Background

Every cell and tissue in the body requires water to function, and the body contains 70% water by weight. Although adequate intake is key for optimal physical and cognitive function, many people don’t drink enough water. This study examined the effects of water supplementation on mood and cognitive function. The investigators also assessed the amount of water needed to counter the effects of 12 hours of water restriction.

The study

In a randomized controlled trial of 64 young adults, the participants fasted (including water) overnight for 12 hours. At 8 a.m. the next day (i.e., the dehydration condition), the researchers measured the osmolality of the blood and the first morning urine as well as mood and cognitive performance. The participants were randomly assigned to four groups: they received 100, 200, or 500 mL of water or no water. The participants in the water groups drank the water within 10 minutes, and the no-water group did not drink any water. At 90 minutes after water consumption (i.e., the rehydration condition) blood and urine osmolality, mood, and cognitive function were assessed again.

The results

Relative to the dehydration condition, any amount of water relieved thirst, improved working memory, and reduced anger, fatigue, and total mood disturbance (TMD). There were no significant differences in thirst, fatigue, or TMD scores between the 500 mL water supplementation and 200 mL supplementation groups, but 500 mL of water was required to cause significant improvements in working memory.

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This Study Summary was published on March 5, 2021.