If there’s one vitamin most people have heard of, it’s vitamin C. Whose mum didn’t urge them to eat fruit – preferably oranges – to keep up their vitamin C levels? When you catch a cold, you drink hot water with lemon – because it contains vitamin C – and even people who are most sceptical of nutritional supplements pop the occasional vitamin C pill when they feel under the weather.
There is lots of research about the efficacy of vitamin C and its role in immunity, particularly in warding off colds and flu. As you head into the traditional season of colds and flu, it seemed a good time to have the vitamin C conversation. So today, I’m going to be talking about whether you really need to supplement, what vitamin C actually does
Do you need to supplement?
…After all, nature wouldn’t have left you defenceless against viruses, would it, if there is a crucial vitamin contained in food. Can you not just eat fruit and veg and be done?
That little may not be enough to ensure optimum immune defence, though. Worldwide, recommendations for vitamin C range from 40 to 220mg per day. Most other animals can make their own vitamin C in the liver. Due to a genetic mutation, humans can’t. Other mammals produce several grams of vitamin C per day. And they can increase production more than 10-fold when under stress.
Humans are not the only mammals that are unable to generate vitamin C. Others are primates, guinea pigs, and fruit bats. As our closest relatives – the great apes – have the same mutation, it stands to reason that humans were already unable to produce vitamin C when evolution sent them off on their own path millions of years ago.
We – and the other non-producing animals – have had plenty of time to adapt. To some extent, we make up for the inability to produce the vitamin by having red blood cells that can recycle “spent” vitamin C and re-use it. But our body cannot store vitamin C; we have to ingest it every single day.
What does vitamin C actually do?
Vitamin C is involved in 15,000 metabolic processes, and no other vitamin has such a wide variety of effects. As it is an antioxidant, ascorbic acid (a form of vitamin C) plays an important role as a free radical scavenger. That means it protects fats, proteins, DNA and cell membranes from damage caused by free radicals. Now, don’t worry, I’m not going to list the 15,000 jobs of vitamin C, but I’d like to highlight a few that are crucial in your immune defence.
Vitamin C protects mucous membranes, your “skin on the inside”, inside the mouth, the nose, the lungs, along the digestive tract, the urethra and the vagina. Vitamin C is crucial for collagen production, a protein that strengthens your skin as well as the mucous membranes. As all of these surfaces are in contact with the outside world and, therefore, potentially nasty microbes, you want them to be healthy, strong and hold tight. Vitamin C also protects those membranes from free radical damage and accelerates healing from injury.
Vitamin C supports the immune response by stimulating the production of special immune cells called B-cells, T-cells and phagocytes. More B- and T-cells means more antibodies to fight against trouble like viruses – and this is a good thing. Phagocytes are immune cells that gobble up intruders like viruses and bacteria, a bit like the iconic arcade game icon Pac Man. Vitamin C protects these phagocytes from oxidative damage. It also keeps them supple, helps them work better, and promotes the “suicide” of damaged cells (called apoptosis).
A crucial function of vitamin C is that it helps dampen down inflammatory cytokines, substances the body produces when under attack. By interfering with the production of certain cytokines, vitamin C can reduce the risk of a “cytokine storm”, which is something you really don’t want happening. It is this phenomenon that is thought to be at the root of mortality with COVID-19.
Vitamin C is a co-factor for enzymes that are responsible for phase 1 of liver detoxification. In that function, it helps your body metabolise medication. It improves iron absorption, reduces the toxicity of heavy metals and promotes their excretion.
As if that wasn’t enough, vitamin C protects proteins from damage caused by eating too much sugar. The damage caused by excess sugar in the bloodstream is how diabetes is diagnosed. The diabetes marker HbA1c is a protein damaged by sugar. Damaged proteins can’t do their job anymore, and it is this that leads to the many symptoms of diabetes.
Vitamin C and infections – what does the science say?
