Oranges and Vitamin C: The Honest Picture

Table of Contents

1. What Vitamin C Actually Does
2. Collagen: The Job Nothing Else Can Do
3. Non-Haem Iron: The Underrated Job
4. How Much an Orange Gives You
5. Where the Ceiling Is: Absorption and Saturation
6. The Common Cold: What the Trials Actually Show
7. Pauling, Cancer and the Mayo Clinic Trials
8. Megadoses: The Real Downsides
9. Whole Orange versus a Glass of Juice
10. Storage, Cutting and Cooking Losses
11. Who Actually Needs More
12. Practical: Getting It From Food
13. Key Research Papers
14. Connections
15. Featured Videos

What Vitamin C Actually Does

Ascorbic acid is a small, water-soluble molecule that gives up electrons very readily. Almost everything it does in the body follows from that one property. Humans, along with other primates, guinea pigs and fruit bats, lost the working gene for the final enzyme in vitamin C synthesis, so we cannot make it. Almost every other mammal manufactures its own in the liver. We have to eat ours — which is why a fruit that is full of it has mattered so much historically.

Ascorbate has three broad jobs:

1. Enzyme cofactor. A family of enzymes called dioxygenases needs a supply of electrons to keep their iron or copper atoms in the reduced state. Ascorbate is the electron donor. These enzymes build collagen, make carnitine (which carries fat into mitochondria to be burned), convert dopamine to noradrenaline, and amidate peptide hormones. When ascorbate runs out, all of these slow down, and the connective-tissue consequences show up first and most dramatically.
2. Water-phase antioxidant. Ascorbate quenches reactive species in blood plasma and inside cells, and it regenerates vitamin E after vitamin E has done the same job in cell membranes. This is real chemistry, but it is also where most of the overselling happens — "antioxidant" on a label is a claim about a test tube, not about your arteries.
3. Immune-cell support. Neutrophils and lymphocytes concentrate ascorbate to levels far above plasma. Carr and Maggini's review sets out how it supports the epithelial barrier, accumulates in phagocytes, and assists their function — and equally, how deficiency impairs immunity and raises susceptibility to infection. The claim that adequate vitamin C supports normal immune function is well supported. The claim that extra vitamin C boosts an already-normal immune system beyond normal is not the same claim, and the trials are covered below.

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Collagen: The Job Nothing Else Can Do

If you remember one mechanism from this page, make it this one. Collagen is the structural protein of skin, tendon, bone matrix, gums, and the walls of blood vessels — roughly a third of all the protein in your body. To be strong, collagen has to be cross-linked and coiled into a triple helix, and that requires specific proline and lysine residues in the protein chain to be chemically modified after the chain is built.

The enzymes that do the modifying are prolyl 4-hydroxylase and lysyl hydroxylase. Both carry an iron atom that gets oxidised during the reaction cycle and has to be reduced again before the enzyme can work a second time. Ascorbate is what reduces it. Myllylä and colleagues showed the stoichiometry directly: ascorbate is consumed in measurable proportion in the uncoupled reaction cycles of both enzymes. No ascorbate, no hydroxylation; no hydroxylation, no stable triple helix; unstable collagen is degraded rather than deposited.

That single chemical fact explains the entire clinical picture of scurvy. Gums bleed and teeth loosen because the periodontal collagen fails. Old, long-healed wounds reopen because the scar was collagen and the scar is no longer being maintained. Blood leaks into the skin as pinpoint spots around hair follicles, and into joints and muscle, because capillary walls lose their collagen support. Bones become fragile and, in children, growth plates deform. Untreated, it kills. It also reverses remarkably fast — days to weeks — once ascorbate is restored, which is exactly what James Lind saw aboard HMS Salisbury in 1747 and what we describe on the Oranges history page.

Pullar, Carr and Vissers extend the same mechanism into ordinary skin health: ascorbate is required for the dermal collagen that gives skin its firmness, and it acts as an antioxidant in the epidermis. This is the honest core of every "vitamin C for skin" claim. What it does not establish is that taking more than enough produces more collagen than enough — the enzymes are cofactor-saturated at ordinary dietary intakes, and past that point the extra ascorbate has nothing further to do there.

