The career of an explorer is risky, and it is chosen by individuals who acknowledge and accept risks beyond those of ordinary daily living. As the disintegration of the space shuttle Columbia upon reentry into the earth's atmosphere in February 2003 so vividly demonstrated, space travel has unique risks. In addition to the tremendous engineering challenges entailed in getting space travelers launched and returned safely, biomedical information collected by the National Aeronautics and Space Administration (NASA) and the Soviet and Russian space programs has revealed that living in space can produce profound physiological and clinical changes. Much less is known about potential longterm effects of space flight or the overall occupational risks of being an astronaut. NASA physicians began thinking about a longitudinal study as early as the late 1970s, and the Longitudinal Study of Astronaut Health (LSAH) was approved in 1992. Ten years later, NASA's Chief Health and Medical Officer asked the Institute of Medicine (IOM) for help in assessing the study and making any necessary midcourse corrections.
ROLE OF THE INSTITUTE OF MEDICINE
A prior IOM report entitled Safe Passage (IOM, 2001c) is recommended as background reading for this study. Despite the fact that it focused on the immediate dangers to the health and safety of astronauts aboard a future mission to Mars, it examined many issues of relevance to the present study, including the role of the astronauts as research subjects and the need for a comprehensive health care system for astronauts.
Presently the IOM, through activities including studies and workshops undertaken at the National Academies under the auspices of its standing Committee on Aerospace Medicine and the Medicine of Extreme Environments (CAMMEE), provides NASA's Chief Health and Medical Officer independent technical advice relevant to aerospace medicine, including medical care of space travelers. In October 2002 NASA's Chief Health and Medical Officer wrote a letter to the IOM project officer that described some tentative findings from a recent analysis of the LSAH database by scientists at the Johnson Space Center (JSC) and requested that CAMMEE examine the LASH and make appropriate medical, scientific, and administrative recommendations for improving the study, as well as recommendations relative to the data trends identified to date. CAMMEE in turn organized the present Committee on the Longitudinal Study of Astronaut Health (CLSAH), which convened for the first time in conjunction with the January 2003 meeting of CAMMEE. NASA had performed some further analysis of the LSAH database in the interim, and after presentation of those analyses, CLSAH's task was revised and expanded to yield the following charge to the committee:
Examine NASA's Longitudinal Study of Astronaut Health (LSAH) and make appropriate medical, scientific, and administrative recommendations for improving the study, as well as recommendations relative to the data trends identified to date, inclusion of astronauts from NASA's international partners, appropriate follow up of findings, and medical care of current and former astronauts, mission specialists, and other space travelers. In so doing the committee will address the potential relevance of lessons learned from historical exposures such as agent orange, radiation among veterans, and industrial beryllium to the configuration of the LSAH with regard to its usefulness in identifying health risks.
GOALS AND DESIGN OF THE LSAH
According to the most recent published description of the LSAH (Hamm et al., 2000), the primary aim of the LSAH is "to investigate and describe the incidence of acute and chronic morbidity and mortality of astronauts and to determine whether the unique occupational exposures encountered by astronauts are associated with increased risks of morbidity or mortality."
The primary focus of the study is the 312 men and women who have been selected as NASA astronauts since the space program began in 1959. All active astronauts participate in the study. Astronauts who have retired or otherwise left NASA are invited to continue in the study, and their participation rate is high (varying from 61 percent to 88 percent over the nine years between 1993 and 2001).
The study also collects health and medical data from a non-astronaut comparison group of JSC employees matched for sex, age, and body mass index (BMI). The study design calls for a 3:1 ratio of comparison participants to astronaut participants, and in January 2003 the comparison group totaled 928.
The primary data for the LSAH are obtained from medical records maintained at the JSC clinics. Annual health evaluations are required of active astronauts and are offered to inactive astronauts. These evaluations consist of a medical history, physical examination, laboratory tests, medical images, and other diagnostic tests. Non-astronaut employees who are participating in this study are offered evaluations every other year. Reports and documentation of interim medical care are obtained as part of the evaluation. These evaluations are referred to as "physical exams" throughout the report, though they clearly include much more. Other study data are obtained from interim visits to the JSC clinics for sick calls, and, for the astronauts, from pre- and post-flight physical exams, medical debriefings following flights, inflight experimental data, and reports of inflight medical events. A questionnaire designed to capture lifestyle factors and health risk data is now mailed to all new participants when they enter the study and every two years thereafter. Biannual searches are done for death certificates of all participants who miss a scheduled physical exam and cannot be contacted by mail or telephone. Copies of autopsy reports and hospital death summaries to support death certificate data are obtained whenever they are available.
