When researchers set out to see if our "cure" for the common cold really was a cure, their analysis of over 30 clinical trials conducted over a stretch of about 40 years uncovered some interesting results. Overall, investigators found no significant effect of supplemental vitamin C on preventing the common cold for most healthy people. I say most because the combined results of six studies detected a 50% reduction in risk of catching a cold for certain groups taking routine doses of 250-1000 mg/day of vitamin C -- marathon runners, young skiers, and soldiers working in freezing temperatures to be exact. So, for the general population, loading up on vitamin C throughout the year or when cold season hits apparently doesn't really fend off those colds, but if you're exposed to extreme physical stress or cold temperatures, it might actually be helpful.
As far as vitamin C's use as a cold remedy goes, the evidence is mixed. Thirty studies exhibited a slight reduction in the duration of colds for adults and children taking daily megadoses of vitamin C compared to those on placebo. What does this amount to? If the average cold lasts about 7 days, this means that a routine vitamin C supplement may lessen the duration of a cold by 1/2 a day for adults and 1 day for children. However, seven studies showed no difference between vitamin C megadoses and placebo for lessening the duration of a cold when supplementation started at the onset of symptoms. In an analysis of 15 studies, regular megadoses or those taken after the onset of symptoms did not significantly affect the severity of cold symptoms.
One important note to make is that vitamin C is a water-soluble vitamin, which means that little of it is stored in the body. A few studies suggest that the body's cells become saturated with daily doses of 200-400 mg and that digestive absorption decreases at doses >200 mg/day. Given some of the hefty doses in available supplements, often around 1000-2000 mg, do you wonder what happens to the excess if our body cannot store it? We eliminate it via the urine. And at intakes >2000 mg/d, one can potentially experience adverse effects, such as kidney stone formation, nausea, abdominal cramps, excessive gas, and diarrhea.
I know...you swear that you take (or have taken) vitamin C and it's truly helped prevent a cold, right? Well, there may be good reason -- placebo effect. In a surprising twist, investigators in one study found that individuals who took placebo but thought they were taking vitamin C recounted fewer colds than those who actually consumed vitamin C but believed they were receiving a placebo.
So, where does this leave us -- the real, live persons surrounded by this onslaught of sneezes and sniffles? If you don't mind sparing the expense and feel that saving yourself from 1/2 a day's worth of a cold (when you catch one) is worth it, then daily supplementation with up to 200 mg of vitamin C may be worthwhile to you. (The recommended intake is 75 mg/d for women, 90 mg/d for men, and an additional 35 mg/d for smokers.) Will you be harmed by taking doses of up to 2000 mg/d? It's unlikely as the risk of potential adverse effects at that level is low. However, one can easily obtain the recommended intake (and more) through food alone by aiming for at least 5 cups of vegetables and fruits daily. Let's see how this is done.
- Breakfast: 1 large orange = 91 mg
- Snack: 2 kiwis = 128 mg
- Lunch: 1/2 c cherry tomatoes = 9.5 mg, 1 c romaine lettuce = 11 mg
- Snack: 1/2 c red bell pepper = 95 mg
- Dinner: 1 large baked sweet potato = 35 mg, 1/2 c broccoli = 40 mg
- Total = 409.5 mg of Vitamin C from the equivalent of 5 c of vegetables and fruits!