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The relationship between vitamin D status and depression in a tactical athlete population

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  • The relationship between vitamin D status and depression in a tactical athlete population

    Data source

    Data for this study were obtained from the Military Health System (MHS) Data Repository (MDR), which contains information from a comprehensive network of military healthcare clinics that serve over 9.5 million beneficiaries [25]. Specifically, data were retrieved from the direct care component of the MDR. These records are referred to as direct care because the services are provided at MTFs operated solely by the Department of Defense (DoD) [25]. The data system, known as the Management and Analysis and Reporting Tool (M2), was used to query the MDR for Comprehensive Ambulatory Provider Encounter Records (CAPERs), which contain outpatient records for all encounters occurring at MTFs. Examples of outpatient encounters include primary care, wellness, specialty care, and group appointments. The M2 database was queried only for approved data and the workstation used for accessing data met DoD security requirements. This study was approved by the Human Protections Administrator at the Army Medical Department Center and School and the Institutional Review Board at Walter Reed National Military Medical Center.
    Extracted data

    Study data were retrieved from the MHS for the years 2013 through 2015. Each record in the dataset contained: a pseudo identification number (an encrypted individual identifier that is comparable across datasets), the treatment facility name and identification, the common beneficiary category (confirmation that the individual was serving on active duty or active duty orders at the time of data retrieval), the specific beneficiary category (to separate Army Guard or Army Reserve on active duty orders from Regular Army status), gender (male or female), age group (four age categories: 18–24, 25–34, 35–44, and 45–64), sponsor rank group (the service members’ pay grade grouped in a broader category: enlisted junior, enlisted senior, officer junior, and officer senior), encounters (a count of records), and diagnosis (a diagnostic code for either vitamin D deficiency or depression as the chief complaint or as any of the secondary diagnoses up to the 10 maximum allowable codes).
    Exposure and outcome variables

    The primary exposure variable, diagnosis of vitamin D deficiency, was defined as having at least one encounter with a primary or secondary Ninth Revision of the International Classification of Diseases, Clinical Modification (ICD-9-CM) code 268.9, Unspecified vitamin D deficiency [26]. The appearance of the diagnostic code for vitamin D deficiency in the record indicated that a clinical provider ordered a reliable laboratory assay to evaluate serum circulating levels of vitamin D prior to diagnosis. The Endocrine Society Clinical Practice Guidelines defines vitamin D deficiency as a 25-hydroxyvitamin D [25(OH)D] level of 13]. Although the Endocrine Society guidelines are commonly used for the testing and diagnosing of vitamin D status, due to limitations of using ICD-9-CM codes as the sole means to confirm diagnosis, this study was unable to verify if providers adhered to these methods.
    The primary outcome variable, diagnosis of depression, was defined as having at least one encounter with either a primary or secondary diagnosis from the ICD-9-CM codes listed in Table1 [26]. A diagnosis of depression is generally symptom-based for a specified period of time and determined using the diagnostic criteria outlined in the Diagnostic and Statistical Manual of Mental Disorders (DSM-V) [27]. The method for identifying diagnoses of depression by ICD-9-CM codes in this study is comparable to strategies used by previous studies [28, 29]. Similarly to the methods used for determining a diagnosis of vitamin D deficiency, the use of ICD-9-CM codes, to confirm diagnosis of depression, does not differentiate whether medical providers diagnosed accurately or within the accepted guidelines.

    Table 1 Selected ICD-9-CM codes for depression and description
    Study population

    Individuals serving on active duty in the United States Army during the study period, with records for selected MTFs, were included for review (n = 483,683). Outpatient records were obtained for six military treatment facilities at varying geographic locations (Watertown, New York; Fairbanks, Alaska; Killeen, Texas; Tacoma, Washington; El Paso, Texas; and Fayetteville, North Carolina) in order to examine latitude as an independent variable (Fig.1). Geographic location was a consideration in this study given that absorption of UV radiation, essential for vitamin D production, varies depending on degree of latitude. In order to capture personnel stationed at installations for a reasonable period of time, selection of MTFs on known training installations was avoided due to the transient nature of this population. Consequently, only MTFs located on installations without Initial Entry Training (IET) programs were included for review.

    Fig. 1Geographic locations and associated latitudes for military treatment facilities where outpatient records were retrieved between the years 2013 and 2015

    In order to associate demographic characteristics and medical outcomes without biasing the data, only one unique record was kept for each pseudo-identification number. Therefore, records with pseudo-identification numbers that appeared more than once (168,052) were reduced so that only the pseudo-identification number associated with the largest number of encounters was retained (n = 71,506), as a duplication indicated that an individual had outpatient encounters at multiple MTFs or had a change in demographic data during the study period. For records with multiple demographic characteristics but no maximum number of encounters, the first appearance in the dataset was kept arbitrarily (n = 6873). Records were eliminated to exclude individuals outside of the predetermined, 18–64 year old age parameter (99 total records excluded); to exclude military ranks other than junior enlisted, senior enlisted, junior officer, or senior officer (11,912 records excluded); and to exclude records without a listed gender (1 record excluded). Finally, individuals with ≥300 encounters were considered outliers and excluded from the dataset (189 total records excluded). After removing duplicates, outliers, and records excluded for the reasons above, 381,818 unique records remained for subsequent data analysis.
    Statistical methods

    All demographic characteristics for this study were categorical and were described as a total number and frequency. A Chi-square test of independence was used to compare frequencies of vitamin D deficiency and depression between MTFs. The primary means of analysis was a binomial generalized linear model with a log link that was used to predict depression diagnosis. An initial model (Model 1) was created and included only vitamin D diagnosis; followed by a secondary model (Model 2) which included vitamin D diagnosis and a group of other covariates (MTF location, gender, age group, service type, career type, and career progression). Finally, a third model (Model 3) included these covariates as well as the number of associated encounters as a continuous variable. In this model, encounters were log transformed to approximate normality. Significance in each model was evaluated using a Type 3 Likelihood Ratio test. Odds ratios (and 95% confidence intervals) for individual parameters were extracted using exponentiated parameter estimates.
    To examine the relationship between MTF latitude and vitamin D diagnosis, a separate model was built to predict vitamin D diagnosis (as in Model 3, above). From this model, the estimated rate of vitamin D deficiency at each MTF was calculated using least square means. These extracted rates were then correlated with the actual latitude of each MTF. Global alpha was set at p
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