Treatment

The following are some food and fluid recommendations. Most will not cure a cold but may help a person deal better with the symptoms:

Drinking plenty of fluids and getting lots of rest when needed is still the best bit of advice to ease the discomforts of the common cold. Water is the best fluid and helps lubricate the mucous membranes. (There is no evidence that drinking milk will increase or worsen mucus, although milk is a food and should not serve as fluid replacement.)
Chicken soup does indeed help congestion and body aches. The hot steam from the soup may be its chief advantage, although laboratory studies have actually reported that ingredients in the soup may have anti-inflammatory effects. In fact, any hot beverage may have similar soothing effects from steam. Ginger tea, fruit juice, and hot tea with honey and lemon may all be helpful.
Spicy foods that contain hot peppers or horseradish may help clear sinuses.
Foods rich in vitamins A and C are always recommended and may be helpful during a respiratory infection. They include oranges, kiwi, and tomatoes for C and sweet potatoes, spinach, and broccoli for A.

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Vitamins

Different studies have found that large doses of vitamin C reduce the duration of a cold by a range of 5 - 50%. Some precautions against taking high doses of vitamin C include the following:

High doses of vitamin C may cause headaches and intestinal and urinary problems and even kidney stones.
Because ascorbic acid increases iron absorption, people with certain blood disorders, such as hemochromatosis, thalassemia, or sideroblastic anemia, should particularly avoid high doses.
Large doses can also interfere with anticoagulant medications, blood tests used in diabetes, and stool tests.
Vitamin E or multivitamin supplements do not appear to be helpful in reducing symptoms of the cold.

Zinc

Zinc appears to have certain important effects on the immune system and it may have a direct effect on viruses. How it works is not entirely clear, however. Zinc preparations in lozenge or nasal gel form are now available as cold treatments. Studies are very mixed on the effects of zinc on colds. The variance may be due to different zinc preparations. Studies are underway to determine advantages, if any. Some examples include the following:

A nasal gel (Zicam), which contains zinc gluconate, has shown some success, possibly because the gel sticks to the nasal passages long enough for the zinc to interact with the virus. In a 2003 study, for example, the nasal gel shortened the duration and severity of the cold compared to placebo when it was started within 14 to 48 hours of the onset of symptoms. The supports earlier studies reporting that it shortened the duration of a cold by about two days.
Zinc lozenges are showing mixed results. One 2000 study suggested that the use of zinc acetate lozenges (e.g., Fast-Dry, Galzin) may be more effective and have a better taste than other formulations, such as zinc gluconate (Cold-Eeze, Orazinc). On the other hand, a 2002 study reported that zinc gluconate reduced cold duration significantly. To further confuse matters, the two zinc lozenge preparations were directly compared in a 2000 study, and neither was effective. The reasons for these conflicting results are not clear.
A small 2001 study on a nasal spray preparation found no benefits. The spray preparation had less zinc than the nasal gel.