WASHINGTON — While high salt intake increases the risk of heart disease in the general public, a new study says the health effects are less clear when salt consumption actually is reduced to below daily amounts recommended by the government.
That’s because recent studies on the issue had “methodological flaws and limitations” and provided “insufficient and inconsistent” evidence, according to a review of the data by an expert committee of the Institute of Medicine, the independent, nonprofit health arm of the National Academy of Sciences.
“These new studies support previous findings that reducing sodium from very high intake levels to moderate levels improves health. But they also suggest that lowering sodium intake too much may actually increase a person’s risk of some health problems,” said Brian Strom, professor of public health at the University of Pennsylvania and chairman of the Institute of Medicine committee that reviewed the studies.
Most Americans average 3,400 milligrams of sodium each day, or about 1.5 teaspoons of salt. About 75 percent of this amount comes from restaurant food and processed food.
But federal dietary guidelines call for less than 2,300 milligrams a day for most people ages 14 to 50 and no more than 1,500 milligrams a day for African-Americans, people with hypertension, diabetes or chronic kidney disease and those ages 51 and older. The recommendations are based on research that links higher sodium intake to high blood pressure, which is a risk factor for heart disease.
“We looked at newer data that have come out focusing on actual patient outcomes, like whether or not people had heart attacks, whether they were hospitalized and whether they died,” Strom said.
While the studies did not convince the Institute of Medicine committee to recommend altering the current U.S. dietary guidelines for sodium, the research did show that low sodium intake could cause health problems for people with mid- to late-stage heart failure who are receiving aggressive treatment for their disease.
Other literature showed possible adverse health effects of low sodium intake for people with diabetes, chronic kidney disease and pre-existing cardiovascular diseases, “the evidence on both benefit and harm is not strong enough to indicate that these subgroups should be treated differently from the general U.S. population,” the report concluded.
Additional research on lower levels of salt consumption are needed to draw stronger conclusions, the report said.
The Institute of Medicine report, “Sodium Intake in Populations: Assessment of Evidence,” was commissioned by the U.S. Centers for Disease Control and Prevention to evaluate new research that looks at the overall health effects of salt consumption rather than just its effect on blood pressure.
“Overall, the committee found both the quantity and quality of relevant studies to be less than optimal,” the report said.
Elliott Antman, a Harvard Medical School professor and a spokesman for the American Heart Association, said the recent studies and their varied findings have caused confusion about what should be a simple message — that lowering sodium levels generally improves health.
“Because of these methodological flaws (in recent studies), the American Heart Association does not wish to have our clinical community and our patients distracted from the important health message that aggressive reduction of sodium intake from its current levels is important to improve overall health and to reduce the risk of developing hypertension, heart disease and stroke,” he said.