The debate about the dangers of eating too much salt has gained a new wrinkle: A federal study suggests that the people most at risk are those who also get too little potassium.
Potassium-rich foods, including fruits and vegetables, have long been recommended as a dietary defense against heart disease and other chronic illnesses. The new research is one of the first and largest U.S. studies to look at the relationship of salt, potassium and heart disease deaths.
"If you have too much sodium and too little potassium, it's worse than either one on its own," said Dr. Thomas Farley, New York City's health commissioner, who has led efforts to get the public to eat less salt. He co-wrote a commentary published with the study in Monday's Archives of Internal Medicine.
Potassium may neutralize the heart-damaging effects of salt, said Dr. Elena Kuklina, one of the study's authors at the Centers for Disease Control and Prevention. Sodium increases the risk of high blood pressure, a major cause of heart disease and stroke. Salt - or sodium chloride - is the main source of sodium for most people.
The research found people who eat a lot of salt and very little potassium were more than twice as likely to die from a heart attack as those who ate about equal amounts of both nutrients. Such a dietary imbalance posed a greater risk than simply eating too much salt, according to the study.
Exactly how potassium and salt interact is not understood, and no one believes that simply taking a potassium pill will protect someone against the dangers of a high-salt diet.
Instead, the take-home message is what health officials have been saying for years: Eat a lot of fresh fruits, vegetables and other potassium-rich foods, and eat less salty, processed foods.
Health officials say no one should eat more than 2,300 milligrams of sodium a day, equal to about a teaspoon of salt. Certain people, such as those with high blood pressure, should eat even less. But it's not just a matter of putting down the salt shaker. More than three-quarters of the sodium in the U.S. diet is in processed foods, and only one in 10 Americans meet the teaspoon guideline.
Americans aren't much better at getting enough potassium. The recommended amount is 4,700 milligrams a day. The average woman gets only about half that; the average man gets slightly more.
Spinach, bananas, broccoli and prunes are among the foods known as good potassium sources.
In the new study, researchers surveyed more than 12,000 U.S. adults ages 20 and older, asking them what they ate the previous day, and calculating their daily consumption of sodium and potassium. The participants were followed for 14 years, and 433 died from heart attacks.
In addition to the increased risk of high sodium and low potassium, the study also found ill effects from high sodium alone. People who consumed 5 grams a day had nearly twice the risk of dying from a heart attack as people who ate 2 grams a day during the follow-up period.
Some experts found the results interesting, but also noted several limitations of the study.
Results are based on what people said they ate on just one day of their life. That day may not have been typical and it may not be representative of their diet in the years since, noted Dr. Robert Eckel, a University of Colorado heart expert.
Also, it's an observational study that shows an apparent link, not the kind of rigorous scientific study used to prove cause and effect, he added.
Health officials have increasingly pushed the public to reduce their salt intake, but the CDC study comes in the midst of some scientific back and forth over how dangerous dietary salt is. In a review published last week of seven, smaller studies, other researchers found no strong evidence that people with high or normal blood pressure reduce their risk of death by reducing sodium consumption. That review, by the Cochrane Collaboration, had limitations because of its size.
Still, it prompted the Salt Institute - an industry group - to call government policy on reducing salt consumption ill-advised.
"In light of this, and other recent research, it is time for the government to cease its costly and wasteful efforts to reduce salt consumption until it can conclusively prove a tangible benefit for all consumers. This can only be done through a large-scale clinical trial on the impact of dietary salt reduction on health outcomes," said Lori Roman, the Salt Institute's president, said in a statement.
Alice Lichtenstein, a Tufts University nutrition scientist, said the attention on salt has created a lot of backlash. The CDC study "is a confirmation that dietary salt does matter, and all these public health efforts and the dietary guidelines are appropriate," she said.