Researchers say that keeping a water bottle close during stressful periods could be beneficial for long-term health

10:49, 22 Aug 2025Updated 13:47, 22 Aug 2025

Woman drinking water from glass looking away at homeThe study looked at the effects of hydration on stress hormones (Alamy/PA)

People are being warned to make sure they drink enough water or they could be more stressed. A study found that those who drink less water have higher levels of the stress hormone cortisol, even though they do not feel any thirstier than those who consume more.

Keeping a water bottle close at hand during stressful times could be beneficial for long-term health, the researchers suggest. The study was conducted by experts at Liverpool John Moores University (LJMU) and involved 16 people who drank less than 1.5 litres of water a day, along with 16 others who regularly met the daily recommended guidelines for fluid intake.

The researchers used the European Food Safety Authority (EFSA) guidelines, which recommend that men should drink 2.5 litres of water a day while women should drink two litres. In the UK, the Eatwell Guide suggests adults should consume between six and eight cups of fluid a day, equivalent to roughly 1.5 to two litres.

However, people may need to increase their water intake when it is hot, if they are highly active, recovering from an illness, or if they are pregnant or breastfeeding.

Over a seven-day period, researchers monitored hydration in both groups using urine and blood samples, after which they were invited into the lab for a stress test.

This test involved an impromptu job interview, for which each individual was given 10 minutes to prepare.

Following that period, participants were ushered into a separate room containing a mock camera setup and instructed to conduct the interview before a trio of individuals wearing white laboratory coats.

After completing the simulated interview, subjects were then required to undertake a mental arithmetic task involving rapid subtraction of numbers.

Professor Neil Walsh, from LJMU’s School of Sport and Exercise Sciences, characterised the assessment as “really flustering”.

He told the PA news agency: “We know that people who have a low daily fluid intake, who don’t meet the recommendations, are likely to be poorly hydrated.

“But what we didn’t know was whether, when you then stress those people under controlled conditions, they would have a greater stress hormone response.”

Scientists gathered saliva specimens from participants both before and following the stress examination to assess cortisol concentrations.

Cortisol, recognised as the stress hormone, is manufactured by the adrenal glands when responding to stress and additionally influences immune function, metabolism and blood pressure.

The research team discovered cortisol concentrations were elevated in those consuming less fluid.

Prof Walsh observed that stress reactions including accelerated heart rate, perspiring palms and parched mouth were comparable across both groups.

He said: “Both groups felt equally anxious and experienced similar increases in heart rate during the stress test.

“But the people who were poorly hydrated, because they were not drinking enough water each day, had much greater cortisol responses.”

The group consuming less fluid also did not report feeling more parched than those who consumed greater amounts, according to Prof Walsh.

He added: “Cortisol is the body’s primary stress hormone and exaggerated cortisol reactivity to stress is associated with an increased risk of heart disease, diabetes and depression.

“If you know you have a looming deadline or a speech to make, keeping a water bottle close could be a good habit with potential benefits for your long-term health.”

Prof Walsh explained that additional research is required to better comprehend the findings, published in the Journal of Applied Physiology, and to determine whether boosting water consumption in those who don’t drink sufficient amounts can reduce responses to daily “micro stressors” such as traffic congestion or workplace presentations.

He said: “We’d like to think that meeting the water intake guidelines could be one of a number of things you could do to blunt that cortisol response day to day.”