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Logo of nihpaAbout Author manuscriptsSubmit a manuscriptHHS Public Access; Author Manuscript; Accepted for publication in peer reviewed journal;
 
Endocrine. Author manuscript; available in PMC 2013 December 1.
Published in final edited form as:
PMCID: PMC3779599
NIHMSID: NIHMS395170

Glucose control in diabetes: the impact of racial differences on monitoring and outcomes

Abstract

Purpose

Type 2 diabetes is the seventh leading cause of death in the US and is projected to increase in prevalence globally. Minorities are disproportionately affected by diabetes and data suggest that clinical outcomes consistently fall below American Diabetes Association recommendations. The purpose of this systematic review was to examine ethnic differences in self-monitoring and outcomes in adults with type 2 diabetes.

Methods

Medline was searched for articles published between January 1990 through January 2012 using a reproducible strategy. Inclusion criteria included: (1) published in English, (2) targeted African Americans, Hispanic or Asian adults, ages 18+ years with type 2 diabetes, (3) cross-sectional, cohort, or intervention study, and (4) measured change in glycemic control, BP, lipids, or quality of life by race.

Results

Twenty-two papers met the inclusion criteria and were reviewed. Overall, significant racial differences and barriers were found in published studies in diabetes management as it pertains to self-monitoring and outcomes. African Americans tend to consistently exhibit worse outcomes and control when compared to other minority populations and non-Hispanic Whites.

Conclusions

Significant racial differences and barriers exist in diabetes management as it pertains to self-monitoring and outcomes when compared to non-Hispanic Whites. Explanatory and intervention studies are needed to determine the mechanisms and mediators of these differences and strategies to reduce these disparities. In addition, more research is needed to investigate the impact of racial differences in self-monitoring and outcomes on quality of life.

Keywords: Diabetes, Racial differences, Self-monitoring, Glucose control, Lipids, Blood pressure

Introduction

Burden of Diabetes

Diabetes affects more than 25.8 million people of the United States' (US) population. In 2010, 10.9 million adults 65 years and older and approximately 1.9 million people between the ages of 20 and 64 were newly diagnosed with type 2 diabetes mellitus (T2DM) [1]. Consequently, diabetes is the seventh leading cause of death based on US death certificates in 2007 [1]. The overall estimated cost of diabetes in the US in 2007, including direct and indirect costs, was $174 billion [1] and is predicted to increase to $192 billion by 2020 [2]. Several comorbid conditions and complications are influenced by T2DM, including but not limited to blindness and eye problems, nervous system disorders, kidney disease, amputations, periodontal disease, heart disease, and stroke [1]. In addition, the number of individuals with T2DM is predicted to increase to 29 million by 2050 [3].

On a global scale it is estimated that 366 million people, or 8.3% of adults, are diagnosed with diabetes, leading to 4.6 million deaths in 2011 [5]. This number is expected to rise to 522 million by 2030, with T2DM prevalence increasing in every country [5]. The greatest number of people with diabetes is in the 40 to 59 age group, and there continues to be more people with diabetes living in urban areas than in rural areas [5]. It is the fourth or fifth leading cause of death in most high-income countries; however 80% of those with diabetes live in low and middle-income countries [5]. While 11% of total healthcare expenditures in adults are spent addressing diabetes, there is a large disparity between regions and countries [5]. Only 20% of the global health expenditures were made in low- and middle-income countries, where often families bear almost the total cost of their medical care [5]. Considering low- and middle-income countries face the greatest disease and economic burden, diabetes is considered one of the most challenging health problems of the 21st century [5].

Ethnic Differences in Burden of Diabetes

Minorities are disproportionately affected by diabetes compared to non-Hispanic Whites. Within the US population, 8.4% of Asian Americans, 11.8% of Hispanics, and 12.6% of African Americans have diagnosed T2DM [1]. Minority populations have also shown an increased likelihood to develop diabetes with African Americans being 77%, Hispanic/Latinos 66%, and Asian Americans 18% more likely to develop diabetes and suffer from diabetes related complications, compared to non-Hispanic Whites [1]. Minority populations tend to suffer a greater burden of disease with African Americans being 2.6-times more likely than that of non-Hispanic Whites to develop end-stage renal disease. Additionally, minority populations have higher mortality rates due to the direct and indirect complications of T2DM [4]. Evidence suggests that minority populations tend to have poorer self-management and diabetes outcomes as compared to non-Hispanic Whites, increasing the already disproportionate burden of disease and diabetes related complications.

