Objective: Drinking ice water is a common daily activity. The safety of ice water ingestion has been questioned due to its possible deleterious effect on heart rate or cardiac rhythm, especially in patients with acute myocardial infarction. Thus, we investigated the heart rate variability (HRV) before and after ice water ingestion in normal subjects to delineate the possible effect of ice water ingestion on autonomic nervous modulation.
Methods: Subjects were volunteers who came to the hospital to receive routine health examination. They were randomly assigned to drinking 250 ml of ice water or room temperature water. Twenty-eight subjects in the room temperature water ingestion group and 25 subjects in the ice water ingestion group were studied. The relationships between the change in HRV measures before and after water ingestion and clinical parameters were assessed by correlation analysis.
Results: After ice water ingestion, the percentage change in mean RR intervals (RRIs) (4 ± 4 vs. -1 ± 4, P < 0.001), standard deviation of RRIs (19 ± 35 vs. 0 ± 21, P = 0.018), high-frequency power (64 ± 90 vs. -3 ± 41, P < 0.001), and normalized high-frequency power (39 ± 99 vs. -5 ± 31, P = 0.038) were higher, while the percentage change in low-/high-frequency power ratio (3 ± 92 vs. 44 ± 97, P = 0.017) was lower, when compared with those after the room temperature water ingestion.
Interpretation: Ice water ingestion can decrease heart rate through temperature stimulus-mediated vagal enhancement in healthy subjects.