Drinking water does not raise blood pressure in healthy......

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I've seen individuals contend that drinking water can induce "dangerous" increases in blood pressure.

Not on this planet, it would appear. However, in individuals with autonomic dysfunction, apparently there can be certain untoward changes in hemodynamics associated with fluid ingestion.

Interestingly, they did find that "pure water" tended to increase "total peripheral resistance". There are some that are presently passionately arguing that this variable is an important indication of how "tightly constricted" the arteries, and thus reflect "arterial stiffness". I personally believe that the myriad of influences upon this variable make it less than useful, although chronic, unremittng states of arterial "stiffness" are probably deleterious.

For instance, a "ridiculous" extension of considering total peripheral resistance to be "bad" would be that drinking water is worse for you than drinking saline solution, as such solutions have no increase in total peripheral resistance associated with them! I cannot accept that line of reasoning yet, although "show me the data" and I might change my mind.

However, what is interesting, is the possibility that the "hypo-osmolality" that intake of hypotonic fluids induce may "intensify" fasting states.

The dangerous thing about taking in too much "water" is that you may go hyponatremic, a risk which is particularly pronounced in athletes prone to sodium depletion stemming from unbridled sweating during physical exertion. In this context, "saline solutions" would definitely have their benefits.

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Am J Physiol Regul Integr Comp Physiol. 2005 Jul 21; [Epub ahead of print]

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Cardiovascular responses to water drinking - does osmolality play a role?Brown CM, Barberini L, Dulloo AG, Montani JP.Department of Medicine, Division of Physiology, University of Fribourg, Fribourg, Switzerland.Water drinking activates the autonomic nervous system and induces acute hemodynamic changes. The actual stimulus for these effects is

undetermined but might be related to either gastric distension or to osmotic factors. In the present study we tested whether the cardiovascular responses to water drinking are related to its relative hypo-osmolality. We therefore compared the cardiovascular effects of a water drink (7.5 ml/kg body weight) with an identical volume of a physiological (0.9%) saline solution in 9 healthy subjects (6 male, 3 female, aged 26+/-2 years), while continuously monitoring beat-to-beat blood pressure (finger plethysmography), cardiac intervals (electrocardiography) and cardiac output (thoracic impedance). Total peripheral resistance was calculated as mean blood pressure/cardiac output. Cardiac interval variability (high frequency power) was assessed by spectral analysis as an index of cardiac vagal tone. Baroreceptor sensitivity was evaluated using the sequence technique. Drinking water, but not saline, decreased heart rate

(P=0.01) and increased total peripheral resistance (P<0.01), high-frequency cardiac interval variability (P=0.03) and baroreceptor sensitivity (P=0.01). Neither water nor saline substantially increased blood pressure. These responses suggest that water drinking simultaneously increases sympathetic vasoconstrictor activity and cardiac vagal tone. That these effects were absent after drinking physiological saline indicates that the cardiovascular responses to water drinking are influenced by its hypo-osmotic properties.PMID: 16037127 [PubMed - as supplied by publisher]

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