FRIDAY, Dec. 19, 2003 (HealthDayNews) -- Doctors typically advise heart and kidney patients to cut their salt intake. But are otherwise healthy Americans getting too much sodium in their diets, too?
A new analysis says more research is needed to demonstrate the toll a high sodium diet takes on the body over a lifetime.
"A lifelong high-salt diet may expedite the stiffening of the arteries," argues Dr. Geza Simon of the Hypertension Clinic at the VA Medical Center in Minneapolis.
But to demonstrate the connection, he says, scientists must conduct long-term experiments using physiologically relevant amounts of salt.
"Only then will our public officials be persuaded to pass legislation to reduce the salt content of processed foods," Simon concludes in a report published in the December issue of the American Journal of Hypertension.
Salt is a necessary component of a healthy diet. People in developed countries consume four to 12 grams a day, Simon reports.
Salt increases average levels of blood pressure, although some people have greater blood pressure responses to salt than others, the National Heart, Lung, and Blood Institute says.
Most Americans consume too much salt, according to the institute. It says people should take in less than 2.4 grams of sodium a day, or roughly 1 teaspoon of table salt a day.
But studies to date have failed to determine whether people are endangering their long-term health by consuming too much salt.
That's partly because of the difficulty of conducting such experiments. Industry is geared toward short-term experiments that produce data in a year or two, Simon explains. And researchers typically publish their data then move on to the next grant application.
It is also "impractical and unethically unjustifiable" to expose human subjects to high amounts of sodium for a long time, he notes.
A simple solution would be to test the life expectancy and cardiac function of laboratory rats exposed to high sodium intake over a lifetime. Such an experiment would take at least five years, from beginning to end, Simon says.
Richard Hanneman, president of the nonprofit Salt Institute, an association of salt producers, agrees that more study is needed. A landmark 1980s study of dietary salt restriction and its effects on blood pressure, dubbed "Intersalt," only fueled debate as scientists interpreted the results differently, he says.
"Proponents of salt restriction just ignored the Intersalt study," he says.
Hanneman maintains that current evidence does not support critics' claims that people are consuming excessive and unhealthy levels of salt.
Simon's paper describes two ways that salt load may have long-term consequences on cardiovascular function and structure. One is a combined increase in cardiac output and regional blood flow, which dilates arteries. The other is an increase in plasma sodium concentration, which may impact vascular health.
Hanneman agrees that high salt diets have been shown to promote the dilation of blood vessels, but he doesn't see that as a health risk. "It's vessel constriction that's unhealthy." That's why people with high blood pressure take drugs like ACE inhibitors and calcium channel blockers, he says.