Lack of Strong Thirst Signals Leads Elderly to Drink TooLittle

TUESDAY, Dec. 18 (HealthDay News) -- Older adults don't drinkenough water and become dehydrated during heat waves because their brainsand bodies don't coordinate sensory signals about thirst, a new Australianstudy suggests.
The researchers aren't sure whether thirst signals from the body orthe interpretation of these signals by the brain cause the problem, saidstudy author Gary Egan, an associate professor at the University ofMelbourne.
Knowledge of this lack of coordination may make it easier to motivateolder people "to make sure they are actively re-hydrating because there isa clear reason why they are not necessarily aware of their own need todrink," Egan said.
Deaths of elderly people from dehydration is a well-known public healthproblem, Egan said. During a French heat wave in 2003, the deaths of14,000 mostly older people were attributed largely to not drinking enoughwater, he said. "This issue becomes of paramount public healthsignificance," he added.
For the study, Egan and his colleagues recruited a group of 10 youngermen (mean age 23.7) and a group of 12 healthy older men (mean age 68.1).The researchers injected saline solution into the volunteers to make themthirsty. Then they were permitted to drink as much water as they liked,Egan said.
The older men drank less water to quench their thirst. PET scans ofareas of their brains activated by thirst showed reactions -- particularlyin the cingulate cortex.
"In the elderly, drinking a much smaller volume of water is needed tocause that area of brain activation to subside," said Egan, who is anexpert on neuro-imaging. "For some reason, elderly people's attention ofawareness of the need to drink to re-hydrate rapidly dissipates after asmall amount of ingested water."
One cause of this could be the result of weaker signals from the body,Egan explained. For example, as people age their stomach muscles weaken.So, when they consume water or food their stomach expands more incomparison to volume, he said.
"When muscles are weaker, there is less sensory input telling you haveeaten or drunk as much as you have," Egan said. Signals come from otherareas of the body, such as the back of the throat, and that is also lesssensitive with age, the study noted.
The study concluded that "scheduled drinking may be a strategy toreduce the risk of dehydration in older people, although care should beexercised to avoid excessive water intake and the associated risks ofcerebral swelling."
The findings are published in this week's edition of Proceedings ofthe National Academy of Sciences.
The work of Egan and his team of scientists from Melbourne and SanAntonio, Texas, is one of many studies of thirst in the elderly, said NeilE. Rowland, a professor of psychology at the University of Florida and athirst researcher. "These studies have had two different results: Thatelderly people experience less thirst and consequently drink less fluid,or that elderly people experience just as much thirst but still drinkless," he said.
"This paper is important because it's really the first study that looksinside the brain to try to find out what might be different" about thethirst mechanism in older people, Rowland said.
The study is also interesting because it looked at the cingulatecortex, a region of the brain that hasn't been studied widely by thirstresearchers, he added.
While the findings are important to basic science, they don't haveimmediate practical consequences, Rowland said. "The authors suggestcontrolled drinking programs so that [older people] take more drinksacross the day. That doesn't follow from this particular research. Thosesorts of programs have been around for a long time."
Scheduled drinking isn't always successful with the elderly, added BarbTroy, a clinical assistant professor of dietetics at Marquette University.Anyone who works with the elderly will say that if you prod them to drinkbeyond their limit, that can be counterproductive, she said.
"They don't ambulate as well. In the middle of the night they don'twant to be running to the bathroom, and that catches up with them."