I couldn’t find information on the vitamin C density of polar bear livers in particular, but from these values, it seems far from clear that polar bear livers are more similar to lemons than limes in that respect. The vitamin C contents of limes and lime juice do not stand out in that list.
Moreover, it seems that it only takes about 10mg of vitamin C per day to prevent scurvy, and the Manual of Nutritional Therapeutics says that the same daily quantity is enough to improve scurvy symptoms, with 60-100mg/day being recommended for full recovery. So it seems that a cup (~240g) of fresh lime juice per day is enough to both prevent and enable recovery from scurvy.
(Scott and Scurvysays that “[t]ests on animals would later show that fresh lime juice has a quarter of the scurvy-fighting power of fresh lemon juice,” but I couldn’t find a source for that, I could find many contradicting it, and the USDA data suggests that it has ~3/4 of the vitamin C density of fresh lemon juice).
So it seems that the lime juice was just not preventing scurvy because it had spent long periods of time open to the air, and had been pumped through copper tubing. And so this paragraph from the post:
“Different kinds of citrus fruits are more like one another than they are like polar bear meat” sounds very reasonable, but in this case it was wrong. Sicilian lemons really ARE more like polar bear meat than they are like West Indian limes, at least for the purposes of treating scurvy.
seems very misleading (especially but not exclusively if you don’t interpret “polar bear meat” as referring to a specific polar bear organ, given that my sources say that fresh polar bear meat has 30x less vitamin C than fresh lime juice).
1. Copper tubing and environmental exposure does destroy vitamin C
So it seems that the lime juice was not preventing scurvy just because it had spent long periods of time open to the air, and had been pumped through copper tubing.
At first glance, I thought you were claiming that copper tubing and air exposure does not destroy vitamin C, but now I think I read you backwards. I think you are claiming that they do destroy vitamin C, and that copper and O2 destruction of vitamin C was the only reason that “lime juice” was failing to prevent scurvy (and that the differences between lemons vs. limes had nothing to do with it). Just to emphasize that vitamin C is susceptible to destruction by copper and environmental exposure, here’s the Australian Ministry of Health:
Vitamin C is very labile [easily broken down or displaced] and its content in foods varies. Vitamin C content can be affected by season, transport, shelf life, storage time, cooking practices and chlorination of water. Cutting, bruising, heating and exposure to copper, iron or mildly alkaline conditions can destroy ascorbate.
2. Liver and vitamin C
Polar bear liver contains massive amounts of vitamin A, enough to kill humans (1, 2). When the Idle Words essay on which the SMTM post is based says “Eat a bear liver every few weeks and scurvy will be the least of your problems,” the proper response is “because you’ll be dead of vitamin A poisoning.” However, the IW post vascillates between saying that the vitamin C in the polar bear comes from “meat,” “liver,” and “kidneys,” and I don’t trust that the author carefully investigated the nutritional value of each of these organs.
However, I did find a source that talks more about the Inuit and early European arctic explorer diet.
In the 1920s, the explorer Vilhjalmur Stefansson threw a wrench in “fresh fruits and vegetables” theory when he reported that the Inuit, who rarely ate plant foods, also did not suffer from scurvy. As it turns out, their Vitamin C came from animal organs: liver, adrenal glands, roe [egg masses in the ovaries], and tongue, to name a few. Traditional cooking methods also helped: Vitamin C is present in raw muscle meat, but harsh cooking destroys it. So by cooking their meat very lightly, the Inuit were preserving the Vitamin C in it. In a year-long experiment, Stefansson and a friend lived entirely on raw or lightly-cooked meat without showing any signs of scurvy.
I think we have adequate evidence to say that bear meat could have prevented scurvy in Arctic explorers if lightly cooked.
3. Sourcing the claims on limes vs. lemons
I found a source containing the claim of lemons being 4x as powerful an antiscorbutic as limes, which may be the origin of the IW/SMTM claim. In fact, it contains several of the essential points in the story conveyed by these blog posts. The source is The Prevention of Scurvy in the Navy by Surgeon-Commander J. L. PRISTON, M.B., M.R.C.P., D.P.H., R.N., from 1926. Unfortunately, neither SMTM nor Idle Words appear to cite this document.
In spite of this [better diet provided after a 1797 mutiny], scurvy continued to be a common disease for many years until, with the introduction of steam, voyages became shorter and fresh food was supplied as a matter of course, not as a rare privilege.
