Mice have the lowest blood pressure when their blood potassium is around 4.5 mM, but higher or lower levels raise blood pressure.

When mice eat a lot of salt, adding a moderate amount of potassium lowers their blood pressure, showing that potassium's main benefit might be fighting high blood pressure caused by salt.

Eating more potassium can lower blood pressure in people who already have high blood pressure, but it doesn’t help people with normal blood pressure — so it’s like a targeted fix just for those who need it.

In mice eating normal salt, too much potassium (over 1.75% of their diet) makes their blood pressure go up during active hours, especially at high potassium levels like 5%, because of increased activity of certain kidney channels.

If you eat more potassium every day—like from bananas or potatoes—your blood pressure might drop just a tiny bit, but not enough to matter for your health if you don’t already have high blood pressure.

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.