Human brains could become 'leaky' during space travel according to research by the University of South Wales.
Professor Damian Bailey found changes in gravity and long-term space flights could weaken the blood-brain barrier that helps protect the brain.
This can then lead to swelling and increased pressure in the brain which, according to Professor Bailey, NASA have identified as "the top health risk for long-duration spaceflight".
The research used weightless environments to simulate spaceflights and then measured blood flow to different parts of the brain.
The research looked at what impact long-term exposure to a weightless environment could have on the human brain and in particular, any link it may have to a condition called neuro-ocular syndrome
The condition, which can be caused by spaceflight, can lead to blurred vision and headaches.
Professor Bailey's research was funded by the French Space Agency (CNES) and used an aircraft dubbed the "vomit comet" which simulates a weightless environment.
The specialist aeroplane, which is based in Bordeaux in France, flies a series of sharp ascents and descents. Zero-gravity is felt during the 20-second dives.
During the experiments, Professor Bailey measured blood flow to different parts of the brain and took blood samples before, during and after the weightless periods
Professor Bailey found that blood flow to the back of the brain increased when it becomes weightless. This then led to a more 'leaky' barrier between the brain and blood.