Hydration In Flight

By Sabine Spiesser BSc Grad Dip Dietetics

The human body requires 1 1/2 to 2 litres of fluid a day in addition to the fluid provided as part of the daily food intake, plus fluids lost due to perspiration. This can easily amount to 4-5 litres per day when we are out on the hot airfield. Most of the fluid losses occur during preparation for flying and the early flight period.

Inadequate fluid intake will lead to dehydration. When we become dehydrated, our heart rate increases, we will become fatigued, lose our ability to regulate body temperature, and lose concentration. Dehydration usually creeps up on us gradually, without any warning signs.

First signs of dehydration may include thirst, loss of energy, diminished performance, cramps and headache. Thirst is not a good indicator of hydration, as the body fails to signal correctly once we pass a certain point. Also, by the time we are thirsty we are usually already well on the way towards being dehydrated. Stretching can help relieve muscle cramps. Cramps are due to fluid loss, not salt loss.
These are serious signs, and should not be ignored. To correct dehydration, drink sports drinks that contain sodium and electrolytes. If you do not recover within a short period, and do not carry sufficient fluids, you are at a high risk of developing heat exhaustion.
Some symptoms of heat exhaustion include headache, nausea, feeling faint or dizzy, cramping, chills, and clammy skin. Heat stroke is characterized by high body temperature, confusion or unconsciousness. Our core body temperature will gradually increase with serious consequences, even death.

Preventing dehydration

  • If you have arrived from overseas, allow for time to acclimatize to the local weather conditions in Benalla/Australia.
  • People have varying fluid requirements; you need to know your personal needs.
  • Drink plenty all day long. Your urine should be almost clear.

Hydration for short flights

Measure your fluid losses/intake during a typical flying day, e.g. when you are doing a small cross-country task. If you want to be more scientific about it:

Calculating needs for short flights

  • Weigh yourself after breakfast, and again later in the day.
  • Record your fluid intake during the day.
  • Fluid requirement = Total weight loss + total fluid intake.
  • Calculate the fluid consumption per hour.

Hydration for long flights

Calculate your fluid intake by considering:

  • Estimated flying time.
  • Safety margin.
  • Emergency supplies for an outlanding.
  • Be optimally hydrated all the time – before and after flying, and every day.

If you don’t have the time for measurement and calculations, ask experienced glider pilots, how much they take along and add some extra as a safety margin. Don’t assume though that all experienced pilots do the right thing. You may be surprised!

Your hydration strategy should start the moment you are getting ready to fly. The more hydrated you start, the better you fare. The next section deals with the best choices of fluids, and the reasons, why they are recommended.

What to drink

Hydration beverages should be easily and quickly absorbed. They should not leave you feeling uncomfortable.

Research has shown, that sports drinks containing 6-8% glucose (or glucose polymers) and a small quantity of salt are absorbed best and fastest. Chilled fluids are better absorbed than warm ones, so keep them well cooled until take-off. Plain water cannot be consumed easily in large quantities, and without salt and glucose it may dilute your blood too much. Fluids, which maintain your blood’s properties are called isotonic solutions. You can drink fair quantities of sports drinks without discomfort.

Recommended brands are Gatorade, Isostar and Isosport (Australian Institute of Sport choice). These have optimal sugar and salt concentrations for easy absorption.

There are others, which do not contain sufficient salt, or the wrong sugars, or too much sugar. Fruit juices are generally not suitable because of their high fructose content (diarrhoea); soft drinks have too much sugar, no salt and can cause bloating.

Sports drinks contain sugars for energy at the same time as supplying you with much needed fluids. They also keep your blood glucose levels constant if sipped at regular intervals. You do not have to spend too much thought on in-flight meals if you consume adequate quantities of sports drinks every 20 -30 minutes.

If you are planning on flying on consecutive days, sports drinks will leave you feeling much fitter and better hydrated, than any other beverage.

Before and after your flight, water is a good hydration choice, as you are able to eat and drink freely. Sports drinks should only be consumed during sport, and not as regular beverages. Your dental enamel will thank you for choosing water.

What not to drink

Caffeine, and it’s cousins theophylline (tea), theobromine (cocoa) and Guarana (energy drinks) have diuretic action, meaning, that they make you pee more, and are not suitable hydration drinks. Caffeine can increase alertness, but in higher doses can cause irritability. If you are a regular coffee drinker, and suffer from caffeine withdrawal symptoms, you may want to take along a bottle of cola to prevent the inevitable withdrawal migraine. Caffeine is not a good fatigue buster though, as it’s effect is only temporary, and usually followed by worsening fatigue. Good sleep is vital for a refreshed flying start.

Alcohol is not suitable for fluid replacement, as it too acts as a diuretic, just as coffee does. Alcohol can disrupt sleep, when consumed in excess and lead to a hangover. This is due to the body’s inability to detox it fast enough. The combination of dehydration, fatigue from lack of sleep and a hangover, are not a good starting point for cross-country flying. It could affect your concentration span and ability to make sound judgments considerably.

On a similar note: post-flight, rehydrate before you hit the bar.

Don’t rely on your luck or guardian angel, but rather think about prevention and GET INTO THE HABIT.