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Is it true that bananas are radioactive, and if you eat too many it can kill you? If yes then how many bananas are good to eat at once.

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    I've read that bananas also do contain some alcohol, which seems to be more relevant. Don't know whether this is a hoax, though. This PDF says "…according to a report published by Indiana University, a standard glass of orange juice contains between .2% and .5% alcohol…". Here is another study about alcohol in certain food. It says that bananas contains 0.4 g ethanol per 100 g fruit. – Uwe Keim Oct 27 '18 at 21:54
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    It's more like bananas is potassium rich and potassium is radioactive (so is almost everything else). – user3528438 Oct 28 '18 at 19:42
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    EVERYTHING living or once-living is radioactive, because of carbon-14 uptake from the food chain. – John R. Strohm Oct 29 '18 at 17:13
  • Harriet Hall , M.D. (ret.) has published a list of all the molecular compounds in a banana. (See skepdoc. info). Her point is that almost any food could carry a warning such as "May contain scary-sounding stuff that you don't understand". – DanielWainfleet Oct 31 '18 at 16:12
  • You should watch Veritasium's videos about radiation.Start with youtu.be/wQmnztyXwVA, and explore other videos in his channel on this topic. Besides being an educator primarily focussing on common people's misconceptions, he has a degree in physics. People are often often scared by the very word "radiation," but we are literally bathing in it, and eating and inhaling radioactive substances. The key is the quantity. (I am not affiliated with Veritasium, but am a big fan of his science ed work. And I have a degree in physics, too). – kkm Nov 1 '18 at 4:29
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Well, yes to both, up to a point. All things are radioactive - radioactive isotopes occur in minute concentrations in nature, so stones, trees, water, air, and indeed fruits are radioactive, and it can be measured too, but only because our instruments are very sensitive. Life has evolved in this environment for ~4 billion years, and it is clearly not enough to harm us. As for the second question - if you will forgive the tongue-in-cheek answer - anything will kill you if you eat too much; that could be concidered the definition of 'too much'. But I think you will have to eat an incredible number of bananas, and it won't be the radiation that kills you, but the overeating.

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bitten by a radioactive banana

Yes, it's true that bananas are radioactive, however, the amount of radiation that you get from eating a banana is negligible. It's also true that eating too many bananas can kill you, but if you manage to eat enough bananas to get radiation poisoning, you're going to die from something else long before potassium exposure comes into the equation - like, say, the death penalty after murdering the next person to bring a banana within 50 miles of you.

relevant xkcd

Source https://xkcd.com/radiation/

Bananas are on the left, third from the top. To better communicate the scale, the top legal (i.e. totally negligible) radiation dose for US workers is equivalent to eating 500,000 bananas/year.

There is actually a unit of radiation exposure measurement called the Banana equivalent dose. Suffice to say, there are about a thousand other sources of radiation in your day to day life that you should worry about before how many bananas you eat starts to become a real concern. You can safely eat as many bananas as you please, at least, from a radioactivity standpoint.

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    In answer to the specific question asked, according to the chart it's one million bananas for a measurable increase in cancer risk, or twenty million bananas for potentially-fatal radiation poisoning. Further, since potassium-40 decays by a mixture of beta emission and electron capture, consuming the bananas is not required: it's sufficient to have them piled on top of you. – Mark Oct 26 '18 at 22:34
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    @Mark somehow, I think someone with 20 million bananas piled on them would not be worried about radiation poisoning. – FuzzyChef Oct 27 '18 at 1:40
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    This place has gone bananas. – copper.hat Oct 27 '18 at 16:43
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    @Mark Beta particles aren't going to do much to you from outside. You need to eat the bananas and absorb the potassium. – Loren Pechtel Oct 28 '18 at 1:34
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    @MikeTheLiar Actually the dose indicated on the graph is correct for the banana irself, but wrong if referred to the person eating it. It's a common mistake. That dose is calculated on the full amount of Potassium in the banana, however when you eat it the body will discard the excess from your body (that means... all the amount in the banana), therefore the dose you actually receive is (in first approximation) only the integral of the decreasing exponential starting at the full content of the banana when you eat it, down to zero in less than a day... much much smaller than you expected. – FarO Oct 31 '18 at 11:58
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In addition to the answers explaining that bananas do contain radioactive potassium, but in small amounts, it's also worth noting that your body maintains a fixed amount of potassium through metabolism.

So even if you somehow manage to consume 5 million bananas, your body won't actually be exposed to 5 million Banana equivalent doses of radiation.

