Astronauts who flew in deep space on the Apollo program have a higher chance of developing cardiovascular disease, possibly because of exposure to radiation. These are the findings of research published in Scientific Reports.

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Astronauts face health risks, including cardiovascular problems.

Astronauts traveled into deep space as part of the Apollo lunar missions. These men were exposed to high levels of galactic cosmic radiation. Astronauts and cosmonauts on other missions did not face such high levels of radiation.

Previous studies have suggested that space travel can lead to stiffening of the arteries. The near-zero gravity experienced during space travel affects blood circulation.

The human circulatory system is designed to pump liquids upward, to counter the Earth’s gravitational force. In space, the face becomes puffy as liquids are not pulled toward the feet.

Past research has indicated that 10 percent of all astronauts who died between 1959-1991 had cardiovascular problems, 5 percent had cancer, 80 percent died in accidents, and 5 percent died of other causes. However, most of these did not fly in deep space.

A team led by Prof. Michael Delp, of Florida State University, wanted to know whether exposure to deep space radiation, weightlessness, or both, would be likely to trigger the cardiovascular problems seen in Apollo astronauts.

The Apollo program operated from 1961-1972. Apollo astronauts included Neil Armstrong, Buzz Aldrin, and Michael Collins. They flew to the moon in 1969 on Apollo 11.

Fast facts about space travel
  • In total, 555 people have traveled in space, including 345 Americans
  • 299 American men and 46 American women have been in space
  • Collectively, humans have spent 132.8 person-years in space.

Between 1968-1972, there were 11 manned Apollo flights. Nine of those flew beyond Earth’s orbit into deep space.

In total, 24 men flew into deep space on the Apollo missions. Eight of them have already died. The researchers looked at data for seven of those men. An eighth, Edgar Mitchell, passed on after the analysis of the data was carried out.

Results showed that 43 percent of the Apollo astronauts who died had a cardiovascular problem. In comparison, astronauts who did not fly had a 9 percent chance of dying of a similar problem. Among the astronauts who flew in low Earth orbit only, the odds of having cardiovascular disease were 11 percent.

The Apollo astronauts were four to five times more likely to die of cardiovascular issues than astronauts who either did not fly or who flew in low Earth orbit.

Those who flew in low orbit experienced weightlessness, and their chance of dying of cardiovascular problems was slightly higher than in those who did not fly. But for those who flew in deep space, exposed to both weightlessness and radiation, the risk was far higher.

This suggests that radiation, rather than weightlessness, is the main factor contributing to cardiovascular disease.

The scientists gave mice similar exposure to the type of radiation that the Apollo astronauts would have faced.

Six months later, which is the mouse equivalent of 20 human years, the mice showed signs of cardiovascular disease.

Their arteries sustained the kind of damage that, in humans, typically leads to atherosclerotic cardiovascular disease. Results suggest that irradiation from deep space leads to a sustained dysfunction in the vascular endothelial cells. This type of dysfunction is known to lead to occlusive artery disease.

According to Prof. Delp, this suggests that deep space radiation can damage vascular health.

We know very little about the effects of deep space radiation on human health, particularly on the cardiovascular system. This gives us the first glimpse into its adverse effects on humans.”

Prof. Michael Delp

Astronauts normally have better healthcare outcomes than most people, as they are highly educated and have access to top medical care.

However, when the Apollo astronauts traveled into deep space, they did something that nobody else has ever done; they are the only people ever to have experienced these particular conditions.

This type of information will no doubt be of interest to government and private organizations that are currently making plans for deep space travel and tourism.

The National Aeronautics and Space Administration (NASA) are planning orbital missions around the moon from 2020-2030, and a manned flight to Mars is a future possibility.

The authors note that a limitation of their study was the small sample size. Now, together with NASA, they are planning further studies into the cardiovascular health of the Apollo astronauts.

Find out more about the health risks associated with space travel.