Woman suffering from influenza


As a general rule, adults with a cold will be able to infect others one day before symptoms appear, and up to five days or so after becoming sick. Infants and children are able to transmit these viral infections for seven days or longer. The precise number of days for transmission can vary from person to person. Those in poor health tend to get infected more easily. Children are also more likely to catch (and transmit) colds.

Cold viruses, abundant in nasal and throat secretions, are mainly transmitted via hands. When you blow your nose, touch your face, or wipe your eyes, the virus transfers to your hands, and then to whatever or whomever you touch. If you contaminate a telephone, the next person who uses it may catch your cold. To avoid spreading or catching a cold, the most important precaution is to wash your hands often and well. Hand sanitizers are a good option when you’re not near a sink.

Coughing and sneezing can also spread the virus, of course. If you don’t have a tissue, instead of sneezing or coughing into your hand, do it into your arm or shoulder, thus avoiding contaminating your hand.

If you think you are getting sick, limit your contacts. Don’t hug and kiss. If you’re around someone who is sick, stay at least six feet away—cold viruses can’t be propelled much farther than that before falling to the ground. Don’t share drinking glasses, utensils, phones, or towels.

Flu viruses may not travel in exactly the same way as cold viruses, but your best bet is to take these same precautions to avoid transmitting or catching the flu.

A cure for the common cold has been a holy grail for medical researchers and drug companies. So far, however, nothing has worked. No wonder, then, that people are tempted by the cold-fighting and/or immunity-boosting claims made for many dietary supplements. But do any stand up to scientific scrutiny? Here’s our take on popular products—from Airborne to zinc.

The best-known supplement that throws the kitchen sink at colds, Airborne contains vitamins (A, C, E), minerals (zinc, selenium, magnesium) and echinacea, ginger and other herbs. Back in 2008 the Federal Trade Commission accused the company of making unproven claims about curing and preventing colds and flu; it had to pay a $30 million settlement. Now the ads and packages just say Airborne “supports” the immune system. Some ingredients in Airborne have been tested, with inconsistent results. No clinical trials testing the specific formulas have been published. Airborne and similar formulas are a waste of money.

Despite a common belief that garlic can prevent colds, there has been remarkably little research on humans to see if it actually does. For instance, a study in Clinical Nutrition found that an aged garlic extract taken for three months did not reduce the incidence of colds or flu, but did reduce their severity somewhat when they did occur. But the bottom line is that garlic is no more likely to keep away colds than to repel vampires, unless you eat it raw and the smell makes cold sufferers stay away from you.

Vitamin C gained popularity back in the 1970s when Linus Pauling claimed it could prevent and alleviate colds. However, numerous studies since then have failed to confirm any benefit. According to a Cochrane Collaboration review, vitamin C supplements do not prevent colds, except perhaps in people exposed to severe physical stress, such as marathon runners and skiers. And research on the vitamin’s potential role in reducing the severity and/or duration of cold symptoms when taken at their onset has yielded mixed results. The tide has turned against vitamin C. If there were a significant benefit, it wouldn’t be so hard to prove.

This mineral is also essential for immunity. In lab studies, large amounts of zinc can block cold viruses from adhering to the nasal lining and/or replicating themselves. A Cochrane Collaboration review concluded that, compared to a placebo, zinc lozenges can shorten colds by a day and reduce their severity, particularly if started the first day of symptoms. Another research review came to similar conclusions. But there is no good research showing zinc prevents colds. Due to possible side effects (nausea, diarrhea, cramps), the Cochrane report said zinc lozenges, taken the first day of symptoms, are “advised with caution.”

There’s no convincing evidence that any supplement can prevent or treat colds. “Cold remedies,” including many over-the-counter drugs, may well make you feel better, since they have a strong placebo effect. That is, if you expect or hope that a remedy is going to help, there’s a fair chance it will, whether it contains vitamins, herbs or just plain old sugar. And, of course, remedies may seem to work because colds go away on their own. Though we don’t recommend them, it probably can’t hurt to take such products when you feel a cold coming on, but taking them throughout cold season, as is sometimes recommended, increases the risk of adverse effects.

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