Water intake and stress hormone response
Studies show higher cortisol levels in people who drink less water. (Source: RTE)
Notably, this group did not feel thirstier, yet their bodies reacted more negatively under stress.
Study design and stress test
The study, conducted by experts at Liverpool John Moores University (UK), involved 32 adults, 16 of whom drank less than 1.5 liters of water per day and 16 who met fluid intake recommendations.
Researchers monitored the hydration status of both groups for seven days through urine and blood samples, then invited them to participate in a laboratory stress test.
The test included a surprise job interview: each person had 10 minutes to prepare, then had to enter another room fitted with fake cameras and answer questions before a “panel” of three people wearing white lab coats. Next, they were asked to do mental arithmetic, subtracting numbers as fast as possible.
According to Professor Neil Walsh of the School of Sport and Exercise Sciences at Liverpool John Moores University, this was described as a "truly baffling" experience.
“We know that people whose daily water intake falls below the recommended level are often dehydrated. But what we did not know was whether their stress hormone response would be stronger when we placed them in a controlled stressful situation,” Professor Walsh said.
Measuring cortisol and comparing the two groups
To measure cortisol levels, the researchers collected saliva samples before and after the test. Cortisol, also known as the stress hormone, is produced by the adrenal glands when the body is under stress and also plays a role in immune responses, metabolism and blood pressure.
Professor Shaw noted that external stress responses such as rapid heartbeat, sweaty hands, and dry mouth were similar in both groups. “Both felt equally anxious and showed similar heart rate increases during the test. However, the group with low daily water intake exhibited a much stronger cortisol response.”
Water intake recommendations and situational needs
The study findings also reinforce advice from health authorities. Specifically, the European Food Safety Authority (EFSA) recommends that men drink 2.5 liters of water per day, while women drink 2 liters. Meanwhile, the UK's Eatwell Guide suggests that adults consume 6 to 8 glasses of water daily, equivalent to 1.5 to 2 liters.
Experts emphasize that the need for water intake can increase significantly in hot weather, during intense physical activity, illness, or during pregnancy and breastfeeding.
According to the research team, keeping a water bottle nearby during stressful times not only helps ease the mind but also benefits long-term health.