While physicians and researchers are studying the effects of high dose intravenous (IV) vitamin C on the new coronavirus, no supplement, including vitamin C, can prevent or treat COVID-19.
This article reviews what vitamin C is, how it affects immunity, how it’s being tried for COVID-19 treatment in a hospital setting, and whether taking an oral supplement is beneficial.
What is vitamin C?
Vitamin C is an essential nutrient with several roles in your body. It’s a potent antioxidant, meaning it can neutralize unstable compounds in your body called free radicals and help prevent or reverse cellular damage caused by these compounds (1).
It’s also involved in a number of biochemical processes, many of which are related to immune health (1).
The Daily Value (DV) for vitamin C is 90 mg per day, but breastfeeding women need an extra 30 mg and people who smoke need an extra 35 mg per day (2).
It’s pretty easy to meet your vitamin C needs through your diet as long as you eat a variety of fruits and vegetables. For example, a single medium orange provides 77% of the DV, and 1 cup (160 grams) of cooked broccoli provides 112% of the DV (3, 4).
How does it affect immunity?
Vitamin C affects your immune health in several ways. Its antioxidant activity can decrease inflammation, which may help improve your immune function (5).
Vitamin C also keeps your skin healthy by boosting collagen production, helping the skin serve as a functional barrier to keep harmful compounds from entering your body. Vitamin C in the skin can also promote wound healing (1).
The vitamin also boosts the activity of phagocytes, immune cells that can “swallow” harmful bacteria and other particles (1).
In addition, it promotes the growth and spread of lymphocytes, a type of immune cell that increases your circulating antibodies, proteins that can attack foreign or harmful substances in your blood (1).
In studies of its effectiveness against viruses that cause the common cold, vitamin C doesn’t appear to make you any less likely to get a cold — but it may help you get over a cold faster and make the symptoms less severe (6).
There’s also some evidence from animal research and case studies in humans that high dose or IV vitamin C can reduce lung inflammation in severe respiratory illnesses caused by H1N1 (“swine flu”) or other viruses (7, 8, 9).
However, these doses were far above the DV, and there’s not enough research to support the use of high dose vitamin C for lung inflammation at this time. You shouldn’t take high doses of vitamin C supplements — even orally — because they can cause side effects like diarrhea (2).
Vitamin C is an important nutrient found in fruit and vegetables that may help shorten the duration and severity of colds. High doses are being studied for their potential to decrease lung inflammation, but more research is needed.
Vitamin C and COVID-19
Doses that are magnitudes higher than the DV are recommended to be given through IV to improve lung function, which may help keep a patient off of mechanical ventilation or life support (10, 11, 12).
Additionally, a 2019 review found that both oral and IV high dose vitamin C treatment may aid people admitted to intensive care units (ICUs) for critical illnesses by reducing ICU stay length by 8% and shortening the duration of mechanical ventilation by 18.2% (13).
Chinese researchers have also registered a clinical trial to further study the effectiveness of IV vitamin C in hospitalized people with COVID-19 (14).
However, it’s important to note that vitamin C is not yet a standard part of the treatment plan for COVID-19 because evidence is still lacking (10, 15).
Though high dose IV vitamin C is currently being tested to see if it can improve lung function in people with COVID-19, no evidence suggests that high doses of oral vitamin C supplements can help with the disease. In fact, they can cause complications like diarrhea (2).
High dose IV vitamin C has been used in China to help improve lung function in people with COVID-19. However, vitamin C’s effectiveness is still being tested. There’s no evidence to support the use of oral vitamin C supplements for COVID-19.
Do you need to supplement?
Currently, no evidence supports the use of oral vitamin C supplements to prevent COVID-19.
Vitamin C may help shorten the duration and severity of colds caused by other viruses, but this is no guarantee that it will have the same effect on the coronavirus that causes COVID-19.
Additionally, vitamin C is a water-soluble vitamin. It dissolves in water, meaning that excess amounts aren’t stored in your body but instead eliminated through your urine. Taking more vitamin C does not mean that your body is absorbing more (16).
High dose vitamin C supplements may even cause diarrhea, as they can signal your body to pull water out of the cells and into your digestive tract (2).
Moreover, although high dose vitamin C appears promising for COVID-19 treatment, these doses were exceptionally high and given via IV — not taken orally. Additionally, it was only given in cases severe enough to require hospitalization.
Your best bet is to eat a diet that’s full of a variety of fruits and vegetables, which naturally provide all the vitamin C a healthy person needs — along with many other nutrients and antioxidants.
Choosing a supplement
If you do choose to take a vitamin C supplement, it’s important to choose one that’s high quality and to take the correct dose.
While supplements are regulated by the Food and Drug Administration (FDA), they aren’t held to the same safety standards as pharmaceuticals. Thus, it’s important to purchase supplements from reputable companies.
Some third-party organizations, such as NSF International, ConsumerLab, and United States Pharmacopeia (USP), test supplements for purity and label accuracy. You may want to choose a vitamin C supplement that has been tested by one of these companies.
Additionally, the Upper Limit (UL) for supplemental vitamin C — the amount most people can consume daily without negative effects — is 2,000 mg (2).
Most vitamin C supplements provide a daily dose of anywhere from 250–1,000 mg, so it can be easy to exceed the UL if you’re not careful. Be sure to read the packaging and take only the recommended dose to avoid complications.
Vitamin C may also interfere with chemotherapy, radiation treatments, or cholesterol lowering drugs (2).
That said, when used in clinical settings treating critically ill patients, very high dose vitamin C treatments are safe and not associated with significant side effects (17).
If you have any concerns about vitamin C supplements, you should consult your healthcare provider before adding it to your routine.
There’s no evidence that vitamin C supplements help prevent COVID-19. In fact, high doses are likely just excreted through your urine. If you do supplement, choose a product tested by a third party and don’t take more than 2,000 mg per day.
The bottom line
Vitamin C is an important nutrient that keeps your immune system functioning properly.
However, there’s no proof that oral vitamin C supplements will help treat or prevent COVID-19.
To get plenty of immune-strengthening vitamin C in your diet, make sure you’re eating a variety of fruits and vegetables.
Though there’s currently no cure for COVID-19, preventive measures like physical distancing and proper hygiene can help protect you from developing the disease.
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