About the year 1860 the Admiralty gave up trying to get good supplies from the Mediterranean and began to use lime juice prepared from the sour lime in the West Indies. It is now known that the fresh lemon is four times as powerful an antiscorbutic as the fresh sour lime. Moreover, the method of preserving Navy lime juice destroys all the vitamin C, so that the Navy lime juice as now supplied has no antiscorbutic power at all.
The name “lime juice” had always been applied indiscriminately both to lemon juice and lime juice.
Arctic explorers, however, noticed from time to time as a puzzling fact that lime juice did not prevent scurvy.
We don’t really know what “fresh” means. Does it mean that both the limes and lemons were recently picked? Or only recently squeezed in the scientist’s lab, perhaps after several weeks in the ice-packed hull of a transport ship? And moreover, we don’t really know whether the “antiscorbutic power” of a citrus fruit scales linearly with vitamin C content, using whatever methods of processing and measurement they applied to generate this finding. Sadly, Priston also does not cite his source when he makes this claim.
Now let’s talk modern data. Is it possible that lemons contain, in some meaningful sense, about 4x the vitamin C of limes?
Key limes weigh about 1oz. Some random poster on a cooking forum says that a pound of key limes gives about 2⁄3 of a cup of juice, so you’d need 1.5 pounds = 24 oz of key limes to get a cup.
I’ve found varying estimates for how much juice is in a large lemon, but 3-5 tbsp seems to be about the range. Here’s a source for 5 tbsp. A 52mg/100g vitamin C lemon would have 1.7x the vitamin C content of an equivalent amount of lime juice, so you’d only need 0.6 cup, or 9.6 tbsp, to get the same amount. Rounding to 10, this would be the juice of two lemons, weighing in at about 8 oz.
By these figures, per unit weight of fresh fruit (as opposed to juice), fresh lemons might have 3x the vitamin C of fresh key limes. We can also imagine that if the scientist who conducted this old study was using lemons and limes purchased in their local market, those fruits might have been picked at different times. If the lemons were a bit fresher, perhaps more of the vitamin C was still stable. If Surgeon-General Priston was rounding up, or if random chance favored the lemon somewhat in the study, it’s possible to imagine a scientific result that at the time showed a pound of lemons being 4x as effective as a pound of key limes at preventing scurvy.
4. Conclusion
Note that these weird, subtle distinctions and epistemic challenges are precisely the point of the sleep/vitamin C comparison. Even if the early scientists studying the antiscorbutic power of lemons and limes wrongly found that lemons are 4x better than limes, this is precisely the point! Without both careful scientific investigation, using multiple lines of converging evidence (including the anecdotes of weirdos like arctic explorers), as well as a mechanistic understanding, it’s very easy for the real complexities of a system to be disguised by intuitive human categorization schemes that wildly miss the mark.
Another comparison is pica. We know that the body can generate cravings for “nutrients” that it does not need, or that are actively destructive (as in addiction or disordered eating), while also failing to give us cravings for nutrients that we do need. So we should keep our minds wide-open to the possibility that we are fundamentally misunderstanding the role of sleep in cognition and functional capacity.
At first glance, I thought you were claiming that copper tubing and air exposure does not destroy vitamin C, but now I think I read you backwards. I think you are claiming that they do destroy vitamin C, and that copper and O2 destruction of vitamin C was the only reason that “lime juice” was failing to prevent scurvy (and that the differences between lemons vs. limes had nothing to do with it).
Yeah, your current interpretation is correct.
This article finds that Musk limes have less than half the vitamin C of lemons, just to gesture in that direction.
It’s not that different from the raw limes in USDA’s data. In the titration method, that article found that musk limes had 42.3% as much vitamin C as lemons, and in the HPLC method, 53.5%. The average of those is 47.9%. My data on non-musk limes suggest they have 54.7% as much vitamin C as lemons.
The quote you gave for lemon vitamin C is the minimum value listed in the source. The maximum is 43.3mg/100g
I’m confused. The number I listed for lemon vitamin C was 53mg/100g.
I think we have adequate evidence to say that bear meat could have prevented scurvy in Arctic explorers if lightly cooked.
To be clear, I wasn’t arguing against that. I was just pointing out that it’s misleading to claim that polar bear meat is more like lemons than limes are. All 3 of those things seem able to prevent scurvy when they’re fresh and consumed in reasonable quantities; even 1⁄4 of the vitamin C concentration of fresh lemon juice is 23.22mg per cup. It’s possible that a citrus species has an abnormally low vitamin C concentration, and it’s possible that 10mg of vitamin C from lime juice is not the same as 10mg of vitamin C from fresh meat. But SMTM was asserting as a known fact that Sicilian lemons are more like polar bear meat than they are like West Indian limes in their ability to treat scurvy, which in expectation causes people who read the post to be worse at predicting the data we found than they would be if they had never read it, and that is what I was objecting to.
