The present study compares different hydration effects from consumption of water, sports drinks, and ORS. We examined water absorption and plasma volume change in athletes based on the measurements of body weight change, cumulative urine output, BHI, and PVC.
Body weight change was significantly smaller for ORS than for water, SpD1, and SpD2, indicating that bodily water loss is smaller following the consumption of ORS than SpD1, and SpD, and water. Cumulative urine output differed only slightly in testing time, although cumulative urine output in 4 hours was lower for ORS, SpD1, and SpD2 than for water, and it was lower for ORS than for SpD2. Thus, we believe that bodily water loss is smaller for ORS than for water and SpD2.
The BHI is the urine output after consumption of water divided by the urine output after beverage consumption, and it is an index commonly used to verify the hydration effect of a beverage(Maughan et al., 2016; Sollanek et al., 2018). In our study, BHI values varied only a little in terms of testing time. However, cumulative urine output in 4 hours was lower for ORS, SpD1, and SpD2 than for water, and it was lower for ORS than for SpD2. This result agrees with the study by Sollanek et al. (2018) that confirmed ORS as an effective hydration method by showing that ORS had a higher BHI value than water, while sports drinks did not. Clarke et al. (2019) showed high BHI for ORS with relatively large quantities of Na+ component. This finding is consistent with our study showing high BHI for ORS containing a large amount of Na+. Moreover, we found that cumulative urine output and BHI were inversely proportional because the BHI was high in the beverages associated with low cumulative urine output. This finding agrees with previous studies that showed BHI as a useful index for differentiating hydration effects.
Our study compared PVC to verify the hydration effects of different beverages, but we found no significant difference. According to Clarke et al. (2019), PVC showed a rapid increase immediately after beverage consumption (0–15 minutes) and then plateaued after 1 hour. We measured PVC at ≥ 1 hour after beverage consumption, which may have been responsible for the insignificant difference. Furthermore, the coefficient of variation (CV) of PVC was 2.35, which is relatively high considering that the CV of cumulative urine output was only 0.27. High CVs mean a substantial difference in PCV for participants, indicating that PVC should be an index with higher sensitivity to an individual's physical characteristics.
In conclusion, our study evaluated the hydration effects of beverages, such as water, sports drinks, and ORS, on athletes. The ORS and sports drinks were more effective for hydration than water, and the difference between ORS and sports drinks varied depending on the type of sports drink.