Study Shows No Reduction in U.S. Salt Intake Over the Past 4 Decades
By Kathleen Doheny
WebMD Health News
Reviewed by Laura J. Martin, MD
Oct. 20, 2010 -- Despite constant pleas by public health experts to hold the salt, the sodium intake of the U.S. population hasn't decreased over the past 46 years, according to a new review.
Most of us eat a lot more sodium than is recommended, says researcher Adam Bernstein, MD, ScD, a research fellow in the department of nutrition at Harvard School of Public Health in Boston.
''We would support the recommendation for 1,500 milligrams-a-day intake," Bernstein tells WebMD, referring to one of various guidelines. In his analysis, he found the average intake was more than two and a half times that amount. The review is published in the American Journal of Clinical Nutrition.
But in the same issue, a critic says ''not so fast" to across-the-board sodium rationing, contending that the new report proves that our bodies have a set point for sodium. Restrictions on sodium should target only some people, not the entire population, says David McCarron, MD, an adjunct professor of nutrition at University of California, Davis, and a consultant for the Salt Institute. He wrote an editorial to accompany the analysis.
With Walter Willett, MD, MPH, DrPH, chair of the department of nutrition at Harvard, Bernstein reviewed studies published in the medical literature from 1957 to 2003 to determine if sodium intake had declined.
They found the average for the U.S. population is 3,712 milligrams of sodium a day -- well above the range of 1,200 to 2,300 milligrams recommended by various organizations, depending on age and health factors.
To arrive at that figure, the researchers first estimated the average 24-hour urine sodium excretion per person -- 3,526 milligrams of sodium. Then, figuring that 95% of dietary sodium intake is excreted in the urine, they computed the average dietary intake at about 3,712 milligrams.
Organizations recommend various limits to sodium, as Bernstein and Willett note in the report. The Institute of Medicine recommends 1,500 milligrams daily for young adults, 1,300 for adults ages 50 to 70, and 1,200 for those 71 and older.
The American Heart Association recommends an upper limit of 2,300 milligrams for those not at risk for high blood pressure; 2,300 milligrams, about a teaspoon of salt, is also the maximum advised under the 2005 U.S. Department of Agriculture Dietary Guidelines.
Bernstein and Willett note in the report that the prevalence of high blood pressure over the past 20 years has risen in the U.S. population and that higher dietary sodium is a factor in the development of hypertension. Overweight and obesity are also important factors.
The researchers cite computer simulation models finding that population-wide declines in sodium intake would decrease cardiovascular disease as well as costs, but say that only a few studies to prove that have been done.
Even so, the Harvard researchers support lowering sodium for all. ''We would support the recommendation for 1,500 milligrams a day," Bernstein says. "We would suggest lower intake for all."
The new review supports the idea of the body having a ''set point'' for sodium, says McCarron. "Your salt intake is a value that is really set by the body and physiology," he tells WebMD.
While most people's sodium intake fluctuates -- one day a high-sodium restaurant meal, the next day more salads and fruits -- it evens out, he says.
The study, he says, suggests the high salt intake found in the U.S. population can't be the fault of the food industry, which has been working to reduce salt content.
Salt intake, he says, "is a physiologically set number."
However, he says, "That doesn't say that certain people shouldn't work very closely to achieve a lower salt intake. Number one would be [those with] cardiovascular disease, with hypertension. Not all with high blood pressure are salt sensitive. It would [also] include some patients with kidney disease."
But he disagrees with across-the-board recommendations to lower salt. "These blanket recommendations are not safe," he says.
Morton Satin, vice president of scientific research for the Salt Institute in Alexandria, Va., reviewed the report for WebMD.
In a blog he wrote in response to the study on his web site, he writes that "the sodium-hypertension link is not what it was quacked up to be!"
For most of the population, he tells WebMD, ''from a health point of view, there's no justification for cutting back on salt."
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