Health Conditions Among Navy Submariners at the End of Active Duty; A Retrospective Cohort Study

ABSTRACT

Introduction

Maintaining healthy, well-trained, and highly qualified armed forces is critical for ensuring military readiness. The purpose of this article is to contribute to the body of research focused on the health of U.S. Navy submariners and to identify the health conditions of U.S. Navy submariners during their final year of active duty service.

Materials and Methods

In this retrospective cohort study, we examined medical records and personnel files of separating U.S. Navy sailors who were: (1) active duty between 2009 and 2018; (2) separated before 2019; and (3) were assigned to a submarine for at least 30 days. Both officers and enlisted service members were included. We linked, described, and analyzed data from the Defense Health Agency, Military Health System Data Repository (MDR), and the Bureau of Naval Personnel (BUPERS). International Classification of Diseases (ICD) diagnoses codes were obtained from MDR. Data collected from BUPERS include age, sex, and rank. We determined the number of individuals who had at least one diagnosed condition (identified as a three-digit ICD code). We report the number of diagnoses and calculate prevalence rates and confidence intervals per condition, as well as prevalence rates per year, using standard formulas. The study was approved by the Naval Submarine Medical Research Laboratory Institutional Review Board.

Results

During the study period, 26,014 submariners separated from the Navy. The average number of separations per year was 2,601. About a third of the separating submariners were in the 25 to 29 age group and over 50% were under 30 years of age. Of the three-digit individual ICD codes, some of the highest operationally relevant rates over the 10-year study period (2009-2018) were for joint disorders (prevalence rate [PR] = 180 per 1,000 submariners), back disorders (PR = 128), and sleep disorders (PR = 134). Three mental-health-related conditions were also among the 20 conditions with the highest rates.

Conclusions

High rates of specific diagnoses such as joint disorders indicate the need for additional study to examine causal relationships, to determine which conditions may contribute to lost work time, early separations, or low rates of reenlistment and which conditions might be a result of specific military occupations or duties. Study strengths are the large number of subjects and the long period of observations. A study weakness was the inability to identify submariners who separated because of health conditions. The overall impact of the study is that it identifies urgent health risks and establishes a way to prioritize future research. Future research should include a focus on medically separated personnel; compare rates for submariners to other military groups including all-Navy and all-Department of Defense; and determine specific and relative risks as a necessary precursor to developing, implementing, and testing risk reduction and health improvement interventions.

INTRODUCTION

The purpose of this article is to identify the health conditions of U.S. Navy submariners during their final year of active duty service. Maintaining healthy, well-trained, and highly qualified armed forces is critical for ensuring military readiness. This foundational examination of the health conditions associated with a particular service’s occupation or duty can lay the groundwork for future studies to:

• Identify unique profession-specific risks;

• Identify factors that may lead to early separations;

• Guide health improvement strategies;

• Identify conditions that may reduce a service member’s likelihood of reenlisting; and

• Lead to the development of profession-specific risk reduction interventions.

In addition, an examination of health conditions can provide insights to the resources veterans and retired service members will most likely need once they have rejoined civilian life.

Military service members may have incentives to not report health conditions during their career (e.g., so as not to leave their team shorthanded, or risk early separation due to medical disqualification). However, those concerns may be obviated at the end of their service time due to their inevitable departure. The potential for veteran’s benefits for health conditions reported before separation may incentivize reporting of all health conditions before separation.^1,2 Thus, an examination of health conditions reported during the final year of service can identify risks and create a strong foundation for developing risk reduction and health improvement interventions.

Service members separate at retirement, at the end of obligated service, or they have an early separation for health- or non-health-related factors. Non-health-related factors that may lead to early separation include family emergency and disciplinary action. A variety of health-related issues may also lead to early separation from the military; they include mental health issues, medical disqualification, physical illness, and injury. Mental health issues may result from numerous causes and result in a wide spectrum of outcomes.

