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Racial Divergence In The Glycemic Control Of Well-Functioning Older Diabetics

To assess the racial differences and the other factors associated with poor glycemic control in well-functioning older individuals with type 2 diabetes, The Laboratory of Epidemiology, Demography and Biometry, National Institute on Aging, Bethesda, Maryland had conducted the following studies, their hypothesis was that glycemic control would be worse among black and other races than the white diabetic individuals but that this association would be explained by differences in severity of diabetes, health status, health care indicators, and social, psychological, or behavioral factors. Researchers had to further hypothesize that the association of the race with poorer glycemic control would be limited to those with lower education or lower income.

In a cross-sectional analysis of 468 diabetic participants among a cohort of 3,075 non-disabled black and white persons aged 70–79 years living in the community enrolled in the Health, Aging and Body Composition Study. Glycemic control was measured on the basis of the level of HbA1c. Taken into consideration a total of 58.5% of the diabetic individuals were black. Although control was poor in all diabetic participants (HbA1c =7% in 73.7%), blacks had worse glycemic control than whites (age and sex adjusted mean HbA1c, 8.4% in blacks and 7.4% in whites; P < 0.01). Race differences in glycemic control remained important, even after adjusting for current insulin therapy, cardiovascular disease, higher total cholesterol, and not receiving a flu shot in the previous year, all of which were associated with higher HbA1c concentrations. Controlling for these factors reduced the association by 27%. Race remained an important factor in the glycemic control, even when results were stratified by education or income. HbA1c concentrations were higher in older black diabetic individuals. Differences in glycemic control by race were associated with disease severity, health status, and poorer quality of care, but these factors did not fully explain the higher HbA1c levels in older black diabetic individuals.

The prevalence of type 2 diabetes varies considerably by ethnic group and is higher among African Americans and Hispanics compared with Caucasians. Poor glycemic control frequently occurs in U.S. patients with type 2 diabetes, particularly in African Americans and Hispanics, and poor glycemic control contributes to increased mortality and complications in these minority groups. Few factors seem to explain racial differences in glycemic control. Researchers further hypothesized that the association of race with poorer glycemic control would be also limited to those of lower socioeconomic status (SES). Glycemic control was assessed by level of HbA1c. All the participants gave written informed consent, and all protocols were approved by the Institutional Review Boards at both study sites. The participants included 1,491 men and 1,584 women, 468 (15.2%) of who identified themselves as having diabetes and/or using any hypoglycemic medication at the time of their recruitment into the study.

Measure of glycemic control

The primary indicator of glycemic control was level of HbA1c (Biorad Variant high-performance liquid chromatography [HPLC] assay.). This measure integrates control over the prior 6–8 weeks. In clinical practice, the goal for good control is HbA1c <7%. Fasting glucose level was also measured.

Severity of diabetes

Severity of diabetes was examined in two ways. First, duration of diabetes was defined as either £5 years, 6–15 years, or >15 years; patients with duration of diabetes >15 years were defined as the reference group. Researchers also characterized current treatment as insulin, oral hypoglycemics, or no medication, with insulin treatment indicating more severe disease.

Health status

Lack of glycemic control might relate to poorer health status; therefore, researchers had assessed diabetes-related illnesses, weight, lipid levels, and functional status. They had also used a combination of self-reported diagnoses and/or medications to establish the prevalence of cardiovascular disease (heart disease or stroke). To assess whether differences in functional status would affect level of glycemic control, researchers used a summary measure that combines usual gait speed, gait speed over a narrow walk course (20 cm), time to complete five chair stands, and standing balance. The measure ranges from 0 to 4; a higher score indicates better function.

SES

The SES variables included education, income, access to care, and indicators of quality of health care. Education was considered in two groups: <12 years of school and =12 years of school. Researchers had also considered other SES indicators, including family income. Income included wages, salaries or retirement benefits, help from relatives, rent from property, and any other source of income in the year before the interview.

Access and quality of care

Access to care and quality of care were important to explore as potential explanatory variables. In cardiovascular care, in particular, individuals of black race have been associated with worse quality of care. Indicators of quality of care included report of receiving a flu shot in the past 12 months and whether two of the following cardiovascular risk factors were below recommended levels: systolic blood pressure (<140 mmHg), diastolic (<90 mmHg), or LDL cholesterol level <130 mg/dl.

