My mother always tells me to bundle up before I go outside during the winter, because otherwise I’ll “catch a cold.” When I first learned about the germ theory of disease, I thought she was wrong. Cold doesn’t make you sick, I thought. Germs make you sick.
Recently, it’s become obvious that I was wrong and she was right. Germs are responsible for disease, but it’s crucial to remember that germs are everywhere. Our immune systems are constantly fighting these microscopic invaders. In fact, we’re probably infected with the common cold to some extent even when we don’t show any symptoms.
During the flu season of 2005, an experiment was performed to test the idea that being cold can make you sick. 90 people kept their feet in a bowl of ice water for 20 minutes, while a control group of 90 people put their feet in an empty bowl for 20 minutes. Over the next 5 days, 29% of the group with chilled feet developed cold symptoms, compared to only 9% of the control group.
Professor Eccles explained this effect by saying that our bodies restrict blood flow to the extremities when we get cold to help conserve body heat for the torso and brain, which really need to be warm. Cutting off the blood flow reduces the supply of white blood cells which are the immune system’s primary weapon against germs.
While his explanation makes sense, there may be a more general effect at work. The human body is a machine that accepts fuel in the form of food, and uses that fuel’s energy to keep us warm and to power our immune systems, muscles and brains. However, in frigid conditions our bodies have probably evolved to say “who cares if I might get sick tomorrow when I might die of hypothermia in an hour?”
In other words, the optimal survival strategy during bitterly cold conditions is probably to divert energy normally used by the immune system into keeping our bodies warm. Mammals whose bodies didn’t make this sacrifice weren’t as susceptible to disease in the long run, but that didn’t matter because they dropped dead of hypothermia before they could enjoy their good health. So that survival strategy would be eliminated by natural selection.
Anyway, the point is I was wrong, and my mother was right. Sorry, Mom!Last modified October 2nd, 2013