Researchers from Texas Tech University have found that dehydration can make it harder to fall asleep and increase feelings of fatigue after waking up. The study results were published in SN Comprehensive Clinical Medicine (CCM).

The experiment involved 18 male students. Over four days, the researchers monitored their hydration levels and sleep quality in a laboratory setting. On the first day, the participants’ baseline hydration status was recorded. On the second day, they arrived well-hydrated — after consuming 500 ml of water in the evening. They were then instructed not to drink water until the next visit, creating mild dehydration by the third day. On the fourth day, they returned to their regular routine.

To assess hydration levels, scientists used three indicators: urine color, urine specific gravity (lower values indicate better hydration), and body weight changes. At the same time, participants filled out questionnaires about their sleep quality — how long it took them to fall asleep, how often they woke up, and how refreshed they felt in the morning.

Data analysis showed that when dehydrated, participants slept an average of one hour longer, but took longer to fall asleep and felt more tired in the morning. This suggests that insufficient water intake negatively affects not only physical condition but also sleep quality.

Although the study was initially conducted in the context of sports medicine, the researchers note that the findings are relevant to the general population. According to the authors, mild dehydration is common in daily life — especially in hot weather or when fluid intake is low.

The research team plans to continue studying how water deficiency affects the immune system. Future studies will also focus on pregnant women and children, who may be particularly sensitive to changes in hydration levels.