Researchers at the Medical School have been studying salt sensitivity — the disproportionate increase in blood pressure in response to eating a high salt diet — and are now focusing on the genetic basis by recruiting volunteers, including students, in clinical trials. Salt sensitivity is a large health problem, as it increases risk for cardiovascular disease and also predisposes people to high blood pressure.
The research team is led by principal investigators Robin Felder, professor of pathology and associate director of laboratory medicine and Professor of Medicine and Dean Emeritus of the Medical School Robert Carey.
“There’s a great debate out there as to whether salt is good for you or bad for you, so we’re trying to sort that out,” Felder said.
According to Felder, his lab has been funded for 12 years for this study on salt sensitivity and has been studying this topic through a variety of techniques, including biochemical experiments, mouse models and human studies. He is now focusing on the genetics of salt sensitivity.
Brandy Patterson, assistant professor of cardiovascular medicine, said in an email statement that eating salt increases the amount of sodium in the bloodstream, which decreases the ability of the kidneys to excrete water.
“The result is extra fluid in the blood vessels,” Patterson said. “Ultimately, this increases the force or pressure against the walls of the blood vessels, which leads to high blood pressure.”
According to Patterson, if a person’s blood pressure increases by 10 percent in response to a high salt load, then that person is salt sensitive.
Moreover, Patterson said there are various factors that affect salt sensitivity, including gender, age, obesity, genetics and various health conditions — such as diabetes and chronic kidney disease.
“Our hypothesis is, specifically, that there are two genes that work together to cause salt sensitivity,” Carey said.
The study focuses on two genes — G-protein-related kinase 4 and the sodium bicarbonate co-transporter SLC4A5. According to Carey, both these genes are associated with salt levels in urine.
“We have evidence from animal in vitro studies and also in vivo studies in animals, showing that these genes are important in the reabsorption of sodium,” Carey said.
As such, the researchers are taking people without high blood pressure and determining whether they have those at-risk genes through genetic tests. Carey said that the participants can be of any age, sex or ethnicity, as long as they do not have cardiovascular disease or high blood pressure.
Zunair Khocka, a research scientist working on the study, said that they specifically target students, as they are consistent and easy to reach out to.
“We have a non-invasive sort of approach, so we table outside of libraries and we get our study out every week in the U.Va. student connection,” Khocka said.
According to Khocka, after the genetic screening, they put the participants on a two-week diet — including one week of high salt and one week of low salt. Then, the researchers measure changes in blood pressure over that period.
The researchers have to follow guidelines related to the ethics of their studies, particularly in advertising, handling privacy issues and recruiting and rewarding volunteers.
“Whenever you think about ethical considerations you have to think about the benefit and the potential for harm and weigh those two,” Carey said. “In this case, for this particular study, the benefit is very high, because of the very high prevalence of salt sensitivity and the bad outcomes that result from that ... harm is virtually none, all it entails really is high or low salt.”
The volunteers receive a $200 compensation at the end of the study.
According to Patterson, this research study will allow for personalized medicine, as clinicians can use results of the trials to prescribe medications that will be effective for salt sensitive patients. Patterson also said this study is crucial for learning about what kinds of patients are salt sensitive.
“For these patients, diet may have a big impact on the development of high blood pressure, as well as the risk for stroke, heart attack, heart failure and chronic kidney disease — all of which can be life threatening,” Patterson said.