transcript: Winter is coming - and we've all been told
to 'put a jacket on outside, or you'll catch a cold!' Of course, the common response of
today has become 'Don't be silly, being cold can't give you a cold!'. Or can it? Who wins
in this battle of beliefs? The correlation between cold weather and sickness
does stand out. Between 5-20% of Americans catch a cold or flu every year around late
fall and winter. Not to mention, it's called a cold. But there are some important things
to consider. First and foremost: colds and the flu are caused by viruses. If there aren't
any around, you won't catch a cold - no matter how cold you get. It's as simple as that. So why the correlation with decreasing temperatures?
Well for one, people tend to stay indoors much more often during the winter, which in
turn, puts them in contact with more people. More people, means more exposure opportunities
for the pathogens to spread. On top of this, humidity plays a role in the spread of some
viruses. As the humidity decreases in the winter, not only does the virus spread more
readily, but the mucus in your nose dries out. Mucus which would otherwise act as a
protective barrier to pathogens. Finally, the lack of Vitamin D which we get from the
sun, can affect our immune systems adversely. Both being inside more often, and the fact
that winter has shorter days makes this a big factor for your health. So you've proven your parents wrong...right?
Not so fast! While some past studies have shown no correlation
to temperature, recent evidence suggests otherwise. One study which put test subjects feet into
ice water found that they were, indeed, more likely to develop common cold symptoms in
the following days, than those who didn't. The developing hypothesis behind these results
is that cold temperatures cause blood vessel constriction, which slows the white blood
cells from reaching the virus, ultimately inhibiting the immune response. Cortisol levels,
which suppress the immune system, are also increased with temperature induced stress.
Furthermore, studies on both mice and human airway cells found that immune reaction to
the common cold virus, is in fact, temperature dependent. Warm infected cells are more likely
to undergo programmed cell death, to limit the spread of infection. Finally, studies of the virus itself have
revealed a secret weapon of sorts. In winter temperatures, the virus's outer layer or envelope
becomes much harder and acts like a shield. This allows it to spread from person to person
much more easily. But at warm temperatures, this layer is more of a gel, which is not
quite tough enough to protect the virus against the elements. As a result, it's spreading
ability is compromised. So, maybe you're parents weren't so wrong
after all. A happy compromise of going outside more often, bundled up, is likely to get you
through the winter unscathed. New to AsapSCIENCE? We've put together a couple
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