When astronauts started going on long-term space missions, their bones got thinner. Without the stress of gravity and regular exercise, the bones became less dense.
Today, astronauts work out hard in space to prevent long-term bone damage, also known as osteoporosis.
Earth-bound bones need exercise, too. It makes them sturdier and boosts their ability to store minerals and produce blood cells. Diet also determines bone health. For instance, muscles and nerves need the mineral calcium, just like bones do. If they don’t get it from milk and green vegetables, then they raid the bones for calcium. As a result, bones become more brittle, a condition called rickets. With exercise and good food, people can ward off many—but not all—threats to long-term bone health.
