You have to stay hydrated to feel well—any athlete will tell you that. But now, a study published in the Journal of Nutrition suggests that even mild dehydration can cause headaches, concentration issues, difficulty on basic tasks and negative mood.

In the study, 25 women participated who were just over 1 percent lower than “optimal hydration levels,” but their health suffered just the same. It’s important to drink up, whether you exercise or not. H2O is a godsend for our skin, immune system, digestive track and overall health.

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