Deep space travel takes its toll on the body – and it’s apparently something you can’t walk away from.
Apollo astronauts who have ventured out of Mother Earth’s protective magnetosphere appear to be dying of cardiovascular disease at a much higher rate than their counterparts—both those who have remained grounded and those who have flown alone in the protective embrace of low orbit. flew to earth. While the data is small — based on just 77 astronauts in total — researchers speculate that powerful ionizing radiation in deep space may be to blame. That hypothesis was supported in follow-up studies in mice that provided evidence that similar radiation exposure led to long-term damage to the rodents’ blood vessels. All data was published in the journal on Thursday Scientific Reports.
The study, while not definitive, may add another warning to the potential dangers of future attempts to fly to Mars and elsewhere in the cosmos.
“These data suggest that human travel to deep space may be more hazardous to cardiovascular health than previously believed,” conclude the study’s authors, led by Florida State University health researcher Michael Delp.
As NASA tries to minimize astronaut exposure to space radiation, it recognized that exposure was essentially an unavoidable part of the job. “Risks of radiation exposure to crew members were assessed and weighed against mission gains,” NASA experts wrote in a 1973 report (pdf) on the Apollo experience.
Since then, other studies have attempted to assess the health consequences of space travel. In many cases, studies have come up relatively empty-handed. However, Delp and his colleagues say some of those studies may be inaccurate because they tried to compare astronaut health statistics with those of the general public. This would likely mask health effects, Delp and his colleagues argue, because astronauts are generally healthier and more health-conscious than the general public. Astronauts are physically fit with a high level of education and consistent access to medical care. In America, those are not necessarily standards.
In the new study, Delp and coauthors compared health records of 42 astronauts who had traveled into space — seven of whom had made it past the magnetosphere and to the moon — with the medical records of 35 astronauts who had been grounded for their careers. The death rate from cardiovascular disease among the Apollo lunar astronauts was a whopping 43 percent, which is about four to five times that of the non-fliers and low-fliers (nine and 11 percent, respectively).
To find out whether ionizing radiation in deep space or perhaps weightlessness could explain the apparent jump in deaths from cardiovascular disease, the researchers turned to a mouse model. Mice were either exposed to a single dose of radiation, their hind legs elevated for two weeks to avoid weight bearing, or they received both treatments. The researchers then allowed the mock astronaut mice to recover for six to seven months, which would be about 20 years in human terms.
The researchers found that the mice exposed to radiation, or both radiation and simulated weightlessness, suffered damage to their blood vessels. The mice had impaired vasodilation, or problems expanding their blood vessels to adjust to blood pressure. This can be a precursor to heart attacks and strokes. In contrast, the mice that just experienced simulated weightlessness appeared normal.
While the rodent data complement the findings in real astronauts, the authors were clear about the study’s limitations. “Caution should be exercised in drawing definitive conclusions about specific health risks,” they concluded. The number of astronauts is very small for an epidemiological study, there may be other factors in the space environment that could explain the possible health effects, and the type of radiation given to the mice was not exactly the same as the type astronauts experience.
Delp and his colleagues are working with NASA on follow-up studies on astronaut health.
Scientific Reports2016. DOI: 10.1038/srep29901 (About DOIs).