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Non-Haem Iron: The Underrated Job

Iron in food comes in two forms. Haem iron, from meat and fish, is absorbed efficiently and is not much affected by the rest of the meal. Non-haem iron — the iron in beans, lentils, greens, nuts, whole grains and fortified foods — is absorbed poorly, and how poorly depends heavily on what it is eaten with. Phytate in whole grains and legumes binds it. Polyphenols in tea and coffee bind it. And ascorbate rescues it, by reducing ferric iron to the ferrous form the intestinal transporter can take up, and by forming a soluble chelate that survives the alkaline environment of the small intestine.

Hallberg, Brune and Rossander measured this directly and found a dose-dependent relationship: adding ascorbic acid to a meal progressively overcame phytate's inhibition of iron absorption, with larger ascorbate doses needed to overcome larger phytate loads. In single-meal studies the effect is dramatic — a few-fold increase in the iron absorbed from the same plate of food.

Here is the honest qualifier, and it matters. Cook and Reddy asked what happens across a complete diet rather than a single test meal. Over three dietary periods spanning mean vitamin C intakes from about 51 to about 247 mg per day, they found no significant difference in mean iron absorption between periods, although regression across the pooled data still showed a positive association with ascorbic acid. Their conclusion was blunt: the facilitating effect of vitamin C on iron absorption from a complete diet is far less pronounced than single-meal studies suggest, which is probably why long-term vitamin C supplementation trials have not moved iron status much.

Both things are true, and the practical reading is a modest one. Pairing vitamin C with a plant-based iron source is a genuinely useful habit — orange segments with a lentil salad, a squeeze of citrus over greens, orange slices alongside a bowl of beans and brown rice — and it is most worth doing if you are vegetarian, menstruating heavily, pregnant, or otherwise working to keep iron up. It is a helpful nudge across a day of eating, not a switch that doubles your iron.

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How Much an Orange Gives You

A medium sweet orange of roughly 130–140 g supplies in the region of 70 mg of vitamin C. Against the United States adult recommended intakes of 90 mg per day for men and 75 mg per day for women, that single fruit covers most of a day, and two cover it comfortably. Smokers are advised to add about 35 mg per day, because smoking increases oxidative turnover of ascorbate — one extra orange handles that too.

Some perspective is useful, because the orange's reputation as the vitamin C food is a historical accident of trade rather than a fact about botany. Per 100 grams, sweet red peppers, blackcurrants, guava, kiwifruit, broccoli, Brussels sprouts, kale, papaya and strawberries all contain as much vitamin C as an orange or considerably more. What the orange has is a combination that is hard to beat in practice: it is cheap, it stores for weeks, it needs no cooking or preparation beyond a thumbnail, it is sweet enough that people eat it voluntarily, and it is available everywhere all year. A nutrient you actually consume beats a nutrient you theoretically could.

Two further points about the fruit specifically. The vitamin C is distributed through the flesh and is higher in the peel and the white pith than in the juice sacs — so zest is a genuine, if small, contributor and stripping every scrap of pith away costs you a little. And oranges deliver ascorbate inside a matrix of fibre, flavanones and carotenoids, which is the difference between eating a fruit and swallowing a tablet.

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Where the Ceiling Is: Absorption and Saturation

The most useful single body of work on vitamin C is the pharmacokinetic series run by Mark Levine's group at the National Institutes of Health. They admitted healthy volunteers to a metabolic ward, depleted them, then repleted them with carefully controlled doses and measured plasma and cellular ascorbate at each step. The 1996 study did this in healthy young men and a 2001 companion study repeated it in healthy young women.

The picture that emerged is a saturation curve with a fairly sharp shoulder:

• Plasma ascorbate rises steeply across the low intakes, then flattens. Around 200 mg per day the plasma concentration is essentially at its ceiling; pushing intake higher moves it very little.
• Absorption efficiency falls as the dose rises. A modest oral dose is absorbed almost completely; large single doses are absorbed to a progressively smaller fraction.
• Above the ceiling the kidney simply excretes the surplus. Levine's group proposed a recommended intake of around 200 mg per day on this evidence — higher than the official RDA, and still an amount reachable from food.

