Medical Discovery News
By Drs. David Niesel and Norbert Herzog

“That’s one small step for a man, one giant leap for mankind.” Since Neil Armstrong uttered those iconic words as he stepped onto the moon for the first time in 1969, researchers have learned that the high levels of radiation astronauts are exposed to while traveling in space can harm them long after they have returned to Earth. As scientists consider the prospect of a manned mission to Mars, the issue of long-term exposure poses a significant obstacle, especially now that it has been linked with Alzheimer’s disease.

Radiation in space is more complex than that on Earth, because it includes galactic cosmic radiation and solar particles normally blocked by Earth’s atmosphere. In addition, the Earth’s magnetic field traps some of the radiation from the sun in belts, which space vehicles fly through on their way to other planets. The longer the trip, the greater the exposure, and within a 750-day roundtrip to Mars an astronaut would be exposed to four times the acceptable lifetime radiation limit for a human.

The average person is exposed to 3 millisieverts (mSv) of radiation each year, from radon that naturally exists in the air, small radioactive particles in water and soil, rays from the sun, and medical tests (a chest X-rays delivers about .02 mSv). But if a person were exposed to 50mSv, their blood would start to change. Exposure to 1,000 mSv causes hemorrhage, vomiting, hair loss, and even death within two weeks, such when an accident occurs at a nuclear energy facility like Chernobyl or Fukushima. Exposure to 20,000 mSv can cause death in minutes, as with a nuclear bomb. 

NASA believes that a 3 percent increase of chance of death due to radiation exposure during a space mission is an acceptable risk for astronauts. This increases the astronaut’s lifetime risk of death from cancer to 23 percent, almost a one in four chance. Now a study reveals an additional risk for astronauts exposed to radiation in space: Alzheimer’s disease.

Scientists at the University of Rochester and Harvard University exposed mice to doses of radioactive iron at levels comparable to those expected on a trip to Mars. Six months after the radiation exposure, the mice showed mental impairments including issues with memory. Furthermore, male mice had accumulated the beta-amyloid protein that is associated with the start of Alzheimer’s, suggesting a more rapid progression in male mice.

Obviously mice are different than humans and space explorers would be exposed to more than one type of radiation, so this model may not exactly mimic what would happen to humans traveling to Mars. However, in addition to the increased risk of cancer and death, space explorers must now consider the increased chance for and more rapid development of dementia. New technology to provide radiation shielding for astronauts could minimize the amount of radiation they are exposed to.  

Medical Discovery News is a weekly radio and print broadcast highlighting medical and scientific breakthroughs hosted by professor emeritus Norbert Herzog and professor David Niesel, biomedical scientists at the University of Texas Medical Branch at Galveston. Learn more at