New research has discovered why as we grow older our thirst mechanism signals us less strongly—showing that we should take conscious steps to avoid dehydration. __________________________ .

Dehydration occurs when the body does not have enough water, and this can happen rapidly in extreme heat or through vigorous exercise. Symptoms of dehydration can include headaches, lethargy and hallucinations. In extreme cases, dehydration may even result in death.

Florey researchers Dr. Michael Farrell and Prof. Gary Egan, along with Florey Founding Director Prof. Derek Denton, discovered that a region in the brain called the mid-cingulate cortex predicts how much water a person needs, but that this region malfunctions in older people.

In the study, older subjects (aged 65 to 74) and younger subjects (aged 21 to 30) drank salty water to make them thirsty, and were then allowed to drink as much fresh water as they wanted.

Reports Dr. Farrell, "Although all participants had the same level of thirst, the older people only drank half as much water as the younger subjects. Using positron emission tomography (PET) imaging we found that in the older people, the mid-cingulate cortex was 'turned off' much earlier by drinking small volumes. This discovery helps explain why the elderly can become easily dehydrated."

An August 2003 European heat wave claimed around 52,000 lives through dehydration and other causes—and many of the victims were older people. As climate change continues to be a growing global issue, the health implications for the elderly from rising summer temperatures add to this concern.

Dr. Farrell recommends that older people ensure they drink enough water during hot weather. "Adults should drink about eight glasses of water per day to prevent dehydration, and physically active people may need to drink more," he says.

The Howard Florey Institute is Australia's largest brain research center. The study was collaboration between the Florey and the Research Imaging Center at the University of Texas, where the PET imaging of the subjects was conducted. This research was published in the Proceedings of the National Academy of Sciences. 

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