Incidence rates for each race/ethnicity were age-standardized to the 2010 US resident population. Error bars indicate 95% confidence intervals. The y axis segments shown in blue indicate range from 0 to 35 in both graphs.
McLeod DSA, Caturegli P, Cooper DS, Matos PG, Hutfless S. Variation in Rates of Autoimmune Thyroid Disease by Race/Ethnicity in US Military Personnel. JAMA. 2014;311(15):1563-1565. doi:10.1001/jama.2013.285606
The relationship between Graves disease and race/ethnicity is undefined. Based on thyroid antibody prevalence, the rates of Hashimoto thyroiditis may be highest in whites and lowest in blacks.1,2
Using a large and comprehensive data set of medical diagnoses for all US active duty service personnel, we calculated age-standardized incidence rates for Graves disease and Hashimoto thyroiditis by race/ethnicity.
The institutional review boards of Walter Reed National Military Medical Center, Johns Hopkins Bloomberg School of Public Health, and University of Queensland School of Population Health approved this study. All data were deidentified and aggregated. No individual consent was required.
The Defense Medical Surveillance System (DMSS) maintains comprehensive records of inpatient and outpatient medical diagnoses among all active-duty military personnel, recorded using International Classification of Diseases, Ninth Revision, Clinical Modification (ICD-9-CM) codes. The study population was all US active duty military aged 20 to 54 years from January 1, 1997, to December 31, 2011.
Race/ethnicity was self-reported at enrollment. The DMSS groups race/ethnicity as non-Hispanic white (white); Hispanic; non-Hispanic black (black); Asian/Pacific Islander, American Indian/Alaskan Native; other; or unknown. Because the latter 3 groups had few cases and were unable to be standardized, we performed an analysis using the first 4 categories. The 2010 US resident population aged 20 to 54 years by race/ethnicity, sex, and age was obtained from the US Census Bureau for use as a standard population.3
Cases were identified with a specific diagnosis of either Graves disease (ICD-9-CM code 242.0) or Hashimoto thyroiditis (ICD-9-CM code 245.2). Cases were defined as individuals with an inpatient ICD-9-CM diagnosis code in any diagnosis position or 2 or more first diagnosis–position outpatient codes separated by at least 7 days.
Because persons with Graves disease and active thyroiditis are not eligible to enlist in the US military, the first diagnosis code was considered the incidence date. We calculated directly standardized incidence of Graves disease and Hashimoto thyroiditis among race/ethnicities, standardized to the 2010 US population, and generated incidence rate ratios (IRRs) using Stata version 12.1 (StataCorp).
The DMSS recorded 20 270 688 person-years of eligible active-duty service during the study period (85.8% male). There were 1378 cases of Graves disease in women and 1388 cases in men and 758 cases of Hashimoto thyroiditis in women and 548 cases in men (Table).
Compared with whites, the IRR for Graves disease was significantly elevated in black women (IRR, 1.92; 95% CI, 1.56-2.37) and men (IRR, 2.53; 95% CI, 2.01-3.18) and Asian/Pacific Islander women (IRR, 1.78; 95% CI, 1.20-2.66) and men (IRR, 3.36; 95% CI, 2.57-4.40) (Figure). In contrast, Hashimoto thyroiditis incidence was highest in whites and lowest in black women (IRR, 0.33; 95% CI, 0.21-0.51) and men (IRR, 0.22; 95% CI, 0.11-0.47) and Asian/Pacific Islander women (IRR, 0.31; 95% CI, 0.17-0.56) and men (IRR, 0.23; 95% CI, 0.07-0.72) (Figure).
To our knowledge, this is the first report to identify that Graves disease is more common in blacks and Asian/Pacific Islanders compared with whites. In contrast, the relationship between Hashimoto thyroiditis and race is well known,1,2 and is confirmed by our results.
The differences in incidence by race/ethnicity may be due to different environmental exposures, genetics, or a combination of both. Our results are not easily attributable to the strongest known environmental risk factor, cigarette smoking.
Smoking is associated with an increased risk for Graves disease and a decreased risk of Hashimoto thyroiditis.4,5 Whites have the highest smoking rates in the US military.6 However, whites had higher rates of Hashimoto thyroiditis and lower rates of Graves disease.
Our data set presumes accurate coding; it is possible that some cases of Hashimoto thyroiditis causing hypothyroidism were coded as unspecified-acquired hypothyroidism and not Hashimoto thyroiditis. The military population may also tend to have lower Hashimoto thyroiditis estimates because it is younger than the general population and has higher smoking prevalence.
Another potential limitation is the misclassification of prevalent cases as incident cases, although this is unlikely to be important because diagnosis during the teenage years is rare. We also cannot rule out military-specific exposures affecting the pattern of autoimmune thyroid disease, which could limit the generalizability of our findings.
Corresponding Author: Donald S. A. McLeod, FRACP, MPH, QIMR Berghofer Medical Research Institute, QIMR Locked Bag 2000, Royal Brisbane Hospital, Queensland, Herston, Australia 4029 (firstname.lastname@example.org).
Author Contributions: Dr McLeod had full access to all of the data in the study and takes responsibility for the integrity of the data and the accuracy of the data analysis.
Study concept and design: All authors.
Acquisition, analysis, or interpretation of data: All authors.
Drafting of the manuscript: McLeod, Matos, Hutfless.
Critical revision of the manuscript for important intellectual content: McLeod, Caturegli, Cooper, Hutfless.
Statistical analysis: McLeod, Matos, Hutfless.
Administrative, technical, or material support: Cooper, Matos.
Study supervision: Cooper, Hutfless.
Conflict of Interest Disclosures: The authors have completed and submitted the ICMJE Form for Disclosure of Potential Conflicts of Interest. Dr Cooper reported receiving royalties for serving as an editor to Up-to-Date. No other disclosures were reported.
Funding/Support: A Cancer Council Queensland PhD scholarship helped support Dr McLeod.
Role of the Sponsor: The Cancer Council Queensland had no role in the design and conduct of the study; collection, management, analysis, and interpretation of the data; preparation, review, or approval of the manuscript; and decision to submit the manuscript for publication.
Additional Contributions: We thank Angie Eick-Cost, PhD (Armed Forces Health Surveillance Center), for her assistance in compiling the data for this study; and Monica Vladut-Talor, MSc, and Noel R. Rose, MD, PhD (both with the Department of Pathology, Johns Hopkins University School of Medicine), and Paul W. Ladenson, MD (Division of Endocrinology and Metabolism, Johns Hopkins University School of Medicine), for their contributions to the manuscript. No compensation was received by any of the acknowledged individuals.