Not getting enough water is enough to make you feel sluggish and give you a headache, but a new Penn State study suggests it may also relate to cognitive performance.
The researchers investigated whether hydration levels and water intake among older adults was related with their scores on several tests designed to measure cognitive function. They found that among women, lower hydration levels were associated with lower scores on a task designed to measure motor speed, sustained attention and working memory. They did not find the same result for men.
“We found a trend suggesting overhydration may be just as detrimental to cognitive performance as dehydration for older adults,” said Rosinger, who also directs the Water, Health and Nutrition Laboratory and was senior author on the study. “Because of this, being in the ‘sweet spot’ of hydration seems to be best for cognitive function, especially for tasks requiring sustained attention.”
According to the researchers, scientists have long suspected that dehydration may have an effect on cognitive performance. However, previous studies have largely focused on young, healthy people who are dehydrated after exercise and/or being in the heat.
Bethancourt said that because exercise and elevated ambient and body temperatures can have their own, independent effects on cognition, she and the other researchers were interested in the effects of day-to-day hydration status in the absence of exercise or heat stress, especially among older adults.
“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,” Bethancourt said. “Therefore, we felt like it was particularly important to look at cognitive performance in relation to hydration status and water intake among older adults, who may be underhydrated on a regular basis.”
“It was interesting that even though the test of attention, processing speed and working memory took only a few minutes, it was the one most strongly associated with lower hydration levels,” Bethancourt said. “Other research has similarly suggested that attention may be one of the cognitive domains most affected by hydration status. This left us wondering what the effects of inadequate hydration might be on more difficult tasks requiring longer periods of concentration and focus.”
Rosinger said the findings suggest older adults may want to pay close attention to their hydration status, by both consuming enough liquids to avoid dehydration as well as ensuring adequate electrolyte balance to avoid overhydration.
“Because older adults may not necessarily feel thirsty when their body is reaching a state of underhydration and may be taking diuretics that can increase salt excretion, it is important for older adults and their physicians to better understand the symptoms of being both under- and overhydrated,” said Rosinger.