MaY/June
2006
Water and Hydration for Health and Sport
Athletic Performance and Hydration
By Doug Cook
The human body requires over 45 nutrients
each and every day to stay healthy. Many of us are familiar
with nutrients such as vitamins, minerals, protein, fat
and carbohydrate, but few may cite water as a key nutrient
even though water makes up about 60 to 70 percent of our
bodies. Water carries out a number of functions from chemical
reactions via metabolism to cushioning the joints and organs.
Regarding its role in sport, water is essential for the
dissipation of heat and temperature regulation through perspiration.
Factors affecting water requirements include individual
habitual intake, physical activity levels and environmental
conditions (heat, humidity, cold and altitude). Fluid requirements
assume 80 percent of the total will come from beverages
and 20 percent from the water content of food. The National
Academy of Science recommend that men 18 years of age and
older get a total 3.7 litres of water daily (three litres
coming from beverages and 700 millilitres from food) and
for women 18 years of age and older, a total 2.7 litres
(2.2 litres coming from beverages and 500 millilitres from
food). The main sources of water from beverages in the Canadian
diet include water, milk, fruit juice, coffee, tea, soft
drinks and sport drinks.
Exercise increases fluid requirements and those involved
in sport and athletics are at risk for dehydration making
hydration a key consideration. The effects of dehydration
range from poor performance to life threatening. Dehydration
can result in decreased motivation, impaired physical and
mental performance, decreased blood flow to the skin impairing
heat dissipation, increased core temperature and heart rate
and decrease cardiac output. Signs of dehydration include
cramps, irritability, headache, flushed skin, thirst, dizziness,
fatigue, disorientation, nausea and vomiting. It doesn’t
take much to reach a level of dehydration where these symptoms
can occur. As little as one to three percent dehydration
can impair performance, which is not uncommon for those
involved in rigorous sport where sweat rates are high –
poor pre-exercise hydration can predispose someone to early
dehydration.
The goal of fluid replacement is to replace that which is
lost and is best assessed by body weight; if weight is stable
post exercise, then there has been adequate fluid replacement.
The recommended take of fluid prior to exercise is:
• Drink 400 to 600 millilitres of fluid two to three
hours before exercise.
• Drink 150 to 350 millilitres of fluid 15 minutes
before exercise.
During exercise, fluid intake should maintain fluid balance.
The recommendation is:
• Drink 150 to 350 millilitres of fluid every 15 to
20 minutes.
The variation in amounts allows for individuals to base
their intake on their sport, exercise intensity and sweat
rate. Because the kidneys will be stimulated when there
is a large amount of fluid intake, extra fluid is needed
to replace that which is lost due to an increase in urine
output. For every kilogram of weight lost due to sweat,
1.5 litres (1.5 kilograms) must be consumed to compensate.
Plain water is not the best fluid to consume when large
amounts of fluid have been lost since water reduces blood
sodium, and decreases the desire to drink (thirst) –
possibly leading to inadequate fluid replacement. Sports
drinks are designed to help athletes meet their fluid requirements
by encouraging voluntary drinking. The main ingredients
are:
Water
• 90 to 96 percent water to replace sweat losses
Flavour
• flavouring helps to increase palatability which
may lead to increased drinking and therefore hydration
Electrolytes
• involved in muscle contraction and signal transmission
through nerves
• sodium
° the primary electrolyte lost in
sweat
° used in drinks to replace losses
° helps to prevent muscle cramps
° helps to prevent low serum sodium (hyponatremia)
° helps to decrease water losses via urine
• potassium
° lost in sweat but in much smaller
amounts
° used in drinks to replace sweat losses
Carbohydrate
• helps to maintain blood glucose levels thereby providing
fuel to working
• helps to encourage voluntary drinking by providing
a sweetness to the beverage
Because the sensation of thirst is not the best indicator
of how much fluid needs to be replaced, it’s best
to gauge how much fluid was lost by subtracting your post-exercise
weight from your pre-exercise weight, add your fluid intake
during exercise and subtracting any urine output –
this will give you the best measure of fluid loss. If measuring
your urine is not your thing, you can also monitor your
urine output and colour post-exercise – if there is
ample volume, light in colour and odourless then you’re
on the right track – if not, drink up until the urine
is lighter in colour like diluted lemonade.
Do not reprint without permission. Copyright
2006 © Wellness Nutrition
Doug Cook
Doug Cook, RD MHSc CDE is a clinical dietitian and certified
diabetes educator working at St Michael’s Hospital
in Toronto and has a private practice at the Yorkville Club,
www.theyorkvilleclub.com. You can contact Doug at dc_dietitian@hotmail.com
or visit his website at www.wellnessnutrition.ca.
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