For some Americans, salt can be deadly. Their bodies store too much of it, putting them at increased risk for serious medical problems. At the University of Virginia scientists are working on ways to test for salt sensitivity.
The kidneys are key to salt regulation in the human body. People who are salt-sensitive store too much of it in their cells, and the condition is often linked to high blood pressure, but UVA Professor Robin Felder says that’s not always the case.
“Fourteen percent of people have perfectly normal or even low blood pressure, and they’re salt sensitive,” he says.
Actually, you might say their blood pressure is high when no one is checking.
“At night, that’s when your body is supposed to rest and repair," Felder explains. "Your blood pressure dips by 10%-15% while you’re sleeping. If you’re salt sensitive you don’t have a dip.”
As a result, these people suffer damage to tiny blood vessels which are prevalent in the eyes, kidneys, heart and brain.
“Their capillaries can’t repair themselves, so I think stroke is the most prevalent result, because of the degree of capillarity in the brain, but next is kidney failure because that’s a very vascular organ, then heart and then the retina where damage leads to blindness,” he says.
Which is why Felder and his colleagues are at work coming up with ways to measure salt sensitivity. One method involves a study of kidney cells in urine. They contain tiny pumps that may be genetically programed to store excess amounts of salt.
“The pump sits back, resting, waiting for a high salt meal. Once you hit that high salt meal, that pump goes into action to decide whether we bring in sodium or eliminate sodium.”
Genetic tests can also show who’s salt sensitive, and Felder has found a ring that can be worn at night to transmit blood pressure data to a person’s cell phone.
“That ring essentially will be your personal intensive care unit on your finger."
Felder adds that people are actually on a continuum – some more sensitive to salt than others. Those who store the most should go on a low sodium diet. Federal guidelines advise consuming no more than two grams daily.
“You can get almost a gram of salt in one slice of bread, so if you have a sandwich with lunch meats and cheese, you’re done for the day for the average American. You need to learn your personal salt index, and our test will be able to determine that. Once you know your zone, if you stay in your zone you’ll probably add 20 years to your life.”
He also hopes to develop a treatment for those little kidney pumps that sometimes malfunction.
“Now that we have a target, we could aim a drug at it, see if we can slow the pump down a little bit, especially after a high salt meal.”
For all of this work, Felder needs volunteers -- people willing to be screened for salt sensitivity and to go on a special diet for two weeks. The university will supply all of their food and pay subjects $200. Details are at SaltStudy.com.