6 mmHg SBP in the normotensive/controlled hypertension subgroups to about 9 - 190 mmHg SBP in the uncontrolled/untreated hypertension subgroups.

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Figure 2 from Gupta et al, JAMA 2023.  Distributions of Within-Individual 24-Hour Ambulatory BP Response to Dietary Sodium Intake, Calculated From High-Sodium Diet Minus Low-Sodium Diet

Though the authors say these are not significantly different based on interaction p values, the subgroups are woefully underpowered to say that. Note that diet allocation was on alternate days, so this was not a randomized trial. Additionally - despite being provided food and daily phone calls, people on low sodium couldn’t stick to the provided saltless diet (24 hour urine sodium 1.7g rather than 0.5 g) and even the high sodium group couldn’t stomach the extra 2.2g bouillon (24 hour urine sodium went up from 4.6 to 5.5 rather than expected 6.8 g/day). So, an extremely low sodium diet does lower BP a bit, but it’s hard to achieve even if you are provided the food. Salt substitutes are so much more pragmatic (NephJC Summary| Podcast)!

Swapnil Hiremath

Introducing NephJC Shorts

In just over a decade of critical appraisal on NephJC, we have done several experiments. Some of them have worked out phenomenally well, such as the Freely Filtered podcast. Others were not ready for the time, such as the Google Hangouts. We want to try another such experiment, and hope we receive feedback to decide if this is something worthwhile that we should continue doing.

There are many studies and many trials and many reviews, and many guidelines that are published in Nephrology every week. Indeed, it is a golden era for randomized controlled trials in Nephrology. On the other hand, NephJC only occurs twice a month. It does take a lot of work, with the detailed critical appraisal, readable summary, visual, abstracts, and the chats. Sometimes the occasional, irregularly irregular podcast. Hence, we cannot deal with all the worthwhile studies that are coming out.

Enter NephJC Shorts. 

This week, we are publishing a few short blogs. The purpose here is to cover some notable studies in brief. They do not receive the full, long, NephJC treatment. The articles we choose are those that the NephJC editorial team fancies, but suggestions are welcome. Since these are a shorter format, we don’t do a deep dive into the methods and don’t have a long list of the limitations and strengths. Think of them as a pithy version of the usual NephJC blog. Feedback welcome! 

The NephJC Editors