Drinking either not enough or too much water can decrease cognitive performance in older women, Penn State University researchers reported in the European Journal of Nutrition. In a nationwide study, 1,271 women and 1,235 men over age 60 gave blood samples, answered questionnaires about the previous day’s food and drinks, and performed cognitive tests to measure working memory, brain processing speed and sustained attention. Women, but not men, performed more poorly if they were not in the “sweet spot” of just enough hydration, typically around two liters a day. “As we age, our water reserves decline due to reductions in muscle mass, our kidneys become less effective at retaining water and hormonal signals that trigger thirst and motivate water intake become blunted,” explains lead author Hilary Bethancourt, in urging greater attention to hydration levels.