Social, psychological, and behavioral indicators

Social health was assessed by social support (i.e., the number of relatives or friends who participants felt close to or could call on for help). Psychological health was assessed by a 20-item CES-D scale, which is used to assess depressive symptoms by self-rated health status.

Statistical methods

Baseline descriptive characteristics of the diabetic study population were compared by sex and race using the 2 test for dichotomous variables and generalized linear models for continuous variables. Researchers then assessed each of these characteristics in relation to glycemic control using HbA1c as a continuous variable in a linear regression model and retained those variables related to both race and glycemic control (P = 0.10) after controlling for age, sex, BMI, duration of diabetes, and study site. They had then created a multivariate analysis to test whether the effect of race on glycemic control could be explained by these variables. HDL cholesterol levels were higher and triglyceride level were lower in diabetic blacks, whereas diastolic blood pressure was higher in black men. BMI was higher in blacks, particularly women. Blacks with diabetes scored more poorly on tests of cognitive function and physical function and reported worse health status.

Correlates of glycemic control

Black race was consistently associated with worse glycemic control, regardless of type of treatment. Among persons using insulin therapy, blacks had worse control than whites (mean HbA1c 8.6 and 7.8%, respectively, in models adjusted for age, sex, BMI, duration of diabetes, and study site; P < 0.05). Even among participants using no drug therapy, there was still a significant difference in levels of HbA1c between race (adjusted mean HbA1c level 8.1% for blacks and 6.6% for whites; P < 0.01). In multivariate models, in addition to race (P < 0.001), male sex (P < 0.01), prevalent cardiovascular disease (P < 0.001), higher total cholesterol (P < 0.01), use of insulin therapy (P < 0.05), as a measure of quality of care, not receiving a flu shot, also was associated with higher HbA1c levels (P < 0.05). Controlling of all the following factors decreased the association between glycemic control and race by 27% (ß-parameter 0.66, P < 0.0001).

SES, race, and glycemic control

To examine whether differences by race existed across the range of SES levels, researchers had to first examine the association of confounding variables with education level and with income level. Participants with <12 years of education were more frequently using insulin therapy and had poorer self-perceived health status. They also had a lower income, poorer quality of care (as indicated by not having a flu shot; P < 0.01), and were less likely to have supplemental insurance or a usual place of care. However, there was no significant interaction between the race and education level or between race and income level, and race was associated with poorer glycemic control in both higher and lower education groups and in both higher and lower income groups.

Although blacks continued to have higher HbA1c levels, this difference was no longer significant.

Shorr et al. had examined data from the National Health and Nutrition Examination Study III and found that many older adults with type 2 diabetes did not achieve targets for glycemic control, but there was no evidence that these community-dwelling diabetic elderly individuals were less well controlled and treated less vigorously than younger diabetic individuals. However, blacks of all ages were approximately twofold more likely to have poorer glycemic control than whites with few differences. There were relatively few blacks >70 years of age in that study, which limited the possibility of exploring explanatory relationships in old age specifically.

Researchers further had examined several factors that might explain the relationship observed between race and glycemic control. One such factor is the severity of diabetes. Duration of diabetes was similar in whites and blacks and was not associated with poorer control, as found in the other studies. Insulin therapy was still associated with poorer control in multivariate models, but controlling for current medication type did not explain the racial difference. A second factor was quality of care received by the diabetic population. Researchers included three direct and indirect indicators of adequate medical care: control of cholesterol, control of blood pressure, and reporting of a flu shot in the past year. A third factor may be level of self-care the researchers did not have a direct measures of self-care for diabetes, but they had to make use of two surrogate measures of self-care: participation in a physical activity or current smoking. These indirect measures of self-care also did not influence glycemic control. There was no data on patient education or self-monitoring of blood glucose on glycemic control; there is evidence that this may influence the level of glycemic control. Given priorities to study health disparities, racial differences in glycemic control should be further studied to identify the factors suitable for intervention. Efforts in this direction are likely to benefit all older individuals of varied races with diabetes.

Authors: Nathalie de Rekeneire, MD, Ronica N. Rooks, PHD, Eleanor M. Simonsick, PHD, Ronald I. Shorr, MD, MS, Lewis H. Kuller, MD, DRPH, Ann V. Schwartz, PHD and Tamara B. Harris, MD, MS