Original ResearchRural–urban disparities in the prevalence of diabetes and coronary heart disease
Introduction
Nearly 21 million persons living in the USA had been diagnosed with diabetes in 2010; this figure is more than three times higher than the number of persons living with diabetes in 1980.1 In the USA, 90–95% of all newly diagnosed cases of diabetes are type 2.2 Patients with diabetes account for more than 27 million annual outpatient office visits in the USA, and more than 68,000 persons die each year from diabetes-related complications.3 It is the seventh leading cause of death in the USA, and also contributes to high rates of morbidity including kidney failure and extremity amputations.3, 4 Complications of diabetes include the development of cardiovascular disease, diabetic neuropathy and retinopathy.5 In 2002, the estimated direct and indirect costs (e.g. lost workdays and disability) attributed to caring for persons with diabetes in the USA were $174 million.6 This likely underestimated the actual costs as it did not include the economic burden of pain and suffering, or the excess costs associated with the treatment of undiagnosed disease.
Obesity, advanced age and ethnicity, particularly being Black and Hispanic, are well-established risk factors for the development of diabetes.7, 8, 9 In the USA, the prevalence of diabetes is lower in women than in men.10 A significant amount of work has been done analysing the prevalence of diabetes as it relates to socio-economic status, using the common measures of income, education and occupation. These markers are often assessed independently, but have also been used together with other variables such as single-parent households, the ability to own a home or car, and postal code of residency to construct indices of social deprivation.
Using markers of income, education, occupation and insurance type, persons of lower socio-economic status living in the USA are more likely to suffer from type 2 diabetes than persons of higher socio-economic status.11, 12, 13, 14 Similarly, persons of lower socio-economic status living in the UK, Israel and Australia are also more likely to be diagnosed with type 2 diabetes, both on an individual basis as well as in aggregate, compared with persons of higher socio-economic status using income, education and tax exemption qualifications, as well as a variety of indices of material deprivation and social position in society.15, 16, 17, 18, 19, 20, 21 Diabetic patients of lower socio-economic status in the UK and Canada are also more likely to experience complications of their disease including diabetic retinopathy, peripheral neuropathy and circulation problems in the legs or feet, and tend to present to care when they are older, more obese and with a worse lipid profile than higher income patients.22, 23 Adverse health outcomes associated with cost-related medication non-compliance and higher rates of mortality are also inversely linked to socio-economic status in the USA and UK.13, 14, 24 A study from Canada revealed that, although mortality among persons with diabetes has declined substantially in recent years, decreased mortality among persons in the highest income bracket was substantially greater than the decline in mortality for those in the lowest income bracket.25 The evidence of the inverse correlation between socio-economic status and diabetic health outcomes appears compelling, although it should be noted that the organization and structure of the healthcare delivery system varies by country and the results of studies conducted in other countries may not be generalizable to the USA.
Coronary heart disease is the leading cause of death in the USA and nearly one of every four deaths (more than 616,000 persons) can be attributed to the disease.26 More than 15 million persons in the USA have angina or chest pain caused by coronary heart disease.27 Approximately 17% of all medical expenditure ($149 billion annually) are attributable to cardiovascular disease.28 Well-established risk factors for coronary heart disease include high blood pressure, hyperlipidaemia, diabetes, age, and tobacco use.29 Existing literature indicates that non-Hispanic Blacks and Hispanics in the USA are less likely to be diagnosed with coronary heart disease than non-Hispanic Whites, although non-Hispanic Blacks are more likely to die from the disease than non-Hispanic Whites.30, 31
Similar to diabetes, US persons of lowest socio-economic status, as measured by income, education and occupation, are three times more likely to have coronary heart disease than persons in the highest income category, and persons living in disadvantaged neighbourhoods are significantly more likely to suffer coronary heart disease than those living in advantaged neighbourhoods.32, 33 Independent of other risk factors, US men of the lowest socio-economic status had a 1.67-fold increased risk of death from coronary heart disease.34 Similar outcomes can be found in Europe where men who have the most difficulty paying bills have a 2.5 times greater risk of fatal and non-fatal myocardial infarction.35 European women of low income are also significantly more likely to suffer recurrent events secondary to coronary heart disease relative to patients of medium and upper income; those that suffer recurrent events are more likely to die from the disease.36 The impact of poverty on cardiovascular health is so profound that recent data support adding socio-economic status to coronary heart disease risk assessment to reduce treatment disparities.37
The relationship between these risk factors and the increased prevalence of diabetes and coronary heart disease is well documented in the USA and other industrialized counties. However, few data are available comparing urban–rural differences in the prevalence of diabetes and coronary heart disease, particularly as they relate to a range of established risk factors. Authors of previous studies have reported a higher prevalence of diabetes in rural locations.38, 39 To examine this question, differences in the prevalence of diabetes and coronary heart disease in rural and urban populations in the USA were examined using data from the US Centers for Disease Control and Prevention's (CDC's) Behavioral Risk Factor Surveillance System (BRFSS), a large nationally-representative population-based survey. The degree to which the well-established risk factors explain the prevalence of diabetes and coronary heart disease in rural and urban populations was also examined.
Section snippets
Methods
Data are available from the US CDC through the BRFSS. During 2008, more than 400,000 persons in the USA were asked about their chronic health conditions, socio-economic status and a variety of risk factors. BRFSS is a cross-sectional telephone survey that is conducted by state health departments using surveys provided by the CDC. These data were then organized by the CDC into metropolitan statistical codes to denote urban and rural populations.
To determine a person's diabetic status,
Results
As shown in Table 2, the crude (unadjusted) prevalence of diabetes and coronary heart disease in rural locations is significantly greater than in urban environments. Specifically, the crude prevalence of diabetes was 8.6% higher (9.7% vs 9.0%; P = 0.001) among respondents living in rural areas compared with those living in urban areas. Similarly, the crude prevalence of coronary heart disease was 38.8% higher (5.5% vs 4.0%; P < 0.001) among respondents living in rural areas compared with those
Discussion
These results indicate that persons living in rural environments in the USA are more likely to be diagnosed with diabetes than persons living in urban areas; they are also more likely to be diagnosed with coronary heart disease. In the case of diabetes, controlling for many of the common risk factors for the disease including income, age, gender, ethnicity and BMI explains the increased prevalence of diabetes in rural areas. However, even after controlling for these risk factors and for tobacco
Acknowledgements
The authors wish to thank Randy Rasch, Rick Watters and Donna McArthur, Vanderbilt University School of Nursing. The focus of Dr O’Connor's research at Vanderbilt was rural–urban health disparities; she completed her doctorate in nursing in 2010.
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