Vitamin C and the Common Cold

Written by: Emily Russo, MS, RD, CDN

Vitamin C supplements are often recommended to boost our defenses against symptoms of the common cold. But when is it most effective to take, and does it really work?

Vitamin C supplements are often recommended to boost our defenses against symptoms of the common cold. But when is it most effective to take, and does it really work?

For everyone who has been struggling with the onslaught of colds, flus, RSV, COVID, etc. this season, I feel your pain. I’m not sure there will ever be a time when someone in our house isn’t sneezing.

Is there any way for us to get ahead of these little buggers (pun intended)?

Some people swear by immunity-boosting Vitamin C supplements. But how do they work, and what has research shown to be the most effective way to take them? There’s no simple answer, but I, for one, could use any glimmer of hope at this point!

A few nutritional facts about Vitamin C (or ascorbic acid)
Even though Vitamin C is essential for human survival, our bodies cannot make it. We have to consume it. Luckily, plants can make Vitamin C from glucose and fructose and that’s why fruits and vegetables are a great source of Vitamin C. Actually, most animals can do it too, though the meat we consume contains very little compared with plants.

Vitamin C is known for its antioxidant properties but also supports healthy teeth and gums, wound healing, and iron absorption, in addition to dozens of other vital functions.

How much Vitamin C do we need?
On average, women need about 75mg a day and men 90mg a day, but needs vary depending on the individual. Because Vitamin C is so prevalent, as long as we are eating enough to maintain daily functions, and maintain weight, we don’t need to think about whether or not we are getting enough Vitamin C in our diets. We just do.

Our bodies maintain tight control over levels of Vitamin C, meaning they know just how much we need to function optimally, and as soon as we have what we need, our kidneys excrete the rest. Vitamin C doesn’t get stored anywhere for later.

Where can we get Vitamin C?
Fruits and vegetables are good dietary sources of Vitamin C, with citrus fruits and bell peppers topping out with some of the highest levels (there’s about 500mg in one orange!). Research indicates that 10mg Vitamin C prevents scurvy (see below), and about half cup of red pepper or a half cup orange juice will get us pretty close to the daily goals noted above.

What happens if we don’t eat enough Vitamin C?
Severe Vitamin C deficiency (or scurvy) is extremely rare in the United States and is most often identified in people presenting with severe malnutrition, cachexia, or alcoholism and drug abuse.

In the setting of very poor nutritional intake, deficiency can develop within 30 days. Some signs of severe deficiency, or scurvy, include bleeding gums, blotchy bruised skin, and fatigue but can be quickly reversed with supplementation.

Why do people take Vitamin C supplements if they don’t have scurvy?
Vitamin C supplements are sometimes taken therapeutically for wound healing (especially with pressure sores in the elderly or malnourished population) or even to aid in iron absorption.

Otherwise, most people choosing to take Vitamin C on a regular basis are likely trying to boost their immunity. And this is where research gets murky.

Can Vitamin C supplements prevent incidence (or onset) of colds?
Not usually, but there may be an exception.

A few studies from the 1960’s and 70’s done on young high-performance skiers and runners in colder weather conditions showed a 50% reduction in incidence of colds. This data may be pertinent to young high-performance, cold-weather athletes. In theory, this is promising, but because these studies were conducted on such a specific group of people under narrow circumstances, results shouldn’t be extrapolated to the general public.

Do Vitamin C supplements reduce duration of colds?
Potentially by a few hours or half a day (measured as an average based on research subjects’ self-reporting), but only if Vitamin C is taken regularly throughout the year. This will not be the case for everyone, and it is unclear how much supplementation is needed on a daily basis to be effective.

Do Vitamin C supplements reduce severity of cold symptoms?
The data is inconsistent, but some studies show that it does if, and only if, supplementation is taken daily throughout the year.

Can Vitamin C supplementation be an effective intervention while we are sick?
One study showed a reduction in duration of symptoms when one gram of Vitamin C supplementation was taken within 24 hours of the onset of a cold. This was difficult to control for and may be due to a placebo effect, so it’s hard to say with conviction.

Overall, there is not strong evidence that therapeutic dosing has an impact on either cold duration or severity, but it doesn’t appear to make things worse!

Are there any downsides to trying Vitamin C supplements?
In high doses (over 2 grams daily) people may experience gastrointestinal discomfort or diarrhea. For those with kidney disease (but not on dialysis), toxicity is possible because they may be unable to excrete excess Vitamin C.

Regular daily dosing of Vitamin C supplements may not be worth it for the possible (and I underline possible) decrease in severity and duration of the common cold.

Your money may literally end up in the toilet!

If you decide to try…
There’s no specific recommended amount of supplementation for Vitamin C among a healthy population. But small doses of plain ascorbic acid (100mg tabs, for example) spread out two to three times during the day will be absorbed more effectively than one large dose. In comparison, products such as Emergen-C® are 1,000mg taken as a megadose all at once.

As always, speak with a physician, pharmacist, and/or dietitian beforehand as supplements may interact with medication or other nutrients (such as iron, but that’s for a different post!), and FDA regulation over supplements is not particularly robust.

Key Takeaways
Evidence that Vitamin C supplements can impact the nuisances of the common cold is inconclusive. However, some studies showed a reduction in severity of symptoms and duration with regular daily supplementation.

Given this uncertainty, I don’t think it’s worth taking daily Vitamin C supplements for this purpose. But besides the financial burden, there are few downsides.

🍊As always, we love hearing from readers. What is your experience with Vitamin C supplements and cold symptoms?

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  1. Georgina Russo

    I always drink a lot of orange juice when I have a cold, especially at first sign of symptoms. If the acid gets to be too much I mix the juice with sparkling water. I think it helps!

    1. Emily Post author

      Gina, I appreciate the comment and share your sentiment! All I want is OJ when I have a cold. I think the sweetness of fresh squeezed gives my throat a nice sugary coating, but agree the acid can be irritating at times. Hydration is really important when we are sick and so if we enjoy OJ and it can help us meet our needs, I’m all for it!