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    This is really the only correct answer. The whole concept of the banana equivalent dose was a nice attempt to educate people about quantitative measures of radiation, but it was fatally flawed for this reason. A better example would be Brazil nuts, which contain trace amounts of radium. Unfortunately, "Brazil nut equivalent dose" just isn't very catchy. – Ben Crowell Oct 27 '18 at 16:56
  • I wonder what it takes to overload that system (e.g. dehydration) and whether a buildup of potassium in your system would cause problems at lower doses than the radiation – Chris H Oct 29 '18 at 7:30
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    @ChrisH: Your body uses certain chemicals like potassium, sodium, calcium, and chloride to make your nerves and muscles work. If they get out of balance, your muscles and nerves would stop working correctly. Elevated potassium levels is called hyperkalemia: en.wikipedia.org/wiki/Hyperkalemia – Dietrich Epp Oct 29 '18 at 21:00
  • @DietrichEpp, yes, I've been reading a bit about electrolyte requirements and balance recently (in the context of endurance exercise). I hadn't really thought about getting too much, rather the opposite, when sweating several litres in a day. I see that even extreme hyerkalemia is only something like a doubling of normal levels, which would be problematic way before radiation could do anything, however the hyerkalemia arose. – Chris H Oct 29 '18 at 21:18
  • @Ben, like with all such measures, the assumption is that you eat all these bananas at once, in a single sitting. This still doesn't make it correct, because the Potassium-40 half-life is enormous and you won't keep yourself exposed for long, but it shows that you'll die from other things :) – Zeus Oct 30 '18 at 0:33
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While it's true that bananas are unusually radioactive (which actually means very slightly), you should keep in mind that all plants and animals are radioactive. For people, about half of our intrinsic radioactivity comes from the potassium in our bodies, and about half from the carbon-14 which we all carry around.

As for safe quantities, that's pretty simple: about 4 liters (9 pounds or so). But this has nothing to do with radioactivity - it's the approximate maximum capacity of the normal human stomach. Eating more than this runs the risk of tearing the stomach and dying.

The question of banana radioactivity has sparked the creation of the Banana Equivalent Dose of radiation. It's about 0.1 μSievert. Since it takes about 5 to 7 Sieverts to kill an adult human, the lethal dose (radiation) for bananas is something like 50 million bananas. And it's even harder to kill somebody that way than that rather silly number suggests. The body has a fairly comprehensive and efficient set of mechanisms for keeping things in balance, and excess potassium is typically excreted within 24 hours. Although, admittedly, the changes needed to support the ingestion of 50 million bananas would almost certainly cause other changes in the (formerly) human body, and any discussion of associated effects become pure speculation.

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    James' answer seems to me to provide the best perspective. Sure, the banana's radioactive, but so are you. Also, every living thing on Earth. – Don Branson Oct 29 '18 at 16:12
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Yes, bananas are radioactive. They contain potassium, and a small part of this comes as a radioactive isotope 40K. The dose of an average banana is (rounded up) around 0.1 μSv. Other potassium-rich foods also naturally contain 40K, e.g. potatoes.

There is absolutely nothing to worry about. Our natural environment and cosmic radiation means our bodies are constantly exposed to radioactive material, but just in trace amounts.

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If you were to somehow actually take all that radioactivity into your body you would be dead long before the radioactivity became an issue. The radioactive element is potassium--and potassium chloride is used as an execution drug.

In practice your body maintains potassium levels at the right amount (too little is also deadly), eating more bananas simply means more potassium in your urine.

Besides, I have a jar sitting here next to me. It's far more radioactive than a banana. It's meant as food, though:

enter image description here

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    Wait, you have a jar containing an execution drug sitting besides you?!?! 😉 – Konrad Rudolph Oct 29 '18 at 17:36
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    @KonradRudolph, sola dosis facit venenum. – Mark Oct 29 '18 at 20:55
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    @Mark In this case it isn't even the dose as the speed. In the old days doctors very occasionally killed accidentally patients this way. The potassium was intentional, of medical benefit if injected into the IV bag, but lethal if injected into the IV line. Now they only have it available pre-mixed in the IV bags to avoid such mistakes. (Taking it slowly and carefully to avoid an oops isn't an option--the problems occurred when patients were crashing.) – Loren Pechtel Oct 30 '18 at 0:32
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When people compare the radiation received from other sources with the radiation from eating a banana, the point of the exercise is not to say that eating bananas is risky. It’s to say that the radiation level you’re exposed to from from things like nuclear power is safe, and you shouldn’t worry about it (or about eating bananas).

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Yes, but it's extremely small.

Bananas do have a very small amount of radioactivity, but as showed by the chart linked in another answer, it's a really small amount, compared to the amount you are exposed to by being around everyday items/doing everyday activities.

You would need to eat several million bananas in a short time span to actually suffer ill effects/die, which we all know is basically impossible. The bananas would've probably killed you some other way.

Basically, don't worry.

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