Vitamin C
"Research has found no evidence that vitamin C prevents colds," says Dr Hasmukh Joshi, vice-chair of the Royal College of GPs.
In 2007, the authors of a review of 30 trials involving 11,000 people concluded that, “regular ingestion of vitamin C has no effect on common cold incidence in the ordinary population”. A daily dose of vitamin C did slightly reduce the length and severity of colds.
When it comes to flu, one person in three believes that taking vitamin C can cure the flu virus. It can’t.
"Studies found that vitamin C offers a very, very limited benefit," says Dr Joshi. "I wouldn't recommend it."
Echinacea
The root, seeds and other parts of echinacea plants are used in herbal remedies that many people believe protect them against colds. There have been a number of studies into echinacea’s effect, but no firm conclusions.
A review of trials involving echinacea showed that, compared with people who didn’t take echinacea, those who did were about 30% less likely to get a cold. However, the studies had varying results and used different preparations of echinacea. It’s not known how these compare with the echinacea in shops.
This review also showed that echinacea did not reduce the length of a cold when taken on its own.
"There is a belief that echinacea aids the immune system, but a survey of studies in 2005 showed that it did not," says Dr Joshi. "I wouldn't recommend that it helps, but if people believe it, they can take it. There's no harm in it."
Zinc
There is some evidence that taking zinc lozenges as soon as cold symptoms appear may reduce how long a cold lasts. However, some trials have found no difference in the duration of colds in people who took zinc compared with those who did not.
There has also been research into nasal sprays containing zinc. "Some people believe that the zinc lines the mucosa [the lining of the nose] and stops a cold virus attaching itself to the nose lining," says Dr Joshi. "Unfortunately, this has been found to be no more effective than a placebo."
Getting cold or wet
The only thing that can cause a cold or flu is a cold or flu virus. Getting cold and/or wet won’t give you a cold. However, if you are already carrying the virus in your nose, it might allow symptoms to develop.
A study at the Common Cold Centre in Cardiff found that people who chilled their feet in cold water for 20 minutes were twice as likely to develop a cold as those who didn't chill their feet.
The authors suggest that this is because some people carry cold viruses without having symptoms. Getting chilled causes blood vessels in the nose to constrict, affecting the defences in the nose and making it easier for the virus to replicate.
"Getting a cold from going out in the cold or after washing your hair is a myth," says Dr Joshi. "Colds are common. If the virus is already there and then you go out with wet hair and develop symptoms, it's common to think that is what caused it."
So what does work?
The flu vaccine can prevent you from catching flu. Apart from that, the best way to protect yourself from colds and flu is to have a healthy lifestyle.
"Eat a healthy diet, take regular exercise and drink plenty of warm drinks in the winter months," says Dr Joshi. "The important thing to remember is that most people are going to catch a cold in winter anyway, because there is no effective cure for cold viruses."