Padayatty and colleagues then made the point that resolves a great deal of old argument: oral dosing cannot produce high plasma concentrations, and intravenous dosing can. Because absorption saturates and renal excretion accelerates, oral vitamin C plasma levels are tightly controlled no matter how much you swallow, whereas an intravenous infusion bypasses the gut entirely and can reach concentrations orders of magnitude higher. Any experiment given intravenously is therefore testing a different exposure from the same number of grams taken by mouth — which turns out to be exactly what went wrong in the cancer literature described below.

For the everyday reader the practical conclusion is cheerful. Three or four servings of fruit and vegetables a day put you at or near the plateau. Two oranges, or an orange plus a handful of strawberries and some broccoli, and you are there. The supplement you are looking at adds a number to the label and almost nothing to your blood.

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The Common Cold: What the Trials Actually Show

This question has been argued for seventy years and has actually been answered. Hemilä and Chalker's Cochrane review restricted itself to placebo-controlled trials using at least 0.2 g per day, and it is worth reading the results in the order it presents them, because each part says something different.

• Does regular supplementation prevent colds in ordinary people? No. Across community trials involving 10,708 participants, the pooled risk ratio for catching a cold was 0.97 (95% CI 0.94 to 1.00) — a difference of no practical consequence. This is the claim most people believe, and it is the one that failed.
• Does it prevent colds under extreme short-term physical stress? Apparently yes, and strikingly. Five trials in 598 marathon runners, skiers and soldiers on subarctic exercises gave a pooled risk ratio of 0.48 (95% CI 0.35 to 0.64) — roughly half the colds. That is a narrow, specific population, not a general recommendation.
• Does regular supplementation shorten a cold? A little. Across 31 comparisons and 9,745 cold episodes, duration fell by 8% in adults (3% to 12%) and 14% in children (7% to 21%). On a seven-day cold, 8% is about half a day — real, consistent, and modest. Severity was reduced as well.
• Does taking it once you already feel a cold coming on help? The trials do not show it. Seven comparisons covering 3,249 episodes found no consistent effect of therapeutic vitamin C started after symptom onset.

The reviewers' own conclusion is that routine supplementation is not justified for cold prevention in the general population; that it may help people exposed to brief periods of severe physical exertion; that regular supplementation shortens colds modestly; and that, given the low cost and good safety record, an individual who wants to test therapeutic dosing on themselves is not doing anything harmful.

There is a good historical reason to be sceptical of the older, more enthusiastic trials. Karlowski and colleagues at the NIH ran a placebo-controlled trial in 1975 and then did something unusual: they asked participants whether they thought they had received vitamin C or placebo. Many could tell, because ascorbic acid tastes sour. When the analysis was restricted to participants who were genuinely blinded, the apparent benefit largely disappeared — suggesting that a good part of the historic vitamin C effect on colds was the placebo effect of knowing you had taken something.

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Pauling, Cancer and the Mayo Clinic Trials

Linus Pauling won two unshared Nobel Prizes and was one of the great chemists of the twentieth century. He was also, from the early 1970s, the most prominent advocate of very high-dose vitamin C, and the story of how that played out is a genuinely instructive piece of medical history — not because he was simply wrong, but because of how the disagreement was resolved.

Pauling's 1971 paper in PNAS re-analysed existing common-cold trials and argued that they showed a real, dose-related effect that the original authors had understated. His subsequent books took the argument to the public, and vitamin C supplement sales have never been the same since.

The cancer claim went further. Working with the Scottish surgeon Ewan Cameron, Pauling reported in 1976 that 100 patients with terminal cancer given 10 g of ascorbate a day survived substantially longer than 1,000 matched controls. The result was dramatic. The design was not: the controls were historical patients drawn from hospital records rather than randomly assigned, and the treated patients were entering the ascorbate programme at a point chosen by their clinicians. That combination is a textbook route to a spurious survival difference, because patients selected earlier in their decline live longer regardless of what is given to them.

The Mayo Clinic tested it properly, twice. Creagan and colleagues (1979) ran a randomised, double-blind, placebo-controlled trial of 10 g/day oral vitamin C in patients with advanced cancer and found no benefit. Pauling objected that most of those patients had received prior chemotherapy, which he argued had damaged their immune systems. So Moertel and colleagues (1985) repeated the trial in patients with advanced colorectal cancer who had had no prior chemotherapy — and again found no benefit over placebo. The exchange became bitter, and the field largely closed the question.