Apologies, I missed several of these points in your OP at first, and edited my post to correct it. Sorry you saw it before it was fixed!!!
I was just pointing out that it’s misleading to claim that polar bear meat is more like lemons than limes are.
I agree with your characterization of SMTM’s argument. It’s hard to parse, given the reference to his own made-up dialog that’s partly to make (supposedly) factual claims and partly to illustrate the challenges of analyzing complex scientific data. However, I read this as SMTM in their authorial voice defending the claim that key limes don’t contain vitamin C and polar bear meat does. We both agree this claim is false. Here’s the relevant quote:
Frolich:Maybe some citrus fruits contain the antiscorbutic [scurvy-curing] property and others don’t. Maybe the British Royal Navy used one kind of lime back when Lind did his research but gave a different kind of lime to Nares and the others on their Arctic expeditions. Or maybe they did something to the lime juice that removed the antiscorbutic property. Maybe they boiled it, or ran it through copper piping or something, and that ruined it.
Maybe there are different kinds of citrus. Maybe some animals need this mystery ingredient and others don’t. Maybe polar bear meat is, medically speaking, more like citrus fruit from Sicily than like citrus fruit from the West Indies. Really???
This looks a lot like special pleading, but in this case, the apparent double standard is correct. All of these weird exceptions he suggests were actually weird exceptions. And while our hypothetical version of Frolich wouldn’t have any way of knowing, these were the right distinctions to make.
I think that SMTM got this fact wrong. However, I think that the essential point of the SMTM article holds, and by extension the analogy I am drawing between vitamin C and sleep.
Thank you for your patience with my original slip-ups in noticing the full content of your preceding comment.
“Different kinds of citrus fruits are more like one another than they are like polar bear meat” sounds very reasonable, but in this case it was wrong. Sicilian lemons really ARE more like polar bear meat than they are like West Indian limes, at least for the purposes of treating scurvy.
Followup: SMTM points out that differences in fertilization and propagation (clonally or by seed) mean that we don’t know whether or not historical key limes had enough vitamin C to cure scurvy. I notice in myself a certain tendency to say oh puh-leeze in response to this, but at the same time, I think the broader point of the original SMTM piece is that it’s precisely this reaction that we ought to be suspicious of. After all, we don’t necessarily know that the arctic explorers who found that lime juice didn’t cure their scurvy were drinking it out of copper tubes, or that the vitamin C in the lime juice they were drinking was oxidized.
SMTM points out that differences in fertilization and propagation (clonally or by seed) mean that we don’t know whether or not historical key limes had enough vitamin C to cure scurvy.
Hm, that would still make the post misleading — “Sicilian lemons really ARE more like polar bear meat than they are like West Indian limes, at least for the purposes of treating scurvy” is a very different claim from “we don’t know whether or not historical key limes had enough vitamin C to cure scurvy.”
[ETA: to be clear, I’m not criticizing the thesis of SMTM’s post here, just pointing out a factual error]
The linked SMTM post is misleading.
Here is the vitamin C content per 100g of some relevant foods, which I found after a few minutes of searching on Google:
Lime juice: 30mg [1]
Lemon juice: 38.7mg [2]
Raw lemons: 53mg [3]
Raw limes: 29mg [4]
Key limes in particular, which Wikipedia says are the same thing as West Indian limes: 31.3mg [5]
Raw caribou liver: 23.874.9 mg [6]
Raw ringed seal liver: 23.873.8 mg [6]
Raw cattle liver: 71.2mg [7]
Raw buffalo liver: 72.4mg [7]
Raw sheep liver: 77.6mg [7]
Raw goat liver: 76.7mg [7]
Fresh/raw polar bear meat: 1mg [8] [9]
I couldn’t find information on the vitamin C density of polar bear livers in particular, but from these values, it seems far from clear that polar bear livers are more similar to lemons than limes in that respect. The vitamin C contents of limes and lime juice do not stand out in that list.
Moreover, it seems that it only takes about 10mg of vitamin C per day to prevent scurvy, and the Manual of Nutritional Therapeutics says that the same daily quantity is enough to improve scurvy symptoms, with 60-100mg/day being recommended for full recovery. So it seems that a cup (~240g) of fresh lime juice per day is enough to both prevent and enable recovery from scurvy.
