December 31, 2019
A new study conducted at Pennsylvania State University suggests that both dehydration and overhydration may impact cognitive function in older women.
For the study, Penn State researchers investigated whether hydration levels and water intake among older adults was linked to their scores on several tests designed to measure cognition. 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. No such link was found for men.
“The study gives us clues about how hydration and related drinking habits relate to cognition in older adults,” said Dr. Hilary Bethancourt, a postdoctoral scholar in biobehavioral health and first author on the study. “This is important because older adults already face increased risk of cognitive decline with advancing age and are often less likely than younger adults to meet daily recommendations on water intake.”
“We found a trend suggesting overhydration may be just as detrimental to cognitive performance as dehydration for older adults,” said Rosinger, who 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.”
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.
Researchers 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.”
For the study, the researchers evaluated data from the Centers for Disease Control’s National Health and Nutrition Examination Survey, in which they looked at a nationally representative sample of 1,271 women and 1,235 men ages 60 and older.
Participants gave blood samples and reported all foods and drinks they had consumed the previous day. The researchers calculated hydration status based on concentrations of sodium, potassium, glucose, and urea nitrogen in participants’ blood. Total water intake was measured as the combined liquid and moisture from all beverages and foods.
The subjects also completed three tasks designed to measure different aspects of cognition, with the first two measuring verbal recall and verbal fluency, respectively.
A final task measured processing speed, sustained attention, and working memory. Participants were given a list of symbols, each matched with a number between one and nine. They were then given a list of numbers one through nine in random order and asked to draw the corresponding symbol for as many numbers as possible within two minutes.
Bethancourt said that when they first plotted the average test scores across different levels of hydration status and water intake, there appeared to be a distinct trend toward higher test scores in relation to adequate hydration and/or meeting recommended water intake. However, much of that was explained by other factors.
“Once we accounted for age, education, hours of sleep, physical activity level, and diabetes status—and analyzed the data separately for men and women— the associations with hydration status and water intake were diminished,” Bethancourt said. “A trend toward lower scores on the number-symbol test among women who were categorized as either underhydrated or overhydrated was the most prominent finding that remained after we accounted for other influential factors.”
The study has been published in the European Journal of Nutritiion.
Research contact: @penn_state