Then the pharmacology reopened part of it. Cameron and Pauling had given their patients ascorbate intravenously first and orally afterwards; the Mayo trials used oral dosing only. Padayatty and Levine's work showed that these are not the same exposure at all — oral dosing is capped by absorption and renal clearance, intravenous dosing is not, and the concentrations reachable only by infusion are the ones with pharmacological (pro-oxidant, tumour-selective) activity in laboratory models. That does not vindicate Pauling's conclusion; the randomised trials that tested his actual protocol found nothing. It does mean the two sides were testing different things, and it is why high-dose intravenous ascorbate remains an active area of oncology research, conducted in registered clinical trials.

The practical bottom line for a reader eating an orange is unchanged, and worth saying plainly: no oral vitamin C regimen, at any dose, has been shown to treat cancer. Anyone offering one outside a clinical trial is not describing evidence.

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Megadoses: The Real Downsides

Vitamin C is genuinely safe, which is part of why the megadose habit persists. But "safe" is not "free", and there are three honest points to make.

• Gut symptoms. The unabsorbed fraction of a large dose stays in the intestine and draws water osmotically. Bloating, cramping and diarrhoea are the usual limit people hit, typically somewhere above 2–3 g in a single dose. The tolerable upper intake level for adults is set at 2,000 mg per day mainly on this basis.
• Kidney stones, and only from supplements. Ascorbate is metabolised partly to oxalate, and oxalate is the main component of the commonest kidney stones. Ferraro and colleagues followed a large cohort and found that supplemental vitamin C intake was associated with a higher risk of incident kidney stones, while total and dietary vitamin C intake was not. That is a clean distinction and a useful one: the orange is not implicated; the 1,000 mg tablet is. If you have had calcium-oxalate stones, this is a real reason to skip high-dose supplements — see Kidney Stones.
• Iron overload conditions. Because ascorbate increases non-haem iron absorption, people with haemochromatosis or another iron-loading disorder should not take large vitamin C supplements. Ordinary fruit is not the concern here; grams of ascorbate with meals is.

Worth noting what is not a real risk: high vitamin C intake from food has no established toxicity, and the "rebound scurvy" from stopping a megadose is largely a theoretical worry that has not been convincingly demonstrated in adults.

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Whole Orange versus a Glass of Juice

This is the most practically important paragraph on the page, so here it is without hedging: a whole orange and a glass of orange juice are not the same food, and the difference is not the vitamin C. Both deliver ascorbate. What juicing removes is the structure.

Squeezing an orange discards most of the fibre — the pectin, cellulose and segment membranes that slow digestion, blunt the glycaemic response, and take up room in your stomach. It also collapses the portion. It takes roughly three to four oranges to fill a standard glass, so the sugar of three or four fruits arrives in about twenty seconds, with no chewing and none of the fullness that eating three oranges in a row would produce.

The epidemiology treats them as different exposures, and it does so consistently:

• Muraki and colleagues, following participants in three large prospective cohorts, found greater whole-fruit consumption associated with lower risk of type 2 diabetes, while greater fruit-juice consumption went the other way.
• Bazzano and colleagues reported the same split in the Nurses' Health Study: whole fruit and vegetables associated with lower diabetes risk, fruit juice with higher.
• Imamura and colleagues, in a BMJ meta-analysis, grouped fruit juice with sugar-sweetened and artificially sweetened beverages when examining incident type 2 diabetes; and Xi and colleagues reached a similar conclusion in their own systematic review of fruit juice specifically.

Flood-Obbagy and Rolls demonstrated the satiety half of the mechanism experimentally, using apples rather than oranges: the same fruit served whole, as sauce, or as juice produced different effects on fullness and on how much people then ate at the meal, with the whole fruit the most satiating and the juice the least.

Two honest counterweights, because this is not a morality tale. First, 100% orange juice really does carry vitamin C, folate, potassium and hesperidin, and the trials showing vascular benefits from citrus flavanones were mostly run using orange juice — see Hesperidin and Blood Vessels. Second, processing is not uniformly bad: Aschoff and colleagues found that the carotenoid β-cryptoxanthin was more bioavailable from pasteurised orange juice than from fresh oranges, because heating and homogenising break down the cell walls that would otherwise trap it. Their companion in-vitro work found a similar pattern for several compounds across processing methods.