(Scott and Scurvy says that “[t]ests on animals would later show that fresh lime juice has a quarter of the scurvy-fighting power of fresh lemon juice,” but I couldn’t find a source for that, I could find many contradicting it, and the USDA data suggests that it has ~3/4 of the vitamin C density of fresh lemon juice).
So it seems that the lime juice was just not preventing scurvy because it had spent long periods of time open to the air, and had been pumped through copper tubing. And so this paragraph from the post:
seems very misleading (especially but not exclusively if you don’t interpret “polar bear meat” as referring to a specific polar bear organ, given that my sources say that fresh polar bear meat has 30x less vitamin C than fresh lime juice).
https://fdc.nal.usda.gov/fdc-app.html#/food-details/168156/nutrients
https://fdc.nal.usda.gov/fdc-app.html#/food-details/167747/nutrients
https://fdc.nal.usda.gov/fdc-app.html#/food-details/1102594/nutrients
https://fdc.nal.usda.gov/fdc-app.html#/food-details/168155/nutrients
https://fdc.nal.usda.gov/fdc-app.html#/food-details/509702/nutrients
https://doi.org/10.1006/jfca.2002.1053
https://doi.org/10.1111/j.1365-2621.1965.tb00287.x
https://www.jstor.org/stable/40508955
https://escholarship.mcgill.ca/downloads/t148fj883?locale=en
1. Copper tubing and environmental exposure does destroy vitamin C
At first glance, I thought you were claiming that copper tubing and air exposure does not destroy vitamin C, but now I think I read you backwards. I think you are claiming that they do destroy vitamin C, and that copper and O2 destruction of vitamin C was the only reason that “lime juice” was failing to prevent scurvy (and that the differences between lemons vs. limes had nothing to do with it). Just to emphasize that vitamin C is susceptible to destruction by copper and environmental exposure, here’s the Australian Ministry of Health:
2. Liver and vitamin C
Polar bear liver contains massive amounts of vitamin A, enough to kill humans (1, 2). When the Idle Words essay on which the SMTM post is based says “Eat a bear liver every few weeks and scurvy will be the least of your problems,” the proper response is “because you’ll be dead of vitamin A poisoning.” However, the IW post vascillates between saying that the vitamin C in the polar bear comes from “meat,” “liver,” and “kidneys,” and I don’t trust that the author carefully investigated the nutritional value of each of these organs.
However, I did find a source that talks more about the Inuit and early European arctic explorer diet.
Raw bear meat has a little more vitamin C (2mg/100g). So this would require eating 500g bear meat/day (about 650 calories, or 1.1lb per day) to get an adequate quantity to prevent scurvy indefinitely, or less merely to prevent it for the duration of the voyage. Scurvy takes 3 months to set in if vitamin C intake is extremely low.
I think we have adequate evidence to say that bear meat could have prevented scurvy in Arctic explorers if lightly cooked.
3. Sourcing the claims on limes vs. lemons
I found a source containing the claim of lemons being 4x as powerful an antiscorbutic as limes, which may be the origin of the IW/SMTM claim. In fact, it contains several of the essential points in the story conveyed by these blog posts. The source is The Prevention of Scurvy in the Navy by Surgeon-Commander J. L. PRISTON, M.B., M.R.C.P., D.P.H., R.N., from 1926. Unfortunately, neither SMTM nor Idle Words appear to cite this document.
We don’t really know what “fresh” means. Does it mean that both the limes and lemons were recently picked? Or only recently squeezed in the scientist’s lab, perhaps after several weeks in the ice-packed hull of a transport ship? And moreover, we don’t really know whether the “antiscorbutic power” of a citrus fruit scales linearly with vitamin C content, using whatever methods of processing and measurement they applied to generate this finding. Sadly, Priston also does not cite his source when he makes this claim.
Now let’s talk modern data. Is it possible that lemons contain, in some meaningful sense, about 4x the vitamin C of limes?
Key limes weigh about 1oz. Some random poster on a cooking forum says that a pound of key limes gives about 2⁄3 of a cup of juice, so you’d need 1.5 pounds = 24 oz of key limes to get a cup.
