Friday, April 11, 2014

Science Friday: Vitamin C

In these last days before spring marathons, runners everywhere are obsessing over possible scenarios that could undermine all their training at the last second. They’ve morphed from running junkies to tapering balls of anxiety, stressing about weather predictions, analyzing the carbohydrate content of their food, and constantly washing their hands. This is not the time to come down with something.

I didn’t take enough precautions before this year’s Rock and Roll Half-Marathon. The week of the race my nose started running, my throat itched, my eyes watered. I was sick. In last minute desperation, I overloaded on anything with vitamin C. I drank orange juice, ate red pepper, snacked on strawberries. (Orange juice has a lot of vitamin C, but oranges themselves are not the only source of vitamin C, nor are they the best one.) Unfortunately, I wasn’t cured before the race. Despite a persistent belief that vitamin C can cure a cold, my personal case study (n=1) would suggest otherwise. But what does the real research say? Should tapering marathoners be vitamin C loading?

There are two key words in that question: marathoners and loading.

First, the marathoners. Last year, a meta-analysis (a review of previous studies) examined the effect of vitamin C on frequency, duration, and severity of the common cold. For the general population, it seems that vitamin C actually doesn’t help prevent a cold, but it can help shorten it or make it less unbearable. (This was true for people who took vitamin C regularly; taking a dose of vitamin C once the cold started didn’t help much, which may explain my trouble trying to load up once I was already sick.)

But the results were slightly different when they looked at studies of people under “heavy acute physical stress.” These studies looked at skiers, soldiers training in the subarctic conditions of northern Canada, and—relevant to this blog—ultramarathoners (participants who ran the Comrades Marathon in South Africa, a 56 mile race). In these groups, vitamin C supplementation halved the risk of coming down with a cold. It should be noted that for the ultramarathon group, researchers only analyzed the likelihood of getting a cold in the two weeks following the race. The vitamin C likely helped because races like marathons deplete our immune system, making us more likely to come down with a cold. The researchers didn’t look at prevention of colds during training or before the race, but assuming hard training (especially the last few monster weeks before tapering) could also deplete the immune system, then marathoners especially could benefit from being extra vigilant about vitamin C.
Which brings me to part 2: Should we load up?

Here the answer is: not so fast. Vitamin C is an antioxidant (generally a good thing), but excessive amounts may actually be harmful and have a negative effect on training and performance. The thinking here is that exercise produces reactive oxygen species. (Caused by the break down of oxygen, reactive oxygen species build up when cells are stressed, and are generally a bad thing.) These “bad” species may actually help induce training adaptations by forcing the muscles to make their own antioxidants and increase mitochondrial growth. In one study, researchers looked specifically at female runners. (Because of estrogen, there may be gender differences in regards to vitamin C effects.) The runners were given either vitamin C (1000 mg daily, 10 times the recommended amount and the equivalent of 12 oranges or 1 Naked Power-C Machine bottle) or placebo during three weeks of training, and then tested twice: a timed 5k and a treadmill test where the speed and incline increased until exhaustion. Vitamin C seemed to decrease the speeds they could hit in practice (during training), but didn’t seem to significantly help or harm the speeds on “race” day (for the 5k and the treadmill test). (It seems possible that not being able to go as fast in training would eventually catch up to you on race day; I wonder if the study was too short to investigate that.) The researchers also measured markers of oxidative stress (those bad species) and found they were higher when the runners were taking vitamin C. The differences here were small, but it suggests a level of caution. 

Just to add another degree of confusion to this debate, vitamin C is water soluble, which is a fancy way of saying that if you take too much, you will pee out the excess. However, overdoses—although rare—can happen and as the above study suggests, excess isn’t entirely harmless.

So the lesson is that regular vitamin C could possibly prevent a cold when your body is depleted (i.e. before you start the taper). Too much vitamin C might prevent training adaptations, so it may be best not to go overboard with supplements and Naked drinks and just adhere to the old standard of Moms everywhere: eat your fruits and veggies.

And keep washing your hands.

Dream big and stay healthy,


  1. Vitamin C doesn't work to avoid a cold because your body doesn't store what it doesn't use right away, it actually flushes it out fast. A viral infection requires a substantial amount of C over what a healthy person can absorb so you'd be giving yourself the runs all the time just to stop a cold before you physically notice it.

    It's all about dosages. What's been researched and reported not to work is small dosages of C. Healthy people start to have the side effects of the body flushing C at about 2 grams a day and the medical/scientific community has decided not to research anything above that amount. Anecdotal evidence has substantiated that the amount of C required to shorten a cold starts somewhere above 10 grams (taken over the course of) a day.

  2. Very interesting! Thanks Teal :)

  3. When I'm depleted and taking it for a cold my body is far more tolerant and needs a lot more to do it's job. I've taken as much as 80g in one day (throughout the day) ... the result was me completely recovering from a horrible terrible nasty cold within 24 hours. It's called bowel-tolerance.

    As for maintenance C levels for training I'm so glad to read you're right on the mark. Vitamin C can make your cellular ecosystem lazy so to speak - the old too much of a good thing. I don't think it's good to take daily. Take in large doses just after super aggressive training, but put your body in as scurvy as a state you can before training, without getting a cold of course. A fine balance there. It's important to taper off usage too when you stop. Rebound scurvy is real. You don't need to taper over a days ... just over 12-24 hours.

    ...just my thoughts on C.