I’m not so much asking about whether people like or dislike the idea, but there are people claiming 3-20g a day of vitamin C intake and I do not understand the biology of that.
So how does bioavailability work at those levels? It was my understanding that absorption follows a curve, absorption is close to 80-100% under 200mg at a time, a lot of what it taken above 200-500mg taken at a time oversaturates the transport system and is just passed into the digestive system and causes bloating, gas and diarrhea. At doses of 1-1.5g the absorption is 33-50%, and at higher doses it drops into the teens.
The impression I am getting is that anything above around 400-1000mg a day *absorbed * (which could mean, in the case of 1g a day, 10g taken at once with 10% absorption, or it could mean 250mg taken 4x a day with 100% absorption) is just not absorbed by the digestive system and if it is, it is removed via the kidneys due to shortening of the half life of vitamin C until it is a low as 30 minutes. Is that a correct assumption?
How long does it take for the transportation system in the digestive system to reset? If someone is taking 250mg at a time and wants to get to 1000mg a day absorbed, how long do they wait between doses?
Do people who take 500-1000mg an hour manage to overwhelm the kidney half life, and get plasma levels above what is normally seen? Or is that passed out of the system too?
The concept of megadoses of vitamin C was fostered by Linus Pauling, who took 18 grams a day. As you know, he was a biologist and had two Nobel awards (a Peace prize and an award based on his work, not anything to do with vitamin C). He, and Albert Szent-Gyorgy (who isolated the vitamin) each took megadoses. Pauling wrote his first book on vitamin C, Vitamin C and the Common Cold. He wrote another book claiming it helped to cure cancer. Critcisms were made of his conclusions, and he rebutted those criticisms (at least in his own mind.) He always maintained that clinical studies did not have enough C. Grudgingly, the establishment upped the recommeded dosage, as you note in one of your links, to 200-400 mg, but I think the RDA remains at 60, for some strange reason. More recent studies, which did try more C, noted slight decrease in severity and longevity of the colds with megadoses, but doses well below 18g.
Anecdotally, when I caught a cold in the past, I would take several grams every several hours, as soon as symptoms rearose, until I got diarhhea. Then I backed off. I found in my experience that continous intake of C stifles the symptoms. (The diarrhea stops once you stop the C.) I found that the temporary diarrhea is a small price to pay to be symptom-free. I think megadoes act in the same way as antihistamines, such as Contacts (if that is still being made).
I’ve read Pauling (he was a chemist, but I don’t know if it matters since his work wasn’t related to his orthomolecular research), and one of his arguments is that animals that make vitamin C themselves up production drastically during times of illness or stress. I was interested in his ideas that arterisclerosis is a tool the body uses to compensate for too little collagen in blood vessels, and that large doses of vitamin C can help prevent this.
The diarrhea itself wouldn’t bother me, but I tried 1000mg pills once a day and got a lot of gas and bloating from doing that. It wasn’t pleasant, and there is no way I could do that for life. However I took a 500mg pill today and so far nothing bad has happened, so I’m assuming most of it was absorbed.
Here is the chart from one of the studies I listed earlier:
It shows pretty drastic improvements in plasma ascorbic acid levels from 0-200mg/day, going from about 8uM up to about 66uM in those doses (people were on a low vitamin C diet before the study started). Going from 200-400mg/day results in a minor boost (maybe from 66 up to 70). But going above that does virtually nothing, everything above 500mg/day is essentially a horizontal line relative to the dose. Raising the dose to 2500mg/day ups the plasma levels to 80uM, up from about 70uM at 400mg.
I don’t get the appeal of going over 500-1000mg a day. Seems like the kidneys just get rid of it, or it isn’t absorbed in the first place.
I didn’t get the gas or bloating. Just diarrhea. I guess everybody reacts differently. But even if the C is just flushed out, wouldn’t the execretory cells absorb some of it on the way out? And if it isn’t absorbed, how does megadoses stifle the symptoms of a cold? It appears to have an antihistamine effect.
