ORLANDO, Fla. — Americans eat, on average, more than 3,400 milligrams of sodium each day — much more than the 2,300-mg current recommended limit for many people. But whether this amount increases a person's risk of heart disease is now being hotly debated by researchers.
There's no doubt that eating too much sodium can cause high blood pressure, said Dr. Paul Whelton, a professor of global public health at Tulane University. And because sodium can cause high blood pressure, it's important to reduce sodium intake to cut heart disease risk, Whelton said in a debate Tuesday (Nov. 10), here at this year's American Heart Association Scientific Sessions meeting.
Whelton was the principal investigator on the recent Systolic Blood Pressure Intervention Trial (SPRINT), which made news when it was abruptly cut short because the results were so significant. In the trial, the researchers found that reducing people's blood pressure with medication to 120 mm Hg or below, rather than aiming to reduce blood pressure to 140 mm Hg, significantly reduced people's risk of death during the study period.
But Dr. Michael Alderman, a distinguished university professor emeritus of epidemiology and population medicine at Albert Einstein College of Medicine in New York City, said he disagrees with the idea that the amount of sodium Americans are eating is dangerous.
In Alderman's view, the evidence linking dietary sodium and heart disease is weak. And, in fact, if people's sodium intake drops too low, they may actually face an increase in heart disease risk, Alderman said. [Heart Disease: Types, Prevention & Treatment]
Here's a look at the researchers' debate.
Sodium should be slashed
The science on sodium and blood pressure is very settled, Whelton said. "There should be no question that sodium reduction lowers blood pressure," and that high blood pressure is, on its own, a very important preventable risk factor for heart disease, he said.
And, in clinical trials that have looked at people's sodium intake and blood pressure, there appears to also be a reduction in heart disease risk when sodium intake goes down, Whelton said. For example, studies have suggested that heart attacks and strokes tend to decrease as sodium intake decreases, he said. However, Whelton acknowledged that the results looking specifically at the risk of heart disease in these trials were not statistically significant (meaning they could have been due to chance), he said.
In fact, there have been no high-quality studies looking specifically at sodium intake and the risk of heart attack, stroke and death, Whelton said. In the studies that have reported on this possible link, the results are inconsistent, he said. One problem is that none of the studies were originally designed to look at the effects of sodium on the risk of these events, he said. Rather, the reports are the results of researchers' attempts to analyze data originally gathered for other reasons, after the fact, he said.
Research on this topic is difficult because sodium intake is difficult to measure, he said. Many studies use food frequency questionnaires, which ask people to recall the foods they ate, making them prone to error, he said. And the "gold standard" of measuring a person's sodium intake — a test that measures the amount of sodium in the urine — can also be inaccurate, he said.
It's also important to consider that the amount of sodium people's bodies actually need in order to function is very low, Whelton said. Kidneys are very good at holding onto sodium in the diet, he said.
Major organizations range in their recommendations, from 1,500 mg to 2,300 mg a day. For example, the World Health Organization recommends keeping sodium intake under 2,000 mg a day, while the Dietary Guidelines for Americans draw the line at 2,300 mg a day for adults who are under age 51, do not have high blood pressure, diabetes or chronic kidney disease and are not African American. For these groups, the recommended limit is 1,500 mg a day.[Hypertension: Symptoms and Treatments]
But most people consume much more sodium than recommended by any of the guidelines, Whelton said.
To reduce Americans' sodium intake, the food industry must make changes — 75 percent of Americans' sodium intake comes from processed foods, Whelton said. A gradual, modest reduction in the addition of sodium to foods is a promising heart disease prevention strategy, he said.
We're safe with sodium
But Alderman holds a very different view, contending that the amount of sodium Americans are getting each day isn't dangerous. Rather, he thinks the amount of sodium that should be considered "too much" is much higher: 5,000 mg.
In addition, Alderman said there is a range of sodium intake that should be considered safe: from 2,500 mg to 5,000 mg. With a daily intake of lower than 2,500 mg of sodium, cardiovascular risk goes up, he argued.
In one meta-analysis study that Alderman co-authored, the researchers found that there was a "J-shaped curve" for the relationship between sodium intake and mortality. That means that the risk of dying during the study period was lowest for the people who consumed middle amounts of sodium, which the meta-analysis defined as between 2,500 mg and 5,000 mg.
For the people at both ends of the spectrum — those who consumed less than 2,500 mg, as well as those who consumed more than 5,000 mg — the risk of cardiovascular disease went up, Alderman said. (Whelton said he disagreed with the conclusions of this meta-analysis.)
When people's sodium intake is too low, there can be negative impacts on health, Alderman said. Insufficient sodium can result in increased levels of kidney enzymes, which can increase blood pressure, more sympathetic nervous system activity (also known as the fight-or-flight response), increased insulin resistance and higher lipid levels — all of which are bad for heart health, he said.
Of course, Alderman was not arguing that sodium intake doesn't affect blood pressure. Any "excessive" intake of sodium will certainly increase a person's blood pressure, he said.
But there isn't enough evidence that links the amount of sodium in the diet to an increased risk of heart disease, Alderman argued. Instead, he believes Whelton's view relies on using blood pressure as a link between sodium intake and heart disease, instead of directly linking sodium intake to heart disease.
Researchers need to do studies to see whether there is a direct link between sodium intake and health outcomes such as heart disease, Alderman said.
Concluding his argument, Alderman said that because there are risks associated with both too much and too little sodium intake, like all other essential nutrients, there is a range for the healthy intake of sodium, and currently, Americans are not exceeding that range.