Yes, It is true that bananas contain radioactive substances. But the same can be said for spinach, potatoes, oranges, Brazil nuts, kitten litter, granite counter tops, even the air you breathe! Radioactivity is unavoidable and all around us. So, what exactly is it?
Everything in the world is made up of elements, which are made up of atoms (remember the periodic table?). Some of these atoms are unstable, and they decay or disintegrate. They emit "radiation" in the form of subatomic particles like as electrons, alpha particles, and neutrons, or electromagnetic waves known as gamma rays, when this happens. All of them have energy and can break down, or "ionize," substances they come into contact with. Radiation illness or cancer can be caused by damage to essential macromolecules such as proteins or DNA. The nature of the radioactive element in question, the amount of the element, the distance we are from the radioactive material, and the presence of shielding substances between us and the source all play a role in the extent of exposure, just as they do with chemical toxins.
Potassium (K) is a common element that contains a low percentage of radioactive atoms (approximately 0.012 percent). These K-40 atoms breakdown spontaneously, emitting both electrons (beta radiation) and gamma rays. Both of these are capable of causing tissue harm. K-40, on the other hand, is not extremely radioactive, with a half-life of 1.3 billion years and only a few thousand atoms decaying every second. The question is, how much damage can this cause? What are the potential dangers of eating a banana? The dosage of radiation absorbed by relevant human tissues, measured in "rem," a unit that takes into consideration the amount of radiation absorbed as well as the medical implications of that radiation, can be used to assess this.
The rem measurement is complicated, but a 10 millirem (mrem) exposure raises the risk of death in an average adult by one in a million. (This is stated to be an increase of 1 "micromort," with 1 mort being certain death.) A banana contains about 450 mg of potassium and exposes the consumer to about 0.01 mrem when eaten due to its K-40 level. A chest x-ray, by comparison, produces 10 mrem. A fast calculation (10/.01) reveals that it would take at least a thousand bananas to cause a 10 mrem exposure, which would increase the chance of mortality by 1 in a million. To put it another way, a million times a thousand, or a billion, bananas would have to be consumed for death to occur. And all of this would have to be done in one sitting. It's going to be a difficult task.
But what about the dangers of eating bananas for the rest of your life? Is there a cumulative effect? That doesn't happen since potassium is a natural component of our bodies (approximately 120 grams), and the body maintains a consistent potassium level (homeostatic control). There is no buildup of radioactive potassium since some potassium is always taken in through the food and some is always expelled. As a result, while bananas are radioactive, the dose of radioactivity they deliver is not harmful. Sleeping next to someone exposes you to more radiation, although it's still negligible. And, because of the C-14 in their exhaled carbon dioxide, their exposure is exacerbated if they are breathing heavily.
In the conclusion, enjoy the world's most popular fruit, the banana. It's actually a berry. That's a story for another day. What about the peel? It can be used to shine your shoes.