I'm sure you've all heard the story of how vitamin C either prevents or cures the common cold. Some of you may also remember that vitamin C prevents or cures scurvy. But what exactly does it do for our bodies? I decided to do a bit of searching and find out.
Clues to what vitamin C does for us can be found in the symptoms of vitamin C deficiency itself. Scurvy is not just the disease where your teeth fall out, though that is one of the symptoms. Bleeding gums, bleeding under the skin (bruising), bleeding in the joints (joint pain), bleeding at hair follicles, and bleeding at previously healed scars start off the list of visible symptoms. Before those is fatigue; after those is death.
All of those bleeding symptoms demonstrate that the body is falling apart and can't keep its blood inside anymore. Quite literally: vitamin C is required for the production of collagen, the structural support cables of our body. They're found basically everywhere, including in bones and teeth, where they're mixed with minerals. Lose the ability to make new cables, and you lose the ability to repair routine damage day to day - and over time you lose the microscale structural integrity that keeps the blood inside your veins, among other things.
Fatigue is so general a symptom it can't really be used to diagnose anything. Besides, you probably just stayed up too late. But even here, it seems that vitamin C plays a role. In addition to being crucial to making collagen, it's also crucial to making dopamine, norepinephrine and epinephrine (adrenaline), and carnitine.
Carnitine is an escort for fatty acids into the mitochondria, according to the link above. Basically it's the fuel injection system for the motors that power our cells. While we get most of our carnitine from our diets, particularly from meat, if we're so low on vitamin C we're suffering from scurvy, we probably have low carnitine intake as well, a double-whammy.
But carnitine is in meat, and vitamin C is in oranges and other tasty veggies and fruits, right? How could the inuit survive on a meat-only diet? Actually, there's vitamin C in meat, too: mostly in organ meat, and the inuit do just fine without vegetables, on their traditional diet.
In fact, it looks like just by eating a reasonably healthy mix of food, you'll get enough vitamin C. Not everybody manages this, but I guess scurvy is rare enough now that people forget about the whole "it keeps you alive" part and instead spend their time thinking about some of its very minor effects.
As for curing the common cold? survey says… taking it when cold symptoms appear does no better than a placebo; taking it every day reduces cold duration by maybe 10%; and if you're physically stressed (i.e., working in a cold climate or running marathons, not just worried) then taking it every day can be justified because it gives significantly more than a 10% benefit.