- Microgravity conditions mimic aspects of aging, including the increased risks for blood clotting.

- Spaceflight increased markers for clot formation in female astronauts.

- Lowered levels of a hormone involved in blood clotting occurred during spaceflight.

Spaceflight Impacts on Blood Clot Risk in Women

Blood clots occur when the blood changes from a liquid to a semisolid state inside a blood vessel. Conditions that can increase the risk of blood clot disorders, called thrombophilias, include increasing age and low levels of certain clotting proteins.

The National Aeronautics and Space Administration (NASA) is interested in blood clot risk in astronauts on long-duration space missions for a number of reasons:

- The microgravity environment of space flight causes accelerated aging responses in many body systems, such as the cardiovascular system.

- Clots can dislodge and potentially block blood flow to essential, life-sustaining organs.

- Risk of blood clots increase in the general population with age. The average age of astronauts continues to increase.

- Female astronauts, particularly after menopause, could be at higher risk of blood clots during space missions.

Methods

This team of scientists examined whether blood clotting markers changed in microgravity conditions. Data came from the blood of 11 male and 7 female astronauts collected before, during, and after long-duration stays on the International Space Station (ISS). The scientists used the blood samples to measure:

- Platelet activation - the process by which platelets become "sticky" and clump together

- Levels of clotting proteins

- Fibrin formation - a key step in blood clot formation

Results

- Significant increases in platelet activation occurred during spaceflight in female astronauts.

- During spaceflight, levels of factors IX and XI, and activity of factor VIII, proteins that are part of the clotting process, increased in female astronauts but decreased in male astronauts.

- Decreased levels of protein C, a hormone involved in preventing clot formation, occurred in female astronauts during spaceflight.

The changes observed during spaceflight in the female astronauts mimic, to some extent, those observed with normal aging in women on Earth, and those related to oral contraceptive use.

Conclusion

These data provide the first assessment of blood clot risk for women living in space. The observations suggest that female astronauts may be at higher risk than male astronauts for blood clot disorders during spaceflight. This observation highlights the need to study in more depth any long-term health consequences of spaceflight on women.