You may have heard that bananas are radioactive. But is this a fun factoid or simply an urban legend?
Bananas are indeed (very slightly) radioactive, but that doesn’t mean you should stop eating them. In fact, they are one of the healthiest snacks you can choose, especially to fuel a workout (plus they’re affordable and conveniently packaged in their own peel). Though they contain plenty of carbs and natural sugar, you’ll also get important nutrients like magnesium, manganese, vitamin B6, vitamin C, fiber, and, of course, potassium.
Potassium is essential for the proper function of many organs and body systems, including your heart, kidneys, muscles, nerves, blood vessels, and lymph vessels. A banana provides around 422 mg, or around 9% of your daily recommended potassium.
Potassium is also the source of a banana’s radioactivity, specifically the radioactive isotope potassium-40. A banana contains approximately 0.1 microsieverts (μSv) or 0.0001 millisieverts (mSv) of ionizing radiation. To put that in perspective, a person who weighs 154 pounds (70 kg) has roughly 140 grams of potassium in their body, of which 16.4 mg is potassium-40.
It's also important to note that the tiny amount of additional radiation exposure from eating a banana is temporary due to the process of homeostasis. Within a few hours of eating a banana, your kidneys will restore the body’s normal potassium content, and the excess will be excreted in your urine.
The amount of ionizing radiation exposure in a 5.3-oz (150-g) banana has been dubbed the “banana equivalent dose” (BED) and is useful as an informal unit of measurement to explain the potential health risks of ionizing radiation. One BED is usually estimated as 0.1 μSv (0.0001 mSv). Typically, people are exposed to around 3 mSv a year (around 30,000 BED) from the environment. Put another way, consuming a banana represents just 1% of your average daily environmental exposure to ionizing radiation.
Bananas aren’t the only foods that contain potassium-40. Potatoes, nuts, and sunflower seeds are also rich in potassium. Brazil nuts are often cited alongside bananas for their radioactivity, as they contain not only potassium-40 but also a measurable amount of radium due to the soil in which they grow. One hundred grams of Brazil nuts provides roughly the same dose of ionizing radiation as 100 bananas, about 10 μSv. This may seem like a lot, but it’s still not a health risk—after all, a transatlantic flight will expose you to around 80 μSv (800 BED).
Don't fear the banana (or the Brazil nut):
- The tiny amount of radioactive material in bananas is nevertheless significant enough to set off sensitive radiation detection devices. For example, a truckload of bananas might have enough radioactivity to trigger a false alarm from a Radiation Portal Monitor.
- The highest level of ionizing radiation you are likely to encounter is undergoing a computed tomography (CT) scan. For example, a chest CT scan delivers a radiation dose of around 7 mSv, which is 70,000 times the radiation in a banana. (To get an acute lethal radiation dose, you’d somehow have to consume tens of millions of bananas.)
- Smoking cigarettes and cigars will also give your body a dose of concentrated radionuclides due to the trace amounts of thorium, polonium, and uranium.