Ethnic Differences in Outcomes

According to the American Diabetes Association (ADA), optimal outcomes for diabetes management in adults living with T2DM, include HbA1c<7.0%, blood pressure <130/80mmHg, and lipid levels of <100mg/dL for LDL and >50mg/dL for HDL [6]. Data on diabetes outcomes have shown that minority populations consistently fall below recommended guidelines in lipid, blood pressure and glycemic control, as well as self-monitoring of blood glucose as compared to non-Hispanic Whites [7-8]. A study recently assessing control for cardiovascular risk factors such as HbA1c >8.0%, BP>140/90mmHg and LDL>100 mg/dL among ethnic minority populations found that Hispanics are less likely to have good control compared to non-Hispanic Whites, with Mexican Americans and African Americans being less likely to obtain good glycemic control as defined by HbA1c<7.0% [9,10].

Patient outcomes above the ADA recommendations are linked to increased risk for microvascular and macrovascular complications [6]. In order to reduce complications, team based approaches to diabetes management are recommended [6]. In one study, racial disparities in lipoprotein cholesterol levels were diminished due to a quality improvement program, but differences in glycemic control continued [8]. Unfortunately, data suggests that disparate quality of care exists among minority populations at both the patient level and at the provider level [11]. Studies have shown that when controlling for socioeconomic variables, as well as access to care, there is an improvement in self-monitoring behaviors; however, the racial/ethnic disparities in diabetes quality of care continued [12].

As a result, it is necessary to understand whether racial/ethnic differences exist in self-monitoring and diabetes specific outcomes as compared to national and clinical recommendations for proper diabetes management. There has been little done to summarize the evidence regarding self-care outcomes by race. The purpose of this systematic review was to examine ethnic differences in self-monitoring and outcomes (including glycemic control, blood pressure control, lipid control and quality of life) in adults (ages 18+) with T2DM using English language literature from 1990-2012.

Methodology

Search Strategy and Eligibility Criteria

Medline was searched for articles published between January 1990 through January 2012 using a reproducible strategy. Fourteen searches were performed producing 1,310 articles. The first two search terms in all searches were race and diabetes. The third search term was different for each and included: self-monitoring, self-management, glycemic control, hemoglobin A1c, HbA1c, blood pressure, BP, lipids, cholesterol, LDL, quality of life, SF-12, SF-36, and SF-20. Duplicates were removed, producing 324 citations. Titles were eliminated if they were obviously ineligible, for instance describing childhood, Type 1 diabetes, or gestational diabetes. This produced 156 abstracts to examine for full article review.

The following inclusion criteria were used to determine eligible study characteristics: (1) full article must be published in the English language, (2) must target African Americans, Hispanic or Asian adults, ages 18+ years with type 2 diabetes, (3) can be cross-sectional, cohort, or intervention study, and (4) must measure a change in glycemic control, BP, lipids, or quality of life by race.

Full articles were read and reviewed using a standardized check-list by three reviewers (JC, RW, BS). A fourth reviewer (LE) was asked to make the final decision regarding eligibility in the case of disagreement. Twenty-two eligible studies were identified based upon the predetermined inclusion criteria.

Data Collection

Data collected from the eligible articles is shown in Tables 1 through through4.4. Data was extracted on the number of participants, sample population, duration of the study, setting of the study, study design, mean change in outcome, statistical significance, major findings, and limitations for the study (Table 1--4).4). A table was compiled for each of the four categories of this review with papers meeting inclusion criteria for: self-monitoring, glycemic control, blood pressure, and lipid control.

