Even mild dehydration can affect mood and concentration, according to study.

Forget the caffeinated buzz of that morning cup of Joe, soda pop, or energy drink—water, plain water, could be all your brain needs for a real pick-me-up.

The brain may be a remarkably complex organ, but it requires water for every one of its cells and their function. Now, research from the University of Connecticut has found that keeping the brain completely hydrated is critical for its happy performance.

In a crossover study, 25 young women performed 40 minutes of treadmill walking in a warmed room as part of three experiments: 1) exercise-induced dehydration plus a placebo; 2) exercise-induced dehydration plus a diuretic; 3) and normal hydration with placebo. The researchers documented the women’s moods and their cognitive function during and after the activity.

The authors report that there were negative affects to vigor, fatigue, and mood after only mild dehydration, which equaled a 1.36 percent drop in body mass from water loss. A 2 percent drop in body mass from water loss is the “red flag” for full-blown dehydration. Also, the subjects’ perception of task difficulty and headache severity increased and their ability to concentrate decreased with just mild hydration.

While the cause of the mood changes is still under discussion, the importance of hydration is not. For the first time, this study shows that mood and concentration can be negatively impacted by a nearly insensible water loss. Simply drinking adequate amounts of water may help maintain mood and fight fatigue.

“This study demonstrates that, not only at rest but also during moderate exercise, a wide variety of adverse changes occur in slightly dehydrated, young, healthy females,” the researchers wrote In the December issue of the Journal of Nutrition. “Maintenance of optimal hydration is essential to ensure optimal mood and reduce symptoms.”

How much water should a person drink daily to prevent mild dehydration? The actual amount can depend on a number of factors including bodyweight, climate, and activity. Water is lost continually through breathing, sweating, urination, and bowel movements.

Standard advice is to drink around eight 8-ounce glasses of water a day. A truer method is to take half a person’s bodyweight in pounds, then divide by half, and drink that much in ounces. On hot days or if performing physical activity, drink a few ounces more or, better yet, drink a sports drink like Want More Energy?® (containing no caffeine or stimulants) that also replenishes lost glycogen, vitamins, and electrolytes.

Based on the conclusions of this study, another approach may be to drink water whenever feeling a lack of energy, sluggish, or a little blue. Keeping an extra glass handy may be all it takes to keep mood and concentration up, leaving you feeling at your best.

Reference: Armstrong LE et al. Mild Dehydration Affects Mood in Healthy Young Women. J. Nutr 2011; doi: 10.3945/jn.111.142000.