Vitamin C: Supplement Review

Vitamin C or ‘C’ as I will refer to it moving forward, plays an active role in immune function and is a micronutrient with strong antioxidant effects. This means it plays a protective role against reactive oxygen species which are produced through normal metabolism, exercise, active immune response, and exogenous toxins. C’s role in immune function is in the production of white blood cells and aiding in their normal functioning. As such, the various types of white blood cells will acquire C as they work against pathogens, like the common cold.

The most common use of C for athletes that I have seen is therapeutically to treat a cold at onset. Less commonly, C is taken as prophylactic leading up to a short-term competition presumptively to reduce the risk of catching a cold. Personally, I have always preferred Emergen-C, a well marketed C supplement that contains 1000mg (1g) of C. I even have a box in my pantry.

The question I want to explore is: does it work? Is 1g enough to make a difference once you have a cold? Is that fun little orange packet going to help my athletes come back from a cold quicker or stop them from getting a cold in the first place?

This blog will look at the totality of research around C. A follow up blog will summarize the data and answer the questions above.

Let’s dive in!

The recommended daily intake of C has been set to maintain a plasma level of ~50umol/L. This level has been deemed an appropriate level to manage oxidative stress, enhance immune function and reduce the risk of scurvy (not necessarily a high bar).

RDA = Recommended Daily Allowance.

There is an ongoing discussion if a RDA of 200mg for adults is more beneficial.

This amount of C should be easily acquired through diet if eating some fruits and veggies during the day or through supplementation with a multi-vitamin. For example, my multi has 100mg of C. Done, RDA met.

Whoever said that oranges were the best source of C must have sold oranges. No love for the bell peppers in the C discussion.

The tolerable upper limit for oral C has been set at 2g/day to limit the likelihood of getting diarrhea, however, many studies test up to 10g/day (IV).

For the purpose of this discussion we will focus primarily on oral C, although, there may be benefit to taking IV-C, if available (more on this later).

The bioavailability of C is frequency and dose dependent. This means that when and how much you take is very important to how much C is in your plasma at any given time.

Take a quick peak at 1g.

It has been determined that ~220umol/L is the max plasma level that can be obtained orally and this is obtained with 3g of C. Anything more is going to make your urine very expensive and you will get no more C in your plasma. The peak plasma level is reached at ~5hr post intake and is back to baseline within 24hr. With more frequent intake, one is able to keep their plasma level at a peak level throughout the day.

If ‘normal’ is ~50umol/L, 1g of C reaches a peak plasma of ~180umol/L at ~3hr post intake and declines quite rapidly after that.

But is 1g, once/day enough? Does taking it therapeutically (once you have a cold) work? Or do you need to be taking it daily in a prophylactic manner?

A meta analysis with 6000 participants provided these results:

• 1g/day: Cold duration decreased 6% among adults and 17% among children

• 2g/day: Cold duration decreased 21% among adults and 26% among children

This lead to the conclusions that supplementation with at least 2g/day of C during a cold had a greater benefit compared to a dose of 1g/day and that C supplementation elicited a more significant effect against colds in children (younger than 16 years of age), compared to adults.

BUT, these results were in people taking C on a daily basis, not strictly as a therapeutic supplement at the onset of cold symptoms. The authors suggest that it is conceivable that the same benefits could be produced therapeutically, with C taken at the start of a cold. This has yet to be shown conclusively.

Other studies have looked at the use of daily, prophylactic C to limit the incidence of colds. There was a modest reduction between 4-14% when taking between 200mg-2g, and was dependent on age. Higher doses could have a greater reduction in incidence, which has been shown in other studies.

Studies looking at C strictly as a therapeutic, have variable and mixed results (due to differences in the dose and frequency taken). What can be said is that, the greatest potential benefit in reducing cold severity and duration comes when C is administered within 24hr of cold symptom onset and is taken for a minimum of 5 days, with higher doses having a greater effect.

So there is a documented effect as a therapeutic, but the lack of consistent dose, frequency, and test parameters makes it impossible at this time to suggest the perfect formula.

Additional Considerations

As usual, athletes have unique physical demands compared to the regular population which means that study results may not directly apply.

Athletes, C, and exercise

A group of 600 marathon runners, skiers, and soldiers who were regularly supplementing with C had a 50% reduction in incidence of the cold. Much higher than the 4-14% reduction I mentioned above. However, this is a specialized group of endurance based athletes, and some were tested in a cold climate. But, this may suggest that those individuals who stress their immune system more with exercise get a larger benefit in cold incidence reduction from C supplementation compared to their equivalents who don’t. No significant studies in team sport athletes have been performed.

Exercising for up to 60 minutes tends to have a positive effect on your immune system, however, there seems to be a tipping point that endurance athletes reach where long bouts of constant exercise create too much oxidative stress. This leads to these types of athletes getting sick more frequently. For the average person exercising, there doesn’t seem to be a significant positive effect of C in enhancing the ‘normal’ exercise-induced immune function. However, as noted above, there does seem to be a positive effect for endurance athletes and this may be able to be extrapolated to other elite athletes with frequent, high intensity exercise demands. Studies of this nature have not been conducted.

Athletes, C, and reactive oxygen species

During strenuous exercise there is a normal release of reactive oxygen species in the body. As an anti-oxidant, C plays a role in mitigating the potential damage done by excess amounts of these oxygen species. However, the same reactive oxygen species also play a role in positive cellular adaptations through down-stream signalling as a response to exercise. So, although the anti-oxidant effect may be positive to reduce muscular damage and reduce muscular soreness, it may also blunt certain positive adaptations you would hope to acquire through exercise.

The authors suggest that C doses of 0.2 to 1 gram per day might reduce oxidative stress, while doses greater than 1 gram per day appear to impair beneficial adaptations to exercise, especially if taken with additional antioxidants like Vitamin E.

Athletes, C, and exercise timing

Timing also seems to matter when discussing C effects related to exercise. If C is taken such that you have a high plasma concentration during and after exercise you are more likely to blunt some of the positive adaptations that the reactive oxygen species induce.

IV-C

There is lots of research on taking C in an IV form at much higher doses to manage severe infections and other more serious diseases. Studies have shown that plasma levels of C can reach up to 70x higher in this form without the GI distress that comes with taking C orally. To my knowledge, this has yet to be extensively studied in cold reduction. This opens up an interesting question of whether this could be applied at the beginning of a cold and how that may impact the duration and intensity of the symptoms. It has not been studied in an athletic population.

Thanks for taking the time to read! Stay tuned for my follow up on this post which will summarize the info and leave you with practical usage suggestions based on the data. Spread the word that bell peppers are the OG C dietary source!

If you are looking for more information on the topic:
https://www.foundmyfitness.com/topics/vitamin-c - Dr. Rhonda Patrick

Disclaimer: I am not a medical doctor and this is not medical advice. You are responsible for your health. Always consult with the appropriate health authority to make sure it’s safe for you to add or change any supplements in your diet.