How Radioactive Are Bananas?

(Last Updated On: March 12, 2023)

Okay you’ve probably heard that bananas are radioactive before as a kind of “haha” fact. Obviously, a lot of us eat bananas quite regularly and a lot of us aren’t dying of radiation poisoning all the time. The short answer to “how radioactive are bananas” that the cautious care about is simply “not radioactive enough to hurt you.” 

Further Reading: Do Radioactive Things Actually Glow?

What Makes Bananas Radioactive?

Bananas are rich in potassium, an alkali metal. Yes, this does mean potassium will explode when mixed with water. 

Potassium is, more importantly but less interestingly, really important to our ability to function. Not as like a “take your vitamins” thing, your cells literally do not function without it. It’s actually a combination of potassium and sodium ions that get your nervous system functioning. You have positive potassium ions inside of your cells, and positive sodium ions on the outside. The concentration of ions on either side (inside or outside) of your cells will differ, and because the ions have a positive electric charge, this creates electric potential between the inside and outside of any given cell. Long short, this potential lets your cells produce an electric discharge, which if you recall, is how your nervous system works. 

Okay, but radioactive potassium. You’re probably aware that potassium isn’t always radioactive. Bananas, specifically, are rich in potassium-40, which is radioactive. It has a half life of 1.25 billion years, which means if you had a hunk of potassium-40 it would take 1.25 billion years for half of it to decay away. 

How Much Potassium Is in Your Banana?

More specifically, you’re probably wondering how much potassium-40 is inside your banana. Luckily, this is calculable. For every 10,000 atoms of potassium, about 1.2 of them are going to be potassium-40. A 154 pound person (70 kg) has about 140 grams of potassium in them, which means there are about 17 milligrams (0.0169 grams) of potassium-40 inside of them. 

A banana has about 422 milligrams of potassium. This is about 0.4 grams, also known as way less potassium than is already in you. 

How Many Bananas Will Do You In?

Ionizing radiation (the kind that will cause you health problems) is measured in sieverts. Getting blasted with a single sievert will probably give you some radiation sickness, and 4-5 sieverts in a short burst will kill about half of a given population over the course of a month. 

Sounds scary, but our radiation exposure is generally measured in millisieverts (0.001 sieverts) or microsieverts (0.000001 sieverts). In a given year, you’re exposed to 2-3 millisieverts just from the radiation around you. An x-ray is only something like 0.02 millisieverts. Which means to get even a single sievert from x-rays alone, you’d need to get 50 back to back to back. 

So, what’s in a banana? Well, the potassium-40 in a banana is enough to hit you with… 0.1 microsieverts. 0.0000001 sieverts. This is an amount so low that eating a banana doesn’t even increase the amount of radiation in your body. But let’s humor this and just… assume one banana is equal to 0.1 microsieverts of radiation exposure. To get one sievert out of your bananas, you’d need to eat 10 million of them. The average weight of a banana is about 120 grams, so you’re eating 1.2 million kilograms of bananas, or 2.6 million pounds. 

We don’t have to put those numbers into any kind of perspective for you to know that you are going to get sick from eating 10 million bananas long before you get any kind of radiation poisoning. 

Just for fun, there’s actually an informal measurement for radiation and bananas. It’s called the banana equivalent dose, and it’s equal to 0.1 microsieverts. 

See if you know who is making the most bananas here.

About the Author:

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Kyler is a content writer at Sporcle living in Seattle, and is currently studying at the University of Washington School of Law. He's been writing for Sporcle since 2019; sometimes the blog is an excellent platform to answer random personal questions he has about the world. Most of his free time is spent drinking black coffee like water.