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Study suggests spaceflight may decrease human immunity
Dolores Beasley Sept. 29, 2004
Johnson Space Center, Houston
STUDY SUGGESTS SPACEFLIGHT MAY DECREASE HUMAN IMMUNITY
A NASA-funded study has found the human body's ability
to fight off disease may be decreased by spaceflight. The
effect may even linger after an astronaut's return to Earth
following long flights.
In addition to the conditions experienced by astronauts in
flight, the stresses experienced before launch and after
landing also may contribute to a decrease in immunity.
Results of the study were recently published in "Brain,
Behavior, and Immunity." The results may help researchers
better understand the affects of spaceflight on the human
immune response. They may also provide new insights to ensure
the health, safety and performance of International Space
Station crewmembers and future spacefarers on extended
"Astronauts live and work in a relatively crowded and
stressful environment," said Duane Pierson, the study's
principal investigator and NASA Senior Microbiologist at
Johnson Space Center, Houston. "Stresses integral to
spaceflight can adversely affect astronaut health by
impairing the human immune response. Our study suggests these
effects may increase as mission duration and mission activity
demands increase," he added.
The white blood cell count provides a clue to the presence of
illness. The five main types of white cells work together to
protect the body by fighting infection and attacking foreign
material. The most prevalent white blood cells are called
From 1999 to 2002, scientists from NASA, Enterprise Advisory
Services, Inc., of Houston, and the Boston University School
of Medicine compared neutrophil functions in 25 astronauts.
They made comparisons after five-day Space Shuttle missions
and after nine to 11 day missions.
Researchers found the number of neutrophils increased by 85
percent at landing compared to preflight levels. Healthy
ground control subjects, who did not fly, exhibited no more
than a two percent increase. Researchers also discovered
functions performed by these cells, specifically ingestion
and destruction of microorganisms, are affected by factors
associated with spaceflight. The effect becomes more
pronounced during longer missions.
The increase in astronaut neutrophil numbers resulted in a
corresponding increase (more than 50 percent) in total white
blood cell counts at landing. The increase is a consistent
consequence of stress.
Pierson emphasized that "no astronauts in the study became
ill; however, longer exploration missions may result in
clinical manifestations of decreased immune response."
Researchers concluded the general effect of spaceflight, pre-
and post flight-related stress decreases the ability of
crewmembers' neutrophils to destroy microbial invaders. This
finding suggests crewmembers returning from longer missions
may be briefly more susceptible to infections than before
launch, because these cells are not as efficient in ingesting
and destroying infectious agents.
"Having a better understanding of the impact of stress on
immunity will help us better understand the risks of
infectious disease for Space Station crewmembers and future
travelers on long-duration missions," Pierson said.
For information about NASA's space research on the Internet,
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