People who gradually increase the amount of salt in their diet, along with people who habitually eat a higher-salt diet, face an increased risk of high blood pressure, according to a study published in the Journal of the American Heart Association.

In a Japanese study of more than 4,000 people who had normal blood pressure, almost 23 percent developed high blood pressure over a three-year period. Those who ate the most salt were the most likely to have high blood pressure by the end of the study. Participants who gradually increased their sodium intake also showed progressively higher blood pressure.

Researchers estimated the amount of salt a person was consuming by analyzing the amount of sodium in urine. At the end of the study, those eating the least amount of sodium were consuming 2,925 mg per day, and those eating the most sodium were consuming 5,644 mg per day.

“In our study, it did not matter whether their sodium levels were high at the beginning of the study or if they were low to begin with, then gradually increased over the years — both groups were at greater risk of developing high blood pressure,” said Tomonori Sugiura, M.D., Ph.D., the study’s lead author and an assistant professor in the department of cardio-renal medicine and hypertension at the Nagoya City University Graduate School of Medical Sciences in Nagoya, Japan.

The study highlights the importance of maintaining a lower-salt diet over a lifetime, and confirms the findings of other studies that show strong associations between salt in the diet and high blood pressure.

Sugiura said that although the research focused on Japanese participants, the findings apply to Americans as well.

“Americans consume an average of nearly 3,500 milligrams of sodium a day, which is about 1,000 milligrams more than any public health group recommends,” Sugiura said. “Reducing sodium intake can save lives, save money and improve heart health — no matter what background or nationality a person is.” The American Heart Association recommends consuming no more than 1,500 mg of sodium per day.

In some people, sodium increases blood pressure because it holds excess fluid in the body, creating an added burden to the heart. High blood pressure is a major risk factor for heart attack, stroke and heart failure.

More than 75 percent of sodium in the U.S. diet is found in the salt added to processed food. In the United States, about nine of every 10 people consume too much sodium. The Salty Six foods — breads and rolls, cold cuts and cured meats, pizza, poultry, soup and sandwiches – are the leading sources of overall sodium in the American diet.