In fact, they age “ten times faster in space than on the ground,” said Dr. Catriona Jamieson, the director of the Sanford Stem Cell Institute at the University of California, San Diego, a lead author of the study.

Stem cells are special cells that can develop into various kinds of tissue. Stem cell aging is potentially worrisome because it diminishes the body’s natural ability to repair its tissues and organs, potentially leading to chronic, age-related conditions like cancer, neurodegenerative diseases and heart problems.