If you google the subject, you will come across plenty of media reports that will tell you not to bother as “Vitamin C doesn’t really help”. But is that true?
A literature review of 2013 found that vitamin C does not reduce your chances of getting a cold. Still, it does reduce the duration of the cold – a benefit worth having, if you ask me! One of the studies reviewed found that there was a significant benefit from an 8g therapeutic dose given at the onset of symptoms. Four years later, the same author was able to add another controlled trial to the success list: There was a significant dose-response for the duration of common cold symptoms with up to 6-8g/day of vitamin C. Three controlled trials found that vitamin C prevented pneumonia. Two controlled trials found a treatment benefit of vitamin C for pneumonia patients. On the whole, the review confirmed that vitamin C does not decrease the average incidence of colds in the general population. Yet, it halved the number of colds in very physically active people. The reviewer concluded that the negative findings of some studies might be explained by the low doses of 3–4 g/day of vitamin C, 6-8g seems to be more promising.
In 2020, the COVID-19 pandemic has, of course, prompted researchers to look into the efficacy of vitamin C in the treatment of the disease. There was already some evidence that vitamin C prevented pneumonia. When COVID-19 – or even the flu or a cold – has a deadly outcome, this is due to pneumonia. So, even if vitamin C didn’t prevent the original infection, if it prevents pneumonia, that’s worth knowing.
Are we vitamin C deficient?
Depending who you ask, you need between 40mg and 3g (=3,000mg) of vitamin C per day – the equivalent of between 1 and 40 oranges per day. That’s a vast difference! And that’s just the daily requirement before you’re even sick and require therapeutic doses. According to trials, only high doses of at least 6g or even 8g made a significant difference.
For us humans, vitamin C is an essential nutrient. It is abundant in fresh fruit and veg. The riper and unprocessed those are, the higher their vitamin C content. Animal products contain vitamin C as well, mainly within offal. Vitamin C is water-soluble and highly sensitive to light, heat and oxidation. That means that storage and processing (including cooking) have a significant impact on the vitamin C content of fruit and veg and can reduce it by up to 90%. So, even if you regularly eat fruit and vegetables – and so many people sadly don’t – you may not get all the vitamin C you need from your diet.
Vitamin-C-producing animals produce ten times more vitamin C than normal when under stress. In humans, stress-related disorders were found to be more common in people with vitamin C deficiency, and improvement was observed when the vitamin was supplemented. This suggests that stress depletes vitamin C – and who isn’t stressed these days?
As I said earlier, vitamin C protects proteins from glucose. Sugar-coated proteins cannot work properly, leading to a variety of symptoms and diseases, e.g. blindness, neuropathy, cardiovascular disease and more. If your diet is high in sugar, a lot of vitamin C is needed to protect your proteins from damage. Another reason why your vitamin C levels may be low.
Medication is another drain on vitamin C supplies. Drugs must be detoxified via the liver, and here vitamin C is required, too. Elderly people need more vitamin C than younger adults. And do I even need to say that smokers and those who drink alcohol have a higher requirement of vitamin C?
Inflammation can greatly reduce how much vitamin C is available to be used (the ‘bioavailability’). For example, a viral infection can cause such a significant decrease in the vitamin C content of immune cells within hours that the scurvy limit is reached. All chronic diseases are associated with some degree of inflammation. Anyone not entirely healthy is likely to have low vitamin C levels even before they contract a viral infection.
So, chances are that many of us are deficient even to begin with, in which case there is very little chance that we can combat an infection with what we’ve got. High dosage supplementation is necessary for a therapeutic effect. A literature review on vitamin C for protection from SARS-CoV-2 and the treatment of COVID-19 recommend oral daily doses of 3-10g.
Could you overdose on vitamin C?
You can absorb 90% of the vitamin C contained in an oral dose of 300mg. However, you can achieve a higher concentration of vitamin C if you take several smaller doses over the course of the day. Immune cells can store ascorbic acid (vitamin C). Their vitamin C level can be 10 to 100 times higher than that of the blood.
