Abstract
This study assesses national trends in cardiovascular risk factors by income level among adults aged 25 years and older using data from the National Health and Nutrition Examination Surveys.
Cardiovascular outcomes vary by income level, contributing to persistent health disparities. Accordingly, during the last decade, the United States has increasingly focused on efforts to reduce the disproportionate burden of underlying cardiovascular risk factors in low-income populations. Yet it is unknown whether differences in cardiovascular risk factors between low- and high-income populations have narrowed. Such insight is critical for guiding national policy and performance improvement campaigns.
Methods
We assessed national trends in cardiovascular risk factors by income level among adults aged 25 years and older using data from the National Health and Nutrition Examination Surveys, a nationally representative, multistage probability sample of the US population, across 5 periods: 2005 to 2006, 2007 to 2008, 2009 to 2010, 2011 to 2012, and 2013 to 2014. The study was deemed exempt from the approval of the Yale Institutional Review Board because the data came from the publicly available National Health and Nutrition Examination Surveys. Because all data are deidentified, patient consent was not required. Individuals were stratified by the poverty-income ratio (PIR), an index of family income relative to the federal poverty level: PIR less than 1 (<100% federal poverty level), PIR 1 to 3 (100%-300% of federal poverty level), and PIR at least 3 (≥300% of federal poverty level). We examined trends in hypertension, diabetes, dyslipidemia, obesity, and smoking (definitions in Table) by PIR strata, applying standard methods and population weights for complex survey data. Analyses were performed in Stata, version 14.1 (StataCorp).
Table. Cardiovascular Risk Factors by Poverty-Income Ratio Strata, 2005-2014.
| Cardiovascular Risk Factors | Weighted %a | ||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| 2005-2006 | 2007-2008 | 2009-2010 | 2011-2012 | 2013-2014 | |||||||||||
| PIR <1 | PIR 1-3 | PIR ≥3 | PIR <1 | PIR 1-3 | PIR ≥3 | PIR <1 | PIR 1-3 | PIR ≥3 | PIR <1 | PIR 1-3 | PIR ≥3 | PIR <1 | PIR 1-3 | PIR ≥3 | |
| Hypertension | |||||||||||||||
| Prevalentb | 47.2 | 49.1 | 44.8 | 49.3 | 46.4 | 44.7 | 50.3 | 47.2 | 41.4 | 49.4 | 48.1 | 45.4 | 50.8 | 50.8 | 40.3 |
| Controlledc | 14.9 | 15.9 | 15.0 | 18.5 | 17.7 | 16.2 | 18.4 | 18.4 | 17.3 | 18.5 | 18.7 | 17.2 | 21.1 | 21.3 | 17.6 |
| Uncontrolledd | 4.9 | 4.3 | 2.4 | 3.0 | 4.3 | 2.7 | 4.7 | 2.8 | 1.8 | 5.2 | 4.0 | 1.9 | 4.0 | 3.1 | 2.3 |
| Diabetes | |||||||||||||||
| Prevalente | 16.8 | 11.9 | 7.4 | 16.6 | 13.9 | 8.4 | 14.8 | 13.6 | 8.2 | 19.2 | 13.5 | 8.1 | 16.9 | 13.6 | 10.2 |
| Controlledf | 7.9 | 7.1 | 4.4 | 7.9 | 7.9 | 4.6 | 7.2 | 7.1 | 4.1 | 9.4 | 6.7 | 4.9 | 8.8 | 7.1 | 5.1 |
| Uncontrolledg | 3.2 | 2.0 | 1.0 | 3.0 | 1.9 | 1.0 | 2.2 | 1.7 | 0.8 | 4.4 | 2.1 | 1.2 | 3.8 | 2.0 | 1.4 |
| Dyslipidemiah | |||||||||||||||
| Prevalenti | 27.3 | 37.4 | 34.6 | 33.7 | 32.1 | 34.6 | 32.1 | 32.8 | 33.5 | 41.5 | 37.6 | 40.8 | NA | NA | NA |
| Controlledj | 18.5 | 27.7 | 27.4 | 22.7 | 24.5 | 28.0 | 22.1 | 22.8 | 25.2 | 31.7 | 29.4 | 31.9 | NA | NA | NA |
| Uncontrolledk | 8.8 | 9.7 | 7.3 | 11.1 | 7.6 | 6.6 | 10.0 | 10.0 | 8.3 | 9.7 | 8.2 | 9.0 | NA | NA | NA |
| Smoking | |||||||||||||||
| Prevalentl | 32.3 | 24.7 | 14.8 | 35.5 | 23.2 | 12.6 | 33.6 | 20.3 | 12.3 | 29.8 | 21.3 | 9.8 | 31.3 | 20.8 | 9.3 |
| Obesity | |||||||||||||||
| Prevalentm | 37.7 | 39.6 | 31.6 | 37.4 | 38.3 | 30.9 | 40.8 | 39.9 | 35.0 | 41.0 | 40.4 | 31.6 | 42.7 | 47.2 | 33.7 |
Abbreviations: BP, blood pressure; NA, not available; PRI, poverty-income ratio.
Sample sizes for the cells in the entire table ranged from n = 724 to n = 10 109.
Participants either self-reported hypertension, were receiving treatment to lower blood pressure, had a systolic BP at least 140 mm Hg, or had a diastolic BP at least 90 mm Hg.
Of those with prevalent hypertension, participants with a BP less than 140 mm Hg/80 mm Hg were considered to have controlled hypertension.
Of those with prevalent hypertension, participants with a BP at least 140 mm Hg/90 mm Hg were considered to have uncontrolled hypertension.
Participants either self-reported diabetes, were receiving treatment to lower blood glucose, or had hemoglobin A1c at least 6.5% (to convert to proportion of total hemoglobin, multiply by 0.01).
