I have taken Vitamin C for several years, because I just feel better when I take it. It can boost nitric oxide and has a lot of great properties that I document in my page on Why Take Vitamin C? However, a couple of recent studies have really made me reconsider. In fact, some of you may have heard or read about a very recent study where Vitamin C was coupled with Vitamin E and produced some quite negative results. Normally, training leads to an increase in mitochondrial content within the muscles and this is a normal training adaptation since mitochondria are the power and energy manufacturers within your cells. However, the Vitamin C and E group had a lower mitochondrial response than the control group, exactly the opposite of what most of us would expect.  Clearly if you're working out, you don't want your supplements sabotaging your results and that is exactly what the Vitamin C and E seemed to be doing.
Unfortunately, it is hard to draw any specific conclusion about Vitamin C from this study, because, for reasons unknown the researchers did not study each vitamin separately. And that's not the first time that has happened. In 2005 a similar and older study that I mentioned in my page on The Potential Dangers of Antioxidants showed combining Vitamin C and Grapeseed Extract led to a ~5 mm rise in systolic blood pressure! And three years later a study showed that a combination of Vitamin C and an SOD-like molecule led to a decreased oxygen supply to muscle tissue.
As you can see, the storm clouds had been gathering, but in every case, Vitamin C fanatics could blame the other molecule and avoid blaming Vitamin C. However, that all changed when a lesser known, but very well done study on both rats and humans came out the same year as the SOD study mentioned above. In this study researchers gave men a gram per day of Vitamin C, which is a very reasonable and common dose, and then monitored how it affected their exercise results.  Many of you know that one measure of cardiovascular fitness is VO2max. What happened is that in the 8-week training period the non-supplemented men increased their VO2max by 20% and, counterintuitively, the Vitamin C supplemented group only increased it by 10%. There was an even greater differential in the animals study. In other words, Vitamin C decreased the training effect instead of increasing it - not good.
What made the results so damning was that the scientists documentedWHY Vitamin C had this negative impact on exercise: it muted key transcription factors that rely on free radical formation. A transcription factor is a protein that is used to convert DNA into RNA. Another way to put this is that free radicals (ROS or reactive oxygen species) actually activate key antioxidant systems. Vitamin C actually stopped this activation in muscle tissue and thus produced the exact opposite of what was intended.
And it didn't stop there: the researchers did a fantastic job of also showing many other transcription factors that were negatively impacted. Many of you know that SOD and glutathione are the two master antioxidants in the human body. Vitamin C lowered the expression of both SOD and glutathione post-exercise. You can see the irony: a health-conscious man takes Vitamin C to promote antioxidant status and instead likely lowers it in many key ways. This was really the final nail in the coffin for me.
For those of you who are have been health-consciour for decades, this will come as quite a shock. In the 80's there was a huge life extension movement that was supposed to cure diseases and extend lifespans and much of the hope was built around antioxidants. However, antioxidant research has been less than spectacular to say the least and has actually received many black eyes, all of which was counterintuitive until a few years ago.
Again, the problem is that the body has a yin and yang interplay between free radical and antioxidant metabolism. It is simply NOT true that free radicals are always bad. In fact, let me mention an example that is near and dear to every male's heart: nitric oxide. Nitric oxide relaxes our arteries, lowers blood pressure and makes erections possible. It is also a potent free radical. So how can something so destructive be so good for us? You'll have to ask Mother Nature that one next time you run into her. And, when you do, you can also ask her to explain how and why nitric oxide is a strong anti-inflammatory as well.
Is there any way out of all of this for Vitamin C? I know a number of guys on the Peak Testosterone Forum have subscribed to "Pauling Theory." For those who don't know, Linus Pauling was the Apostle of Vitamin C and he had a theory that was built on the fact that virtually all animals except man manufacture their own Vitamin C. Therefore, we have much lower levels of Vitamin C than all other creatures around us and have not been able to fully adapt or compensate. His theory, called Pauling Theory, was that man simply needed to replensih these lost stores of Vitamin C by megadosing Vitamin C. He claimed this could cure many cancers, stop arterial plaque in its track and many other things as well.
Someone still clinging to Pauline Theory could still claim that megadosing Vitamin C, while lowering training beneftis, still provides so many other positives that it is a net gain. This seems like a weak argument to me, since it is essentially lowering the body's own natural antioxidant systems. Vitamin C, as powerful as it is, should not be lowering the master antioxidants, SOD and glutathione. And it doesn't unless you start megadosing of course.
1) J Physiol, 2014 Apr 15, 592(Pt 8):1887-901, "Vitamin C and E supplementation hampers cellular adaptation to endurance training in humans: a double-blind, randomised, controlled trial"
2) Am J Clin Nutr, Jan 2008, 87(1):142-149, "Oral administration of vitamin C decreases muscle mitochondrial biogenesis and hampers training-induced adaptations in endurance performance"