Americans need to do more than stop reaching for the salt shaker if they want to cut back on the amount of sodium in their diets, according to a new study.

Only a small fraction of sodium in most people's diets in the U.S. comes from salt added at the table, researchers found. The majority comes from manufacturing processes and what's added to foods during cooking at restaurants.

"Only 11% is coming from home – from salt shaker or cooking," said lead author Lisa Harnack, of the University of Minnesota School of Public Health in Minneapolis. "The rest is coming from other sources."

Most Americans consume too much salt. Since 1980 the Dietary Guidelines for Americans put out by the government urged reducing sodium, Harnack and colleagues note in the journal Circulation May 8th.

The current recommendation is that people get less than 2,300 mg of sodium per day, which is the amount in about 1 teaspoon of salt. The Institute of Medicine (IOM) in 2010 recommended reducing sodium in commercially packaged and prepared foods.

To determine the sources of salt in people's diets, the researchers recruited 450 adults from Birmingham, Alabama; Minneapolis, Minnesota; and Palo Alto, California between 2013 and 2014.

The participants were interviewed to determine everything they ate over 4 days. They were also seen in clinics, and provided the researchers with a plastic bag containing the same amount of salt they added when eating foods.

The average amount of sodium in people's daily diets was 3,501 mg, on average, the researchers found.

Some groups had more sodium in their diets than others. For example, men ate more sodium overall than women. Black or Asian participants tended to add more salt to their food than Hispanics. Also, people with lower levels of education tended to consume more sodium than those with higher levels.

For all groups, sodium added during the manufacturing process was the leading source in the diet.

The researchers found that 71% of sodium in the participants' diets came from outside the home, through restaurants or processed foods. Another 14% occurred naturally in food.

About 6% of sodium came from what people added during meal preparation, and 5% came from what they added while they were eating.

Less than 1% of sodium came from dietary supplements and water sources.

Harnack said the results show most sodium is coming from items bought in stores – like potato chips – or foods like hamburgers ordered at restaurants.

"They really need to be reading the nutrition panels in grocery stores and choose carefully at restaurants," said Harnack.

The results have implications for patients, doctors and policy, Dr. Lawrence Appel and Kathryn Foti of Johns Hopkins University in Baltimore, write in an editorial published with the study.

People should focus on product selection, they add, and doctors should also emphasize this to patients. For policymakers, they say the study reinforces the 2010 IOM recommendation to reduce sodium in products.

"Efforts to reduce the sodium content in our food supply have tremendous potential to lower (blood pressure) and prevent cardiovascular disease," Appel and Foti conclude.

—Andrew M. Seaman