When mice eat a lot of potassium for three weeks, their blood pressure goes up mostly at night, no matter how much salt they eat or what form of potassium they consume.

For a few days, extra potassium lowers mice's blood pressure, but after three weeks, it starts to raise it again.

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.

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.

Long-term high potassium makes a kidney channel more active, and blocking that channel with a drug lowers blood pressure in mice.

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.