Two groups of researchers focused on the role that mental health issues play in early separations. Hourani et al. found that some marines who were separating from the service had higher risks for mental health problems (depression, anxiety, and post-traumatic stress disorder); higher levels of pre-separation combat exposure, post-separation stress across multiple life domains, and multiple areas of pain may be contributing factors. The same authors found that protective factors include having higher scores on pre-separation resilience and perceived social support at follow-up.³ Schmied et al. followed 28,693 male marines and found that several specific categories of mental health disorders predicted lower odds of reenlistment; the disorders included: personality disorders, substance use disorders, and post-traumatic stress disorder.⁴

In research that may have some overlap with mental health issues, Gundlapalli et al. analyzed records of 448,290 active duty service members separated between 2001 and 2012 and found that individuals separated for misconduct were about six times more likely to be homeless within five years compared to all separated members.⁵

In addition to mental health issues, researchers have identified other health conditions associated with early separation. Rogers et al. found that obstructive sleep apnea may be associated with increased rates of separation.⁶ New-onset asthma may also lead to early separation.⁷ Cook et al. found that a history of three or more lifetime concussions was associated with a higher likelihood of separation.⁸

Some health conditions may arise because of, or are associated with, military service. Uptegraft and Stahlman looked at health conditions reported in the last six months of active duty service compared to earlier in a member’s career. They found that health conditions with the highest increased rates of reporting included mental health conditions, back disorders, sleep disorders, and disorders of the ear.¹ One study examined diagnoses entered into a service member’s chart for the first time during the six months before retirement. Among 206,591 service members who retired between 2003 and 2009, 146,860 (71%) had diagnoses that were entered into their charts for the first time within six months of retirement. Of these, the most common were for disorders of the ear, sleep disorders, and hearing loss.⁹ An examination of service members with 20 years of active service found that the rates of illness and injury diagnoses were about 57% higher for members within six months of retirement compared to members who were 18-24 months pre-retirement.²

Schmied found that there is a gap in “the research pertaining to the health and performance of shipboard Sailors.”¹⁰ Among studies of health conditions of submariners, one found that the risks of at-sea injuries were found to vary by age, experience, and job assignment among submariners.¹¹ Beardslee et al. noted the need for more up-to-date research on this population.¹² Because Navy submariner is a unique and critical profession, additional research is needed to identify their unique risks. Next steps should include efforts to determine attributable risk as a way to inform injury prevention efforts.

The objective of this study is to describe the health conditions of submariners during each separated sailor’s last year of active duty. During this foundational examination of the health conditions associated with submarine service we calculated the rates of the most frequent three-digit level diagnoses. In this way, we were able to determine the most common health conditions among separating submariners. This research will contribute to a better understanding of the long-term health effects of specific occupational risks and exposures. These new insights will create a foundation for the development of injury prevention programs and other interventions designed to reduce risks and improve both health and readiness of Navy sailors.

METHODS

Study Design

This was a retrospective cohort study. We examined medical records and personnel files of separating U.S. Navy submariners. We included officers and enlisted service members who separated due to retirement, end of agreed service (e.g., at the end of enlistment), or early separation (i.e., leaving the service before the agreed-on end of active duty date). We linked, analyzed, and described data from the Defense Health Agency (DHA), Military Health System Data Repository (MDR), and the Bureau of Naval Personnel (BUPERS).

Participants

The study population included all U.S. Navy sailors who met all four of these criteria: were active duty in the Navy between 2009 and 2018; had a duty code of a Virginia, Los Angeles, Seawolf, or Ohio class submarine; were assigned to a submarine for at least 30 days; and were separated from the Navy before 2019. The study population includes both officers and enlisted personnel; Navy reservists were not included. “Separation” includes retirement (service of at least 20 years) and end of active duty with less than 20 years of service for any reason (including medical discharge, end of obligated duty, etc.). The study population is the 26,014 sailors who met the study criteria.

Variables

The key variable is the set of diagnoses codes described in the World Health Organization’s International Classification of Diseases (ICD).¹³ During the study period the DHA used both ICD-9 and ICD-10 versions of the codes.¹⁴ For the purpose of this study we have back-matched all ICD-10 codes to their corresponding ICD-9 codes. There were 130 unique encounters that resulted in ICD-10 codes that could not be automatically back-mapped to ICD-9; the research team was able to successfully back-map them manually. Other variables include the submariner’s sex, age, and rank.

