Citizenship Status and the Prevalence, Treatment, and Control of Cardiovascular Disease Risk Factors Among Adults in the United States, 2011–2016

The adult immigrant population has doubled from approximately 19 million in 1990 to 42 million in 2017, accounting for 17% of all US adults.¹ However, noncitizens, which account for half of immigrants,¹ encounter significant barriers to healthcare access.² For example, noncitizens without documentation are ineligible for publicly-funded health insurance, as are many documented noncitizens—their eligibility depends on their specific visa status.² Noncitizens also disproportionately face structural factors, such as poverty and residence in underserved communities, that adversely impact health and healthcare access regardless of cultural or racial/ethnic background.^1,3 Therefore, citizenship status—categorized as US-born citizen, foreign-born citizen, and noncitizen—may contribute to disparities in cardiovascular disease (CVD), the leading cause of morbidity and mortality among immigrants.^4,5

While the management of CVD risk factor—such as hypercholesterolemia, hypertension, and diabetes—is critical for CVD prevention, immigrants facing barriers to healthcare are less likely to be treated or achieve control than their US-born counterparts.⁶ However, examining differences between US-born and immigrant populations is not sufficient because considerable disparities exist within immigrant groups in the prevalence and management of CVD risk factors.^6,7 While citizenship status may be an important contributor to these disparities, differences in the prevalence, treatment, and control of CVD risk factors by citizenship status are unknown. Understanding these disparities is important considering the increasing number of policies that exclude noncitizens from the social safety net and healthcare access^3,8 and may impact the management of these risk factors.

Using the National Health and Nutrition Examination Survey (NHANES), we estimated the prevalence, treatment, and control CVD risk factors (hypercholesterolemia, hypertension, and diabetes) among adults, overall and by citizenship status.

METHODS AND RESULTS

Data for this study is made publicly available by the National Center for Health Statistics and may be accessed at https://wwwn.cdc.gov/nchs/nhanes/. Additional materials are available from the corresponding author upon reasonable request.

NHANES is a nationally representative survey of the US population which uses a stratified complex multistage probability survey design, described in detail elsewhere.⁹ Surveys were conducted in English or Spanish; interpreters were used when necessary. We used data from 2011/12 to 2015/16. This study was considered exempt from human subjects approval by the institutional review board at the University of Illinois at Chicago because NHANES is de-identified, publicly available data.

Citizenship status was determined by asking “in what country were you born?” and “are you a citizen of the United States?” Less than 1% of adults sampled refused to report this information. Sociodemographic characteristics included age, gender, race/ethnicity, and poverty (family income below poverty line). Acculturation characteristics included foreign language preference (responded in Spanish or using an interpreter) and years in the US. Access to care was based on having a usual source of care and health insurance. Additional characteristics included CVD (coronary heart disease, myocardial infarction, angina, or stroke), obesity, and smoking status.

Hypercholesterolemia was defined as total cholesterol (TC) ≥240 mg/dL, high-density lipoprotein (HDL) <40 mg/dL, low-density lipoprotein (LDL) ≥160 mg/dL, or lipid-lowering medication use.¹⁰ Hypertension was defined as systolic blood pressure (BP) ≥140 mmHg, diastolic BP ≥90 mmHg, or antihypertensive use.¹¹ Diabetes was defined as fasting glucose ≥126 mg/dL, 2-hour–postload plasma glucose ≥200 mg/dL, hemoglobin A1c (HbA1c) ≥6.5%, or antidiabetic use.¹²

Based on prescription-medication inventories, we defined hypercholesterolemia, hypertension, and diabetes treatment as the use of statins, antihypertensives, or antidiabetics, respectively. Hypercholesterolemia and hypertension control were defined as serum/examination values below diagnostic thresholds. Diabetes control was defined as an HbA1c <7.0%.¹² To evaluate differences in the treatment and control of CVD risk factors, we restricted these analyses to participants with hypercholesterolemia, hypertension, and/or diabetes; control was estimated among treated participants.