Table 1
Articles Reviewed that Focused on Racial Differences in Self-Monitoring
Table 4
Articles Reviewed that Focused on Racial Differences in Lipids

Results

Twenty-two papers met the inclusion criteria set for this analysis. Three provided outcomes for self-monitoring, 17 provided outcomes for glycemic control, 6 provided outcomes for blood pressure, and 8 provided outcomes for lipids. Of the 22 meeting inclusion criteria, 8 studies measured glycemic control, lipids and blood pressure within one analysis. These outcomes were extracted and discussed independent of one another. No papers reviewed provided outcomes for quality of life and met inclusion criteria. Twelve were cross-sectional studies, 9 were cohort studies, and 1 was a pooled dataset of intervention studies. Sample sizes ranges from 283 to 80,207 participants. Table 1 provides the results for self-monitoring articles, Table 2 provides the results for glycemic control outcomes, Table 3 provides the results for blood pressure outcomes, and Table 4 provides the results for lipid outcomes.

Table 2
Articles Reviewed that Focused on Racial Differences in Glycemic Control
Table 3
Articles Reviewed that Focused on Racial Differences in Blood Pressure

Racial Differences in Self-Monitoring

Based on inclusion criteria of the database search, 3 papers were reviewed that examined racial difference in self-monitoring among those with T2DM. Two studies were cross-sectional and 1 study was a cohort study; no intervention studies were reviewed. The number of participants across studies ranged from 1,720 to 4,565, with sample populations including Hispanics, African Americans and non-Hispanic Whites in adult managed care settings. Outcome assessments included likelihood, regularity and incidence of self-monitoring of blood glucose (SMBG). Studies measured absolute change in outcome by race using odds ratio and hazard ratio. Major findings were consistent across studies with African Americans and Hispanics being significantly less likely to have control in SMBG as compared to non-Hispanic Whites [12-14].

Although the evidence supporting the efficacy of SMBG in those diagnosed with T2DM has not been widely documented, data suggests that individuals who maintain self-monitoring behaviors are more likely to achieve optimal outcomes in diabetes care [13]. The data retrieved from the current studies also indicates that there are racial/ethnic barriers that exist in quality of care, including initiation and in maintaining of SMBG [13]. In examining the racial differences between African Americans and non-Hispanic Whites in SMBG, Mah et al assessed if the provision of free home glucose monitors would impact self-monitoring among African Americans as compared to non-Hispanic Whites, and found that when both groups received free monitors, African Americans were as likely as non-Hispanic Whites to initiate self-monitoring behaviors and showed an increase in use up to 6 months following receipt of the monitor [14]. However, the data showed that African Americans were at a higher rate of discontinuation than that of non-Hispanic Whites during follow up periods [14]. This is suggestive of differences in rates of self-monitoring by race, indicating that differences in the barriers to SMBG may exist by ethnicity [14]. Other studies examining racial differences in SMBG among individuals with type 2 diabetes found significant racial/ethnic differences in self care behaviors. However, when controlling for socioeconomic variables and access to care variables, the racial/ethnic differences in SMBG between Hispanics, African Americans and non-Hispanic Whites were nonexistent. Overall, data extracted from the current studies showed a consistent trend in racial differences among SMBG, with African Americans and Hispanics being less likely to self-monitor their blood glucose as compared to non-Hispanic Whites [12-14].

Racial Differences in Outcomes

Glycemic Control

Using the search strategy, 17 articles were retrieved that provided glycemic control outcomes by race/ethnicity. Of those meeting inclusion criteria, 9 were cross-sectional studies, 7 were cohort studies and 1 was a pooled dataset of intervention studies [10, 15-29]. Sample sizes ranged from 283 to 80,207 participants. While the level of evidence based on study design alone is relatively low, most studies included large sample sizes and agreement in results suggested higher HbA1c scores in minority participants [15-29]. Though there were a number of cohort studies, the changes in racial/ethnic gap in HbA1c over time were not often assessed [8,23-28,]. As a result, impacts on disparities in outcome cannot be addressed with the evidence at this time.

Since only one study meeting inclusion criteria was an intervention study, selection bias may be a concern for most of the available data [29]. Four studies used nationally representative NHANES data, 4 studies used specific practice or insurance groups and 2 studies investigated Veterans [8, 10, 16-22, 25-28]. Nine studies provided outcomes by point estimate of HbA1c and 8 provided outcomes relative to a threshold [8, 10, 15-29]. Of the 8 studies using thresholds, 5 provided odds ratios and 3 provided percent above or below the threshold [8,10,20-22,25,27,28]. All thresholds set were HbA1c of 7%, except Jackson et al, which set the threshold at 9% [27]. Two studies investigated whether HbA1c was above the threshold and 6 investigated whether HbA1c was below the threshold [8, 10, 20-22, 25, 27, 28]. Overall, regardless of study population or the outcome measure used, a difference in glycemic control by racial/ethnic group was observed [15-29]. Unfortunately, without randomization it cannot be concluded with certainty whether these differences across studies are due to selection bias within the groups investigated or are representative of what obtains in the population overall.

