Can shields, exercise, or medicine cut space radiation and bone loss on long trips?

"secondary particles, including neutrons emitted at low energy from the spacecraft shielding, may be common in deep space and may preferentially target surface tissues such as the eyes and skin"

"a "bath of radiation" composed of residual rays and fast neutrons inside the spacecraft may present a concern for deep tissues such as bones and the cardiovascular system"

"skin melanoma, cataracts, loss of bone mass, and aging of the cardiovascular system are possible, dependent on the dose, dose-rate, and individual factors"

"The impacts of heavy ions are rare and their contribution to radiation dose may be low during low Earth orbit"

"But during long duration missions beyond LEO there is a real danger that crews may be exposed to acute doses that may lead to acute radiation syndrome (ARS). To be prepared for such missions, space agencies must be prepared to anticipate radiation exposures and be able to deal with the consequences [1–4]."

"Kouvaris JR, Kouloulias VE, Vlahos LJ. Amifostine: the first selective-target and broad-spectrum radioprotector. Oncologist. 2007;12(6):738–47."

"Landauer MR, Srinivasan V, Seed TM. Genistein treatment protects mice from ionizing radiation injury. J Appl Toxicol. 2003;23(6):379–85."

"Davis TA, Landauer MR, Mog SR, Barshishat-Kupper M, Zins SR, Amare MF, et al. Timing of captopril administration determines radiation protection or radiation sensitization in a murine model of total body irradiation. Exp Hematol. 2010;38(4):270–81."

"Guan J, Wan XS, Zhou Z, Ware JH, Donahue JJ, Biaglow JE, Kennedy AR. The effects of dietary supplement agents on space radiation-induced oxidative stress in Sprague-Dawley rats. Radiat Res. 2004;162:572–9."

"the rover has passed a series of other interesting terrains where we find decreases in the dose rate reaching 19%. This radiation reduction is due to extra shielding provided by the nearby surface structure"

"confirming the potential use of surface structures for radiation protection of humans on Mars."

"We finally estimate that on a flat surface the albedo radiation is between ∼18% and 24% of the total surface dose."

"With the support of university-based research groups and partner space agencies, NASA has identified exercise to be the primary countermeasure for long-duration space flight."

"Results showed that leg volume and muscle isokinetic strength decreased, maintenance of aerobic capacity improved with increasing exercise intensity, and postflight recovery schedules were reduced with increasing exercise intensity (1, 15)."

"Since that flight, other missions have accommodated experiments on radiation exposure, pulmonary function, risk of kidney stone development, presence of a natural cardiovascular reflex to counteract light-headedness upon return to Earth’s gravity, changes in skeletal muscle, factors of dysfunctional locomotion upon return to Earth’s gravity, and foot ground reaction forces during normal activities"

"The approach for this period of space exploration was to adopt aspects of the Russian Countermeasures Program, which was based on the past history of Russian expert opinion, experience, and research in crew health maintenance (1)."

"Attempts to come up with a simple way to express the amount of loss usually estimate it at about 0.5% to 1% per month (417, 418, 425, 426), roughly similar to postmenopausal bone loss rates over a year."

"By these estimates, on flights up to about 6 months, it takes 2 to 3 times the mission duration to recover the lost bone."

"bone resorption increases during spaceflight and bone formation decreases or does not change significantly, substantiating that spaceflight disrupts the balance between bone resorption and formation, which can lead to a net loss in bone mass."

"Bone mineral density losses at landing after 6-month ISS missions are estimated to be 2% to 9% for different bone sites (419), with significant site-to-site and individual-to-individual variability."

"Analysis of bone recovery data from dual- energy x-ray absorptiometry (DXA) analyses suggests that while regional differences exist, the half-life of bone recovery after flight is on the order of 5 to 9 months after flight (420, 672)."

"Bone remodeling markers suggest a decreased bone formation coupled with an increased bone resorption."

"This bone loss can be slowed down by exercise on treadmills or resistive apparatus."

"Weightlessness increases both bone loss and kidney stone formation risk."

"Different types of exercise and pharmacological treatments with bisphosphonates, RANKL antibody (receptor activator of nuclear factor κβ ligand antibody), proteasome inhibitor, pan-caspase inhibitor, and interleukin-6 monoclonal antibody decrease bone resorption and promote bone formation."

"These drugs increase bone mass, thus reducing fracture risk, but also lead to increased levels of fatigue microdamage."

"Additionally, recombinant irisin, cell-free fat extract, cyclic mechanical stretch-treated bone mesenchymal stem cell-derived exosomes, and strontium-containing hydroxyapatite nanoparticles also show some positive effects on bone loss."

"Exposure to Galactic Cosmic Rays (GCR) presents significant health risks to astronauts during long-duration deep space missions."

"The model predicted bisphosphonate treatments with low to intermediate suppression of remodeling activation and that create higher bone balance ratios cause reductions in fracture risk."

"Light elements such as hydrogen-based materials are considered more effective shields than Al (Guetersloh at al.2006)."

"Postflight changes were minimal for treatments with intermediate suppression."

"However, for high-energy GCR, which deeply penetrate materials, aluminum offers only modest attenuation."

"For treatments highly suppressing remodeling activation, these predicted postflight changes included decreased BMD and increased damage accumulation."

"Zeitlen et al. demonstrated that liquid hydrogen provides optimal performance but is impractical for space missions (Zeitlin et al.2008)."

"A multi-layer configuration of PE materials led to a significant reduction (approximately 10%) in the secondary neutron flux."