Credit Oscar Gronner
I’ve become somewhat known for medical myth-busting (having been a co-author of three books on the subject), so a fairly large number of emails sent to me are from people with articles or studies that they think prove me wrong.
This week, as a few of us sniffle with summer colds, the emails are all about a new study that they think proves that cold weather makes you more likely to catch a cold.
I’m sorry to say that this continues to be a myth. Research doesn’t support it.
This latest study, published in the Proceedings of the National Academy of Sciences, is complicated research of cells in laboratory conditions. The researchers showed that cells kept at 37 degrees Celsius were more likely to undergo apoptosis (basically, cell suicide) than cells kept at 33 degrees Celsius. Apoptosis is a way that we protect ourselves from infection. If the infected cells kill themselves, then there’s fewer chances for replication of the viruses that infect them.
This study has led a number of news sources, and many people who email me, to argue that this is more evidence that you’re more likely to get sick in cold weather. If your immune system can’t function as well when it’s cold, then infections must take advantage of cold weather, right?
That’s just not as clear as it looks. First of all, 33 degrees Celsius is not cold weather. It’s 91.4 degrees Fahrenheit. And 37 degrees Celsius is 98.6 degrees Fahrenheit. In other words, 37 degrees Celsius is close to a body’s core temperature, and 33 degrees is closer to what it might be in your nostrils. I have no trouble believing that some viruses, like cold viruses, do better in your nose than deep in your body because that’s where they first attack, and also where they often set up shop.
This isn’t the first time this lab produced work that has been interpreted this way. About a year and a half ago, it published another study, this one in mice cells, that showed that rhinovirus replicates better at 33 degrees Celsius than at 37 degrees. Again, I have no trouble believing that — but it doesn’t prove that cold weather makes you more likely to get a cold. Nonetheless, many interpreted it that way.
There are better ways to try proving that. Those studies have actually been done.
Back in 1958, researchers conducted a randomized controlled trial of people to see if being cold made them more likely to get sick. They had one group sit in a room that was 10 degrees Fahrenheit dressed in street clothes, overcoats, hats and gloves. They had another group sit in their underwear in a room that was 60 degrees Fahrenheit. A third group sat in 80 degrees Fahrenheit, also in their underwear. All of them were “inoculated” with the mucus of a sick person in their noses and then followed to see if they became ill.
Don’t ask me who volunteers for such things. But thanks to them, we know that the temperature didn’t seem to have any effect on their chances of getting sick.
In 1968, another study was published in The New England Journal of Medicine. This one gathered volunteers from federal or state penitentiaries in Texas and subjected them to a variety of conditions, with temperatures ranging from 4 to 10 degrees Celsius. They even submerged them in water baths at 32 degrees Celsius. As in previous studies, they inoculated the subjects with rhinovirus and then followed them clinically and with many cellular and antibody studies.
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They found no differences in how people became infected, how they reacted if they were infected, and how they recovered based on exposure to cold.
People’s feelings about colds, like a lot of medical myths, become entrenched. It seems that no matter how hard you push back on them, they refuse to change their minds. It doesn’t matter that some research shows that being exposed to the cold actually stimulates the immune system rather than impairing it.
It may also be, as a 2005 study in The Journal of Family Practice showed, that people who are exposed to cold are more likely to report symptoms, even if they aren’t actually infected more often. Perception, and even potentially a belief in this explanation, may contribute to its longevity.
Viruses are also seasonal. Some are more likely to get you in the winter than the summer. Additionally, our response to cold weather may be more to blame than the cold weather itself. It has been postulated that when it’s cold, people tend to congregate inside. This behavior makes it easier, of course, for viruses to be spread from person to person. My kids are much more likely to sneeze on me when we’re cooped up in the winter than when they’re running around outside in the summer.
To be fair, you can point to papers that seem to disagree with me. A review article published in The International Journal of Tuberculosis and Lung Disease in 2007 argues that exposure to cold can result in responses in the body that could leave one more susceptible to infection. I’d argue, however, that the focus of this paper was more on extended exposure to extreme cold (think potential hypothermia) than on the usual “cold weather leads to colds” argument.
These recent studies are also of cells, not all of them human, in the lab, under controlled conditions. We can’t make an easy leap to how bodies, let alone people, might be similar or different in real-world situations.
None of this is to fault the science or the methods of these experiments. The studies from this research group do seem to confirm findings that various viruses seem to thrive in the relatively warm temperatures of the nose rather than the slightly hotter temperatures found deeper in our bodies. They provide an explanation for why viruses affect some parts of the body more than others.
That’s not, however, the same thing as proving that cold weather makes you more likely to get a cold.
Aaron E. Carroll is a professor of pediatrics at Indiana University School of Medicine who blogs on health research and policy at The Incidental Economist and makes videos at Healthcare Triage. Follow him on Twitter at @aaronecarroll.