Many people take vitamin C assuming that it is healthy, without knowing the correct dosage amount. The dosage levels vary for different people, depending on some one's age, gender and habits from day to day. According to the American Dietetics Association, Institute of Medicine and the Food and Nutrition Board, the Dietary Reference Intake (DRI) of Vitamin C is 90mg for an adult male, and 75mg for an adult female. If you are a smoker, you must add 35mg to this DRI. The reasoning for this is that smoking fills your body with what is known as "free radicals". These work in the body by destroying any cells they hit, and sometimes alter the DNA within the cell (hence cancer-causing free radicals). Vitamin C works as an antioxidant, which helps in the elimination of these free radicals. There are studies being conducted on using vitamin C to treat cancer, but there is no evidence yet.
Vitamin C has a very low toxicity level, which allows it to be taken in mega-doses (anything excessive, such as 1000-2000mg/dose). This can cause gastrointestinal symptoms in some people, which happens when your body does not absorb the high levels properly. Some studies even suggest that 1000mg or more may produce kidney stones, but there are conflicting finding on this matter. Some studies have shown that taking mega-doses for long periods of time cause a vitamin C resistance in the body, actually leading to a deficiency.
So how much is too much? As a rule, you want to do what your body is programmed for. If you are eating a diet rich in fruits and vegetables, then you will get the amount of Vitamin C you need. Taking supplements (such as Emergen-C) should be used when you have a cold, but not on a daily bases. Some people take mega doses due to the antihistamine affects on allergies, but this should be done under a doctor's supervision only.
Oranges are Highest in Vitamin C, Right?
Wrong! Oranges seem to be very accessible to many people, especially fortified juices. However, the highest fruit is actually the guava, followed by the red pepper, then kiwi, then oranges. Vitamin C is not stored in the human body, so we must take it in every day through our diets. It is also water-soluble, which means that you need enough water to effectively use the vitamin, and that it is not stored in the body. Also, too much may leave the body through urine, which is not very cost-effective in supplement taking.
Vitamin C is Used to Treat Colds
Actually, vitamin C is necessary in the body to do many different things. It helps the body form collagen in bones, cartilage, muscle, and blood vessels. It also is required for your body to absorb iron properly. Back when swash-buckling pirates roamed the seas, a common problem was scurvy, which causes gum disease, hemorrhages, weakness and other symptoms. Eventually it was realized that this was caused by a simple vitamin C deficiency. After this, sea-faring men and women started taking citrus fruits along with them on their voyages.
As for colds, studies have shown no benefits for prevention of getting one (unless you are a military personnel or an extreme athlete, or basically work out constantly). There is a small amount of evidence that supports vitamin C shortening the duration of a cold. The studies conducted so far also show that vitamin C has no effect on how severe a cold symptom may be.
There has also been some evidence that vitamin C increases side effects from Tylenol, Aspirin (and Aspirin decreases your vitamin C level), Warfarin and any medicine that effects the kidneys. You should always consult your doctor when taking any medication and vitamin or herbal supplement.