According to a study, the brains of astronauts are affected by frequent and extended periods of space travel.

As we enter a new era in space travel, a study looking at how the human brain responds to travel outside Earth’s gravity suggests that frequent flyers should wait three years after longer missions to allow physiological changes in their brains to reset.

The researchers studied the brain scans of 30 astronauts before and after space travel. Their findings, reported in Scientific reportsrevealing that the ventricles of the brain expand significantly in those who complete longer tasks for at least six months, and that as little as three years may not provide enough time for the ventricles to fully recover.

The ventricles are cavities in the brain filled with cerebrospinal fluid, which provides protection, nutrition, and waste removal to the brain. Mechanisms in the human body distribute fluid effectively throughout the body, but in the absence of gravity, the fluid shifts upward, pushing the brain higher into the skull and causing the ventricles to dilate.

“We found that the more time people spent in space, the larger their ventricles,” said Rachel Seidler, a professor of physiology and applied kinesiology at the University of Florida and an author of the study. “Many astronauts travel to space more than once, and our study shows that it takes about three years between flights for the ventricles to fully recover.”

Based on the studies conducted to date, ventricular dilatation is the most permanent change in the brain resulting from spaceflight, said Seidler, MD, a member of the Norman Fixell Institute for Neurological Diseases at UF Health.

“We don’t yet know for sure what the long-term consequences of this will be for the health and behavior of space travelers. So allowing the brain time to recover seems like a good idea,” she said.

Of the 30 astronauts studied, eight have flown on two-week missions, 18 have been on six-month missions, and four have been in space for nearly a year. The study authors reported that ventricular hypertrophy diminished after six months.

“The biggest jump comes when you go from two weeks to six months in space,” Seidler said. “There is no appreciable change in the size of the ventricles after just two weeks.”

With the increased interest in space tourism in recent years, she said, this is good news, as shorter spaceships seem to cause small physiological changes in the brain.

While researchers can’t study astronauts who have been in space for more than a year, Seidler said it’s also good news that the expansion of the ventricles in the brain stops after about six months.

“We were glad the changes don’t add up dramatically, considering we’ll eventually have people in space for longer periods,” she said.

Seidler said the study’s findings may influence future decision-making regarding crew travel and mission planning.