FINDINGS TO DATE
Several analyses of the LSAH database have been published in peer-reviewed journals, the earliest a 1993 report on astronaut mortality from 1959 though 1991 that also addressed the hypothesis that astronauts are at increased risk for fatal cancers. Updated and expanded analyses were published in 1998 and 2000; a paper devoted to cataracts in astronauts was published in 2001; and in meetings held early in 2003 the committee was briefed by JSC scientists on more recent analyses of morbidity and mortality. Chapter 2 summarizes the three published studies as well as the briefings, but since the latter built on and were consistent with the earlier reports, only the latest analyses are reported in this summary.
Overall mortality has been significantly higher for the astronaut group in every analysis. Data presented to the committee in January 2003, just prior to the loss of the space shuttle Columbia and its crew of 7, showed 29 deaths among the 312 astronauts in the LSAH database and only 17 deaths among the 912 comparison participants. Accidental deaths, including 8 in spacecraft losses, accounted for 20 of the astronaut deaths (versus only 2 in the comparison group). The groups did not differ significantly in mortality from any other cause.
LSAH data on cataract incidence was combined with individual radiation exposure data from 295 astronauts in a study by Cucinotta and colleagues (Cucinotta et al., 2001; Cucinotta, 2003) which suggested increased incidence and earlier appearance of cataracts in astronauts exposed to higher amounts of space radiation (>8milliSieverts). A follow up study is using digital photography and computer image analysis to better quantify cataract incidence and progression using a group of current and former military pilots as controls.
Because of the known association of some cancers with radiation exposure, surveillance of astronauts for malignancies was planned from the beginning of the LSAH. Craig Fischer briefed the committee on the comparison of cancer incidence among the astronauts (Fischer, 2003), the LSAH comparison participants, and an age- and sex-matched sample of the National Cancer Institute's Surveillance, Epidemiology and End Results (SEER) database. Fourteen cases of cancer (excluding 33 cases of non-melanoma skin cancer) were diagnosed among the 312 astronauts followed from 1959 to the present. This is 59 percent higher than the comparison group per person/year (not statistically significant), but 46 percent lower per person/year than the SEER data (statistically significant).
The LSAH database also played a role in correcting a serious problem involving excessive iodinization of space shuttle drinking water. A physician monitoring the health and safety of four astronauts in a ground-based test of space shuttle life-support systems discovered marked elevations in thyroid stimulating hormone (TSH)-an indicator of potentially abnormal thyroid gland function-in all four after only 30 days of the 90-day test. She noted that iodine introduced into the test subjects' drinking water as a bacteriocide was increasing the astronauts' iodine intake to levels long recognized as detrimental to thyroid function. Installation of anion exchange filters sharply reduced the iodine concentration at the ground study tap, and the astronauts' TSH levels gradually returned to normal. A retrospective review of LSAH data showed no significant difference between the astronauts and the comparison participants in clinical thyroid disease but that elevations of TSH during flight had been common, with gradual return to normal after return to earth. Anion exchange filters are now a standard component of the drinking water systems on the space shuttle, and transient elevations in TSH no longer occur.
PROBLEMS IN DESIGN AND EXECUTION
To obtain an unbiased estimate of risk, the astronauts and their comparison group controls should (1) be equivalent at baseline in all factors that influence risk of disease or adverse health outcomes; (2) have equivalent exposures in day-to-day life except for those related to spaceflight or preparation for space flight; (3) have equivalent monitoring for disease by observers blinded to whether or not they were exposed to spaceflight or spaceflight preparation; and (4) participate fully from study entry to the outcome of interest. Like many expensive, long-running epidemiological studies, the LSAH has had to make a number of compromises. Chief among these have been a less than ideal match between comparisons and astronauts on a number of other potentially relevant physical and psychosocial variables, increasing disparities in the surveillance of health problems in the astronaut and comparison groups, and a lower participation/ followup rate of the comparison group. The proposed inclusion of astronauts and cosmonauts from NASA's international partners into the LSAH would only add to these problems for interpretation, although some of the data from longterm missions would be valuable independent of its contribution to the LSAH.
