Potassium -40.

Banana contains the radioactive isotope Potassium-40.
The more potassium the body accumulates, the higher its radioactivity. Yet it does not exceed those values ​​to which a person is adapted. Fortunately, both radioactive potassium-40 and, for example, non-radioactive potassium-39 are easily excreted from the body if there are suddenly too many of them. The body keeps potassium in balance, and with-it natural radiation.
You can calculate how many bananas you need to eat at a time in order to receive a dangerous dose of radiation. For example, if one banana contains about 0.1 μSv of radiation, and a single dose of less than 25 mSv is not perceived by the body, then you need to eat at least 250 thousand (!) pieces at a time.

Why are men more radioactive than women? Among the natural elements, there are also radioactive elements. For example, potassium-40. It is absolutely identical in chemical properties to non-radioactive potassium - a biogenic element, which means it is present in our body! The body of an adult contains about 170 g of potassium, of which 20 mg of radioactive potassium-40. Due to this radionuclide alone, about 300 thousand radioactive decays occur every minute in the human body! True, there are much fewer other radionuclides in our body.