Descriptive statistics were used to estimate the prevalence of CVD risk factors (age-standardized) and their treatment and control rates. Differences in the prevalence were determined using adjusted Wald tests. Differences in treatment and control rates were determined using Pearson’s χ²-tests. Poisson regressions with robust standard errors were used to evaluate the associations between citizenship status treatment of CVD risk factors, resulting in rate ratios (RR). All estimates, confidence intervals (CI), and statistical tests were weighted using Taylor linearization methods to incorporate sample weights that adjust for differential probability of selection and nonresponse. P-values were 2-sided. Analyses were completed using Stata-15.

This study included 16,986 adults aged ≥20 years (Figure I in Data Supplement). Of whom, 82.1% were born in the US and 17.9% were immigrants, including foreign-born citizens (8.6%) and noncitizens (9.3%) (Table I in Data Supplement). The median age of noncitizens was 38 years, younger than both US-born (48 years) and foreign-born citizens (49 years) (P<.001). Race/ethnicity varies across citizenship status. For example, less than 10% of US-born adults were Hispanic/Latino or Asian, yet these ethnicities constitute the majority of foreign-born citizens (36.9% and 31.0%) and noncitizens (60.4% and 22.4%) (P<.001). A greater proportion of noncitizens lived in in poverty (35.9%) than US-born (13.7%) and foreign-born citizens (17.5%) (P<.001). More noncitizens preferred to speak a foreign language (63.4% vs. 32.2%, P<.001) and have resided in the US for less than ten years (41.3% vs. 6.3%, P<.001) than foreign-born citizens. Noncitizens were more likely to report no usual source of care (34.5%) than US-born (14.6%) and foreign-born citizens (14.3%). Noncitizens were also more likely to be uninsured (52.2%) than US-born (13.6%) and foreign-born citizens (16.2%) (P<.001).

Fifty-five percent (54.6%) of US adults had hypercholesterolemia (41.7%), hypertension (33.7%), or diabetes (13.2%) (Figure). When compared to US-born citizens, immigrants—regardless of citizenship status—have a lower prevalence of hypertension (29.0% vs. 34.8%, P<.001) and a higher prevalence of diabetes (15.7% vs. 12.8 %, P<.001).

Figure:

Prevalence, Treatment, and Control of Hypercholesterolemia, Hypertension, and Diabetes Among US Adults, by Citizenship Status, 2011–2016. Overall sample includes 16,986 adults, including US-born citizens (n=11,680), foreign-born citizens (n=2,752), and noncitizen (n=2,554). Error bars represent 95% confidence intervals. Prevalence of cardiovascular disease (CVD) risk factors were age-standardized (US adult population) and differences by citizenship status were determined using adjusted Wald tests. Treatment was estimated among participants with hypercholesteremia, hypertension, and/or diabetes. Control was estimated among treated participants. Differences in CVD disease risk factor treatment and control by citizenship status were determined using Pearson’s χ² tests. ** P<.01.

Noncitizens had considerably lower treatment rates of hypercholesterolemia (16.4% vs. 45.5% and 43.3%), hypertension (60.3% vs. 81.1% and 79.6%), and diabetes (51.2% vs. 69.5% and 66.6%) than US-born and foreign-born citizens (all P<.001) (Figure). Considering the magnitude of these differences, we examined these disparities in detail and found that they persisted over multiple characteristics (Figure II in Data Supplement). For example, Hispanic/Latinos had lower treatment rates than other racial/ethnic groups and fewer noncitizen Hispanic/Latinos were treated for hypercholesterolemia (13.7% vs. 28.4% and 36.7%), hypertension (60.3% vs. 75.4% and 81.1%), and diabetes (50.7% vs. 67.6% and 64.8%) than their US-born and foreign-born citizen counterparts (all P<.01). Similarly, while nonelderly adults, men, and those with prevalent CVD had lower treatment rates of CVD risk factors, these rates were even lower among noncitizens. Hypercholesterolemia, hypertension, and diabetes treatment rates were also very low among noncitizens without a usual source of care (2.7%, 22.2%, and 15.5%, respectively) or health insurance (8.1%, 39.1%, and 28.6%, respectively).