So the sensible position is the boring one. Eat the fruit most of the time. Keep juice to a small glass, with food, and treat it as a pleasant drink with some nutrition in it rather than as a fruit serving. Orange-flavoured sugar drinks are a different product entirely and have nothing to do with either.

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Storage, Cutting and Cooking Losses

Ascorbate is the most fragile common nutrient. It is destroyed by heat, by oxygen, by light, by alkaline conditions and by copper and iron surfaces, and it leaches into cooking water because it is water-soluble. Practical consequences:

• A whole, intact orange is a very good container. The peel is an oxygen barrier, and refrigerated whole oranges hold their vitamin C well for two to three weeks. This is a real advantage over leafy greens, which lose ascorbate quickly.
• Cut fruit loses faster. Once segments are exposed, oxidation starts. Cut oranges are best eaten the same day or the next.
• Fresh juice starts losing immediately. Squeezed juice left in a jug in the fridge loses vitamin C measurably over a few days, faster if the container is half-empty and full of air. Drink it soon after squeezing, and keep it in a full, closed, cold container if you cannot.
• Do not cook oranges for their vitamin C. Marmalade, syrups and baked dishes will have lost most of it. That is fine — eat those because they taste good, and get the ascorbate from raw fruit.
• Zest is worth using. The peel carries more vitamin C by weight than the flesh, along with the aromatic oils, and adds essentially no sugar. Wash the fruit well first, or buy organic, since the peel is where surface residues sit.

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Who Actually Needs More

Most people eating a reasonable amount of fruit and vegetables are fine. The groups where vitamin C intake is worth actively thinking about are fairly specific:

• Smokers — higher oxidative turnover; an extra 35 mg per day is recommended, which is one more piece of fruit.
• People who eat very little fresh produce — and this is a broader group than most clinicians expect. Scurvy still occurs in wealthy countries, in people with restricted diets from alcohol dependence, severe mental illness, eating disorders, extreme food selectivity in autism, isolation, poverty, or after bariatric surgery. It is regularly missed because doctors assume it is a historical disease.
• Vegetarians and vegans — not because they are short of vitamin C, which they usually are not, but because pairing it with plant iron sources is worth doing deliberately.
• People with malabsorption — inflammatory bowel disease, coeliac disease, and post-surgical states.
• People under sustained heavy physical stress — the Cochrane subgroup above. Athletes in heavy training blocks are the realistic case.
• People healing a wound or recovering from surgery or burns — because collagen synthesis is the rate-limiting step in repair, and requirements rise.

Notice what is missing from this list: healthy adults who already eat fruit, who make up most of the people buying vitamin C supplements.

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Practical: Getting It From Food

None of this requires a plan, but a few habits make it effortless:

• One orange, most days. That is the whole strategy. It covers the requirement, keeps for weeks, needs no equipment, and costs very little.
• Spread it out. Because absorption efficiency falls as the dose rises, vitamin C from two or three moderate servings across a day reaches your tissues better than the same amount in one hit. Fruit at breakfast, vegetables at dinner.
• Pair citrus with plant iron. Orange segments in a lentil or bean salad; a squeeze of citrus over sautéed greens; fruit alongside a bowl of beans and brown rice. Coffee and tea do the opposite, so keep them away from the iron-heavy meal.
• Do not trim all the pith. The white layer is bitter but carries fibre and the flavanones covered in the hesperidin article. Leaving some on costs nothing.
• Vary the source. Peppers, broccoli, kale, strawberries, kiwifruit and blackcurrants all supply more per 100 g than oranges do. Variety also brings the other things those foods carry.
• Eat the fruit, drink less of the juice. If you like orange juice, have a small glass with a meal rather than a large one on its own.

