It's hot out there, so how do you stave off dehydration and what happens if you don't?
It's summer - at last - and with the heat comes a real danger
of dehydration, so how do you know whether you're dehydrated and
how much water should you be drinking when you're on the hill?
Why does it matter?
There are tests that show as little as five per-cent dehydration
can decrease your physical performance by as much as 30 per-cent.
That's the last thing you need when you're on the hill working hard.
As things get worse, dehydration massively increases the risk of
heat illness at which point you're you're talking headaches, cramps,
fatigue, vomiting, coma and death...
You can lose 2% of your bodyweight through dehydration in as
little as one hour, in 2-3 hours that could be 4-6% and after four
hours or so, 7-8% at which point you're at serious risk of
potentially fatal heat stroke.
In between heat exhaustion will massively reduce your ability to
function with fatigue, nausea and high temperatures kicking in.
| As little as 5% dehydration could lead to a 30% reduction in performance. Any more increases the risk of heat exhaustion, heat stroke and, eventually, death. |
Prehydrate or dry...
Your thirst mechanism lags behind your actual hydration level, so
by the time you're feeling thirsty, you're already dehydrated -
there's a time delay if you like. Keep an eye on your urine, it
should ideally be clear or at worse, a light straw colour.
Remember the maxim: 'A good mountaineer, always pees clear.' Okay
it's trite but it's a good guide.
Your body will function best if you're already hydrated before you
set off, so drink little and often over the 24 hours before your
trip. Not only will you start hydrated, but it improves your chances
of staying topped up as the body absorbs fluid most effieciently from
a comfortably full gut.
| By the time you feel thirsty, it's too late - you're already dehydrated, so top up before you head out. |
How Much Fluid Do You Need?
On a hot day, you can lose between 500ml and 2000ml - yep, two
litres - per hour when working hard. Ideally you want to replace as
much as that as possible. We'd suggest an absolute minimum of
500ml per hour and ideally more like one litre per hour as
a starting point, more on really hot days or if you're working hard -
that may mean you need to top up your supplies during the day, but
the pay off is worth it.
| Ideally you should aim to drink around one litre of water every hour, more in very hot conditions or if you're working particularly hard. |
What Should You Drink?
Water's an excellent start, but you can also use sports drinks
which include energy and, in some cases, replacement electrolytes and
minerals which you're also losing through sweat.
If you do use a sports drink, choose one based on glucose polymers
- maltodextrins are the things to go for - and in hot weather mix the
drink more dilutely than the instructions suggest.
Over-concentrated drinks containing too high a concentration of
carbohydrate will slow down fluid absorption. Finally avoid
sugar-heavy soft drinks for the same reason and diuretics like tea
and coffee.
| If you use an energy and electrolyte replacement drink in hot conditions, mix it more dilute than the instructions to speed up absorption. |
How Should You Drink It
Little and often is the most effective way of absorbing fluid
efficiently, rather than just sluicing a litre at a time down your
throat, in which case the fluid which can't be absorbed will be peed
out rapidly.
The easiest way of achieving that is with a hydration
system that you can sip from on the move. As a bonus a single
hydration bladder could hold up to three litres of fluid, far more
than any single bottle. Virtually all modern packs have the facility
to mount a bladder and tube conveniently.
| Drinking little and often - every 15 minutes say - means fluid is absorbed faster. Hydration systems are ideal for this. |
Cold Water Absorbed Faster
Finally, some research shows that your body absorbs cooler water
faster, so Camelbak suggests that before a hot day on the hill, you
half fill your bladder with water then freeze it. The big chunk of
ice will melt slower than ice cubes and your water will stay cold
longer.
| Pre-freeze your bladder before heading out as cool water is absorbed faster than warm stuff. |
More Information
See the links to previous OM health and fitness articles listed below. For gear advice see our review system or ask in the OM forums for friendly input from other OM members.
