Effects of space flight on sperm function and integrity: A systematic review

Abstract

With the advancement in space exploration and the intention to establish an inhabitable human settlement on Mars, it is important to investigate the effects of exposure to space/microgravity and the associated radiations on procreation. Sperm function and integrity are fundamental to male reproduction and can potentially be affected by the environmental changes experienced in space. Therefore, this study was conducted to systematically gather, filter, and collate all the relevant information on the effects of spaceflight on male reproductive parameters and functions. A search was performed utilizing the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. Data were extracted from the major electronic databases including PubMed, and other credible literature sources. MeSH search terms that were employed included “spermatozoa”, “microgravity”, and “ionizing radiation”. The literature search did not discriminate against papers published before a certain date due to the very limited number of articles available. However, there was a restriction on the male gender and language (English). The parameters included in this study are sperm motility, total sperm count, sperm DNA fragmentation hormonal levels and testicular histology. Following a comprehensive literature search, a total of 273 articles were retrieved and screened, 252 articles were excluded due to the irrelevance to the topic, duplication, and non-original articles. A total of 21 articles met the inclusion criteria and are included in the current study. Findings from these studies showed that sperm motility was decreased after exposure to microgravity and ionizing radiation. Total sperm count was also found to be reduced by microgravity only. Sperm DNA fragmentation was increased by both ionizing radiation and microgravity. Testosterone levels and testicular weight were also decreased by microgravity. Although there is a dearth in the literature regarding the effects of microgravity and ionizing radiation on male reproductive parameters, the available findings showed that exposure to microgravity poses a risk to male reproductive health. Therefore, it is essential to develop countermeasures to either manage, treat, or prevent these consequential adverse effects. Hence, this review also highlights some potential countermeasure approaches that may mitigate the harmful effects of microgravity and associated exposures on male reproductive health.

Long-term space missions’ effects on the human organism: what we do know and what requires further research

“…Studies found, among other things, impaired spermatogenesis ( Strollo, 1999 ; Ahrari et al, 2022 ), reduction in the total number of sperm cells and their motility, and sperm cells DNA fragmentation ( Ahrari et al, 2022 ). At the hormonal level, both actual and simulated spaceflight conditions inhibit androgen production.…”

“…At the hormonal level, both actual and simulated spaceflight conditions inhibit androgen production. Testosterone levels decrease, resulting in hypogonadism ( Mishra et al, 2016 ; Ahrari et al, 2022 ). Serum levels of luteinizing hormone (LH) increase, which is associated with reduced negative testicular feedback ( Mishra et al, 2016 ).…”

Homo sapiens—A Species Not Designed for Space Flight: Health Risks in Low Earth Orbit and Beyond, Including Potential Risks When Traveling beyond the Geomagnetic Field of Earth

“…Such radiation can result in damage to multiple physiologic systems, resulting in an increased risk for cancer, cardiovascular disease, central nervous system alterations, and others [ 73 , 108 , 109 , 110 ]. In addition, for long-term flights with the intent to colonize places such as Mars, radiation could also negatively impact the ovaries and sperm of astronauts [ 111 ]. This risk has prompted the investigation of potential countermeasures to diminish or prevent such risks [ 109 ].…”

Epidemiology of sperm DNA fragmentation in a retrospective cohort of 1191 men

“…For example, positive correlations were reported with biological factors (age, infection, presence of varicocele, obesity), lifestyle choices (smoking, drugs, medication) and environmental factors (pollutants, heat, exposure to ionizing or/and electromagnetic radiations), as reported in several reviews in the last few years. [10][11][12][13][14][15] However, the reported studies were often underpowered, mainly because of small cohort sizes.…”