Water is therapeutic. People flock to bathe in thermal springs, embark on ocean swims and treat themselves to hot baths. But how often do we pay attention to our need to actually drink the stuff?
We know we need to hydrate for healthier skin and to aid digestion, but what many of us may not know is that our brains get thirsty, too. The brain actually shrinks when we're dehydrated, making it harder to concentrate and fend off irritability.
"Dehydration has a negative effect on some elements of cognitive function and,in particular, it seems to reduce alertness," says Professor Andrew Scholey, director of the Centre for Human Psychopharmacology at Swinburne University in Melbourne.
"If you're feeling a bit thirsty, there's a good chance that you're dehydrated. Essentially, the equilibrium - the balance of your individual salts within cells and within the space between cells - goes awry, and that can have subtle changes on some elements of cellular function, including in the brain."
Even mild dehydration affects mood in healthy young women, according to a study published in 2012 in The Journal of Nutrition. It compared results from the women, who participated in a dehydrating exercise either with a diuretic, without a diuretic or with a placebo. They underwent various assessments, including cognitive tests that showed adverse effects in those who were dehydrated. "Mild levels of dehydration result in adverse changes in key mood states such as vigour and fatigue, as well as increased headaches and difficulty concentrating," the authors concluded.
A 2012 study in the journal Appetite, involving Swinburne University researchers, found 84 per cent of children from hot-climate regions of Italy started their school day in a state of mild dehydration, and their water intake was dependent upon the individual school's water-intake policy. "It might render the school day more challenging for children," the authors say, adding that high levels of hydration are linked with high levels of vigour in children.
Scholey, who will deliver a free lecture called "Food for Thought" at Swinburne University on March 4 as part of the Melbourne Food & Wine Festival, says dehydration can affect alertness, calmness and bring on fatigue. How do we know we're dehydrated? Look for darker-coloured urine, a reduction in alertness and an inability to respond or react as quickly as you normally would.
Scientia Professor Perminder Sachdev, co-director of the Centre for Healthy Brain Ageing at the University of NSW, says fluid is drawn out of brain cells during dehydration, with some shrinkage of the brain. "While not all studies have shown significant cognitive effect," says Sachdev, "there is some evidence to show the brain has to work harder in that state of dehydration."
The good news is that rehydration reverses any ill-effects, such as fatigue or irritability. "When you rehydrate the body, that shrinkage reverses - it's not going to be a permanent effect," says Sachdev.
Many health experts have long urged us to drink eight glasses of water each day for good health, but Scholey says this is not strictly true - we can top up with other fluids like herbal teas and other non-caffeinated drinks. We can also stay hydrated from foods such as soup, as well as fruit and vegetables with a high water content like cucumber, watercress, tomatoes, broccoli, celery, strawberries, watermelon and citrus fruit.
"There is some suggestion that a good rule of thumb is something like one millilitre for every calorie [four kilojoules] of food that you consume," says Scholey. "But what a lot of people don't realise is that we can also get fluids from certain foodstuffs - there's a bit of a myth that is all has to come from water."
Do you believe eating superfoods makes you healthier?Related story: (See story)