In the ICD-9, the World Health Organization classifies all the ICD codes into 17 major categories and two supplementary categories¹⁵; we did not include the two supplementary categories (“Supplementary Classification of External Causes of Injury and Poisoning” and “Supplementary Classification of Factors Influencing Health Status and Contact With Health Services”). Under the 17 major categories are almost 1,000 three-digit codes, and about 12,000 sub-conditions are described by four- and five-digit codes.¹⁶ For example, the most common three-digit code in this study population was “367 – Disorders of refraction and accommodation.” Under 367 are a variety of conditions including Astigmatism (367.2), Regular Astigmatism (367.21), Irregular Astigmatism (367.22), Anisometropia (uneven focus) (367.31), and Presbyopia (farsightedness) (367.4).¹⁷

Data Sources/Measurement

BUPERS data include:

• Demographic data including sex and date of birth;

• The personal identification numbers issued by the Department of Defense (DoD; DoD ID); and,

• Career data including date joining the Navy, current rank, current job, unit identification codes (assigned work location), and date and reason for separation.

Using BUPERS data, we selected the DoD ID for sailors who met the study criteria. We classified subjects by demographic factors based on the classification in their BUPERS file on their last day of service. We used those DoD IDs in a search of the MDR database.

The MDR includes codes from inpatient and outpatient medical encounters with both military and private care providers. The MDR “is the centralized data repository that captures, archives, validates, integrates and distributes Defense Health Agency (DHA) corporate health care data worldwide.”¹⁸ The MDR contains an electronic health record for every sailor.

The military medical community uses the electronic health record to “capture, manage, and share data on care provided in garrison/installation and on the battlefield, as well as share pertinent health information with the VA.”¹⁹ In addition to routine visits, urgent care, and hospitalizations, separating sailors are required to have a separation physical exam and any diagnoses noted during that exam are entered as ICD codes into the sailor’s electronic health record.

From MDR, we downloaded all ICD codes entered into the submariners’ electronic health record during the final year of each individual’s service. ICD data per year were based on the submariner’s last day of active duty. Therefore, if a submariner separated on June 1, 2015, that submariner’s ICD codes from June 1, 2014, to May 31, 2015, were all allocated to 2015. The health record includes a “primary diagnosis” field as well as additional diagnoses fields; we include all codes in any diagnosis field. The data were downloaded in late 2019 so, even if there is a few months lag time between a patent’s visit and the record appearing in the database, we feel confident that all the 2018 data were captured.

Once all the ICD codes were identified, we collapsed all the four- and five-digit codes into their common three-digit codes and, for each submariner, we counted each three-digit code no more than once. For example, if an individual submariner’s record had entries for Irregular Astigmatism (367.22), Anisometropia (uneven focus) (367.31), and Presbyopia (farsightedness) (367.4), we counted only one code of 367 for that submariner. Therefore, the maximum number of times that any single three-digit code could be counted was 26,014 (the total population).

Bias

Retrospective studies have some inherent risks of bias. We minimized the risk of selection and information bias by evaluating all available data from our data sources that met the study’s criteria. These data are collected and used to make medical decisions and military deployment decisions and for payroll and promotions; therefore, there is every reason to believe that they have a high level of accuracy. There was no way for subjects to opt out of the study or to self-select for inclusion.

The individuals making the medical diagnoses (and entering the ICD codes) are all physicians for the Navy. There is no reason to believe that there was any differential referral or diagnoses of any individuals or groups in the study. There is a possibility of some misclassification bias in that some codes may have been entered erroneously, but we have no reason to believe that misclassification is systematic or frequent.

Statistical Methods

We calculated the prevalence rates²⁰ (page 12) and the confidence intervals²⁰ (page 139) using standard formulas.

Ethics

This study received Institutional Review Board approval under protocol NSMRL.2011.0003 as a minimal risk study. Waiver requests of informed consent and The Health Insurance Portability and Accountability Act of 1996 authorization were granted.

