Future Tense

Two Big Problems With That Study Suggesting Space Travel Could Cause Alzheimer’s

U.S. astronaut Kevin Ford and Russian cosmonauts Oleg Novitskiy and Evgeny Tarelkin prepare to head to the International Space Station.


“In space I see things that are not there,” astronaut Don Pettit wrote last year from aboard the International Space Station, about 200 miles above Earth’s surface. When he saw flashes that looked like “luminous dancing fairies,” Pettit wasn’t losing his mind. He and other astronauts “see” radiation when it hits their retinas.

Space is hostile to life not only because it is empty, but because it’s not quite empty enough. Radiation that endangers astronauts spurts through space in two main forms: galactic cosmic rays and protons ejected by the sun. Both sources of radiation are potentially dangerous to human life. Even though galactic radiation can be more energetic, the number of particles in a burst of solar radiation can be as much as 100 million times larger than the galactic background, which is much more immediately dangerous for astronauts.

Pettit and his colleagues on the ISS are relatively safe, though, because they are orbiting within Earth’s magnetic field. Magnetic fields deflect charged particles that account for most of the radiation—both solar and galactic. Travel beyond low Earth orbit—to the moon or beyond—is much riskier. NASA, which has displayed an unsteady commitment to such exploration, has funded research in how to mitigate radiation risk in haphazard fashion in the past, according to a 2008 National Research Council report. The latest widely reported study to come out of NASA’s efforts was published earlier this week in PLOS ONE, a scientific journal.

The study, done at the University of Rochester, claims that galactic cosmic radiation may lead to an increased risk of Alzheimer’s disease. But it is flawed in two ways that are indicative of what’s wrong with both NASA and with much modern medical research.

The first problem is a mousy approach to risk management. Radiation from the sun and cosmic radiation are both significant dangers to astronauts. While the cosmic radiation is chronic, solar radiation can suddenly spike, catastrophically ending a mission by giving the astronauts radiation sickness, which could be fatal, especially if there is no advance warning. (One such solar storm took place in 1972—just after the Apollo 16 astronauts had returned to Earth and before Apollo 17 took off. It put a scare into NASA’s ranks.)

There are plenty of people who would be willing to go to Mars even if it meant an incrementally higher risk of Alzheimer’s some time after they were to return. The real worry is whether the mission itself can succeed. That means research should focus on how to take shelter from solar radiation. NASA is sponsoring some work on new techniques to electromagnetically protect astronauts instead of relying on materials to stop radiation, which they are not very good at doing. (Some space suits in fact make radiation worse because they themselves become radioactive when bombarded by protons in space and emit secondary radiation.)

The second basic flaw in the University of Rochester study is that it relies on subjecting mice to acute doses of radiation and measuring the effects, instead of saying anything about how humans deal with radiation. As Daniel Engber has written in Slate, this is a line of research that may be reaching the limits of its effectiveness. The researchers acknowledge these limitations in print, though they don’t seem to take their own caveats seriously: “Differences in mouse strain, timing, and radiation beam energy limit our ability to extrapolate from these studies,” they write at one point. They later continue, “while many of the pathological processes are believed to be similar, this model does not reflect the complete human condition.”

So headlines like “Study: Space Radiation Could Cause Alzheimer’s” are true in a narrow sense: Space radiation could cause Alzheimer’s. But this study doesn’t establish that it does. The real news here is that overreliance on mouse models continues, as does selective interpretation of data. In this study, significant changes in the amount of brain plaque thought to contribute to Alzheimer’s were seen only in male mice—but there’s little discussion of the fact that female mice appeared relatively unscathed. All of the mice had been genetically engineered to be susceptible to Alzheimer’s, something not likely to be true of astronauts. Even so, irradiated mice performed differently to non-irradiated mice in only two of three simplistic cognitive tests.

It is impossible to get to Mars or to travel elsewhere in space without risk. How radiation affects astronauts is an important question. But worrying excessively about what the after-effects of travel might be saddles would-be pioneers with the bureaucratic mentality of the Occupational Safety and Health Administration. Such safeguarding is necessary on Earth to protect workers who may be exploited by their employers—but it is a millstone weighting down highly educated astronauts who voluntarily take seats atop huge tanks of explosives that propel them to space. (It would be another issue if astronauts risked being stricken with Alzheimer’s while behind the controls of a spacecraft, but there is no evidence from this study that suggests the response, even of the susceptible mice, is immediate.)

If we are to get to Mars, it’s best not to worry about mice that may or may not have somewhat increased amounts of brain plaque. Pettit, at least, knew he was seeing things that are not there. But he might not be the only one.