Most Astronauts Experience ‘Space Headaches’ While on the ISS, Study Finds

Astronauts tend to experience headaches during long trips to space, a new study finds, and scientists are trying to figure out why.

These headaches occurred frequently, spanning both early and late stages of flight. The astronauts in the study mostly experienced tension headaches, though they also experienced migraines, despite having no history of recurring headaches, researchers reported last week in the journal Neurology.

Alexandra Sinclair, a neurologist at the University of Birmingham in England who did not contribute to the findings, tells Scientific American’s Joanna Thompson that the study is “really important and interesting.”

Previous research suggested astronauts may experience headaches early in flight, when many are suffering from motion sickness, the study authors write. But the researchers wanted to examine whether headaches persisted later on in spaceflight, which would have implications for longer missions.

The study surveyed 24 astronauts that took trips to the International Space Station between November 2011 and June 2018. All but one of the astronauts were men, and they were 46.7 years old on average. Their stints on the station lasted up to 26 weeks, and the astronauts were from NASA, the European Space Agency and the Japanese Aerospace Exploration Agency.

Astronauts completed a questionnaire about their headache history before launch. Only three reported having a headache that interfered with daily activities in the previous year, and none of them had a history of recurrent headaches or migraines.

The astronauts also filled out a questionnaire daily for the first seven days of their spaceflight and weekly after that. All but two of the astronauts reported headaches during their flight, and half of those experiencing headaches reported more than ten of them.

Crucially, the headaches didn’t just occur during the start of the trip—20 people reported headaches after the first week. Their headaches were mostly mild and most commonly accompanied by nasal congestion and sleeplessness.

Around 90 percent of the reported headaches had symptoms of tension headaches, which are marked by dull, aching head pain. Ten percent had symptoms of migraines, which can include throbbing or pulsing pain, nausea or sensitivity to light.

Migraines were more common in earlier stages of spaceflight (24 percent of all headaches) than in later stages (5 percent of headaches). The researchers aren’t exactly sure what causes the headaches, but they hypothesize that two different mechanisms are involved.

“In the first week, the body has to adapt to the lack of gravity, known as space adaptation syndrome. This phenomenon is similar to motion sickness and can cause nausea, vomiting and dizziness and headaches,” Ron van Oosterhout, lead author of the study and a neurologist at Leiden University Medical Center in the Netherlands, tells Reuters’ Will Dunham. The researchers found that symptoms of nausea, vomiting and vertigo occurred almost exclusively in the early headaches, supporting the idea that they were linked to space adaptation syndrome.

“The later headaches, we think, could result in an increase in intracranial pressure due to the cephalad fluid shift,” van Oosterhout tells MedPage Today’s Judy George. “Due to microgravity, there is more fluid accumulating in the upper part of the body and head—both the intracranial and extracranial—thereby resulting in higher pressure in the skull.”

Other research has uncovered a litany of effects of microgravity on the human body. The shifting of blood and cerebrospinal fluid toward the head is thought to be the underlying cause of vision problems experienced by some astronauts. A study last year found that fluid-filled cavities in the brain that expand during spaceflight can remain enlarged for years after astronauts return to Earth. Long-term exposure to microgravity has also been linked to loss of bone density and muscle atrophy, as well as blood indicators of brain damage.

“It is clear that even short-term—days or weeks—to medium-term—weeks or months—duration exposure to microgravity already has some effects, mostly reversible, on the human body,” van Oosterhout tells Reuters.

The researchers also surveyed an additional 42 astronauts who had previously traveled in space. More than half (55 percent) said they had experienced headaches during spaceflight.

None of the astronauts in the study reported headaches in the three months after returning to Earth. Sinclair notes to Scientific American that a limitation of the study is its small sample size, a common issue for space travel research.

Additionally, “one of the problems with evaluating headaches is that they are subjective, and [headache recall is] prone to reporting bias,” Sinclair tells the publication. Astronauts might intentionally downplay their symptoms, for example, to avoid becoming grounded for medical concerns.

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Will Sullivan is a science writer based in Washington, D.C. His work has appeared in Inside Science and NOVA Next.