Structure

The structure of this article was based on the international “STrengthening the Reporting of OBservational studies in Epidemiology” (STROBE) statement for observational studies.²¹

RESULTS

During the study period, 26,014 submariners separated; the average number who separated per year was 2,601.

Descriptive Data

Table I shows the number of submariners separated per year for 2009 to 2018 by the demographic factors sex, age, and rank. About a third of the separating submariners were in the 25 to 29 age group and over 50% were under 30 years of age. Almost 60% of the submariners are in the ranks E-4 to E-6 and 84% are enlisted.

TABLE I.

Number of Separating Submariners per Year by Sex, Age, and Rank. 2009 to 2018. (N = 26,014)

	2009	2010	2011	2012	2013	2014	2015	2016	2017	2018	Total
Male	2,697	2,636	1,921	2,315	2,408	2,574	2,592	2,911	2,977	2,946	25,977
Female	0	0	0	0	2	4	4	11	8	8	37
Total	2,697	2,636	1,921	2,315	2,410	2,578	2,596	2,922	2,985	2,954	26,014
18-20	69	71	0	0	1	2	1	1	1	3	149
21-24	619	634	378	486	465	470	414	468	491	514	4,939
25-29	855	764	687	715	800	927	927	991	982	945	8,593
30-34	309	333	284	343	396	444	498	542	563	531	4,243
35-39	313	289	192	218	213	246	248	344	354	368	2,785
40-44	337	346	248	315	336	297	297	375	378	367	3,296
45-49	156	149	99	167	128	134	154	145	153	144	1,429
50-59	39	50	33	71	71	58	55	54	63	81	575
≥60	0	0	0	0	0	0	2	2	0	1	5
Total	2,697	2,636	1,921	2,315	2,410	2,578	2,596	2,922	2,985	2,954	26,014
E-1 to E-3	307	317	69	172	228	271	196	239	267	221	2,287
E-4 to E-6	1,582	1,555	1,263	1,398	1,444	1,537	1,560	1,724	1,679	1,731	15,473
E-7 to E-9	471	469	307	410	425	382	392	427	429	445	4,157
O-1 to O-3	178	149	124	154	138	211	238	315	355	285	2,147
O-4 to O-6	151	133	148	166	152	158	191	196	244	258	1,797
O-7 to O-10	2	3	2	3	4	3	2	1	0	2	22
Warrant Officer	6	10	8	12	19	16	17	20	11	12	131
Total	2,697	2,636	1,921	2,315	2,410	2,578	2,596	2,922	2,985	2,954	26,014

MAIN RESULTS

Once we identified all the submariners who had at least one diagnosis in each of the three-digit level categories, we determined that there were 117,866 individual diagnoses. Figure 1 illustrates the distribution of those diagnoses among the 17 major ICD categories (for Fig. 1, the nine categories with the smallest numbers are collapsed into “Other”). The categories with the largest number were Nervous System, with 23,311 diagnoses (20%) and Musculoskeletal with 20,576 (17%). Figure 1 also illustrates the major three-digit ICD codes within the Nervous System and Musculoskeletal categories.

FIGURE 1.

Distribution of diagnoses among the 17 major International Classification of Diseases (ICD) categories. The nine major categories with the smallest numbers are collapsed into “Other.” The categories with the largest number were Nervous System, with 23,311 diagnoses (20%), and Musculoskeletal with 20,576 (17%). It also illustrates the major three-digit ICD codes within the Nervous System and Musculoskeletal categories.

Note that each separating submariner could be counted only once in the three-digit level diagnoses but could be counted in the major category level more than once. For example, under the Nervous System major category, submariners could be counted more than once if they had a refraction-related diagnosis and a sleep-disorder diagnosis during the year before separation.

Outcome Data

Table II lists the 27 three-digit ICD codes with the highest PRs among separating submariners. The table includes the rank order by rate, major category, ICD-9 code number, the diagnosis, the number of submariners diagnosed (count), prevalence rate (PR) per 1,000 submariners, and the 95% confidence interval of the rate.

