The next “giant leap” for humans maybe a trip to Mars, but having enough oxygen-carrying red blood cells for the journey might present a challenge, new research suggests.

Axar.az reports that even space tourists lining up for short trips might have to stay home if they are at risk for anaemia, or red blood cell deficiency, researchers said.

Astronauts are known to experience “space anaemia” but until now, it was thought to be temporary. One NASA study called it “a 15-day ailment”.

But in fact, anaemia is “a primary effect of going to space,” said Dr. Guy Trudel of the University of Ottawa, who led a study of 14 astronauts funded by the Canadian Space Agency.