I’ve found varying estimates for how much juice is in a large lemon, but 3-5 tbsp seems to be about the range. Here’s a source for 5 tbsp. A 52mg/100g vitamin C lemon would have 1.7x the vitamin C content of an equivalent amount of lime juice, so you’d only need 0.6 cup, or 9.6 tbsp, to get the same amount. Rounding to 10, this would be the juice of two lemons, weighing in at about 8 oz.
By these figures, per unit weight of fresh fruit (as opposed to juice), fresh lemons might have 3x the vitamin C of fresh key limes. We can also imagine that if the scientist who conducted this old study was using lemons and limes purchased in their local market, those fruits might have been picked at different times. If the lemons were a bit fresher, perhaps more of the vitamin C was still stable. If Surgeon-General Priston was rounding up, or if random chance favored the lemon somewhat in the study, it’s possible to imagine a scientific result that at the time showed a pound of lemons being 4x as effective as a pound of key limes at preventing scurvy.
4. Conclusion
Note that these weird, subtle distinctions and epistemic challenges are precisely the point of the sleep/vitamin C comparison. Even if the early scientists studying the antiscorbutic power of lemons and limes wrongly found that lemons are 4x better than limes, this is precisely the point! Without both careful scientific investigation, using multiple lines of converging evidence (including the anecdotes of weirdos like arctic explorers), as well as a mechanistic understanding, it’s very easy for the real complexities of a system to be disguised by intuitive human categorization schemes that wildly miss the mark.
Another comparison is pica. We know that the body can generate cravings for “nutrients” that it does not need, or that are actively destructive (as in addiction or disordered eating), while also failing to give us cravings for nutrients that we do need. So we should keep our minds wide-open to the possibility that we are fundamentally misunderstanding the role of sleep in cognition and functional capacity.
Yeah, your current interpretation is correct.
It’s not that different from the raw limes in USDA’s data. In the titration method, that article found that musk limes had 42.3% as much vitamin C as lemons, and in the HPLC method, 53.5%. The average of those is 47.9%. My data on non-musk limes suggest they have 54.7% as much vitamin C as lemons.
I’m confused. The number I listed for lemon vitamin C was 53mg/100g.
To be clear, I wasn’t arguing against that. I was just pointing out that it’s misleading to claim that polar bear meat is more like lemons than limes are. All 3 of those things seem able to prevent scurvy when they’re fresh and consumed in reasonable quantities; even 1⁄4 of the vitamin C concentration of fresh lemon juice is 23.22mg per cup. It’s possible that a citrus species has an abnormally low vitamin C concentration, and it’s possible that 10mg of vitamin C from lime juice is not the same as 10mg of vitamin C from fresh meat. But SMTM was asserting as a known fact that Sicilian lemons are more like polar bear meat than they are like West Indian limes in their ability to treat scurvy, which in expectation causes people who read the post to be worse at predicting the data we found than they would be if they had never read it, and that is what I was objecting to.
Apologies, I missed several of these points in your OP at first, and edited my post to correct it. Sorry you saw it before it was fixed!!!
I agree with your characterization of SMTM’s argument. It’s hard to parse, given the reference to his own made-up dialog that’s partly to make (supposedly) factual claims and partly to illustrate the challenges of analyzing complex scientific data. However, I read this as SMTM in their authorial voice defending the claim that key limes don’t contain vitamin C and polar bear meat does. We both agree this claim is false. Here’s the relevant quote:
I think that SMTM got this fact wrong. However, I think that the essential point of the SMTM article holds, and by extension the analogy I am drawing between vitamin C and sleep.
Thank you for your patience with my original slip-ups in noticing the full content of your preceding comment.
There was also another relevant passage:
Followup: SMTM points out that differences in fertilization and propagation (clonally or by seed) mean that we don’t know whether or not historical key limes had enough vitamin C to cure scurvy. I notice in myself a certain tendency to say oh puh-leeze in response to this, but at the same time, I think the broader point of the original SMTM piece is that it’s precisely this reaction that we ought to be suspicious of. After all, we don’t necessarily know that the arctic explorers who found that lime juice didn’t cure their scurvy were drinking it out of copper tubes, or that the vitamin C in the lime juice they were drinking was oxidized.
Reality is surprisingly complex.
Hm, that would still make the post misleading — “Sicilian lemons really ARE more like polar bear meat than they are like West Indian limes, at least for the purposes of treating scurvy” is a very different claim from “we don’t know whether or not historical key limes had enough vitamin C to cure scurvy.”
Thanks for contacting them, though!
Agreed!
I will see if I can get in touch with SMTM and IW, I’d be curious what they have to say about this.