Salt raises blood pressure in some people. The UAB study asks: who? – New

UAB is participating in a multicenter clinical trial that will explore the link between hypertension and salt intake.

Written by: Matt Windsor
Media Contact: Bob Shepard

High blood pressure – hypertension – is the leading underlying cause of death worldwide. More than 1.25 billion people suffer from hypertension, including more than 100 million Americans. Most people around the world also eat more salt than recommended. Is there a link?

Cora Lewis, MD, professor and chair of the department of epidemiology at the University of Alabama at Birmingham in the School of Public Health, is UAB’s principal investigator for a multicenter clinical trial, which is currently recruiting participants , which explores two related questions:

  • How common is salt sensitivity in blood pressure?
  • What mechanisms can explain it?

“A number of studies link high salt intake and high blood pressure to a higher risk of premature death and cardiovascular disease, including heart attack and stroke,” Lewis said. “From randomized controlled trials, the gold standard type of clinical study, we know that a low sodium diet lowers blood pressure on average. But there is great variability in the blood pressure response to salt.

A new clinical trial explores two crucial questions

Some people, for reasons still unknown, are more sensitive to salt than others. Identifying these people is important because studies show that salt-sensitive people are at higher risk of mortality, Lewis says.

According to current estimates, about half of people with high blood pressure are salt sensitive, while the figure is only about 25% for people with normal blood pressure. Lewis also adds that black people tend to be salt-sensitive more often than white people.

But few studies, especially in the past few decades, have looked at the relationship between blood pressure and salt intake experimentally. Instead of relying on food diaries and blood pressure spot checks, Lewis’s study recruits participants to follow high-salt and low-salt diets for a week each, with blood pressure measured continuously. for 24 hours using a small device that participants take home. .

“There has been some controversy in some circles about the relationship between sodium intake and cardiovascular disease, at least in part because many of the studies we have are observational and not clinical trials,” said Lewis. “This is especially true for larger, longer-term studies of dietary sodium and its relationship to actual cardiovascular disease outcomes. This is where our study comes in. »

How the study works

The study, also taking place at Northwestern University and coordinated by a Vanderbilt University researcher, is recruiting volunteers between the ages of 50 and 75 who have normal blood pressure or treated and controlled high blood pressure. Participants begin by eating their normal diet for a week to establish baseline data on salt intake, blood pressure and more. This is followed by a week each of a high-salt diet – the participant’s normal diet plus packets of broth to make a savory soup that you can easily buy at the grocery store – and a low-salt diet, with any the food for the week provided by the study researchers. Participants are also provided with bottled distilled water to drink, as tap water may contain salt.

Participants are randomized to start with the low-salt or high-salt diet, in case the order affects the results. At the end of each week, participants will wear a special blood pressure monitor for 24 hours and collect urine samples for 24 hours. Full-day urine sampling is the best way to measure how much salt a person has consumed because it tends to be cleared from the body quickly.

Collection of crucial data

The study will also look at possible mechanisms that could explain the impact of salt on blood pressure. Blood samples, taken during four weekly visits, will allow Lewis and his co-researchers to study how the amounts of various immune cells change with diet.

“Consuming a high-salt diet can trigger inflammation,” Lewis said. “We will investigate whether the immune system responds to the high-salt diet versus the low-salt diet.”

Inflammation, a sign of an immune response, affects the arteries and is a key factor in atherosclerosis, sometimes called “hardening of the arteries”, which underlies heart attacks and many strokes.

Reducing salt can clearly have beneficial effects. In a large study in rural China, published in the New England Journal of Medicine in 2021, researchers randomized nearly 21,000 participants to use regular salt or a salt substitute with 75% sodium and 25% potassium.

“Those who received the surrogate had lower rates of stroke, cardiovascular disease and death from any cause,” Lewis said. “The trial results highlight that we need to know more about sodium and how it might affect the cardiovascular system. We’re working on that in this blood pressure salt sensitivity study.

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