Dear Doctors: Our 11-year-old son is fascinated with those astronauts who are stuck on the space station. One of the things he asks about a lot is how being in space for that long affects the human body. Do you know what the latest research says about that?
Dear Reader: You are referring to two American astronauts who arrived at the International Space Station last June for what was planned to be an eight-day mission. When the experimental spacecraft they had piloted developed technical difficulties, however, NASA decided the pair should wait for the arrival of a replacement spacecraft to make the return trip. As of New Year’s Day, the two astronauts had logged more than 200 days in space. They are not scheduled to return to Earth until at least March.
As the astronauts await their ride home, they are undergoing significant physiological changes. That’s because our bodies have evolved to both overcome and to utilize the pull of gravity. The absence of that constant resistance affects every cell, tissue, structure and biological system. That’s why astronauts in space spend hours each day exercising.
Without the pull of gravity to work against, muscle mass decreases and muscles begin to atrophy. Within several weeks, astronauts lose up to 10% to 20% of their lean muscle mass. Weightlessness erases the physical cues that trigger bone remodeling. This is the process in which new bone continuously replaces old bone. As a result, bone mass in astronauts decreases by 1% to 2% every month they spend in space.
Fluids change their behavior in the microgravity of space, as well. This adversely affects the heart, circulation and blood pressure; leads to persistent nasal congestion; causes tissues of the face and upper body to become swollen; affects the inner ear and vision; and even results in increased flatulence and constipation.
The vacuum of space also interferes with the production of red blood cells, resulting in a condition dubbed “space anemia.” Astronauts are exposed to higher amounts of ionizing radiation, which can increase cancer risk. There is also emerging evidence that space travel affects the structure of the human brain.
The newest research has found that living in space even causes changes to human DNA. This was discovered in a fascinating study of identical twin brothers Scott and Mark Kelly. Both are astronauts who have spent time in space. From March 2015 to March 2016, while Mark remained on Earth, Scott lived on the International Space Station. Upon Scott’s return after a year spent living in zero gravity, genetic analysis found that almost 1,000 of his chromosomes and genes worked differently than those of his twin brother.
The good news is many of the adverse effects of space travel resolve upon return to Earth. Some, such as the effects of fluid shifts, take only a short time. Others, including loss of muscle mass, bone density and cognitive effects, can take many months and intense rehabilitation to overcome. Some can be permanent. That has made the development of space suits and space craft to mitigate these effects a priority within the global space community.
(Send your questions to askthedoctors@mednet.ucla.edu, or write: Ask the Doctors, c/o UCLA Health Sciences Media Relations, 10960 Wilshire Blvd., Suite 1955, Los Angeles, CA, 90024. Owing to the volume of mail, personal replies cannot be provided.)
