Re: Can being cold increase your chance of getting sick?

	It's getting to be the time of year for coats again, isn't it?   It's 
true that bundling up prevents heat loss.  According to one source, 55% of 
heat is lost through radiation, most of which can prevented by the simple 
act of wearing a hat!

	There are several common cold related injuries and illnesses that occur 
upon exposure to cold.  To understand those, first understand what happens 
when you go out on a cold day (below freezing) with only a light jacket and 
pants on, i.e. underdressed.  Temperature receptors on your skin send a 
message to your brain and nervous system that cause two things to happen.  
Your brain sends signals that tell you to seek warmth and shelter.  The 
nervous system instructs the blood vessels in the periphery of the body to 
constrict; this vasoconstriction prevents further heat loss by keeping the 
blood away from cold areas of your skin.  It also helps conserve heat for 
the core, or inner organs.  Also, you will begin to shiver; shivering 
occurs when your muscles contract to create energy in the form of heat.  
Metabolism also increases as your body uses more calories to stay warm.  
There are varying degrees of this response to cold that the body employs 
depending on factors such as actual temperature, wind chill, and length of 
exposure.  
	The colder your body gets the more stressed it becomes.  The dropping 
of body core  temperature and the associated physiological changes are 
referred to as hypothermia.  Hypothermia ranges from mild to severe.  
Severe hypothermia can cause death from cardiac problems.  If the rewarming 
process for severe hypothermia is not done correctly, the heart can become 
arrhythmic, and the skin can be damaged if rubbed when still too cold.

	You mentioned frostbite as a lasting effect.  It occurs when the deep 
skin layers become so cold that ice crystals actually form in the tissues, 
a damaging event.  Severe frostbite leads to destruction and loss of the 
tissue because even if the tissue is rewarmed it cannot perform its 
function.
	
	Now let's consider less obvious effects of being cold.  When your body 
goes into heat conservation mode and begins to get stressed, it turns off 
non-essential processes to conserve energy.  The immune system is one of 
the first to get curtailed.  Consider this, a recent study showed that mild 
hypothermia induced by anaesthesia can lead to suppression of the immune 
system.  Doctors noticed that mild hypothermia during surgery (a common 
condition that occurs when a patient is anaesthetized) slowed the rate of 
wound healing, increased the incidence of bacterial infections, and 
accelerated protein breakdown and the loss of nitrogen in the urine.  The 
research found that the effect of some immune cells is suppressed for up to 
24 hours after mild hypothermia!
	Walking out of the house without a scarf on does not guarantee you will 
come down with a cold.  The increase of colds, which are caused by viruses, 
during the winter months is better attributed to a change in indoor 
habitats.  People stay inside much more often and buildings are insulated 
against the outside.  This means that there are more people coming in close 
contact with each other (and thus spreading germs) and that there is less 
air movement and changeover to clear the germs. However, you can imagine 
that if you were cold, or  recovering from being cold, your immune system 
may not be completely ready to defend against germs you encounter.
	
	Finally, did you know that the number of deaths due to heart attacks 
increase each winter?   Shoveling snow in the cold is much different than 
exercising in warm temperatures.  One study found that up to six hours 
after being cold, blood viscosity remained 21% thicker which can lead to 
circulation problems.
 
	In summary, there are lasting effects, only some of which have been 
covered here.  My recommendation is to listen to those voices:  your mother 
who tells you to keep warm and your brain that tells you when it's time to 
head inside!
-Tinsley

Want more info on hypothermia?  Princeton's outdoor program maintains a 
page with extensive information http://www.princeton.edu/~oa/safety/
hypocold.html

Here are the references I used:
"Effects of temperature and snowfall on mortality in Pennsylvania" Gorjanc, 
et al.  1999. American journal of Epidemiology.  149:1152-60.

Cold injuries: Protecting your patients from the dangers of hypothermia and 
frostbite. 1999. Kanzenbach and Dexter.  Postgraduate Medicine.  105:72-8.

"Effects of mild perioperative hypothermia on cellular immune responses. 
1998. Beilin et al.  Anesthesiology.  89:1133-40.