TABLE II.

The 27 Three-digit International Classification of Diseases (ICD) Codes with the Highest Prevalence Rates (PRs) among Separating Submariners. Includes the Rank Order, Major Category, ICD Code Number, Diagnosis, Number of Submariners, the Prevalence Rate (PR) per 1,000, and the 95% Confidence Interval (CI). Arranged by Major ICD Category. 2009 to 2018. (N = 26,014)

Rank	Major category	Code	Diagnosis	Submariners	PR	CI low	CI high
9	Endocrine	272	Disorders of Lipoid Metabolism	2,480	95	91.6	99.1
12	Endocrine	278	Overweight, Obesity and Other hyperalimentation	1,881	72	69.0	75.6
18	Mental	300	Anxiety, Dissociative and Somatoform Disorders	1,326	51	48.2	53.7
8	Mental	305	Nondependent Abuse of Drugs	2,648	102	97.9	105.7
13	Mental	309	Adjustment Reaction	1,682	65	61.6	67.7
4	Nervous	327	Organic Sleep Disorders	3,477	134	129.2	138.1
1	Nervous	367	Disorders of Refraction and Accommodation	8,730	336	328.5	342.6
21	Nervous	388	Other Disorders of Ear	1,171	45	42.4	47.6
23	Nervous	389	Hearing Loss	1,131	43	40.9	46.0
11	Circulatory	401	Essential Hypertension	1,983	76	72.9	79.6
27	Respiratory	465	Acute Upper Respiratory Infections of Multiple or Unspecified Site	1,045	40	37.7	42.6
22	Respiratory	477	Allergic Rhinitis	1,158	45	42.0	47.1
15	Digestive	530	Diseases of Esophagus	1,571	60	57.4	63.4
2	Musculoskeletal	719	Other and Unspecified Disorders of Joint	4,671	180	174.4	184.7
26	Musculoskeletal	723	Other Disorders of Cervical Region	1,059	41	38.3	43.2
5	Musculoskeletal	724	Other and Unspecified Disorders of Back	3,322	128	123.4	132.0
14	Musculoskeletal	726	Peripheral Enthesopathies and Allied Syndromes	1,639	63	60.0	66.1
25	Musculoskeletal	728	Disorders of Muscle Ligament and Fascia	1,071	41	38.7	43.6
10	Musculoskeletal	729	Other Disorders of Soft Tissues	2,024	78	74.4	81.2
3	Symptoms	780	General Symptoms	4,514	174	168.5	178.6
19	Symptoms	782	Symptoms Involving Skin and Other Integumentary Tissue	1,254	48	45.5	50.9
16	Symptoms	784	Symptoms Involving Head and Neck	1,567	60	57.3	63.2
7	Symptoms	786	Symptoms Involving Respiratory System and Other Chest Symptoms	2,662	102	98.4	106.2
17	Symptoms	787	Symptoms Involving Digestive System	1,376	53	50.1	55.7
24	Symptoms	789	Other Symptoms Involving Abdomen and Pelvis	1,104	42	39.9	44.9
20	Symptoms	796	Other Nonspecific Abnormal Findings	1,179	45	42.7	47.9
6	Symptoms	799	Other Ill-Defined and Unknown Causes of Morbidity and Mortality	2,819	108	104.4	112.4

Naval officers reviewed Table II and selected the six most operationally relevant ICD-9 codes with the highest rates over 10 years (2009 to 2018) to illustrate the prevalence rate per 1,000 submariners over time in Figure 2. The six codes by rank, major category, ICD code, diagnosis, and overall rate were:

FIGURE 2.

Prevalence rate (PR) per 1,000 separating submariners of diagnoses by International Classification of Diseases (ICD) code, for six of the most operationally relevant diagnoses among the highest rates, over 10 years (2009-2018).

