Table 1.
The effect of drinking compared with not drinking on hydration indices and heart rate variability.
| Study 1 | Study 2 | |||
|---|---|---|---|---|
| No Water | Water | No Water | Water | |
| Weight lost before urination (%) | −0.40 (0.01)** | −0.01 (0.03)** | −0.32 (0.04)** | −0.08 (0.04** |
| Weight lost after urination (%) | −0.59 (0.03)** | −0.26 (0.05)** | −0.54 (0.05)* | −0.36 (0.05)* |
| ∆ Osmolality (mOsm/kg) | 219.77 (57.50)** | −190.00 (55.47)** | 116.88 (33.66)* | −9.03 (33.66)* |
| ∆ Temperature (°C) | 0.75 (0.11) | 0.50 (0.19) | 0.32 (0.07) | 0.32 (0.07) |
| ∆ Thirst (VAS) | 24.40 (4.64) | 12.30 (5.92) | 18.82 (6.62) | 5.96 (6.62) |
| ∆ R-R interval | 17.75 (19.47)* | 88.42 (31.90)* | 20.90 (27.44)** | 160.94 (27.44)** |
| ∆ SD of R-R interval | 12.59 (10.43)* | −12.80 (5.68)* | −5.34 (4.38)* | 8.77 (4.38)* |
| ∆ RMSSD | 3.87 (6.96)* | 13.38 (5.89)* | −0.67 (4.44)* | 13.21 (4.44)* |
Data are mean (s.e.) for change scores across each morning (end of the morning minus baseline) for study 1 and study 2. In both studies, compared to when they drunk, when participants did not drink they lost more weight both before and after urination and their osmolality increased. They had a significantly greater increase in HRV (RR interval, SDNN, RMSDD) when they drunk compared to when they did not drink. ∆ Change across the morning, *Water vs. No water significant at p < 0.05, **Water vs. No water significant at p < 0.001. RR, interbeat interval, SDNN, standard deviation of normal to normal R-R interval, RMSSD, root mean square of the standard deviation.