Edwards Tory, Buono Michael J
School of Exercise and Nutritional Sciences, San Diego State University, San Diego, CA, United States.
Curr Res Physiol. 2022 Jun 24;5:251-255. doi: 10.1016/j.crphys.2022.06.007. eCollection 2022.
To investigate how rapid changes in hydration affect urine color expressed in CIE Lab* colorspace.
This study was a two-day crossover design where subjects (N = 30) came in one visit dehydrated, after a 15 h overnight fluid deprivation, and rapidly rehydrated by drinking at least 1000 mL of water in 2 h. On the other visit subjects reported euhydrated and then rapidly dehydrated 2% by walking (3 mph) in a heat chamber (100°F, 50% humidity) for 2 h. Urine samples on both days were collected pre- and post-dehydration/rehydration. Urine osmolality, urine specific gravity, subjective urine color and objective urine color expressed in CIE Lab* colorspace were measured.
In the dehydration trial participants experienced a significant weight loss of approximately 2% of their starting, euhydrated body weight. The CIE urine color L*-value significantly decreased (-2.3 units) while the b*-value significantly increased (16 units). Subjective urine color significantly increased (1 unit). Urine osmolality increased (25 mmol/kg) and urine specific gravity increased (0.002 g/mL) between the pre- and post-dehydration conditions, however, neither of these changes were statistically significant. In the rehydration trial participants had a significant 1.5% increase in body weight after the ingestion of water. Significant increases were observed in the CIE urine color L*-value (7 units) and a*-value (1.1 units), while the b*-value significantly decreased (-24 units). Subjective urine color significantly decreased (-3 units). Urine osmolality (-600 mmol/kg) and urine specific gravity (-0.018 g/mL) significantly decreased between the pre- and post-rehydration conditions.
Traditional markers of hydration, including urine osmolality and urine specific gravity, did not significantly change in the acute dehydration trial, suggesting that these values may not be responsive to rapid changes in hydration status. However, the CIE L*- and b*-values of urine color significantly decreased in the rapid dehydration trial and significantly increased in the rapid rehydration trial. Thus, the results of the current study suggest that urine color L*- and b*-values expressed in the CIE Lab* colorspace were more responsive to changes in hydration status during rapid dehydration than traditional indices of urine concentration and thus may be better markers under such conditions.
研究水合状态的快速变化如何影响在CIE Lab*颜色空间中表示的尿液颜色。
本研究采用为期两天的交叉设计，受试者（N = 30）在一次就诊时处于脱水状态，经过15小时夜间禁水后，在2小时内通过饮用至少1000 mL水迅速恢复水合状态。在另一次就诊时，受试者报告处于正常水合状态，然后在热室（100°F，50%湿度）中以3英里/小时的速度行走2小时，迅速脱水2%。在脱水/复水前后两天均采集尿液样本。测量尿液渗透压、尿比重、主观尿液颜色以及在CIE Lab*颜色空间中表示的客观尿液颜色。
在脱水试验中，参与者体重显著减轻，约为初始正常水合体重的2%。CIE尿液颜色L值显著降低（-2.3个单位），而b值显著增加（16个单位）。主观尿液颜色显著增加（1个单位）。脱水前后尿液渗透压增加（25 mmol/kg），尿比重增加（0.002 g/mL），然而，这些变化均无统计学意义。在复水试验中，参与者在摄入水后体重显著增加1.5%。CIE尿液颜色L值（7个单位）和a值（1.1个单位）显著增加，而b*值显著降低（-24个单位）。主观尿液颜色显著降低（-3个单位）。复水前后尿液渗透压（-600 mmol/kg）和尿比重（-0.018 g/mL）显著降低。
包括尿液渗透压和尿比重在内的传统水合状态指标在急性脱水试验中无显著变化，这表明这些值可能对水合状态的快速变化不敏感。然而，在快速脱水试验中尿液颜色的CIE L值和b值显著降低，在快速复水试验中显著增加。因此，本研究结果表明，在CIE Lab颜色空间中表示的尿液颜色L值和b*值在快速脱水期间对水合状态变化的反应比传统尿液浓缩指标更敏感，因此在这种情况下可能是更好的指标。