1	Musculoskeletal	719	Other and Unspecified Disorders of Joint	179.6
2	Nervous	327	Organic Sleep Disorders	133.7
3	Musculoskeletal	724	Other and Unspecified Disorders of Back	127.7
4	Mental	305	Nondependent Abuse of Drugs	101.8
5	Endocrine	272	Disorders of Lipoid Metabolism	95.3
6	Circulatory	401	Essential Hypertension	76.2

DISCUSSION

The major ICD category with the largest number of diagnoses was Nervous System with 20%; Musculoskeletal system disorders accounted for 17% of the diagnoses. At the three-digit code level, the code with the highest rate was Disorders of Refraction and Accommodation, ICD-9 code 367, with a PR of 336. This diagnosis includes conditions such as nearsightedness, farsightedness, and astigmatism; conditions affecting a majority of the U.S. population. The major category Nervous System also includes three other three-digit codes with high rates: organic sleep disorders (PR = 134), ear disorders (PR = 45), and hearing loss (PR = 43).

Although the reliability of comparing these two study results is limited, Uptegraft and Stahlman found that the rate for separating DoD members, for ICD code 327 (organic sleep disorders), was 44.2 per 1,000 personnel,¹ compared to the rate of 134 for submariners in this study.

The Uptegraft and Stahlman results showing that 71% of retiring service members had diagnoses entered into their records for the first time during their last six months of duty reinforces the value of evaluating service members at the end of active duty in order to identify all health conditions.

Among separating submariners, the major category with the second highest number of diagnoses was musculoskeletal system and connective tissue; the three-digit code with the second highest rate was for joint disorders. These findings are important because injuries are the cause of 30% to 50% of disability cases.²² Abt et al. found that a large percentage of musculoskeletal injuries among special operations personnel were due to training²³; our data did not identify pre-injury activities but future submariner research should examine training as a risk factor. Balcom and Moore found that the relative risk of in-port injuries was 3.5 times higher than at-sea injuries²⁴; future research among submariners should also determine the relative risks of at-sea and in-port injuries.

Mental disorders was the major ICD category with the fourth highest number of diagnoses among separating submariners, and three of the top 20 three-digit level codes were associated with mental health issues. In contrast, for all DoD members, of the 18 diagnoses with the highest rates entered during the 6-month period before retirement, none were mental health related.⁹

High rates of mental health issues among separating submariners raise concern in part because of Schmied et al.’s findings that mental health disorders predicted lower odds of reenlistment.⁴ Brigone et al.’s finding that service members who develop mental health conditions have a much higher rate of discharge for disqualification or misconduct²⁵ invites the evaluation of interventions to prevent or reduce the incidence or development of mental health issues among service members. The fact that a high proportion of all military medical evacuations from submarines were associated with mental health emergencies^26,27 highlights the potential operational and strategic value of efforts to mitigate mental health conditions. High rates imply the need to evaluate additional mental health screening tools and to consider periodic rescreening. The embedded mental health program is an example of one intervention. That program began in 2012 and embedded behavioral health providers in submarine fleets; it has shown a statistically significant reduction in mental-health-related career terminations among submariners.²⁸

The diagnosis of “organic sleep disorders” was listed in the top 10 highest prevalence rates for submariners. A study of ICD codes that occurred for the first time in the six months before retirement across the DoD found that sleep disorders was the diagnosis with the second highest number of new cases.⁹ A high rate of sleep disorders raises concerns because of findings that such conditions may be associated with: a “profound negative impact on most domains of health-related quality of life”²⁹; increased rates of occupational injury^30,31 and early separation⁶; and increased risks of mental health conditions^32,33 and prostate cancer.³⁴

The finding of a high rate of hearing disorders is in line with the U.S. Department of Veterans Affairs statement that hearing problems, including tinnitus, are the most prevalent service-connected disability among U.S. veterans.³⁵

Although dental disorders were not among the highest rates found in this study, there were 308 dental-related diagnoses reported during the study period. Deutsch found a rate of 5.0 dental disorders per 100,000 person-days at sea among submariners³⁶; 6% of all MEDEVACS from submarines were related to dental emergencies.²⁷ Future research should focus on ways to reduce dental-related emergencies.

