Hydration

Stay hydrated:
Experts recommend drinking water (or other non-alcoholic non-caffeine beverages) to avoid increased blood viscosity during air travel. In a study by Hamada, twenty test subjects drank plenty of water, one cup per hour, during a nine hour flight. They developed significant increases in blood thickness and urine output. Blood samples from arm and lower leg were taken. Viscosity (thickness) increased in the lower leg, exactly where clots are likely to form.

Twenty other people drinking an electrolytic beverage did not have increased blood viscosity and urine output. Apparently drinking an electrolytic beverage is a much better choice for staying hydrated during air travel. See Hamada in Bibliography.

Expert review
Airhealth.org sent Hamada's study to several experts such as Bo Eklof and Gianni Belcaro for opinions. All said it looks reasonable but Belcaro wondered if it would cause line-ups at the lavatories. As a small unscientific test, Airhealth.org Executive Director Mike Reynolds drank one cup per hour of Gatorade on a recent flight to Paris. He drank this plus all the non-alcoholic beverages offered in cabin service. He used the lavatory no more than usual, i.e. once about four hours into the seven hour flight.

Logistics
Airlines don't serve electrolytic beverages. You have to bring your own. At the recommended one cup per hour, for an eight-hour flight you need 64 ounces. Three 20 oz. bottles of a sports drink will do nicely, and they fit in the seat-back pocket. If you drink one cup on the hour every hour, even during cabin service, it is easier to remember.

Finding an electrolytic beverage in some countries may be a challenge. In Paris, at the huge Decathlon store catering to runners, Airheatlh.org's Mike Reynolds found many powdered drink mixes overloaded with performance-enhancing carbohydrates, vitamins, etc. Only one came close to the 110 mg per cup of sodium and 30 mg per cup of potassium tested in Hamada's study. But the powder has to be mixed with water. Can you use the water available on the plane?

Don't drink the water :
A November Wall Street Journal report found serious contamination of airline tank water, the water flowing from taps in the galley and in the lavatory. No airline had drinkable tap water. Water served for drinking is usually bottled water, but sometimes it runs out.

Using airline tap water to mix with powdered electrolytic beverages would be a serious mistake. To avoid carrying any more bottled water than necessary, you could bring two 20-oz (or so) wide-mouth bottles of clean water. Mix the powder into one bottle and, when it runs out, refill it from bottled water in the galley and mix in more powder. Keep the other bottle in reserve in case they run out of bottled water in the galley.

Calories: During air travel you don't need energy-boosting carbohydrates. If you are counting calories, look for stores carry low-calory isotonic beverages. Or you might prefer low-calory isotonic powder mixes such as Isostar, especially if you want to avoid the bulk and weight of bottled drinks.

Pretzels: If you search "hydration" on Google, you will find other alternatives such as drinking water and munching a few pretzels, but this leaves a lot to chance. Until further scientific studies are done, one cup per hour of an isotonic beverage seems prudent.