Vitamin C for Endurance Athletes: Help or Hindrance?


poor immune systemWith cold and flu season upon us, in addition to the ongoing COVID-19 pandemic, there’s a massive desire to boost one’s immune system.  For this, many people reach for vitamin C.  With good reason, vitamin C is critical for immunity.  Numerous studies show that it can indeed provide a boost to our immune systems.   Studies indicate that taking 1000-2000 mg (1-2g) of vitamin C in supplemental form may help prevent certain infections and reduce the duration of the common cold (Hemilä & Chalker, 2013).  Compare that amount to the RDA for adults of 75 mg for women and 90 mg for men, and there’s reason to believe that supplements are at times necessary.

At the very least, there’s no doubt we require sufficient amounts, at least the RDA (probably more), to maintain optimal immune function.


Vitamin C is an antioxidant.  We all know that antioxidants are great for various health aspects, including neutralizing reactive oxygen species (free radicals) in the body.  High-intensity and/or prolonged exercise results in a temporary rise in reactive oxygen species (ROS). Vitamin C will significantly reduce exercise-induced ROS dependent on dose.  Vitamin C can also reduce exercise-induced immune dysfunction, muscle damage, and fatigue.  So, what’s not to love, right?!  Hold on!  Close Amazon, take the vitamin C out of your cart, and read the next section.


Remember how I said vitamin C negates reactive oxygen species after exercise? I hope so; it was the last paragraph…Anyway, while this sounds like purely a GOOD thing when it comes to exercise adaptation, this is not necessarily the case. You see, reactive oxygen species are thought to be at least partially responsible for the positive adaptations from training, likely playing a role in muscular adaptation. Additionally, evidence suggests that an exercise-induced increase in reactive oxygen species is unlikely to be detrimental to overall health (Powers et al., 2020).

High doses of antioxidants (like vitamin C) have also been shown to diminish mitochondrial biogenesis after exhaustive exercise (Merry & Ristow, 2016). What does this mean? Well, we all remember from high-school biology that the mitochondria are the “power-houses” of the cells, right? The mitochondria are responsible for producing the energy we need to do…everything.  This energy is called ATP.  Mitochondrial biogenesis (drastically oversimplified) is the increase in mitochondrial mass. More mitochondrial mass = increased ability to create ATP (energy).  Mitochondrial biogenesis is a direct benefit of both high-intensity and aerobic exercise.


It’s not a number set in stone, but around 200mg is thought to be sufficient to provide benefits without impairing training adaptations (Braakhuis, 2012). Obtaining 200mg without supplementation should be relatively easy to achieve by endurance athletes eating a nutrient-dense diet. Think 5-6 servings of fruits and vegetables per day, and you’ll be good to go. Let’s be honest; you should be doing this anyway! There is no evidence to suggest that consuming higher quantities of vitamin C from food is detrimental. So if you consume more than 5-6 servings of fruit and veggies/day,I say, great job!  Keep doing that.Vitamin C rich diet

Keep in mind that a typical supplemental dose is around 1000mg, which is on par with the dose used in most of the studies that indicated impaired adaptation. So when taking a standard supplement, you are getting FIVE TIMES that 200 mg, and you haven’t even accounted for food, a multivitamin, etc. Bottom line, eat a high-quality, nutrient-dense diet, and you’ll be great.


The biochemical products produced due to inflammation and stress from exercise are needed for optimal adaptation from training.  High intake (supplemental doses) of antioxidants, like vitamin C, have been shown to offset or reduce some of these biochemical products (Paulsen et al., 2014).   Numerous studies indicate that this leads to a direct impairment in the positive adaptation from high-intensity and/or prolonged exercise (Braakhuis, 2012).

Supplemental doses are likely harmless and possibly beneficial for those not participating in high-intensity or endurance exercise.  However, here at Ultraverse Supplements, we specialize in making you the best possible athlete you can be.  Therefore, none of our products contain vitamin C or vitamin E.  Check out our ULTRA-premium supplements!



