Bananas contain potassium-40, a naturally radioactive isotope,
but the radiation is extremely low and harmless.
The human body itself contains much potassium,
tightly regulated by the kidneys to keep blood levels safe between about 3.5 to 5.0 mmol/L.
Excess potassium is quickly excreted, preventing buildup.
High potassium levels can be dangerous,
affecting heart and muscle function, but
the tiny amount from bananas is negligible and
does not impact the body's potassium balance or safety.
Eating bananas is perfectly safe.