One of his other ideas was that C is a hormone and most other animals synthesize it (except for primates and possibly one or two others - I don’t recall), and if we were to synthsize it, we would be synthesizing 20g a day, but we lost the ability to do so since C was so abundant in our food.
(You are, of course, right in that he was a chemist. I didn’t think I was right when I typed biologist.)
As to the interesting questions you asked, I have no idea, but would like to know myself.
“Ascorbic acid (vitamin C) is commonly used as a dietary supplement, often in megadoses. However, as the daily oral dose is increased, the concentration of ascorbic acid in the plasma and other body fluids does not increase proportionally, but instead tends to approach an upper limit…This analysis is based on the renal clearance of ascorbic acid, which rises sharply with increasing plasma concentrations as a result of saturable tubular reabsorption. The analysis indicates that both saturable gastrointestinal absorption and nonlinear renal clearance act additively to
produce the ceiling effect in plasma concentrations. As a consequence of this ceiling effect, there is no pharmacokinetic justification for the use of megadoses of ascorbic acid.”
Linus Pauling was a brilliant man, but his foray into vitamin C as a cure-all was not one of his finer achievements.
Even if the vitamin C is absorbed in the digestive system it seems like the kidneys would just get rid of it. The half life seems to change based on plasma levels. It said in one of the articles the half life can drop to 30 minutes if plasma levels are too high, but can be extended to 83 days if you are in a very vitamin C deficient environment (like one that causes scurvy).
I have no idea how the cold symptoms work wrt vitamin C. I don’t understand tons about it but earlier I mentioned how proponents of megadose theory talk about how animals that produce their own vitamin C produce higher amounts when sick. Studies on megadoses seem to have been done on healthy people. I wonder if the absorption or plasma levels would differ for those under physical or psychological stress, as both can increase the need for vitamin C.
That study found giving mice vitamin C helped them cope with stress better, and the dose for the mice at 200mg a day, which seems like it works out to about 10g/kg of bodyweight, considering that mice weigh about 20g. Mice make their own vitamin C though, so I don’t know how all of that would ft together.
Even though there are foods high in vitamin C, there is nowhere near 20g a day available via diet. Strawberries are one of the highest vitamin C per calorie food out there, they have more vitamin C per calorie than oranges (about 200mg vitamin C per 100 calories, vs about 100mg per 100 calories in an orange). But even if you eat nothing but strawberries and ingest 3000 calories a day, that is still only 6g a day of vitamin C. Far far short of the 20g megadoses people say we’d be producing inside our own body. And diets are going to be far more varied than just strawberries. Even in a diet high in citrus fruits and green vegetables I would assume that average vitamin C intake rarely goes over 1-3g a day or so.
Yeah, I always wondered how our ancestors would’ve gotten so much abscorbic acid from diet alone. However, even if in megadoses much is not absorbed and excreted through the renal system, couldn’t some be absorbed in the urinary tract? Further, in megadoses it does have an antihistamine effect.
You may want to investigate something called liposomal vitamin C.
It is a form of vitamin C encapsulated in fat the is absorbed through the liver rather than the intestine, allowing for much higher absorption and blood plasma levels and none of the gas or diarrhea.
Just search the term “liposomal vitamin C”. You can form your own conclusions.
I have tried it. I have no conclusive results to report.
The study I and someone else posted earlier on ascorbic acid showed the plasma concentration of vitamin C growing rapidly at low doses, going from near zero up to about 60 uM/L at 180-200mg, then tapering off drastically only growing to 85 uM/L at doses as high as 2500mg a day.
The study I just posted above found a 1,000mg dose of lipo-C resulted in plasma concentrations of 400uM/L, which is far higher than what people who took 2500mg of ascorbic acid in the other study had (85uM/L).
However, that doesn’t change the fact that the kidneys would eliminate it pretty rapidly at that kind of concentration.
Yes we all know if it’s on the internet, it must be true. And wow 2 whole test subjects? Sure sounds conclusive to me. I noticed you didn’t point out any specific links (there are only about 100 on the site you referenced).
You can’t be serious. If you call that “proof” then I feel sorry for you and the naive/deluded world you inhabit.