Wonders of Water

You're soaking in it

You hear it from the experts all the time. The mantra of life. Drink plenty of water. But do you know why?

All of our bodies' normal chemical reactions take place in water. It's also needed to digest food, absorb and transport nutrients around our bodies and eliminate waste. It also helps keep our body temperature stable.

That's why a good percentage of your body is water - between 50% and 80%, in fact. An average, lean 70 kg person, for example, consists of around 42 litres of water. The leaner you are, the higher your water percentage. So generally men have a higher proportion of water than women, due to their lower body fat levels. Excluding sweat losses, the normal (daily?) turnover of water is about 4% of an adult's body weight, or around 2500 - 3000 mL in a 70 kg adult.

Around a quarter of an adult's water intake comes from the foods we eat, and the rest from fluids. Around 70% of the water in children's diets comes from beverages and milk, with the remaining 30% from foods.

As grown-ups, most of us need between 8 and 10 cups of fluid a day, according to the bods at the National Health and Medical Research Council. While experts recommend that water makes up the bulk of our fluid intake, other drinks, like milk and juice, also count. So a bottle of your favourite Spring Valley Juice or Smart Water can help contribute to your daily fluid needs, as part of a balanced diet.

Below is a summary of the Australian and NZ guidelines on fluid intake.

Total water (food + fluid)/day Fluids (water, milk, juice etc)/day
1-3 years 1400 mL 1000 mL
4-8 yrs 1600 mL 1200 mL
Boy 9-13 yr 2200 mL 1600 mL
Boy 14-18 yr 2700 mL 1900 mL
Girl 9-13 yr 1900 mL 1400 mL
Girl 14-18 yr 2200 mL 1600 mL
Men 3400 mL 2600 mL
Women 2800 mL 2100 mL

Listen to your hypothalamus

So how do you know how much water you need? The answer is you should drink as much fluid as you need to stay hydrated. About as clear as mud, right? The good news is that all healthy people have an inbuilt low water levels warning system called thirst.

When water is lost from the body through sweat and breath exhalation, the blood becomes a bit more concentrated and your mouth becomes dry. The change in blood concentration is sensed by the thirst control centre in the hypothalamus part of the brain and you start to feel thirsty. Drinking water in response to thirst returns the blood concentration back to normal.

As a 2004 report by the Institute of Medicine of the National Academies in the US noted:

  • The vast majority of healthy people adequately meet their daily hydration needs by letting thirst be their guide.
  • Prolonged physical activity and heat exposure will increase water losses and therefore may raise daily fluid needs, although it is important to note that excessive amounts can be life-threatening.

Dehydration is a dry argument

Dehydration. Seriously. You don't want to go there if you can help it as it causes:
  • a drop in both mental and physical performance4
  • decreased alertness, concentration and short-term memory
  • increased tiredness and headaches7.

Acute dehydration results in:

  • impaired cognition, moodiness
  • poor body temperature control
  • reduced heart function
  • impaired physical performance7.

We dehydrate when we restrict our fluid intake or when there's excessive water loss through sweating. Always make sure you drink enough fluids every day and replace any fluids lost through perspiration promptly. Elderly people and children need to be particularly careful as their thirst mechanisms can be weaker.

If you're pretty active, with exercise or sport, for instance, you'll need more fluids. Sports Medicine Australia recommends that active athletes drink:

  • approximately 500mls (2 glasses) in the 2 hours prior to exercise
  • 2-3 cups (500-700ml) of cool water or sports drink during exercise longer than 60 minutes

After exercise, make sure you replenish your fluids to ensure you are fully re-hydrated, but not over-hydrated.

For a final word on why you don't want to go there:

"The reported health effects of chronic mild dehydration and poor fluid intake include increased risk of kidney stones, urinary tract cancers, colon cancer and mitral valve prolapse as well as diminished physical and mental performance".

National Health & Medical Research Council. Nutrient Reference Values for Australia and New Zealand - Including Recommended Dietary Intakes. Commonwealth of Australia 2006

To find out more:

http://www.nhmrc.gov.au/publications/synopses/dietsyn.htm

The Australian Institute of Sport http://www.ais.org.au/nutrition/FluidFacts.asp

Sports Medicine Australia http://www.sma.org.au/pdfdocuments/Hot_Weather_Guidelines.pdf

The Beverage Guidance Panel http://www.beverageguidancepanel.org/

Nutrition Australia: http://www.nutritionaustralia.org/Food_Facts/FAQ/drinks_meals_faq.asp

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