Based on the 17 studies meeting inclusion criteria, African Americans, Hispanic, and Asian Americans show higher HbA1c values than non-Hispanic Whites [15-29]. When compared to non-Hispanic Whites, the difference in average HbA1c for statistically significant point estimate studies ranged from 0. 2 to 0.9 for African Americans, 0.28 to 0.76 for Hispanics, and 0.4 to 0.5 for Asian Americans/Pacific Islanders [15-19,23,24, 26,29,]. Seven of the 9 studies using thresholds showed significantly better control in non-Hispanic Whites than in minority populations [8,10,20-22,25,27]. Studies reported different groups of racial/ethnic minorities, however when measured, Hispanics showed worse control in 2 of 3 studies, African Americans showed worse control in 5 of 7 studies, Mexican Americans showed worse control in 2 of 3 studies, and Asian Americans showed worse control in 1 of 2 studies [15-29].

Based on a clinically significant difference in HbA1c of 0.5, and the ADA clinically recommended threshold for HbA1c of 7%, these disparities in glycemic control by racial/ethnic group appear to be clinically important [30]. Since most studies were cross-sectional or cohort designs the reasons for these differences cannot be determined. Additionally, when cohort designs are used, the change in HbA1c within a race/ethnicity has been investigated, but rarely has the change over time between racial/ethnic groups [8,23-28]. This is an important trend to understand in order to investigate and influence apparent disparities in glycemic control.

Blood Pressure

Six papers examining racial differences in blood pressure among individuals with T2DM were reviewed based on inclusion criteria. Three of those studies were cross sectional, 2 were cohort studies, and 1 was a retrospective cohort study [7,15,17 25, 27,28]. Across studies, participants included Hispanics, African Americans, Asian Americans, and non-Hispanic Whites, with sample size ranging from 998 to 80,207 within managed care clinics and Veteran Administration Medical Center (VAMCs) [7,15,17 25, 27, 28]. Study timeframes ranged from 1 to 10 years, no intervention studies were reviewed in the search. Outcome assessment of blood pressure across papers was BP>140/>90 mmHg [7,15,17 25, 27, 28].

Of the studies reviewed, 4 reported statistically significant racial differences in BP outcome assessments at p<0.05 [7,15,17,27]. Lower levels of control in BP among minority populations were consistently reported among study samples; with African Americans showing consistently lower rates of BP control as compared to non-Hispanic Whites and other minority populations [7,15,17, 25, 27,28]. Axon et al, 2010 found in a retrospective cohort study that among veterans in the southeastern United States that ethnic veterans with T2DM were at an increased risk of poor BP control when compared to non-Hispanic Whites [7].

Although awareness, promotion and treatment of hypertension has increased in recent years, little progress has been seen in the treatment outcomes of diabetics who have co-morbid conditions such as hypertension, a major risk factor of cardiovascular disease [7]. Investigations within the current literature search suggest that hypertension among ethnic minority populations are consistently less controlled to that of their non-Hispanic White counterparts. Consequently, the racial and ethnic differences among those with T2DM who suffer from high blood pressure still persist.

Lipids

Using the search strategy of electronic databases, 8 studies met the inclusion criteria for having an outcome measure of lipids. Two of the studies were cohort observational studies and 6 were cross-sectional studies; [15,17,20-21,25,27-28,31]. All studies assessed the difference in lipids, whether HDL, LDL, triglycerides, or a comprehensive lipid panel, which includes HDL, LDL, and triglycerides. There were no intervention studies that met our predetermined study requirements. Within the studies that were included, 4 reported their results in terms of odds ratios, 2 used percentages within each race to express proportions of the race that had American Diabetes Association recommended lipid levels, and the 2 remaining studies used the mean lipid level for each race evaluated [15,17,20-21,25,27-28,31].