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Key Research Papers

1. Carr AC, Maggini S. Vitamin C and immune function. Nutrients. 2017;9(11):1211. — doi:10.3390/nu9111211. The reference review on how ascorbate supports barrier and phagocyte function, and what deficiency does to immunity.
2. Pullar JM, Carr AC, Vissers MCM. The roles of vitamin C in skin health. Nutrients. 2017;9(8):866. — doi:10.3390/nu9080866. Collagen synthesis and antioxidant roles in skin.
3. Myllylä R, Majamaa K, Günzler V, Hanauske-Abel HM, Kivirikko KI. Ascorbate is consumed stoichiometrically in the uncoupled reactions catalyzed by prolyl 4-hydroxylase and lysyl hydroxylase. J Biol Chem. 1984;259(9):5403–5405. — doi:10.1016/S0021-9258(18)91023-9. The mechanism behind every symptom of scurvy.
4. Levine M, Conry-Cantilena C, Wang Y, et al. Vitamin C pharmacokinetics in healthy volunteers: evidence for a recommended dietary allowance. Proc Natl Acad Sci U S A. 1996;93(8):3704–3709. — doi:10.1073/pnas.93.8.3704. The depletion–repletion study that mapped the saturation curve in men.
5. Levine M, Wang Y, Padayatty SJ, Morrow J. A new recommended dietary allowance of vitamin C for healthy young women. Proc Natl Acad Sci U S A. 2001;98(17):9842–9846. — doi:10.1073/pnas.171318198. The companion study in women.
6. Padayatty SJ, Sun H, Wang Y, et al. Vitamin C pharmacokinetics: implications for oral and intravenous use. Ann Intern Med. 2004;140(7):533–537. — doi:10.7326/0003-4819-140-7-200404060-00010. Why oral and intravenous ascorbate are different exposures, and why that mattered for the cancer dispute.
7. Hemilä H, Chalker E. Vitamin C for preventing and treating the common cold. Cochrane Database Syst Rev. 2013;(1):CD000980. — doi:10.1002/14651858.CD000980.pub4. RR 0.97 for prevention in the community; RR 0.48 in marathon runners, skiers and soldiers; 8% shorter colds in adults, 14% in children; no consistent therapeutic effect.
8. Karlowski TR, Chalmers TC, Frenkel LD, Woolridge NH, Lynch JM, Lynch JM. Ascorbic acid for the common cold: a prophylactic and therapeutic trial. JAMA. 1975;231(10):1038–1042. — doi:10.1001/jama.1975.03240220018013. The trial that showed much of the apparent benefit tracked with participants correctly guessing their assignment.
9. Pauling L. The significance of the evidence about ascorbic acid and the common cold. Proc Natl Acad Sci U S A. 1971;68(11):2678–2681. — doi:10.1073/pnas.68.11.2678. Pauling's own case, worth reading in the original rather than in summary.
10. Cameron E, Pauling L. Supplemental ascorbate in the supportive treatment of cancer: prolongation of survival times in terminal human cancer. Proc Natl Acad Sci U S A. 1976;73(10):3685–3689. — doi:10.1073/pnas.73.10.3685. The historical-control study whose design is the whole problem.
11. Creagan ET, Moertel CG, O'Fallon JR, et al. Failure of high-dose vitamin C (ascorbic acid) therapy to benefit patients with advanced cancer. N Engl J Med. 1979;301(13):687–690. — doi:10.1056/NEJM197909273011303. The first Mayo randomised trial.
12. Moertel CG, Fleming TR, Creagan ET, Rubin J, O'Connell MJ, Ames MM. High-dose vitamin C versus placebo in the treatment of patients with advanced cancer who have had no prior chemotherapy. N Engl J Med. 1985;312(3):137–141. — doi:10.1056/NEJM198501173120301. The second Mayo trial, designed to answer Pauling's objection to the first.
13. Hallberg L, Brune M, Rossander L. Iron absorption in man: ascorbic acid and dose-dependent inhibition by phytate. Am J Clin Nutr. 1989;49(1):140–144. — doi:10.1093/ajcn/49.1.140. Ascorbate progressively overcomes phytate inhibition of non-haem iron absorption.
14. Cook JD, Reddy MB. Effect of ascorbic acid intake on nonheme-iron absorption from a complete diet. Am J Clin Nutr. 2001;73(1):93–98. — doi:10.1093/ajcn/73.1.93. The honest qualifier: across a whole diet the effect is far smaller than single-meal studies imply.
