A new study found that astronauts have a higher level of DNA mutations after space travel, and that could be a sign of an increased risk of cancer.

The main concern is about radiation, which occurs at higher levels above earth's atmosphere. Exposure to excessive radiation is one of the known risk factors for cancer.

The researchers discovered the astronauts were more likely to have somatic mutations in their genes, compared to people who haven't been to space.  Somatic mutations occur in DNA after conception and involve cells other than sperm or egg cells, meaning they're not passed down to offspring.

The mutations identified found in the astronauts resulted in the overrepresentation of blood cells derived from a single clone, a process called clonal hematopoiesis. That process is at the root of several types of blood cancer, including chronic myeloid leukemia.

"Astronauts work in an extreme environment where many factors can result in somatic mutations, most importantly space radiation, which means there is a risk that these mutations could develop into clonal hematopoiesis," said David Goukassian, the study's lead author and a professor of cardiology at Icahn Mount Sinai in New York, in a statement.

He added: "Given the growing interest in both commercial spaceflights and deep space exploration, and the potential health risks of exposure to various harmful factors that are associated with repeated or long-duration exploration space missions, such as a trip to Mars, we decided to explore, retrospectively, somatic mutation."

Using DNA sequencing and bioinformatics analysis, researchers identified 34 mutations in 17 genes in the astronauts. The most common mutations were in TP3, a gene that produces a tumor-suppressing protein, and DNMT3A, one of the genes most likely to mutate in acute myeloid leukemia.

Although these mutations were elevated, they didn't exceed two percent, an official threshold of concern. But the researchers had recommendations for NASA going forward.

"The presence of these mutations does not necessarily mean that the astronauts will develop cardiovascular disease or cancer, but there is the risk that, over time, this could happen through ongoing and prolonged exposure to the extreme environment of deep space," said Goukassian.