In addition, study timeframes differed ranging from 1 to 8 years (median 2.5 years). Two studies lasted for 1 year, but only 1 indicated statistical significance [21, 27]. The 8-year observational study showed no statistical significance in the difference of lipids over time by race [31]. Based on these results, the length of a study may not give greater insight into significant differences in lipids by race. In addition, the absence of intervention studies decreases the level of evidence concerning lipid outcomes by race in those with type 2 diabetes.

Along with low levels of evidence, sample population characteristics and sample size also varied, which could have affected the outcome measure and statistical significance [15,17,20-21,25,27-28,31]. All studies included participants who had been diagnosed with type 2 diabetes; however, there were several differences between sample populations. For instance, Zhu and colleagues had a sample population of 4,350 adult diabetics with at least one pharmacy claim for a statin; Chew and colleagues had over 14,000 participants who had to have had continuity of care for at least 2 years with at least 2 outpatient interactions in 1 of 6 hospitals; and Harris conducted a study that included 1,480 participants and defined adults as individuals 25 years and older [20,25,31]. Each study tailored its sample population for a specific purpose; therefore, the sample populations may not be comparable.

Despite the variation in sample size and sample population characteristics, the studies did show differences between minority groups in lipid control [15, 17, 20, 21, 25, 27, 28, 31]. Zhu and colleagues found that African Americans were more likely to have poor lipid control than non-Hispanic Whites and 2 observational cohorts showed that at least 13% of their cohorts had lipid levels above recommended levels [25, 28, 31]. Two studies showed Hispanics are more likely to have poor lipid control but only one study was statistically significant [20,31]. An additional 2 studies indicated that only 20-25% of Mexican Americans in the sample population had ADA recommended lipid levels [25,28]. Asians were less likely to have poor lipid control than any other minority group [20, 27].

Quality of Life

As previously mentioned, no papers that investigated quality of life by race and met the inclusion criteria were reviewed for this review.

Summary of Evidence

In this literature review, racial differences in monitoring and outcomes among individuals with T2DM was examined by self-monitoring, glycemic control, blood pressure control, lipid control and quality of life. Of the 22 papers reviewed, 3 papers provided outcomes for self-monitoring, 17 for glycemic control, 6 for blood pressure and 8 for lipid outcomes by racial/ethnic group [12-31]. Of the self-monitoring papers reviewed all 3 reported statistical significance in racial differences in self-monitoring when compared to non-Hispanic Whites, suggesting race/ethnicity as a barrier to self-monitoring behaviors [12-14]. Fifteen of the 17 glycemic control studies reported statistical significance in racial differences for glycemic control with a persistent racial gap being present between African Americans and non-Hispanic Whites [8,10,13,15-20,23-27,29]. Of the 6 papers reporting differences in blood pressure control, 4 reported statistical significance among minority populations compared to non-Hispanic Whites [7,15,17,27]. Lastly, among the 8 studies examining lipid outcomes between races, 5 reported statistical significance, however sample sizes and the lack of intervention studies may have reduced the level of statistical significance [15,20,25,27-28].

Overall this review reveals that significant racial differences and barriers exist in diabetes management as it pertains to self-monitoring and outcomes when compared to non-Hispanic Whites. Explanatory and intervention studies are needed to determine the mechanisms and mediators of these differences and strategies to reduce these disparities. In addition, more research is needed to investigate the impact of racial differences in self-monitoring and outcomes on quality of life.

There are several limitations to this systematic review worth addressing. First, the search was limited to articles published in English between 1990 and 2012. Second, since studies with positive results are more likely to be published, the studies in this review may reflect this publication bias. Lastly, the small number of randomized controlled trials and differences in study methodology prevented a meta-analysis from being performed. Conclusions from this review are therefore qualitative and meant to guide future research rather than provide conclusive answers.

Evidence provided from this search shows that racial/ethnic disparities exist as compared to national and clinical recommendations for proper diabetes management. African Americans tend to consistently exhibit worse outcomes and control when compared to other minority populations and non-Hispanic Whites. Further research is needed to determine the barriers leading to these disparities, and investigate the impact on quality of life.

Footnotes

Conflict of interest: The authors declare that they have no conflict of interest.

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