Potassium/
Bananas are rich in a mineral called potassium. This mineral is important as it helps maintain fluid levels in the body and regulates the movement of nutrients and waste products in and out of cells.
Potassium also helps muscles to contract and nerve cells to respond. It keeps the heart beating regularly and can reduce the effect of sodium on blood pressure.
Potassium may reduce the risk of kidney stones forming as people age. In turn, healthy kidneys make sure that the right amount of potassium is kept in the body.
Source: https://www.medicalnewstoday.com/articles/271157.php