NASA rehydration technology has "the right stuff" for astronauts

John Greenleaf with a bottle of the NASA-developed rehydration beverage in a lab at NASA’s Ames Research Center in Moffett Field, Calif. 

Credit: NASA /Dominic Hart

How is living in space like playing in the Super Bowl? Both involve circumstances that cause the body to involuntarily lose water.

Astronauts and athletes with low body water can suffer physical performance impairments and can develop symptoms such as headaches, fatigue, muscle cramps, light headedness, disorientation and, in severe cases, loss of consciousness.

With crew members living and working now and for years to come aboard the International Space Station, this is a real concern.

A rehydration beverage developed by John Greenleaf, physiologist and former researcher at NASA's Ames Research Center in Moffett Field, Calif., to treat low body water, or hypo-hydration, in astronauts is now being used to improve human performance under various demanding conditions on Earth.

Astronauts involuntarily lose body water during space missions. Body fluid that is usually pulled towards the feet by Earth's gravity shifts rapidly during spaceflight, moving from the legs into the upper body.

This fluid shift increases pressure in the head and torso, and body water loss soon follows.

Unless astronauts take countermeasures to restore their body water levels prior to re-entry, they can experience serious symptoms of dehydration when they return to Earth and gravity once again shifts their body fluid downwards.

"We set out to solve the problem of involuntary dehydration for astronauts," said Greenleaf. "Our goal was to improve their performance after descent or during the physically demanding work of extravehicular activity during spaceflight."

For astronauts to rehydrate themselves effectively, they must take in both water and electrolytes—or salts. Both the quality and quantity of electrolytes critically affect how water is absorbed and distributed within the body.

Early in the space program, astronauts were given water and salt tablets—specifically, sodium chloride—with instructions to consume both prior to descent.

This approach was unreliable. Some astronauts took only the salt tablets, which worsens dehydration; some only drank the water, which simply is excreted and offers no hydration benefit and an inconveniently full bladder; while others ingested varying proportions of salt and water, which provided less than optimal results.

Water that contains 0.9 percent dissolved sodium chloride—also known as isotonic or normal saline, commonly used for intravenous hydration—contains the right amount of electrolytes for optimal hydration, but is problematic as a consumable rehydration beverage.

Not only does isotonic sodium chloride taste bad, ingesting it can cause diarrhea.

To help ensure that astronauts would consume correct proportions of electrolytes and water, Greenleaf developed a pre-mixed beverage that was acceptably palatable.

Using bad-tasting isotonic saline as a starting point, Greenleaf replaced half of the sodium chloride with sodium citrate and added a non-caloric sweetener.

These modifications eliminated the gastrointestinal side effects associated with drinking isotonic saline, improved the taste, and maintained an optimal amount of electrolytes for rehydration.

The NASA rehydration beverage contains no sugar or carbohydrates and is distinctly salty-tasting.

"This is not a recreational beverage for casual drinking," said Greenleaf. "It is optimized for effective hydration rather than flavor."