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Name: Melissa
Status: educator
Grade: other
Location: OH
Date: May 2007

Question:
It is said that you won't be comfortable in cold weather until your blood thickens up. What does this mean? Is this true?



Replies:
Sounds like "an old farmer's tale" to me.

J. Elliott


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 pressure.

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 comparatively minor.

Burr



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