True. When an astronaut spends a long duration in a weightless space station, they experience a decrease in bone mass. This is because in the microgravity environment of the space station, the lack of gravity's pull on the body causes the bones to lose minerals and become less dense. This phenomenon is known as spaceflight-induced osteoporosis. To confirm this information, you can refer to scientific studies and reports on the effects of long-duration space missions on astronauts' health.
