You have probably heard the old wives tale- take your Vitamin C to stave away a cold. Though not all old wives tales are true, this one actually does have a lot of basis in reality.
Though Vitamin C can stop the severity and duration of a cold in its tracks, it will not stop the frequency. In other words, take it daily and add a little extra when you are sick to stop your cold from becoming worse than it would without the extra.
Also known as ascorbic acid, Vitamin C is found naturally in many fruits and vegetables. Though oranges seem to be the most recognizable, there is actually more Vitamin C found in vegetables such as broccoli. Rose hips are another good source of the nutrient.
This nutrient is only stored in the blood for so long therefore some people advocate taking mega-dosages well beyond the recommended 400mg per day (as recommended by the NIH or National Health Institute). The problem with this is that a mega-dose at some point can have an adverse affect on your health, such as causing diarrhea or other bowel problems.
Diarrhea means that your food goes through your body too quickly, therefore not allowing nutrients to absorb. It can also cause dehydration.
It is recommended to get the 400mg per day and some extra during pregnancy and illness. Anything else is just extra and won't help you enjoy the other benefits. Those benefits include better vision, reduced risk of some cancers and cataracts and may even be useful in preventing autism in children. And don't forget the great effects on that nasty head or chest cold that everyone gets at some point or another.