Study: Sodium-to-potassium ratio a key to heart health

Scientists have long suspected that the ratio of the two nutrients in our diets is important, but there hasn't been strong enough evidence to say for sure. In the new study, Nancy Cook, a statistician at Brigham and Women's Hospital and associate professor at Harvard Medical School in Boston, and colleagues were able to test the idea with data from two large trials originally designed to see how blood pressure responds to a variety of factors, such as diet and weight loss.

The studies involved thousands of people and took place in the late 1980s and early '90s. For either 18 months or three years, some participants were assigned to cut sodium intake by up to 35%. Others went along eating like they always did. A handful of times over the course of the study, participants provided all their urine over a 24-hour period. Then, by analyzing the urine, scientists could accurately determine what nutrients each person was eating. (Prior studies relied on people reporting everything they ate -- a method that is notoriously inaccurate.)

One earlier report from this project, published in the British Medical Journal in 2007, found that participants who had been instructed to reduce sodium intake, even for just a few years, were 25% less likely to die from cardiovascular disease 10 to 15 years later than were those who kept eating larger amounts of sodium.

In the current study, the researchers looked at the other group -- those who had continued to eat as they normally would. They found that people who ate more potassium tended to have a slightly lower long-term risk of death from heart disease.

But they also found that people who had consumed the highest levels of potassium and the lowest levels of sodium (about twice as much potassium as sodium) were 50% less likely to die of cardiovascular disease than those who ate the most sodium and the least potassium (about four times as much sodium as potassium).

The ratio of the two nutrients mattered more than the amount of either one when it came to predicting cardiovascular disease, the study found.

Scientists aren't sure how potassium dampens the heart-damaging effects of salt. One possibility, Cook says, is that potassium may prevent the body from absorbing as much sodium. But regardless of the mechanism, trying to boost your ratio is pretty much guaranteed to improve your health because you'll eat more fruits and vegetables, says Edgar Miller III, an epidemiologist at Johns Hopkins Medical University in Baltimore.