You probably know that blood pressure responds to the amount of salt (sodium chloride) that you eat. That has been known for more than a century. But more recently experts have discovered that blood pressure in some people rises anywhere from moderately to dramatically when excess salt is consumed.
This condition is known as salt sensitivity, and it can affect people with or without high blood pressure. Salt sensitivity may be as dangerous for your heart as high blood pressure, research has shown, even if your resting blood pressure is normal.
Cardiovascular risks of salt sensitivity
The American Heart Association (AHA) estimates that slightly more than half of people with high blood pressure are salt sensitive to some degree. And one of every four people with normal blood pressure is also salt sensitive and may eventually develop hypertension because of the excess amount of salt consumed in a typical Western diet.
The AHA considers salt sensitivity to be nearly as strong a cardiovascular risk factor as chronic high blood pressure.
An early study in 1997 involved 62 salt-sensitive and 94 salt-resistant patients, all of whom had hypertension. It showed that over an average follow-up of seven years, the salt-sensitive patients had twice as many fatal and nonfatal cardiovascular events than those who were not salt sensitive. The study suggested that blood pressure, smoking, and salt sensitivity were all independent risk factors.
But the risks go beyond heart problems and stroke. A high intake of salt is associated with an increased risk of stomach cancer and kidney disease and may also have an adverse effect on metabolism, leading to obesity.
Possible causes of salt sensitivity
Salt is the main source of sodium, a mineral your body needs, but too much sodium can result in your body holding onto excess water, a load that puts a strain on your heart and blood vessels and can raise your blood pressure.
Salt sensitivity is a genetic trait that researchers still know little about. While they have identified a few genes that may play a role, they don’t know enough to explain the network of gene variations that affect hypertension in humans.
Genes, though, are not the only issue. Other factors influence the way blood pressure responds to salt. Some of them include:
- Sex. Women are more likely to be salt sensitive than men.
- Age. People older than 45 are more prone to developing salt sensitivity, and the likelihood of doing so increases with age.
- Race and ethnicity. Nearly three of every four African Americans with high blood pressure are also salt sensitive.
- Clinical conditions. Hypertension, diabetes, and chronic kidney disease all increase the likelihood of developing salt sensitivity.
The tests to determine salt sensitivity
Not everyone with hypertension is sensitive to salt. In fact, one of every three people with hypertension is salt resistant. This means that their blood pressure doesn’t respond in an exaggerated way to excess sodium.
Currently, it is not practical for doctors to try to determine whether a patient is salt sensitive or not. There is no blood test (biomarker) that can determine if a person is salt sensitive. Other ways of detecting it are time consuming and expensive.
What is known comes from carefully controlled research that examined individuals with and without salt sensitivity. Data from those studies were used to determine cutoff points for people with and without hypertension. People with blood pressure increases greater than the cutoff point are salt sensitive. Those with changes below that point are salt resistant. This simple measure may work in a research lab, but the testing is too cumbersome to be performed in a doctor’s office.
Two different tests can be used to determine salt sensitivity. One involves two weeks of closely monitored diets to control sodium intake: one week for a diet low in sodium intake, the second for a diet high in sodium intake.
A series of tests is then needed to verify the accuracy of dietary intake, and a strict protocol must be followed to accurately measure changes in blood pressure.
The other test requires three days of hospitalization. During that time, subjects receive sodium both intravenously and orally. They also take a diuretic to facilitate the excretion of sodium. A strict protocol dictates how blood pressure is measured. Results show the patient’s responses to both sodium and the diuretic. Based on the magnitude of the responses, the individual is classified as either sensitive or resistant to salt.
Researchers are currently looking for more practical ways to identify salt sensitivity. One way is to find a biomarker. A biomarker is a characteristic, such as a measurable substance in the blood, that accurately indicates a medical condition. In this case, researchers are searching for a biomarker that would separate salt-sensitive from salt-resistant individuals.
So doctors have no clear way to diagnose salt sensitivity and don’t know enough about why it occurs. Without clearly understanding the mechanisms involved there is no way to develop a drug therapy to effectively treat salt-sensitive patients.
What you can do
Talk with your doctor about your salt intake. It’s likely that the results of ongoing research will make it possible for doctors to easily identify individual patients with salt sensitivity. Then they’ll be able to offer specific therapies to help reduce the level of risk those patients face.
Right now, your doctor can help you understand your risk for becoming salt sensitive. Some factors that contribute to salt sensitivity are within our control, such as maintaining a normal weight, while others are not, such as sex or ethnicity. While you may not be able to avoid becoming salt sensitive, you can become more informed about the role salt plays in your healthand how to protect yourself.
"Salt Sensitivity: The Surprising Danger to Your Heart" first appeared on Health Central.
Also see How to Shake the Salt Habit.