If there’s one vitamin most people have heard of, it’s vitamin C. You probably know that you can get it from oranges and other citrus fruits. When you catch a cold, you drink hot water with lemon – to give you a boost of vitamin C. Even people who ‘don’t believe’ in taking nutritional supplements will admit to knocking back the occasional effervescent vitamin C tablet dissolved in water, when they’re feeling under the weather. But does that actually do any good? In short, yes!
And as we’re in the middle of the winter cold and flu season, as well as a COVID-19 pandemic, then it’s worth taking a closer look.
What does vitamin C actually do?
Vitamin C (ascorbic acid) is essential for many different metabolic processes in the body and no other vitamin has such a wide variety of effects. It acts as a powerful antioxidant, protecting fats, proteins, DNA and cell membranes from free radical damage.
It also plays a crucial role in our immune function – both in our innate immune system, which is our first line of defence, and our adaptive immune system, which is the slower, but more specialised and longer lasting response to pathogens.
Vitamin C protects mucous membranes inside the mouth, nose and lungs, along the digestive tract, the urethra and the vagina. It is crucial for collagen production, a protein that strengthens your skin as well as the mucous membranes. All of these surfaces are in contact with the outside world and potentially harmful microbes, so we need them to be healthy and strong. Vitamin C also protects those membranes from free radical damage and accelerates wound healing.
Vitamin C supports the adaptive 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 pathogens like viruses – and this is a good thing. Phagocytes gobble up intruders like viruses and bacteria. 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” – when the body’s immune system goes into overdrive and starts to attack more than the original pathogen, i.e. healthy tissue. 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 involved in 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.
And 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.
Vitamin C and infections – what’s the evidence?
Vitamin C for the prevention and treatment of the common cold has been a controversial topic for many years. 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”.
However, a 2013 review of 29 trials found that, whilst vitamin C does not reduce your chances of getting a cold, it can reduce the duration and severity of the cold. One of the studies reviewed found that there was a significant benefit from an 8g therapeutic dose given at the onset of symptoms. Another study, four years later, found a significant response 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. Overall 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 conclusion was that the negative findings of some studies might be explained by the low doses used (3–4 g/day), while 6-8g of vitamin C seems to be more effective.
The COVID-19 pandemic has 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, and many patients with COVID-19 – or even flu or a cold – can go on to develop pneumonia. So, even if vitamin C doesn’t prevent the original infection, if it prevents pneumonia, that’s worth knowing.
So are you getting enough?
Most animals can produce their own vitamin C, but somewhere over the course of evolution, we humans have lost the ability to do so. In addition, vitamin C is a water-soluble vitamin and we are not able to store it, so regular daily intake is needed.
The good news is that it is abundant in fresh fruit and veg – the riper and less processed the better. The bad news is that it is highly sensitive to light, heat and oxidation, which means that storage and processing (including cooking) can have a significant impact and can reduce the vitamin C content by up to 90%. So, even if you regularly eat your 7 a day – and sadly many people don’t even get to the old target of 5 a day – 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?
A high-sugar diet can inhibit the absorption of vitamin C, as both sugar and vitamin C enter our cells via the same receptor. And you may actually need more vitamin C to neutralise the free radicals created by the excess sugar.
Medication is another drain on vitamin C supplies. Drugs are detoxified via the liver and this process requires vitamin C. The elderly need more vitamin C than younger adults, as do smokers and those who drink alcohol (25mg of vitamin C is lost with every cigarette smoked).
Inflammation can greatly reduce how much vitamin C is available to be used (the ‘bioavailability’). A viral infection can cause such a significant and rapid (within hours) decrease in the vitamin C content of immune cells 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 many of us are deficient to begin with, before we have to try and fight an infection. High dosage supplementation is necessary for a therapeutic effect. A current literature review and petition to recommend the use of vitamin C for the treatment of COVID-19 recommends oral daily doses of 3-12g.
Do you need to supplement?
Based on the above, yes.
In the UK the NHS recommends an adult daily intake of vitamin C of 40mg – the equivalent of a large clementine. That’s the minimum requirement to prevent illnesses such as scurvy, and to support wound healing. But it is unlikely to be enough to ensure optimum immune defence. Worldwide, recommendations range from 40 to 220mg per day.
Given the stressful lives most people have these days it is likely that most of us need to boost our levels. Supplementing with 500mg twice a day can help increase levels for much of the day, increasing to hourly doses of 1g at the first sign of a cold.
Could you overdose on vitamin C?
Vitamin C is water-soluble and cannot be stored in the body, so any excess is excreted. Single high doses over 2g, taken orally may cause digestive distress for some people – usually loose stools. But considering that most people have a high requirement due to stress, inflammation, smoking, alcohol, medication and more, 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).
No harmful side effects have been observed with daily oral doses of up to 10g over a long period of time and the formation of kidney stones in healthy people due to high doses of vitamin C has been refuted. High dose vitamin C supplementation is, however, contra-indicated in people with iron storage problems (haemochromatosis), and some other disorders including renal insufficiency.
How can you increase your vitamin C levels?
- Eat 7-10 portions of fresh seasonal and ideally local fruit and vegetables every day. As well as citrus fruits, other good sources of vitamin C are kale, cauliflower, broccoli, Brussels sprouts, cabbage, spinach, bell peppers, kiwi and papaya.
- Reduce stress and practise relaxation techniques.
- Get enough sleep – between 7-9 hours.
- Quit smoking
- Reduce or cut out alcohol