As cold/flu season hits, vitamin C supplementation becomes common. But, is more necessarily better? I often come across recommendations of mega-doses and, unfortunately, vitamin C absorption doesn’t quite work like that. Let me explain:
Sodium-dependent vitamin C transporter (SVCT1) is the main carrier for vitamin C (which takes place throughout the small intestine) as ascorbic acid. It allows vitamin C to be absorbed even in excess of cellular needs but is greatly down-regulated by superphysiological doses. Even though vitamin C from food sources is found as a different form than ascorbic acid, it’s turned quickly turned into it by an enzyme. The point is, we’re dealing almost entirely with ascorbic acid here.
When vitamin C oral intake is low (<180 mg), absorption is high. As oral intake increases, its absorption drops. Vitamin C through an IV is a nice hack to get around this. But at what point does your body “cap out” in vitamin C stores? Well, the amount able to be stored in the tissue is higher than that in the plasma, with different tissues storing different amounts. The highest being your pituitary at about 30-50 mg. The maximal vitamin C pool is roughly 2 grams. That’s it. Keep in mind that this is a pool, not daily intake. This means that oral intake of 100-200 mg per day can elevate plasma concentrations to 1 mg/dL. According to a 2004 study by Said HM, intake of 1.25 grams of vitamin C generates a peak plasma concentration of 2.37 mg/dL.
So, is it really worthwhile to mega-dose vitamin C as a way to fight a cold? Probably not, but at least one researcher, Dr. Steve Hickey, would dispute this. It certainly aids in the proliferation of immune cells, increases natural killer cells, and destroys histamine, which has been shown to be accomplished with consistent use of 1 gram per day. Newer data supports longer exposure being more effective, so multiple doses throughout the day may be best.
With science, our current understanding is always up for debate, change, and evolution. In fact, how we thought fat leaves the cell and makes its way to the liver is about to change substantially – what’s currently taught in the textbooks is wrong. As such, maybe Dr. Steve Hickley is entirely right, and our current view is wrong. Maybe it’s the other way around. What I’ve come to learn is that good research rests upon the shoulders of those who foster an ego. Rather, they seek the truth no matter how far it strays from their prior beliefs. In fact, knowledge isn’t so much about what you know, it’s about acknowledging the things you do not know. As I write this (or any blog post for that matter), I can’t help but to question every sentence. You should do the same.