In unadjusted analyses, we found no differences in the treatment of CVD risk factors between US-born and foreign-born citizens (Table II in Data Supplement). However, noncitizens had lower treatment rates of hypercholesterolemia (RR 0.36 [CI 0.30– 0.44]), hypertension (RR 0.75 [CI 0.69–0.82] and diabetes (RR 0.74 [CI 0.64–0.85] than US-born citizens (all P<.001). Reporting no usual source of care or health insurance was significantly associated with lower treatment rates of hypercholesterolemia, hypertension, and diabetes. Therefore, adjusting for access to care attenuated treatment differences between noncitizens and US-born citizens for hypercholesterolemia (RR 0.56 [CI 0.47–0.67], P<.001), hypertension (RR 0.86 [CI 0.80–0.92], P<.001), and diabetes (RR 0.87 [CI 0.75–1.01], P=.07). Further adjustment for sociodemographic, acculturation, and cardiovascular characteristics (Table III in Data Supplement), did not explain differences in the treatment of hypercholesterolemia (RR 0.67 [CI 0.50–0.90], P<.001) or diabetes (RR 0.80 [CI 0.63–1.02], P=.07).

Among adults treated for CVD risk factors, there were no significant differences across citizenship status in the control of hypercholesterolemia (38.1%) and hypertension (71.1%) (Figure). However, diabetes control rates were lower among noncitizens (35.3%) than among US-born (51.2%) and foreign-born citizens (46.9%) (P<.001).

In sensitivity analyses, we found that observed disparities by citizenship status remain unchanged even if alternative clinical guidelines are used (Table IV in Data Supplement). For example, the American College of Cardiology/American Heart Association recommends cholesterol management with statins based on the presence of high CVD risk.¹³ Using this guideline, we found that fewer noncitizens (21.9%) were treated than US-born (41.9%) or foreign-born citizens (38.5%) (P<.001). Similarly, using an alternative Hba1c threshold (<8.0%), noncitizens (55.9%) had lower rates of diabetes control than US-born (73.0%) and foreign-born citizens (74.7%) (P<.001).

COMMENT

One in two adults in the US has hypercholesteremia, hypertension, or diabetes. Although we found limited differences in the prevalence of these risk factors across citizenship status, our findings indicate substantial disparities in their treatment. Noncitizens were consistently undertreated in comparison to US-born and foreign-born citizens. These treatment disparities persist across race/ethnicity, suggesting that citizenship status plays an important role in promoting access to treatment in diverse immigrant populations. Furthermore, undertreatment of CVD risk factors may contribute to CVD disparities in subpopulations with a large proportion of noncitizens. For example, recent findings suggest that immigrant Hispanic/Latinos, which disproportionately lack citizenship,¹⁴ have a greater CVD mortality rate than their US-born counterparts.¹⁵ Noncitizens may also face increasingly high cardiovascular risks as this relatively young population ages because noncitizens who are young and in need of primary prevention are considerably undertreated.

Differences in access to care largely explained treatment disparities based on citizenship status. However, recent policies, including the Affordable Care Act—which sought to ensure equitable access to care—have continued to exclude certain noncitizens.² This has widened gaps in access to care between citizens and noncitizens¹⁶ and may further exacerbate treatment disparities. Nonetheless, when appropriately treated, noncitizens can achieve equitable control of CVD risk factors, as in hypercholesterolemia and hypertension. Therefore, to manage CVD risk factors and prevent CVD, it is important to address treatment disparities by expanding health insurance coverage and ensuring access to a usual source of care to noncitizens.

Our study has some limitations. Notably, NHANES does not distinguish between noncitizens with or without documentation and immigrants may overreport citizenship. As a result, we may understate differences across citizenship status. However, nearly all adults surveyed respond to questions about place of birth/citizenship and the percentage of immigrants in NHANES is similar to national estimates.¹⁴

Despite these limitations, our study has several strengths. To our knowledge, this is the first study to examine differences in the prevalence, treatment, and control of CVD risk factors by citizenship status. We use data with the necessary sample size to examine differences across citizenship status. Our conclusions are also robust to various sensitivity analyses.

In conclusion, our study draws attention to citizenship status as a structural factor that influences disparities hypercholesterolemia, hypertension, and diabetes, conditions that together impact one in two US adults. Treatment of these risk factors was drastically lower among noncitizens in comparison to US-born and foreign-born citizens. Efforts to prevent CVD morbidity and mortality among immigrants should address the undertreatment of CVD risk factors by ensuring access to care among noncitizens.