Astronauts in a weightless environment usually lose 5 to 7 percent of their bone density in six months even while exercising two hours per day. In the study conducted by researchers of the Japan Aerospace Exploration Agency, Tokushima University and others, five astronauts, including Koichi Wakata and Soichi Noguchi, who stayed in space for 137 days and 163 days, respectively, exercised daily and took bisphosphonates used to treat osteoporosis once a week during their stay on the ISS. As a result, researchers found almost no bone density loss in the astronauts.