gaps will do much to illuminate the directions in which research and development will be going within NASA” (IOM, 2008, p. 80). The current risk report has added a list of gaps, but as noted above they are not as detailed as they need to be in order to assess the knowledge needed.
The 2008 report stated that the evidence report “describes a necessary, but not sufficient, overall approach to the provisioning of autonomous health care resources and, at least as importantly, the enumeration of conditions that will be left untreated during exploration-class missions.” This assessment remains true of the current report.
SUMMARY
This is the fifth of five letter reports that have reviewed the series of NASA’s evidence reports on human health risks. This letter report reviewed five evidence reports and provided the committee’s responses to the questions detailed in the statement of task. The evidence reports are quite thorough in their review of the evidence of spaceflight risks, although they vary in format and in the consistency and quality of the writing.
With respect to the closely related reports on fracture and osteoporosis, the committee believes that the report appropriately develops the risk context, but that there is an over-reliance on the Factor of Risk model. A better model for fracture risk would include more of the anticipated risk factors associated with long-duration missions. Osteoporosis is correctly mentioned as a contributing factor, but it is not adequately considered as something to monitor and address during a long mission beyond low Earth orbit. The relationship of such weakening to fracture risks and to requirements for countermeasures and for in-flight monitoring should be emphasized. Input from the field of endocrinology (bone metabolism) should be sought. Current countermeasures, including ARED and antiresorptive agents, are not fully adequate to prevent bone loss and potential fractures (Orwoll et al., 2013), and significant bone loss occurs in some individuals even with ARED and bisphosphonates (Orwoll et al., 2013). As with most risks, there is significant individual variability in DXA scores before and after exposure to microgravity as well as in long-term recovery after return to Earth. This variability may be due to genetic, epigenetic, hormonal, or other influences, and it provides an opportunity to apply the principles of personalized medicine. Attention needs to be paid to these and other individual variations as relevant to each risk. The management of fractures during a mission should be included in the evidence report on
bone fracture. Obviously, life-long monitoring for subsequent fractures (e.g., fragility fractures) in former astronauts is important, but this might fit more naturally into the evidence report on osteoporosis. Additional input from the field of orthopedics would be helpful.
In two of the areas reviewed—cardiac rhythm problems and renal stone formation—the reports convey a traditional view of underlying physiology that has been substantially revised by contemporary medical science, and thus a more substantial reformulation of these risk reports is warranted. In particular, the arrhythmia report should be refocused to incorporate current understanding of which mechanisms of arrhythmia cause clinically insignificant arrhythmias and to add a more comprehensive description of other cardiac risks.
Finally, the report on medical care would benefit from greater clarity in risk context including consideration of all of the phases of a mission and all the different possible mission architectures. Risks associated with surface operations, many of which are dangerous when performed on Earth and might be more so on the surface of another planetary body, are not adequately considered. The concept of personalized medicine should be expanded to include more than just the incorporation of genetic and genomic information into preventive and therapeutic strategies.
The committee has noted throughout its series of five reports that conveying the information on the interactions across risk domains is one of the biggest challenges for the NASA evidence reports. The set of evidence reports could benefit from a more systematic approach to considering interactions with other risks. NASA should consider adding a standardized section or table in each report that shows the relationship of the risk described in the report with all other risks, noting whether and how each is related to the main topic of the report.
The committee greatly appreciates the opportunity to review the evidence reports and applauds NASA’s commitment to improving the quality of its reports. The evidence reports provide the basis for the work of NASA’s HRP, and the in-depth review that they provide will contribute to improving the health and performance of future astronauts and enhancing future human spaceflight endeavors.
Sincerely,
Carol E. H. Scott-Conner, Chair
Daniel R. Masys, Vice Chair
Committee to Review NASA’s Evidence Reports on Human Health Risks
