This Healthline article claims:

According to the Centers for Disease Control and Prevention, 1-2 mg/kg is a fatal oral dose of cyanide for a 154 lbs. (70 kg) man. You would need to finely chew and eat about 200 apple seeds, or about 20 apple cores, to receive a fatal dose.

Is this true? Has there been a documented case?

  • 1
    Related question: Do apple seeds contain arsenic? – Oddthinking May 30 '17 at 20:39
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    @Oddthinking Aresenic =/= cyanide – tuskiomi May 30 '17 at 20:39
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    @tuskiomi: Uh yes, thanks. The questions are still related though. The answers even more so. – Oddthinking May 30 '17 at 20:40
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    anecdote - I usually eat the core and seeds. So I must have had thousands of apple seeds over the years. "I aten't dead yet" – Rory Alsop May 30 '17 at 23:08
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    @RoryAlsop I am drinking a lot of water, but I haven't drowned yet. Cyanide is rapidly metabolised by the human body at a rate of about 0.1mg/kg/h and not accumulated. With the lethal dose some times quoted as low as 0.6mg/kg, you could in theory consume four such lethal doses each day without running into any risk at all. – Tor-Einar Jarnbjo May 31 '17 at 11:32

No, that estimate is far too low (you'd need seeds of 1-2 orders of magnitude more apples)

The amygdalin contents of the apple seeds could gener- ate between 0.06 and 0.2 mg cyanide equivalents per gram of apple seeds; these values are relatively high. Acute cyanide toxicity can occur in humans at doses between 0.5 and 3.5 mg kg⁻¹ body weight (Speijers, 1993). In a previous study, Haque and Bradbury (2002) reported the amygdalin contents of Fuji apple seeds to be 5.4 mg g⁻¹.
Bolarinwa et al.: Determination of amygdalin in apple seeds, fresh apples and processed apple juices, Food Chemistry, 170 (2015), 437–442. DOI 10.1016/j.foodchem.2014.08.083

1000 seed weight is 26.74 g according to Kew Gardens seed database.

0.06 - 0.2 mg CN⁻/g apple seed gives 1,6 - 5.3 mg CN⁻/1000 apple seeds

My old paper pharmacology and toxicology textbook (Estler: Lehrbuch der allgemeinen und systematischen Pharmakologie und Toxikologie, Schattauer 1990.) gives 1 mg CN⁻/kg body weight as lethal dose. The CDC info linked by the claim agrees with that.

Thus, for the standard human of 70 kg, about 70 mg of CN⁻ are lethal. I.e. eating (and chewing) 350 - 1170 g of apple seeds, which translates to roughly 13000 - 44000 seeds.

Now, I didn't find citable numbers of seeds per fruit for apples (the claim assumes 10 seeds/apple - which I judge is a plausible number), but for the claim that 20 apples contain a fatal amount of CN⁻ to be true, with the numbers above, each apple would need to contain 660 to 2200 seeds. I'd judge that this is about 2 orders of magnitude off.

Possible source of the error:

While the claim correctly cites the lethal dose of 1-2 mg/kg bodyweight their wording

1-2 mg/kg is a fatal oral dose of cyanide for a 154 lbs. (70 kg) man.

suggests that they apparently did not understand the meaning of dose given as amount per kilogram of body weight (1-2 mg/kg BW is independent of the body weight). According to the numbers given above, 200 apple seeds contain 0,32 - 1.06 mg cyanide. So this could explain the discrepancy (assuming the lower end of fatal dose range, and a comparably high estimate of amygdalin content in apple seeds).

  • Another thing to keep in mind: amygdalin content is not equal to cyanide content. Amygdalin is a condensation product of cyanide, benzaldehyde and two glucose. 1 mmol = 457.4 mg of amygdalin yields 1 mmol = 26 mg of CN⁻. Taking amygdalin content for CN⁻ content would lead to estimates being a factor of 18 off.
  • Are you sure that you interpret the seed database you are linking to correctly? You seem to link to the entry for wild apples, which have much smaller seeds than commercially cultivated species. I could of course weigh one, but don't have a precise scale at hand. Other resources I find online claim the average apple seed weight to be around 750mg or 30 times the number you are calculating with. – Tor-Einar Jarnbjo Jun 6 '17 at 15:40
  • @Tor-EinarJarnbjo: can you link some other source, please? I didn't find one. As a rough guesstimate for plausibility checking 1/2 * 3 x 4 x 8 mm ≈ 48 mm³ (1/2 for a very roughly elliptical shape). So at density 1 g/ml would be 48 mg, at ϱ = 0.8 g/ml -> 38 mg. So the wild seed may be factor 2 or 3 off, but probably not a factor 10. 750 mg at ϱ = 1 g/ml would need something like 8.5x10x18 mm - that would be approaching small almonds or plums (Zwetschgen). – anonymized Jun 6 '17 at 16:45
  • I can't post many links in a comment, but Google is your friend. Several articles (all about cyanide poisoning) quote numbers in that range directly or use similar numbers to convert between weight and number of seeds. One example, an article from The Guardian: theguardian.com/technology/2015/oct/11/… Your calculations seem reasonable though and for the sake of science, I just ate an apple, which I honestly usually don't do. It was a small apple with small seeds and they weigh each about 50mg. – Tor-Einar Jarnbjo Jun 6 '17 at 19:10
  • I am wondering if the source of confusion might be a mix up of grains and grams at some point. An apple seed seem to weigh just about 0.7 grains and at least some articles on the subject seem to get the correct weight of a potentially fatal amount of apple seeds, use however 0.7 grams per seed as a factor to estimate the number of seeds required for a fatal dose: authoritynutrition.com/are-apple-seeds-poisonous – Tor-Einar Jarnbjo Jun 6 '17 at 19:23
  • @Tor-EinarJarnbjo: thanks. 1 grain = 65 mg => 0.7 grain = 45.5 mg gets us into the same order of magnitude (and I disregarded newspaper sources in my search - I was directly looking for seed weights). Moisture level may explain the rest, and I guess a factor of 2 may occur between different varieties (even cultivated ones) - and then it would be interesting to link seed size to amygdalin content - which IMHO is however outside the scope here. – anonymized Jun 6 '17 at 19:44

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