Vitamin C graphic - Does Vitamin C Benefit Colds?

Does Vitamin C Benefit Colds?

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Vitamin C can help with a common problem. Fall and winter are just around the corner and with that, the chances of ‘catching’ a cold will increase. The common cold (acute viral rhinopharyngitis) is the most common infectious disease in humans. Believe it or not, the average person gets 2 to 4 colds per year.


And yes, viruses cause the common cold. Colds are not caused by getting wet, drafts, or forgetting to wear a scarf or hat. It’s amazing to hear this kind of medieval shite as a health professional working in a hospital. Educated doctors and nurses should know better ya?


What’s a person to do?

There are more than 200 viruses that cause the common cold. Sadly, therefore, the human body can never build up resistance to all of them. This is why colds are so common and often return.


We are exposed to cold and flu viruses 24/7, they are not JUST around in the winter but we don’t get sick all of the time. True, some of the old viruses make the rounds again and again, and if you’ve had that particular strain, you’ll be immune to it.


In reality, though, your body is fighting (potential) infections all of the time; not every exposure leads to the sniffles (and hacking, and coughing, and fever, and stuffiness).


People hate being sick; let’s face it, it sucks, so wouldn’t it be great if there was something simple, safe and inexpensive that you could take that might reduce both the effects (symptoms) of colds and the length of time you are sick?


Wouldn’t it be even better if that ‘something’ benefited other parts of your body and helped with improving your overall health?


Would you want to know about it? I would.


The good news is, vitamin C (ascorbic acid) fits the bill. And for all the folks who just rolled their eyes, it’s important to understand why some of the research hasn’t found a benefit with vitamin C and the common cold and why other studies have.


Vitamin C basics

Humans are one of a handful of animals that don’t produce their own vitamin C.


We have most of the same machinery as vitamin C producers do but the weak link in the biochemical pathway is the last enzyme which produces vitamin C in other species; sadly ours is non-functional.


Eons ago, the human race experienced a genetic mutation that prevents us from the final conversion of glucose (yes, blood sugar) into vitamin C. Animals that do make their own vitamin C make it from glucose in their liver and/or kidneys.


Some experts are going as far as to say that our ascorbic acid requirements should really be reframed as an inborn error of carbohydrate metabolism rather than seeing vitamin C as a vitamin.


If we had a functioning enzyme in that last step, we’d be producing all the ascorbic acid we needed based on actual need versus an amount just needed to prevent scurvy.


What’s unique about this, is that vitamin C producing species have a steady stream of vitamin C in their blood 24/7 whereas the levels in our blood will ebb and flow depending on dietary intake.


The kidneys will hold on to vitamin C to help prevent a complete loss but it begs the question as to whether or not consistently higher levels might not offer greater benefits for human health.


FUN FACT: when vitamin C is consumed either from food, or a supplement, the blood level peaks about 2-3 hours afterwards and then returns to baseline (the level it was prior to consumption) within about 6 hours.


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Does vitamin C help with the common cold?

In a word, yes. The trouble with vitamin C is that people assume that any old dose will do including those designing vitamin C research.


Even those involved in establishing our vitamin C recommendations (especially the RDA or Recommended Dietary Allowance) never took into account how vitamin C is absorbed, distributed or excreted by the body (a.k.a. vitamin C’s pharmacokinetics).


To understand how this lack of understanding of vitamin C’s pharmacokinetics influenced the RDA, get the technical paper here: Ridiculous Dietary Allowance – A Challenge to the RDA for Vitamin C


As a result, most vitamin C supplement research looked at the impact/effect of vitamin C on colds using either a single dose or very small dose of vitamin C.


Considering vitamin C’s pharmacokinetics, a single/small dose of vitamin C wouldn’t impact the blood levels of vitamin C in the long run. A single dose would only raise blood levels temporarily; returning to baseline within 6 hours or so.


Achieving a steady-state offers the best insights into how vitamin C benefits the impact of colds, flu, and other infections. This is similar to medications. A steady-state is needed to achieve what is referred to as a ‘”therapeutic level”.


For the real geeks out there interested in more on this very issue, check out the technically dense paper Ascorbate – The Science of Vitamin C


Vitamin C and the common cold research review

A review of 29 studies, looking at 11,306 subjects, using 200 mg/day or less of vitamin C found no benefit when it came to reducing the risk for catching a cold. They did find that a supplemental dose of 1 – 2 g/day (1000 – 2000 mg) was enough to shorten the length of having a cold by 18% in children (1).


Looking at higher doses, research has found benefit with doses in the 6-8 g/day range (6000 to 8000 mg).


Vitamin C doesn’t appear to prevent colds but does reduce the severity of cold symptoms and how long they last. Some studies found that vitamin C prevented pneumonia while others found treatment with vitamin C benefited pneumonia (2).


Vitamin C and Infections


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A lack of positive findings with other vitamin C studies might be explained by what is referred to as “low doses” of 3-4 g/day of vitamin C (3). To achieve a therapeutic level of vitamin C in the blood, you need to spread out higher doses throughout the day.


In this sense, you need to ‘stack’ your vitamin C given how relatively quickly it is excreted. We wouldn’t have to do this if we could produce vitamin C 24/7 like other species.


Getting more vitamin C. What’s the evidence?


How DOES vitamin C help with colds?

Vitamin C plays a big role in immune function starting at the very beginning with young white blood cells that are maturing in lymph nodes to how those white blood cells use vitamin C in the fight against viruses and bacteria (4).


Vitamin C supports the immune system by enhancing:

  1. antibody production (B-lymphocytes, humoral immunity)
  2. interferon production
  3. phagocytic (scavenger cell) function
  4. T-lymphocyte function (cell-mediated immunity)
  5. B-lymphocyte and T-lymphocyte proliferation. Enhanced natural killer cell activity (very important anti-cancer function)
  6. prostaglandin formation
  7. nitric oxide production by phagocytes


FUN FACT: both a clinical deficiency and a functional deficiency (where you’re getting enough vitamin C to prevent scurvy but not enough to reap the full benefits) weakens the immune system, immune response (think sluggish) and increases the risk for infections (4).


Bottom line

Best evidence suggests that getting more vitamin C, via supplements, won’t reduce your chance of catching a cold or flu. But, taken in larger doses throughout the day, will likely reduce your symptoms and shorten the duration of your cold.


Upping your intake of vitamin C won’t help either if you only do it for a few days. You need to start at the first sign of a cold. Then stick to it, and see it through and take it for the duration of your cold.


Vitamin C has never been shown to increase the risk of kidney stones. This is a myth that’s been around for decades. Because vitamin C can increase oxalate in urine, people have jumped to the conclusion that this means kidney stone risk.


Vitamin C and stone risk is the Loch Ness monster of the nutrition world. People have heard about it, think they’ve seen a study showing vitamin C caused kidney stones but it’s an urban legend.


Some will also fear monger that vitamin C will cause diarrhea in doses above 2000 mg per day; this one is partly false. Taking too much vitamin C at once can increase gas. If taken to extreme may cause harmless, but inconvenient, loose stools.


Taking several grams throughout the day will prevent this and you won’t experience any issues. Of course, everyone’s situation is different so speak with a knowledgeable health care practitioner on this subject.


Doug Cook RDN is a Toronto based integrative and functional nutritionist and dietitian with a focus on digestive, gut, and mental health.  Follow me on Facebook, Instagram and Twitter.