The CARDIA-SSBP trial involved 213 individuals aged 50-75 years, including those with and those without hypertension, and showed that the decline in blood pressure brought about by a low-salt diet was independent of hypertension status and antihypertensive medication use. It was also generally consistent across subgroups and did not result in excess adverse events.
“The blood pressure reduction we see here is meaningful, and comparable to that produced by one antihypertensive medication,” lead investigator Deepak Gupta, MD, Vanderbilt University Medical Center, Nashville, Tenn., said in an interview.
Dr. Gupta presented the CARDIA-SSBP study on Nov. 11 at the American Heart Association scientific sessions, held in Philadelphia. The study was published online in JAMA. The exact menus used in the study are available in a supplement to the JAMA paper.
“In order to live a healthy lifestyle, understanding what we eat has important health effects. Raised blood pressure contributes to one out of every eight deaths worldwide,” Dr. Gupta noted. “If people want to lower their blood pressure, attention to dietary sodium is one part of that. If individuals can stick with a low sodium diet, they may be able to stop taking one of their antihypertensive medications, and those who are normotensive will be less likely to develop hypertension.”
Commentators said the study had significant implications for public health, but they pointed out that maintaining a low-sodium diet over the long term is challenging, given the high salt content of generally available foods.
Dr. Gupta noted that the study did use commercially available products in the low-sodium diets and the menus are available for people to follow, making it more accessible than some diets used in previous studies.
“What may also be attractive to people is that you don’t have to wait for months to see an effect. If you start to consume a low-sodium diet, you can see results on blood pressure rapidly, within a week,” he said.
The diet in this study brought about a large reduction in dietary sodium, but Dr. Gupta says any reduction in dietary sodium is likely to be beneficial.
“If you go to the level that we got to, you could expect to see a reduction of around 6 mm Hg. But it’s like walking – you don’t necessarily need to get to 10,000 steps every day. Any amount of walking or physical activity is of benefit. The same is probably true for salt: Any reduction that you can make is probably of benefit.”
For the study, participants had their blood pressure measured by 24-hour ambulatory monitoring while on their usual diets. They were then randomly assigned to either a high-sodium diet or a low-sodium diet for 1 week. Participants then crossed over to the opposite diet for 1 week, with blood pressure measured over a 24-hour period on the last day of each diet.
As assessed by 24-hour urine excretion, the usual diet of participants was found to already be high in sodium (median, 4.45 g/d). This increased to a median of 5.00 g/d when on the high-sodium diet in the study and decreased to 1.27 g/d while on the low-sodium diet.
Results found participants had a median systolic blood pressure of 125 mm Hg on their usual diets. This was raised to 126 mm Hg on the high-sodium diet and lowered to 119 mm Hg on the low-sodium diet.
The researchers also reported that 75% of individuals showed a blood pressure reduction on the low-sodium diet and are thus defined as “salt-sensitive.” This is a higher percentage than found in previous studies.
“Of those that didn’t show a blood pressure reduction with a low-sodium diet in this study, it appears that they may not have been so adherent to the diet as those who did show a blood pressure reduction,” Dr. Gupta said.
He noted that hypertension is the most common chronic disease condition worldwide, with about 1.3 billion people affected, and although it has been known for some time that dietary sodium affects blood pressure, there have been some gaps in previous studies.
For example, many studies have excluded individuals who were already taking antihypertensive medications and people with diabetes, and they have generally not included many older individuals. The current study found that all of these groups showed significant blood pressure reductions by reducing dietary sodium.