Cold Weather Acclimation
Date: May 2007
It is said that you won't be comfortable in cold weather
until your blood thickens up. What does this mean? Is this true?
Sounds like "an old farmer's tale" to me.
First, let me start with my credentials:
I was born in Michigan, and have lived in Chicago, Dallas, and San
Francisco. I'm not a doctor though.
Very literally, the blood does not "thicken" in cold weather. This is just
an expression. The balance of water and electrolytes and cells in the blood
is very precise, and large changes would not be good. However, that does not
mean there are no changes. To keep warm, your body does have to pump more
blood. More blood in the same arteries means higher blood pressure. There
are reports also that the arteries constrict in cold weather as well. Blood
pressure is generally higher in cold weather for this reason.
More broadly, in the very short term (hours), people do change how they act
in cold (or any) weather. We dress differently, we eat different foods, etc.
These changes can have real effects on your comfort level, and can affect
your blood (pressure and composition). People's response to weather is
certainly partially state-of-mind too, and stress can certainly affect blood
In the very long term (thousands of years), we have also changed.
Populations from different regions of the planet exhibit clear differences
in skin color -- as well as other physiological differences. A lot of the
differences have to do with Vitamin E production and heat. Colder climate
peoples tend to have lighter skin (to enhance vitamin E production in
lower-sunlight climates) and more body hair (insulation). Warmer climate
peoples tend to have darker skin (protect against sunburn / UV damage due to
more sun) and less hair. There may be overall differences in the blood
between warm- and cold- acclimated peoples, although I would guess they are
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Update: June 2012