Researchers at the University of Lorraine in France and the University of Luxembourg report stresses felt during launch, in zero gravity and on landing can disrupt the body's natural defenses against infection.
Such changes to the immune system need to be researched before astronauts undergo longer space missions such as a voyage to Mars, they said.
The researchers sent Iberian ribbed newt embryos to the International Space Station before the embryos started to develop an important antibody called Igm, which is also found in humans and is the largest antibody that circulates in blood.
Upon landing, they were compared with embryos grown on Earth and found gravity changes during development affect antibodies and the regeneration of white blood cells, which are important in defending the body against infectious diseases.
These changes could also occur in humans, the researchers said, and require further research to see how gravity can influence the immune system and white blood cell function, which play a role in many human diseases including cancer and diabetes.