Study Strengths and Limitations

The major strengths of the study are the large population, and 10 years of data from multiple data sources.

An ideal way to determine health at separation would be to examine the record of that exam and describe those findings. However, during the study period, the physicians conducting those exams used an article document that was then scanned and appended to the sailor’s medical record. That format makes an examination of the record difficult and time consuming. However, in addition to the article form, the examining physician does enter ICD codes related to findings or follow-up care directly into an electronic database. In order to do an analysis within the time parameters of this project, the research team examined the ICD codes for the sailor’s last year of service. Those are the codes the team used for this study. Currently practicing undersea medical officers assured us that any health conditions found during the separation physical do result in a corresponding ICD code being entered into the sailor’s electronic health record. However, any text comments made by the examining physician were not included in this study. We have no reason to believe that any major findings were missed by analyzing only the ICD codes, however it is possible.

This study analyzes only diagnoses made within the last year of active duty service and could include some medical conditions that were determined during the separation process. It is possible that many conditions, for example the need for corrective lenses, may have been present for many years before separation. Therefore, the high rates of conditions such as disorders of refraction and accommodation (ICD code 367) should be interpreted with caution pending further research.

The available data did not identify sailors who had an early separation due to a health condition. Future research should focus on that group. In order to better determine unique risks to submariners, future analyses should include comparisons of separating submariners to non-separating submariners, all Navy members, all DoD service members, and all separating DoD service members. Those analyses would help identify, for example, any attributable risk and relative influence of submarine work on the development of visual, musculoskeletal, sleep, hearing, or other disorders.

Although there were only 37 female submariners during the study period, the number of female sailors assigned to submarines is growing and future research should focus on identifying any unique health risks that submarine duty may pose for females.

A weakness in this study is the lack of age-adjusted rates; we plan to obtain those data and conduct those analyses for future reports. Future research should also differentiate injuries by those occurring on duty and off duty, those at sea and in port, and those that occur while training versus non-training. Analyses of those data could further define the types of risks faced by submariners. The findings in this study will be most applicable to submariners in the Navy, but some may be generalizable to other branches of the U.S. Armed Forces and to military personnel worldwide.

CONCLUSIONS

An examination of 26,014 separating submariners found that the health conditions with the largest prevalence rates included joint disorders, back disorders, sleep disorders, and three mental-health-related conditions. Study strengths included the large number of subjects and 10 years of data. A weakness was the lack of age-adjusted rates; those analyses are planned for future reports.

This analysis documents current risks and creates a foundation for interventions. High rates for specific diagnoses indicate the urgent need for follow-up research. That future research must examine causal relationships to determine which conditions may contribute to early separations and which conditions might be a result of specific military occupations. That research must determine specific and relative risks as a necessary precursor to developing, implementing, and testing risk reduction and health improvement interventions.

ACKNOWLEDGMENTS

The authors wish to extend special thanks to Erica Casper for her expert contributions to this article and to Naval Submarine Medical Research Laboratory Librarian Cheryl Baker for her help with the literature search. I have obtained written permission from all persons named in Acknowledgments.

FUNDING

This work was supported by the Defense Health Program, funding work unit number F1806.

CONFLICT OF INTEREST STATEMENT

The authors report no conflicts of interest.

DATA SHARING

No additional data are available.

Author notes

Abstract accepted for poster presentation at the 2021 Military Health System Research Symposium (MHSRS), Kissimmee, Florida. August 23 to 27, 2021.

Authors of this study include military service members and employees of the U.S. Government. This work was prepared as part of their official duties. Title 17, U.S.C., §105 provides that copyright protection under this title is not available for any work of the U.S. Government. Title 17, U.S.C., §101 defines a U.S. Government work as a work prepared by a military service member or employee of the U.S. Government as part of that person’s official duties.

This study was approved by the Naval Submarine Medical Research Laboratory (NSMRL) Institutional Review Board under protocol NSMRL2011.0003.

The views expressed in this journal article reflect the results of research conducted by the authors and do not necessarily reflect the official policy or position of the Department of the Navy, Department of Defense, nor the U.S. Government.