15. Teucher B, Olivares M, Cori H. Enhancers of iron absorption: ascorbic acid and other organic acids. Int J Vitam Nutr Res. 2004;74(6):403–419. — doi:10.1024/0300-9831.74.6.403. Review of how ascorbate and other organic acids act on non-haem iron.
16. Ferraro PM, Curhan GC, Gambaro G, Taylor EN. Total, dietary, and supplemental vitamin C intake and risk of incident kidney stones. Am J Kidney Dis. 2016;67(3):400–407. — doi:10.1053/j.ajkd.2015.09.005. Supplemental vitamin C tracked with higher stone risk; dietary and total intake did not.
17. Khaw KT, Bingham S, Welch A, et al. Relation between plasma ascorbic acid and mortality in men and women in EPIC-Norfolk prospective study. Lancet. 2001;357(9257):657–663. — doi:10.1016/S0140-6736(00)04128-3. Plasma ascorbate as a marker tracks inversely with mortality — an association, in a population where it also marks fruit and vegetable intake.
18. Hemilä H. Vitamin C and infections. Nutrients. 2017;9(4):339. — doi:10.3390/nu9040339. A wider review of the infection literature by the Cochrane review's lead author.
19. Muraki I, Imamura F, Manson JE, et al. Fruit consumption and risk of type 2 diabetes: results from three prospective longitudinal cohort studies. BMJ. 2013;347:f5001. — doi:10.1136/bmj.f5001. Whole fruit and fruit juice pointing in opposite directions.
20. Bazzano LA, Li TY, Joshipura KJ, Hu FB. Intake of fruit, vegetables, and fruit juices and risk of diabetes in women. Diabetes Care. 2008;31(7):1311–1317. — doi:10.2337/dc08-0080.
21. Imamura F, O'Connor L, Ye Z, et al. Consumption of sugar sweetened beverages, artificially sweetened beverages, and fruit juice and incidence of type 2 diabetes. BMJ. 2015;351:h3576. — doi:10.1136/bmj.h3576.
22. Xi B, Li S, Liu Z, et al. Intake of fruit juice and incidence of type 2 diabetes: a systematic review and meta-analysis. PLoS One. 2014;9(3):e93471. — doi:10.1371/journal.pone.0093471.
23. Flood-Obbagy JE, Rolls BJ. The effect of fruit in different forms on energy intake and satiety at a meal. Appetite. 2009;52(2):416–422. — doi:10.1016/j.appet.2008.12.001. Run with apples, but the clearest experimental demonstration of why whole fruit fills you and juice does not.
24. Aschoff JK, Kaufmann S, Kalkan O, et al. In vitro bioaccessibility of carotenoids, flavonoids, and vitamin C from differently processed oranges and orange juices. J Agric Food Chem. 2015;63(2):578–587. — doi:10.1021/jf505297t.
25. Aschoff JK, Röhrig T, Steingass CB, et al. Bioavailability of β-cryptoxanthin is greater from pasteurized orange juice than from fresh oranges — a randomized cross-over study. Mol Nutr Food Res. 2015;59(10):1896–1904. — doi:10.1002/mnfr.201500327. The counterweight: for one carotenoid, processing helps.
26. Linus Pauling Institute Micronutrient Information Center — Vitamin C: lpi.oregonstate.edu — vitamin C
27. PubMed topic search — vitamin C requirements and pharmacokinetics: pubmed.ncbi.nlm.nih.gov — vitamin C pharmacokinetics

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Connections

• Vitamin C — the full topic page.
• Vitamin C Deficiency — scurvy, and why it is still diagnosed today.
• Vitamin C Toxicity — the upper limit and what happens above it.
• Vitamin C Sources — the foods that beat an orange per 100 g.
• Oranges — varieties, nutrition and safety.
• Oranges: History and Origins — Lind, the Royal Navy, and the discovery of ascorbic acid.
• Fiber, Pectin and Limonoids — the rest of the whole-fruit-versus-juice case.
• Iron — the mineral ascorbate unlocks.
• Iron-Deficiency Anaemia
• Kidney Stones — the one place high-dose supplements genuinely matter.
• Broccoli, Kale and Strawberries — other strong vitamin C foods.
• Antioxidants — what the word does and does not mean.
• All Food

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