Think of these as absolute MINIMUMS.  In comparison, a vitamin C supplement is typically 500-1000mg/capsule.  As mentioned before, this amount is not recommended for athletes but may provide an immune boost.


Kids (1–3 years) 15 mg
Kids (4–8 years) 25 mg
Adolescents (9–13 years) 45 mg
Teens (14–18 years) 65–75 mg
Adult women (aged 19 and older) 75 mg
Adult men (aged 19 and older) 90 mg
Pregnant women (aged 19 and older) 85 mg
Breastfeeding women (aged 19 and older) 120 mg


FRUITS HIGH IN VITAMIN COranges are full of Vitamin C

Orange – 1 medium 70 mg 85%
Kiwifruit – 1 medium 64 mg 78%
Strawberries – ½ cup 49 mg 59%
Grapefruit – ½ medium 39 mg 47%
Cantaloupe – ½ cup 29 mg 35%
Honeydew – ½ cup 15 mg 18%
Blueberries – ½ cup 7 mg 8%


Bell peppers contain vitamin CVEGETABLES HIGH IN VITAMIN C

Bell Peppers – 1 cup chopped 120-190 mg depending on color 145-230%
Kale – 1 cup chopped 80 mg 97%
Broccoli – 1 cup 78 mg 94%
Cauliflower – 1 cup 52 mg 63%
Tomato – 1 medium 17 mg 21%
Potato – medium baked 17 mg 21%
Spinach 8.5 mg 10%


RECOMMENDED SUPPLEMENT FORM: Ascorbic Acid.  Ascorbic acid is likely the most bioavailable form of vitamin C.



Vitamin C significantly increases iron absorption.  This can prevent iron deficiency anemia.  On the other hand, it could present a problem for those with already elevated levels of iron.  People with certain iron-related conditions such as hemochromatosis should always consult their physician before increasing vitamin C intake.

Vitamin C is not the only antioxidant shown to impair exercise adaptation.  Supplemental doses of vitamin E have also been shown to be detrimental.  Like vitamin C, Vitamin E is a powerful antioxidant and likely impairs adaptation for the same reasons mentioned above.  The advice is the same for vitamin E in regards to endurance athletes.  Obtain vitamin E from food, not supplements.




Braakhuis, A. J. (2012). Effect of vitamin C supplements on physical performance. Current Sports Medicine Reports, 11(4), 180–184.

Hemilä, H., & Chalker, E. (2013). Vitamin C for preventing and treating the common cold. The Cochrane Database of Systematic Reviews, 1, CD000980.

Merry, T. L., & Ristow, M. (2016). Do antioxidant supplements interfere with skeletal muscle adaptation to exercise training? The Journal of Physiology, 594(18), 5135–5147.

Paulsen, G., Cumming, K. T., Holden, G., Hallén, J., Rønnestad, B. R., Sveen, O., Skaug, A., Paur, I., Bastani, N. E., Østgaard, H. N., Buer, C., Midttun, M., Freuchen, F., Wiig, H., Ulseth, E. T., Garthe, I., Blomhoff, R., Benestad, H. B., & Raastad, T. (2014). Vitamin C and E supplementation hampers cellular adaptation to endurance training in humans: A double-blind, randomised, controlled trial. The Journal of Physiology, 592(8), 1887–1901.

Powers, S. K., Deminice, R., Ozdemir, M., Yoshihara, T., Bomkamp, M. P., & Hyatt, H. (2020). Exercise-induced oxidative stress: Friend or foe? Journal of Sport and Health Science, 9(5), 415–425.


Disclaimer – Use common sense, and always listen to your doctor over a blog post. They know more about your personal health situation than anybody behind a keyboard. As someone who has a Graduate degree in Clinical Nutrition, I realize the variance that certain medical conditions create when it comes to optimal nutrition and supplementation. If you have underlying medical conditions, always check with your doctor before starting a new supplementation routine.

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