RECOMMENDATIONS FOR CHANGE
Implementing the following recommendations, which subsume many offered by the LSAH staff, will inevitably involve additional expenditures, but the committee believes they are essential for the validity of the data gathered through the LSAH and ultimately for the creation of a safer space travel program.
NASA should recognize that the LSAH can and should serve the two separate and potentially conflicting goals of occupational surveillance of the health of current and former astronauts and research into the long-term health risks associated with manned space flight (and to make these activities safer for future astronauts).
a) For the surveillance portion of the survey, participation of the astronauts is mandatory; for the research portion it is voluntary. Consequently, for the research portion, the astronauts need to sign an up-to-date informed consent document, and the research portion of the study should be reviewed on a regular basis by an IRB.
b) The database should be reviewed no less often than annually by LSAH staff, and analyses should be conducted for areas of potential risk, e.g., cancers, hearing loss, cataracts, bone strength. The committee is not convinced, given the low power of the study, that traditional "statistical significance" should be the sole trigger for concern, so in addition, it recommends that routine surveillance for unexpected and sentinel events be carried out by the oversight committee described below.
c) There should be a formal mechanism for flight surgeons to discuss both among themselves, and with those involved in the LSAH, any outlier or sentinel events, so that clinical suspicions are shared and checked for generality; such a system should complement the database surveillance system described above.
d) More information should be provided to participants on emerging findings and possible risks (possibly via their examining physician). The current newsletter system could be supplemented by a clinical synopsis with an expert commentary as key findings are published.
e) A formal process should be established to determine and implement corrective actions that follow from database surveillance or adverse event reporting. This process should enable the most learning to occur so that current and future astronauts are enabled to lead less risky lives, at least in their calling as explorers.
f) The Health and Lifestyle Questionnaire should be regularly reviewed with outside experts and updated as recommended.
NASA should recognize that no comparison group can meet every goal of the LSAH. Although use of the existing comparison group can be improved (see below), other hypothesis-specific comparison groups will be needed for definitive assessment of specific risks identified in the astronaut population. The comparison group should be seen primarily as a means to detect possible anomalies. Only after anomalies are identified can the most appropriate control group be identified and a definitive assessment of risk made. Specific suggestions for the current comparison group are:
a) The ratio of three comparison participants for each astronaut selected should be maintained. JSC contractor (e.g., Wyle Labs) personnel should be added to the comparison participant pool if the civil servant population can no longer provide adequate matches for new astronaut classes.
b) NASA should continue to seek international partner astronauts' medical data, but we do not recommend pooling such data with the LSAH data. Greater priority should be given to more thorough data gathering from the existing participant groups.
NASA should take steps to increase the quantity and improve the quality of the data collection and management of the data of the LSAH. The Committee was concerned by the marked variation in the content of the screening examinations that the existing LSAH groups (astronauts, retired astronauts, civil servants, and retired civil servants) are currently receiving, by the extent of missing data in some areas, and by the lack of justification for including some screening examinations and omitting others. These issues should be reviewed in accordance with the following principle: Exact or near-exact similarity of examination content in all four groups is more important than close similarity of examination frequency. Specific steps might include:
a) Pay travel expenses for comparison participants who no longer work at JSC and live outside the Houston area. Former astronauts who live outside the Houston area are already reimbursed for travel expenses, as are active astronauts and JSC civil servant participants, if they incur any expenses.
b) Offer to pay for an equivalent examination to be performed at a site convenient to comparison participants outside the Houston area. Occupational health clinics at other NASA centers, Federal Aviation Agency medical examiners, or private primary care providers could be given a standard protocol.
Excerpted from REVIEW OF NASA'S Longitudinal Study OF Astronaut Health Copyright © 2004 by National Academy of Sciences. Excerpted by permission.
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