Of those with prevalent diabetes, participants with hemoglobin A1c less than 7% were considered to have controlled diabetes.
Of those with prevalent diabetes, participants with hemoglobin A1c greater than 9% were considered to have uncontrolled diabetes.
Blank cells indicate that the data were not made publicly available at the time of this study.
Participants either self-reported dyslipidemia, were receiving treatment to lower blood cholesterol, or had uncontrolled dyslipidemia.
Of those with prevalent dyslipidemia, participants meeting their specific Adult Treatment Protocol III guideline were considered to have controlled dyslipidemia.
Of those with prevalent dyslipidemia, participants not meeting their specific Adult Treatment Protocol III guideline were considered to have uncontrolled dyslipidemia.
Participants reported being a current smoker.
Participants had a body mass index of at least 30.0 (calculated as weight in kilograms divided by height in meters squared).
Results
A total of 23 693 adults 25 years and older participated in the National Health and Nutrition Examination Surveys between 2005 and 2014 and had nonmissing income data. The estimated percentage of individuals in the lowest PIR group increased from 10% in 2005 to 2006 to 14% in 2013 to 2014; the highest PIR group decreased (55% to 51%).
The prevalence of hypertension increased in the lowest PIR group and declined in the highest PIR group, widening the absolute difference between groups (2.4%; 95% CI, −5.5% to 10.2% in 2005-2006 vs 10.5%; 95% CI, 6.2%-14.8% in 2013-14) (Figure). The prevalence of controlled hypertension increased in both groups and more so in the lowest PIR group (−0.1%; 95% CI, −4.9% to 4.8% in 2005-2006 vs 3.5%; 95% CI, −0.8% to 8.8% in 2013-2014).
Figure. Gaps in Cardiovascular Risk Factors Between Poverty-Income Ratio at Least 3 and Less Than 1, 2005 to 2014.
Body mass index is calculated as weight in kilograms divided by height in meters squared.
Diabetes prevalence in the lowest PIR group did not change, although it increased in the highest PIR group, resulting in persistent but smaller differences between groups (9.3%; 95% CI, 5.1%-13.6% in 2005-2006 vs 6.7%; 95% CI, 3.3%-10.1% in 2013-2014). Rates of uncontrolled diabetes were consistently greater in the lowest PIR group than the highest PIR group, with slight differences between the groups over time (2.2%; 95% CI, −0.2% to 4.5% in 2005-2006 vs 2.4%; 95% CI, 1.0%-3.9% in 2013-2014).
Dyslipidemia prevalence increased in the lowest and highest PIR groups between 2005 to 2006 and 2011 to 2012 (most current data available). We observed a 2-fold greater increase among the lowest PIR group compared with the highest PIR group, with nonsignificant differences over time (7.3%; 95% CI, −2.8% to 17.5% in 2005-2006 vs 0.7%; 95% CI, −6.9% to 5.6% in 2011-2012). Obesity increased in the lowest and highest PIR groups but by a greater magnitude in the lowest PIR group (6.1%; 95% CI, 1.1%-11.2% in 2005-2006 vs 9.1%; 95% CI, 4.8%-13.3% in 2013-2014). Smoking prevalence declined in both groups but declined more in the highest PIR group, widening the difference (17.5%; 95% CI, 13.0%-22.0% in 2005-2006 vs 22%; 95% CI, 17.8%-26.2% in 2013-2014).
Discussion
Disparities in cardiovascular risk factor burden between low- and high-income groups have not improved during the last decade and, in some cases, have widened. Half of people living below the federal poverty level have hypertension and one-third smoke; since 2005, these rates have not changed, although declines were observed among the high-income group. Despite population-wide efforts to improve risk factors, economic disparities in cardiovascular health may be worsening.
Limitations
Limitations of this study include a narrow definition of economic status, which may not fully capture the challenges low-income individuals face in managing cardiovascular risk factors. Additionally, fluctuations in estimates across some years may be owing to the National Health and Nutrition Examination Surveys sampling strategy.
Conclusions
To reduce health disparities, there is an urgent need to identify and scale efforts that effectively target the cardiovascular health of low-income populations.
References
- 1.Kanjilal S, Gregg EW, Cheng YJ, et al. Socioeconomic status and trends in disparities in 4 major risk factors for cardiovascular disease among US adults, 1971-2002. Arch Intern Med. 2006;166(21):2348-2355. [DOI] [PubMed] [Google Scholar]
- 2.Diez Roux AV, Merkin SS, Arnett D, et al. Neighborhood of residence and incidence of coronary heart disease. N Engl J Med. 2001;345(2):99-106. [DOI] [PubMed] [Google Scholar]
- 3.Spatz ES, Beckman AL, Wang Y, Desai NR, Krumholz HM. Geographic variation in trends and disparities in acute myocardial infarction hospitalization and mortality by income levels, 1999-2013. JAMA Cardiol. 2016;1(3):255-265. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 4.Record NB, Onion DK, Prior RE, et al. Community-wide cardiovascular disease prevention programs and health outcomes in a rural county, 1970-2010. JAMA. 2015;313(2):147-155. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 5.Pearson TA, Bazzarre TL, Daniels SR, et al. ; American Heart Association Expert Panel on Population and Prevention Science . American Heart Association guide for improving cardiovascular health at the community level: a statement for public health practitioners, healthcare providers, and health policy makers from the American Heart Association Expert Panel on Population and Prevention Science. Circulation. 2003;107(4):645-651. [DOI] [PubMed] [Google Scholar]
- 6.National Center for Health Statistics. National health and nutrition examination survey: questionnaires, datasets, and related documentation. http://www.cdc.gov/nchs/nhanes/nhanes_questionnaires.htm. Published 2016. Accessed April 1, 2016.
