More than half of Japanese elementary and junior high school students are "underhydrated," a Niigata University-led research team has found.
It is important to drink water frequently to avoid dehydration not only in summer, but also in the cooler seasons, the group of researchers said.
In the study, Tatsuro Amano, an associate professor at the university, and colleagues analyzed urine samples from 349 students at elementary and junior high schools affiliated with the university in the city of Niigata.
Students collected the samples first thing in the morning at home on a single school day in April and then in July 2021.
They were also asked to self-evaluate the color of their urine based on an 8-point scale to monitor their hydration status.
The researchers said urine osmolality, which goes up as water intake declines, was at levels considered to indicate insufficient hydration in 66% of the April samples and 50% of the July samples.
However, only about 30% of those "underhydrated" students came up with urine color assessments consistent with the osmolality readings.
The result suggests children have a hard time recognizing a lack of water in their bodies from the color of their urine, the team said.
Although the risk of heatstroke has sharply risen this summer again, Amano said, "Children can maintain good hydration levels by drinking water frequently, not just when they play sports or are exposed to heat."