A big concern for the health of astronauts is exposure to radiation. On Earth, we are protected from most space radiation by the planet’s atmosphere, but on the space station and further afield, this is not the case and astronauts are exposed to far more. Radiation damages DNA and damaged DNA can lead to cancer, raising fears that astronauts and cosmonauts have an increased risk of cancer from their time spent in space. NASA lists “Risk of radiation carcinogenesis from space radiation” as one of its top research priorities.
A new study published today in Scientific Reports, by researchers at Mortality Research & Consulting, Inc looked at data from all NASA astronauts who had flown in space at least once since 1959 and all cosmonauts since 1961, collecting data until the end of the follow-up periods in 2018 or 2017, respectively. Historical data from 301 astronauts and 117 cosmonauts involving over 10,000 person-years of follow up time, averaging out as 24 years per astronaut and 25 years per cosmonaut was reanalyzed using new statistical methods.
During the study period, there were 53 astronaut deaths and 36 cosmonaut deaths, with 16 and 10 deaths from cancer, respectively, representing just under a third of all deaths in both groups. In the U.S., around 22% of all deaths are caused by cancer according to the CDC, suggesting a slightly higher rate of cancer in people who have been to space, but the study authors conclude this is unlikely to be significant, partly due to the relatively low numbers of astronauts and cosmonauts available to be studied. Additionally, of the astronauts, 8 of the 53 deaths (15%) were caused by cardiovascular disease, compared to 23% of all Americans, which is perhaps unsurprising considering the high fitness levels astronauts must maintain.
The study included many astronauts who may have spent only a few days or weeks in space, particularly those in the earlier crewed Gemini and Apollo space missions where spaceflights sometimes lasted just a few days. Many of those astronauts would return to space, some even on the space shuttle missions, picking up more time. But their times typically pale in comparison to the duration spent in space by more modern astronauts, partly due to longer missions to space stations past such as Skylab and Mir and the ISS at present. For example, Russian cosmonaut Gennady Padalka has spent 879 days in space, the current world-record. Astronaut Peggy Whitson currently holds the record for an American, at 665 days.
The more time someone spends in space, the more radiation they will be exposed to and the more DNA damage they will, in theory, accumulate. As to whether this DNA damage actually increases an individual’s risk of cancer or not is certainly more nuanced and is influenced by numerous other environmental and genetic factors. For example, it would likely be fair to say that modern serving astronauts are likely to be among some of the fittest people on the planet, likely to have healthy diets, exercise a lot and not smoke, nor drink to excess. All of these will reduce their chances of getting cancer.
As a cancer research scientist who works on DNA damage and how it causes cancer, I am not surprised that this study concluded no substantial effect on cancer risk. However, in a decade or two time the picture may be very different. Larger numbers of astronauts who have spent great spans of time in space will be reaching old age where even normal people are quite likely to get cancer. It may be that historically shorter spells in space have little-to-no effect, but those with longer stints start to show an increased risk of cancer.
A study published in April this year by led researchers at The University of Arizona in partnership with NASA looked at the function of Natural Killer (NK) cells, a crucial part of the immune defense against cancer, in astronauts who had been on the International Space Station for roughly six month missions. They found that the function of the cells was impaired and although there is currently no direct evidence linking this to cancer risk, it is certainly a cause for concern and requires further investigation.
With future crewed space missions likely to involve travel further afield, for example to Mars – astronauts will experience greater and greater cumulative doses of radiation .For now, monitoring the health of recently-retired and currently serving astronauts with projects such as the one-year mission will hopefully provide more information about the cancer and other health risks associated with space travel.