Blood Pressure, Salt, and Potassium

We know that diets low in sodium (salt) help to lower blood pressure. What you may not know is that diets that are high in potassium, such as vegetarian diets and those high in fruits in vegetables, can also help reduce blood pressure.

Researchers in Australia noted that the Australian intake of fruits and vegetables tends to be a good 50% higher than the American diet - meaning that it's much higher in potassium. Previous research in Australia showed that those Australians with mild high blood pressure benefitted from a diet low in sodium - would those Australians who did not have high blood pressure also benefit from a low-sodium diet, given that their typical diet is high in potassium already?

To find out, the researchers recruited 92 men and women with normal or slightly elevated blood pressures to participate in a dietary study (J Nutr 2003:133(12):4118-4123). The participants were all taught to follow a low-sodium, high-potassium diet for 8 weeks, while their blood pressures were monitored regularly. The goal of the diet was to cut their usual sodium intake by more than half, and to help reach that goal the researchers provided the participants with salt-free bread, salt-free margarine, and other low-sodium ingredients. (Note that they were not instructed to use salt substitutes containing potassium.) The participants were instructed to avoid processed foods and higher-sodium snack foods and to replace their snack foods with vegetables, fruits, and nuts - all high in potassium.

For the first four weeks of the study, half of the participants received sodium supplements intended to return the sodium levels of their diet to the higher levels found in a typical Australian's diet. The other half of the participants received a placebo. For the second four weeks, the two groups switched: instead of salt tablets, the first group received the placebos, while the second group received the salt tablets. This allowed the researchers to compare the effects of a high-sodium diet with high potassium levels with the effects of a low-sodium diet with high potassium levels.

They found that even those whose diets were already high in potassium would indeed benefit from a reduced-sodium diet: those participants who started the study with normal blood pressures saw their systolic blood pressure (the first number) reduced by about 2.5 points when they followed the high-potassium, low-sodium diet (the placebo phase). Even more importantly, when the subjects were following the low-sodium, high-potassium diet and were receiving the salt tablets, their blood pressures were still lower than when they started the study - although not as low as when they received the placebos.

What this means for you

By no means should you take this as a directive to go out and take a potassium supplement to significantly increase your potassium intake. (Extremely high potassium levels can in fact be deadly.) Bear in mind that the participants in this study increased their potassium intake simply by replacing their more processed snacks with more fruits, vegetables, and nuts - something you can easily do yourself (and should).

First posted: August 1, 2012