People in China who lowered the balance of salt to potassium in their urine the most over three years ended up with much smaller increases in their blood pressure — some didn’t even see their bottom number (diastolic) go up at all, and their top number (systolic) only rose a little.

In China, when people were encouraged to eat less salt over three years, their urine showed a big drop in salt relative to potassium—and the people who started with high blood pressure saw the biggest changes. This suggests cutting salt might help those at highest risk for heart problems the most.

If you have heart disease and eat more salt, your blood pressure tends to go up — for every extra gram of salt you excrete in urine, your top blood pressure number goes up by about 1.3 points and your bottom number by about 0.5 points.

For every 1/4 teaspoon of salt you cut out of your diet, your systolic blood pressure drops by about 1 point, and your diastolic by about 1/3 of a point.

For people with heart disease, the more potassium their body gets rid of in urine, the higher their blood pressure tends to be — every extra gram of potassium excreted per day raises systolic pressure by about 1 point and diastolic by about 0.6 points, which is the opposite of what doctors usually expect.

Cutting back on salt can lower blood pressure, but sometimes it doesn’t do much at all—why? It depends on the person, how you measure it, and how much potassium they eat.