The study – published in the British Journal of Nutrition – reports that the mild dehydration which occurs even before we become thirsty could be enough to alter mood and energy levels.
Led by Professor Lawrence Armstrong of the University of Connecticut, USA, researchers revealed that the adverse effects from mild dehydration (defined as an approximate 1.5% loss in normal water volume) at were the same whether people were sitting at rest or active and exercising.
Armstrong said the results assert the importance of staying properly hydrated at all times, and not just during exercise, extreme heat, or exertion.
"Our thirst sensation doesn't really appear until we are 1 or 2 percent dehydrated. By then dehydration is already setting in and starting to impact how our mind and body perform," said Armstrong – an international expert on hydration.
"Dehydration affects all people, and staying properly hydrated is just as important for those who work all day at a computer as it is for marathon runners, who can lose up to 8 percent of their body weight as water when they compete," he affirmed.
"Even mild dehydration that can occur during the course of our ordinary daily activities can degrade how we are feeling – especially for women, who appear to be more susceptible to the adverse effects of low levels of dehydration than men," explained Dr Harris Lieberman, a co-author of the research.
The researchers noted that the dehydration studies were supported by Danone Research of France and were conducted in partnership with the U.S. Army Research Institute of Environmental Medicine, and several universities in the USA.
The researchers tested two groups of young men and women, who were “healthy, active individuals, who were neither high-performance athletes nor sedentary – typically exercising for 30 to 60 minutes per day.”
As part of the evaluation, the subjects were put through a succession of cognitive tests that measured vigilance, concentration, reaction time, learning, memory, and reasoning while mildly dehydrated – either from gentle walking activity or simply from being sedentary.
The results were compared against a separate series of tests when the individuals were not dehydrated.
In the tests involving the young women, mild dehydration caused headaches, fatigue, and difficulty concentrating, said Armstrong and his team. They added that female subjects also perceived tasks as more difficult when slightly dehydrated – though said there was no substantive reduction in their cognitive abilities.
For assessments involving men, mild dehydration caused some difficulty with mental tasks, particularly in the areas of vigilance and working memory, they reported.
Armstrong and his team said young men also experienced fatigue, tension, and anxiety when mildly dehydrated, though they added that adverse changes in mood and symptoms were "substantially greater in females than in males, both at rest and during exercise."
Lieberman – a research psychologist with the Military Nutrition Division of the U.S. Army Research Institute of Environmental Medicine – said the adverse mood changes in both sexes “may limit the motivation required to engage in even moderate aerobic exercise.”
“Mild dehydration may also interfere with other daily activities, even when there is no physical demand component present," he suggested.
Last year the European Food Safety Authority’s (EFSA) health claims panel, the Panel on Dietetic Products, Nutrition and Allergies (NDA), delivered a negative opinion on a health claim linking water consumption and dehydration.
The water-dehydration article 14 claim submitted by two German professors was rejected because dehydration was deemed a “measure of disease” and not a disease risk reduction factor, and therefore not permissible under the nutrition and health claims regulation (NHCR).
The two professors - Dr Moritz Hagenmeyer and Dr Andreas Hahn – proposed the claim: “Regular consumption of significant amounts of water can reduce the risk of development of dehydration and of concomitant decrease of performance”.
But the Panel found these were “measures of water depletion and thus are measures of the disease (dehydration).” It therefore concluded: “…the proposed claim does not comply with the requirements for a disease risk reduction claim pursuant to [the NHCR].”