title: Cardiovascular and metabolic responses to tap water ingestion in young humans: does the water temperature matter?
abstract: OBJECTIVE
  Drinking water induces short-term cardiovascular and metabolic changes. These effects are considered to be triggered by gastric distension and osmotic factors, but little is known about the influence of water temperature.
  
  
  METHODS
  We determined, in a randomized crossover study, the acute cardiovascular and metabolic responses to 500 mL of tap water at 3 °C (cold), 22 °C (room) and 37 °C (body) in 12 young humans to ascertain an effect of water temperature. We measured continuous beat-to-beat haemodynamics, skin blood flux with laser-Doppler flowmetry and resting energy expenditure by indirect calorimetry starting with a 30-min baseline followed by a 4-min drink period and a subsequent 90-min post-drink observation.
  
  
  RESULTS
  Ingestion of cold- and room-tempered water led to decreased heart rate (P < 0.01) and double product (P < 0.01), and increased stroke volume (P < 0.05); these effects were not observed with body-tempered water. Drinking cold- and room-, but not body-tempered water, led to increased high frequency power of heart rate variability (P < 0.05) and baroreflex sensitivity (P < 0.05). Cold- and room-tempered water increased energy expenditure over 90 min by 2.9% (P < 0.05) and 2.3% (ns), respectively, accompanied by a diminished skin blood flux (P < 0.01), thereby suggesting that both small increases in heat production together with decreased heat loss contribute to warming up the ingested water to intra-abdominal temperature levels.
  
  
  CONCLUSIONS
  Overall, ingestion of cold- and room-, but not body-tempered water reduced the workload to the heart through a reduction in heart rate and double product which could be mediated by an augmented cardiac vagal tone.
authors.affiliation: Department of Medicine, Division of Physiology, Laboratory of Integrative Cardiovascular and Metabolic Physiology, University of Fribourg, Fribourg, Switzerland.
authors.forename: M
authors.initials: M
authors.lastname: Girona
authors.forename: E K
authors.initials: EK
authors.lastname: Grasser
authors.forename: A G
authors.initials: AG
authors.lastname: Dulloo
authors.forename: J P
authors.initials: JP
authors.lastname: Montani
mesh_terms: D000328:Adult; D017704:Baroreflex / Q000502:physiology; D002319:Cardiovascular System; D018592:Cross-Over Studies; D004326:Drinking / Q000502:physiology*; D005260:Female; D006339:Heart Rate / Q000502:physiology; D006439:Hemodynamics / Q000502:physiology*; D006801:Humans; D008297:Male; D013696:Temperature; D014867:Water; D055815:Young Adult
chemical_list: D014867:Water
keywords: baroreflex; haemodynamics; vagal; variability