Low salt diet benefits women more than men, study suggests

12 Dec 2018 --- Following a low salt diet is more effective in lowering blood pressure in women than men, according to a study from the Medical College of Georgia at Augusta University. Even though the levels of salt retention are similar in both sexes, the researchers found that blood pressure was more elevated in females.

The study, published in the journal Hypertension, also suggests that the use of aldosterone-blocking drugs may benefit women. Aldosterone is a hormone and blood vessel constrictor that is naturally found at higher levels in females and is further elevated by high-salt diets.

Dr. Eric J. Belin de Chantemele of Augusta University, co-author of the study, says that when testing on mice, the team found that after seven days on a high-salt diet there was a reduction in female mice’s blood vessel relaxation while their blood pressure increased.

“When we gave mice a high-salt diet for a week, we saw an increase in the blood pressure of the female mice of about 10mmHg, which is clinically significant,” says Dr. Jessica L. Faulkner, MCG Postdoctoral Fellow and the study’s first author.

Eplerenone, a steroidal antimineralocorticoid of the spironolactone group that is used as an adjunct in the management of chronic heart failure, was used to restore the blood pressure to a healthier level and promote the ability of blood vessels’ lining to relax, according to de Chantemele.

“Salt (sodium chloride) is essential for proper body function, but only a small amount is needed. The average adult sodium intake in the US is more than double the American Heart Association’s recommendation for ideal heart health. A large volume of scientific research shows that reducing sodium can help people lower their blood pressure, get healthier and even save lives. That’s why we want to reduce sodium in the food supply,” tells NutritionInsight, Lawrence J. Appel, M.D., M.P.H., chair of the American Heart Association’s Sodium Reduction Taskforce.

Previously, Faulkner and de Chantemele had discovered that the levels of aldosterone are higher in females, while blood pressure is the same in both sexes. This is a typical difference between males and females they say.

“We thought that if the female mice have more aldosterone than the males, they should be more salt-sensitive,” says de Chantemele. “That is what really pushed us to do this study.”

One of aldosterone’s functions is to increase sodium and fluid retention by the kidneys. When one consumes too much salt aldosterone levels go down to avoid excessive salt retention, which increases fluid retention and blood pressure.

The researchers found that in males, the aldosterone-salt interaction works in a way that increased salt intake suppresses aldosterone, which helps protect males from this path to hypertension. While for females a high salt intake does not suppress aldosterone levels as much, so the hormone increases fluid retention and blood pressure. 

In this case, instead of retaining more fluid and salt, the hormone seems to cause problems by impairing the ability of blood vessels to relax. The study found that the kidneys were functioning normally. Both sexes excreted more sodium when they consumed more of it. In fact, females actually excreted the most.

“In the salt-sensitivity field there are two main concepts,” says de Chantemele. “One is it’s mediated by the kidney retaining more salt. Another one suggests that it’s an improper relaxation of the blood vessels in people who are salt-sensitive. Our data support that second concept.”

The use of eplerenone was found to restore blood pressure and endothelial function in the females.

Clinical studies have indicated that females are generally more salt-sensitive.

It decreased both day and nighttime measures of the systolic blood pressure (top number which indicates pressure when the heart is contracting), diastolic pressure (bottom number, which indicates pressure when the heart is relaxed) and mean arterial pressure (an average between the two which gives an overall idea of blood flow).  In male mice, the use of eplerenone didn’t have any effect.

The study findings point towards aldosterone possibly being beneficial for more pathological problems that females face like obesity and salt-sensitive hypertension.

Female mice experienced lower activity of the renin-angiotensin system, a kidney-based system for regulating blood pressure and fluid levels often targeted by common hypertension medications like angiotensin-converting-enzyme (ACE) inhibitors.

The team’s previous work has shown that female mice are particularly susceptible to mineralocorticoid receptor activation and aldosterone-mediated hypertension mechanisms. Mineralocorticoids are steroid hormones produced by the adrenal gland that affect salt and water balance in the body. Aldosterone is the primary mineralocorticoid and works directly in the kidneys to get these to retain sodium and water.

Sodium is included in most foods and the effects of a diet high in salt have long been the subject of study. 

Clinical studies have indicated that females are generally more salt-sensitive, but those findings have not held up in animal studies – which mostly have been done in male rodents – until now.

“There are many ways other than salt to flavor food. Lemon juice, citrus zest or hot chilies can add extra flavor without the extra sodium,” adds Appel.

The results of a recent study, also published in the journal Hypertension, showed that people eating higher amounts of salt had higher blood pressure – no matter how healthy the person’s overall diet. 

The excessive consumption of salt is known to affect heart health and blood pressure, but research by scientists at Weill Cornell Medicine has now underlined its negative effect on cognitive health. Meanwhile, another study showed that for the vast majority of communities, sodium consumption is not associated with an increase in health risks except for those whose average consumption exceeds 5g/day.

By Kristiana Lalou