Some health professionals dismiss even the positive studies on the efficacy of vitamin C when it comes to reducing the duration of a viral infection, because they consider the necessary dosages at least 6-8g as too high. After all, more than 1g vitamin C taken orally could cause digestive distress. It is true that the most common side effect of vitamin C toxicity are loose stools, but considering that most people have a high requirement due to stress, inflammation, smoking, alcohol, medication and more (see above), toxicity is very, very rare. If loose stools should occur, you can take that as a good sign: You have decent vitamin C levels and can reduce your dose back down to bowel tolerance (the point at which your bowel movements become normal again).
According to Wehrmann (2020), no harmful side effects have been observed with daily oral doses of up to 10g over a long period of time and with short-term high-dose therapies of up to 1.5g/kg body weight per day. The formation of kidney stones in healthy people due to high doses of vitamin C has been refuted. Oxalate excretion in urine is only slightly increased by supplemental vitamin C. High dose vitamin C supplementation is, however, counter-indicated in people with iron storage problems (haemochromatosis), renal insufficiency, disorders of oxalic acid metabolism, retinal bleeding and favism, a hereditary disorder causing allergy-like reactions to broad (fava) beans.
What can you do to increase your vitamin C levels?
- Reduce stress and practise relaxation techniques.
- Quit smoking
- Reduce or cut out alcohol
- Eat lots of fresh seasonal and ideally local fruit and vegetables every day. Aim for 7 to 10 servings. Great sources of vitamin C are citrus fruits, such as oranges, lemons, tangerines and grapefruit, but also plants from the cabbage family or brassica: kale, cauliflower, broccoli, Brussels sprouts, red, white and pointed cabbage. Other excellent sources are bell peppers and potatoes, rosehips, chillies, parsley, kiwi and papaya.
What if you already have an infection? Nutritional therapist Patrick Holford recommends taking 1-2g at the first sign of a cold and then another gram of vitamin C every hour until your symptoms go away. He assumes, however, that an infection with SARS-CoV-2 may call for higher dosages.
There is currently no evidence that vitamin C helps protect from, shortens the duration or promotes mild progression and less severe outcome of COVID-19, but that is because there has not been time. One controlled trial with intravenous vitamin C given to COVID patients in intensive care finished on 30 September 2020. At the time of writing, the paper awaits peer review before publication in the journal Pulmonology. While only a small trial (28 or 26 patients per group respectively), the results detailed in the draft paper were promising: Vitamin C almost halved deaths of hospitalised COVID patients and cut it by two-thirds among the critically ill.
Supplementing high dose vitamin C at the onset of any viral infection (bearing the counter-indications in mind) is not going to do you any harm, yet may do you good without any adverse effects save lose stools – which you can stop by reducing the dose. I’d say it’s worth a shot, don’t you?
 Carr AC, Lykkesfeldt J (2020): Discrepancies in global vitamin C recommendations: a review of RDA criteria and underlying health perspectives, Critical Reviews in Food Science and Nutrition.
 Drouin G, Godin JR, Pagé B (2011): The Genetics of Vitamin C Loss in Vertebrates
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 Tang, Y, Liu J, Zhang D et al (2020): Cytokine Storm in COVID-19: The Current Evidence and Treatment Strategies. Front Immunol. 2020; 11: 1708.
 https://www.bbc.co.uk/programmes/articles/4BZR74LjnDSq4Qly69sZrbk/can-vitamin-c-cure-a-cold BBC, Trust me, I’m a doctor.
 Hemilä H, Chalker E (2013): Vitamin C for preventing and treating the common cold. Cochrane Database of Systematic Reviews 2013, Issue 1. Art. No.: CD000980.
 Hemilä H (2017): Vitamin C and Infections. Nutrients 2017, 9(4), 339.
 Wehrmann M (2020): Vitamin C zum Schutz vor SARS-CoV-2 und zur Behandlung von COVID-19.
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