“Don’t go outside without a jacket, you’ll catch a cold”, you probably heard your grandmother or mother say this to you a few times as a kid during cold season. The common cold that most of us seem to inevitably catch in the winter is caused by a variety of different viruses. The most common virus is the rhinovirus but the common cold can also be caused by up to 200 different viruses. The sheer number of viruses that can cause the common cold as well as the different subtypes or flavours of each virus is what makes designing a vaccine for the common cold next to impossible. Rhinovirus itself has over 99 subtypes. While there is no evidence that going out in the cold weather will actually give you a cold, new research suggests grandma may have been onto something.
The research, published in PNAS, found that cold temperatures can make it easier for the virus to infect cells by dampening your body’s immune response to the virus. The researchers took cells from the airways of mice and cooled them down to 33oC (about the temperature inside your nose) and tried to infect them with rhinovirus. The cells that were cooled down were less able to fight off the virus when compared to cells that were at the normal body temperature (37oC) because they had their normal immune response disrupted.
When cells in your body are infected with a virus they send out a variety of signals that alert your immune system and the surrounding cells to the invasion. These signals act to attract your immune cells (white blood cells) to the site of infection and to also help prevent the spread of the virus to other cells in your body. When the white blood cells arrive they start to destroy the virus and the infected cells. A side effect of this fight and the signals associated with it are the development of symptoms that we commonly associate with getting a cold. These include coughing, lots of mucus, runny nose and sore throat. While the symptoms are annoying, they are a sign that your body is trying to fight the invader.
So what does this research mean in the context of catching or preventing colds? Most research on cold exposure and your body’s immune system show that cold temperatures may actually activate your immune system, just slightly. This research seems to go against previous research. The disagreement between results may come down to what cells were looked at in each study. In past research, the white blood cells were the centre of attention and they were in fact more active in cold weather. In the recent research, the cells lining the airways or your nose (epithelium) were looked at; these cells are the first ones the virus comes in contact with when you breathe it in and are responsible for alerting the immune system to the viruses presence. What it seems to indicate is that the cold interferes with the danger signal but not the immune systems response. Think of it this way, a poor cell phone connection will make it harder to call 911 in an emergency but will not likely affect how the police respond when they get the call. The activation of your immune system by the cold may help counteract the dampening of the danger signal, but this needs to be confirmed by experiments.
The research was done in mice so it would be nice for it to be confirmed in human cells before we jump to any conclusion about the research. It would also be interesting to know how temperatures even colder than 33 degrees would affect the results. Your elders were on the right track though, just had the wrong explanation. Cold weather won’t make you sick, on the contrary it may help you fight off the infection, but it will limit the ability of your body to send out danger signals when it is infected. So bundle up because being warm is better than being cold and sick.