
Originally Posted by
Splifton
It has to due with your body's physiological response to cold. Majority of blood reverts inward towards the core region due to our programmed survival adaptations telling us to maintain thermogenic activity in our vital organs. This leads to a dysfunction in how our renin-angiotensin-aldosterone system maintains fluid homeostasis due to an irregularity with the secretion of a key regulator, our neuropeptide arginine-vasopressin. (antidiuretic properties.) Generally you actually are becoming dehydrated, but the brain isn't receiving the sufficient neurotransmission to validate increasing plasma concentration. The reasoning behind this if I remember correctly... is when dehydration occurs our blood volume decreases along with an increase in sodium concentration. This is the two markers telling our hypothalamus to secrete the hormone. In the case of cold, our body can't correctly validate the blood volume and incorrectly believes the volume is correct. (vasoconstriction imitates a higher blood volume) The kidney's never get the signal to retain water and the brain never receives information to produce a thirst sensation. I'd be cautious about drinking a lot of warm water because it's been advised before for relieving chronic constipation. I'm sure it's laxative properties are pretty miniscule. I'm sure the hot water claim with increased bowel movements was a pretty subjective statement.