Link Between Blood Pressure and Salt Stirs Up Seasoned Debate
Feb. 21, 2000 (Washington) -- Though federal health authorities maintain that lowering salt intake helps reduce blood pressure, researchers at a scientific meeting Monday say that advice is leaving a bitter taste in their mouths. Unlike those pre-eminent dietary villains fat and cholesterol, salt's role in causing hypertension, or high blood pressure, is a matter of ongoing debate.
In fact, one of the landmark studies in the field of hypertension research, the Intersalt study, came under attack by doctors and statisticians gathered here for the American Association for the Advancement of Science's annual conference.
The huge international salt analysis published in 1988 found a direct correlation between salt and high blood pressure.
David McCarron, MD, a nephrologist at Oregon Health Sciences University in Portland, was one of the researchers raising an eyebrow at Intersalt's findings. He says the results of the study, which examined data collected over the years from 52 locations, looked almost too good to be true. He also says it's a myth that all salts increase blood pressure, and he questions the validity of studies conducted in rats which he says amount to human's eating a pack of salt-laden chips every 20-minutes around the clock.
Intersalt also came under attack by a statistician from the University of California at Berkeley. David Freedman, PhD, says that a different analysis of the data turns up different, even paradoxical, results. "As salt goes up, blood pressure goes down. So the relationship is the exact opposite of what the Intersalt investigators expected," says Freedman.
What Freedman sees in the numbers is that age appears to be a more significant factor in increasing blood pressure than salt.
"In the early part of your life, you want to live in a high-salt country, so that your blood pressure will be nice and low. Then switch to a low-salt country so you will have the benefit of a nice slow rise in blood pressure from age," he says. However, Freedman's purpose isn't to recommend how much salt to eat, but rather point out what he sees as flaws in the Intersalt study.
"The take-away message, I think, is that you cannot draw conclusions about what to eat ... from the sort of data Intersalt collected," Freedman tells WebMD. His take on Intersalt has yet to be published.
The lead researcher for Intersalt, Jeremiah Stamler, MD, professor emeritusof preventive medicine at Northwestern University Medical School, was traveling and couldn't be reached for comment. However, in a previous defense of his work he wrote, "Reducing sodium intake ... over time, is scientifically justifiable."
The National Heart, Lung, and Blood Institute (NHLBI) says Americans should consume no more than 2,400 mg of sodium a day -- a recommendation identical to the one contained in the 1995 dietary guidelines published by the Department of Health and Human Services.
"Various studies have provided strong evidence that consuming a moderately reduced intake of sodium contributes to lowering blood pressure," says a 1998 statement from NHLBI.
But McCarron says NHLBI has undertaken a salt education program that goes beyond the scientific facts. And to try and curb a salt appetite that's driven by the brain is a "hopeless task." He says studies show we're not that far off the mark in terms of what our salt consumption ought to be.
Since only about 20-30% of the public has blood pressure that fluctuates with salt intake, McCarron says he believes weight gain may be a more appropriate target in terms of curbing blood pressure.