<p>&#160; &#160;&#160;All organisms survive and multiply under the geomagnetic magnetic field (GMF) <sup>[1]</sup>. With the launch of the Moon and Mars space program, during long-distance space mission, astronauts will inevitably be exposed to an environment with a hypomagnetic field (HyMF), which several thousand times weaker than GMF<sup>[2]</sup>. Spatial hypomagnetic field exists on the surface of the moon or in the deep space of the solar system, and its magnetic intensity is less than 5 &#956;T<sup>[3]</sup>. At present, the research on the effects of HyMF on the health of astronauts is mainly focused on the conditions of ground simulation experiments, including the central nervous system, blood system and brain cognition <sup>[4,5]</sup>. However, relevant safety of the skeletal system studies about HyMF are deficient. Our recent research indicated that the effects of HyMF on bone cannot be overlooked. In vivo, our study found that HyMF aggravated bone loss induced by hindlimb unloading (HLU) in rats and mice, which related to the changes in iron metabolism<sup>[6,7]</sup>. In addition, HyMF also inhibited the recovery of simulated microgravity-induced osteoporosis of mice, probably by restraining elevated iron return to normal levels<sup>[8]</sup>. Meanwhile, we found that HyMF can inhibit osteoblast differentiation and mineralization<sup>[9]</sup>, promote osteoclast formation and bone resorption in vitro<sup>[10]</sup>. The research results have significant academic values in the field of magneto-biology and the potential application values in space activities for the manned moon landing exploration.</p><p><strong>Key words:</strong>&#160;</p><p>Hypomagnetic field, geomagnetic field, safety management, iron storage.</p><p><strong>References</strong></p><p>[1]Dubrov A P. The Geomagnetic Field and Life: Geomagnetobiology. Bioscience. 1978. 978-1-4757-1610-8.</p><p>[2]Belyavskaya N. Biological effects due to weak magnetic field on plants. Advances in space Research, 2004,&#160;34(7): 1566-1574.</p><p>[3]Mo W C, Ying L & He R Q. Hypomagnetic field, an ignorable environmental factor in space? Science China -Life Sciences, 2014. 57(7): 726-728.</p><p>[4]Mo WC, Liu Y & He RQ. A biological perspective of the hypomagnetic field: from definition towards mechanism. Prog Biochem Biophys, 2012, 39: 835&#8211;842&#160;</p><p>[5]Jia B, Zhang WJ, Xie L, Zheng&#160; Q, Tian ZC & Shang P<em>. </em>Effects of hypomagnetic field environment on hematopoietic system in mice. Space Medicine &Medical Engineering, 2011.24(5): 318-322.</p><p>[6]&#160;Jia B, Xie L, Zheng Q, Yang P F, Zhang W J & Shang P. A hypomagnetic field aggravates bone loss induced by hindlimb unloading in rat femurs. PloS one, 2014, 9(8): e105604.</p><p>[7]&#160;Yang J, Meng X, Dong D, Xue Y, Chen X & Shang P. Iron overload involved in the enhancement of unloading-induced bone loss by hypomagnetic field. Bone, 2018 Sep;114:235-245.</p><p>[8]Xue YR, Yang JC, Luo J, Ren L, Shen Y & Shang P, Disorder of iron metabolism inhibits the recovery of unloading-induced bone loss in hypomagnetic field. Journal of bone and mineral research.2020. DOI: 10.1111/JBMR.3949.</p><p>[9]Yang J, Zhang J, Ding C, Dong D & Shang P. Regulation of Osteoblast Differentiation and Iron Content in MC3T3-E1 Cells by Static Magnetic Field with Different Intensities. Biological trace element research, 2017, 184(7): 1-12.</p><p>[10]Zhang J, Meng X, Ding C, Xie L, Yang P & Shang P. Regulation of osteoclast differentiation by static&#160;magnetic fields. Electromagnetic biology and medicine, 2017, 36(1): 8-19.</p><p>&#160;</p>
