Despite warnings about the risk, Americans have not reduced the salt in their diets in 50 years, Harvard School of Public Health researchers conclude.

Using data gathered in 38 studies between 1957 and 2003, Adam Bernstein and Walter Willett analyzed urine samples from more than 26,000 people. Unlike previous research that estimated salt consumption by comparing eating diaries to the salt content in particular foods, the urine samples allow researchers to measure the sodium excreted by the body, which is reliably about 95 percent of what is consumed.

“It’s a more accurate reflection of how much salt or sodium we are taking in rather than having to refer to food data bases,” Bernstein told Reuters Health.

They found that regardless of what year the sample was taken, people in the studies consumed about 3.7 grams of sodium every day. That’s more than 1.4 grams over the 1 teaspoon-a-day recommended for most people, and more than twice as much as a person with high blood pressure, or at risk of developing it, should be getting.

There was little difference in urine sodium excretions between blacks and whites, old and young. Although men did tend to have higher levels of sodium than women, that’s explained by their higher calorie intake, Bernstein told Reuters Health; “they eat more.”

The researchers had expected to find an increase in salt consumption based in part on changes in eating habits over the last 50 years. Americans eat more processed foods today and a “large majority of sodium in the U.S. diet is added in manufacturing and food services,” they write in the American Journal of Clinical Nutrition.

While salt consumption has remained relatively stable over the past half-century, rates of heart disease and high blood pressure have gone up, leading the researchers to conclude that the rise in total number of calories eaten every day (and the resulting obesity) “may be a more important determinant of the increased prevalence of hypertension than sodium intake.”

That’s not to say too much emphasis is placed on reducing salt consumption. The authors point to multiple studies showing that higher levels of sodium intake raise blood pressure and the risk of developing hypertension, or chronically high blood pressure.

A report by the Institute of Medicine earlier this year urged more federal regulation of the salt content in food because of the demonstrated association between high sodium consumption and high blood pressure, as well as heart and kidney disease. High blood pressure, the IOM stated, is a “neglected disease” that costs the U.S. health system $73 billion a year.

“Salt is a worthwhile target that should and can be modified by policy and industry and any way to try to reduce the burden of heart disease and high blood pressure is warranted,” Bernstein said. “There are multiple issues to address; obesity is one and salt consumption is another.”

SOURCE:  The American Journal of Clinical Nutrition, online September 8, 2010.