Results
In the overall sample, the frequencies (95% standard error [SE]) of CKD and prior MS were 15.2% (0.3) and 11.5% (0.3) (Table 1). The proportion (SE) with CKD was significantly higher among those with prior MS vs the overall population: 22.7% (0.7) vs 15.2% (0.3) (P < .001). Significant associations with CKD were observed (P < .05) by age, sex, race and ethnicity, family poverty, school education, health insurance, smoking, body mass index, diabetes, hypertension, cardiovascular disease, and malignancy. Within those reporting prior MS, the proportion (SE) with CKD differed by era: 1999 to 2002, 18.9% (1.1); 2003 to 2006, 24.9% (1.5); 2007 to 2010, 22.3% (1.5); 2011 to 2014, 24.3% (1.7); and 2015 to 2018, 24.0% (1.8) (P = .02) (Figure 1).
Without covariate adjustment, prior MS was significantly associated with an increased risk of CKD (unadjusted odds ratio [OR], 1.78; 95% CI, 1.64-1.93; P < .05) (Table 2). Prior MS was significantly associated with CKD in the following subgroups: 2003 to 2006, 2011 to 2014, 2015 to 2018, age groups of 40 to 64 years and ≥ 65 years, male sex, non-Hispanic White and Hispanic ethnicity, school education of grade 0 to 11, and private or other health insurance. Additional comorbidities strongly associated with CKD included hypertension (OR, 6.37; 95% CI, 5.37-7.55), diabetes (OR, 4.16; 95% CI, 3.45-5.03), and cardiovascular disease (OR, 4.20; 95% CI, 3.57-4.95).
In the population reporting prior MS, the unadjusted OR of CKD vs 1999 to 2002 was greater for all other examined eras; with the greatest likelihood observed for the 2003 to 2006 era. Unadjusted ORs of CKD differed in groups with and without prior MS (P value for interaction < .05) for 2003 to 2006, those aged 40 to 64 years and ≥ 65 years, female sex, non-Hispanic African American and Hispanic race and ethnicity, family poverty, high school education, private health insurance, any smoking history, diabetes, hypertension, and cardiovascular disease (Figure 2A).
Following adjustment for age, sex, and race and ethnicity, MS was associated with a 17% higher likelihood of CKD (adjusted odds ratio [AOR], 1.17; 95% CI, 1.06-1.28; P < .01) (Table 3). Prior MS was significantly associated (P < .05) with CKD in the subgroups: age groups 40 to 64 years and ≥ 65 years, non-Hispanic African American, and body mass index ≥ 30. Among those with prior MS, comorbidities strongly associated with CKD in adjusted models included hypertension (AOR, 3.86; 95% CI, 3.18-4.69), diabetes (AOR, 3.05; 95% CI, 2.44-3.82), and cardiovascular disease (AOR, 2.51; 95% CI, 2.09-3.01). In the population with prior MS, the adjusted likelihood of CKD vs 1999 to 2002 was similar across all eras. Adjusted associations of CKD differed in groups with and without prior MS for age groups 40 to 64 years and ≥ 65 years, female sex, and family poverty (P < .05) (Figure 2B).
Discussion
We observed that prior MS was associated with CKD, all eras were associated with CKD in the subgroup with MS, and risk factors for CKD differed among many subgroups both with and without MS history, a finding that remained present in adjusted models. In addition, the finding of CKD was relatively common among those with prior MS (approximately 15%) and was most strongly associated with increasing age and comorbidities frequently associated with CKD.
Although many studies have demonstrated associations of US veteran status with various comorbidities, including hypertension, obesity, and diabetes, these studies often are limited to those both qualifying and receiving care within the US Department of Veterans Affairs (VA) health care system.6-9 The crude proportion of individuals reporting multiple chronic conditions, which included hypertension, diabetes, and weak or failing kidneys, was 49.7% for US veterans compared with 24.1% for nonveterans.2 Large-scale, nationally representative cohorts for use in this context have been limited by the heterogeneity of definitions of CKD applied with limited timeframes yielding variable estimates.1,10 Moreover, few studies have examined the clinical epidemiology of CKD more broadly in the US among those with prior MS. For example, a PubMed search on March 3, 2022, with the terms “epidemiology”, “military service”, and “chronic kidney disease” produced only 9 citations, one of which examined trends among a non-US cohort and quantifying disease burden another among adolescents.
Whether or not prior MS confers a unique risk profile for CKD is unknown. While our findings of an increased CKD burden among those reporting MS may partially reflect observed increases in baseline comorbidities, the observed excess CKD among those with MS remained across multiple categories even after adjustment for baseline demography. As several studies have demonstrated, enlistment into MS may select for a more diverse population; however those enlisted personnel may be of lower socioeconomic status and possibly at higher risk of CKD.11,12 Our findings of important differences in baseline determinants of health mirror this. The proportion of MS respondents with CKD vs CKD alone reporting a high school education or lower was higher (36.0% vs 21.8%) as well as among those with a history of family poverty (21.1% vs 18.0%).