Diabetes --- United States, 2004 and 2008

Gloria L. Beckles, MD1

Julia Zhu, MS2

Ramal Moonesinghe, PhD3

1National Center for Chronic Disease Prevention and Health Promotion, CDC

2Epidemiology and Analysis Program Office, CDC

3Office of Minority Health and Health Disparities, CDC

Corresponding author: Gloria L. Beckles, MD, Division of Diabetes Translation, 1600 Clifton Road, NE, MS K-10, Atlanta, GA 30333. Telephone: 770-488-1272; Fax: 770-488-8364; E-mail: glb4@cdc.gov.

Diabetes is a serious, costly, and potentially preventable public health problem in the United States (1--3). Both the prevalence and incidence of diabetes have increased rapidly since the mid-1990s, with minority racial/ethnic groups and socioeconomically disadvantaged groups experiencing the steepest increases and most substantial effects from the disease (1,4--6).

To assess disparities in the prevalence and incidence of medically diagnosed diabetes, CDC used data from the 2004 and 2008 National Health Interview Survey (NHIS), an ongoing, cross-sectional, in-person household interview survey of the civilian, noninstitutionalized U.S. population. A randomly selected adult (aged ≥18 years) in each family was asked whether they had ever been told by a health-care professional that they had diabetes; those who reported having diagnosed diabetes were asked the age at which they received the diagnosis. Respondents who were the same age when interviewed as when they received a diabetes diagnosis were considered to have a case of incident diabetes (Age at interview -- Age at diagnosis = 0 years). In addition, half of the cases among respondents who were aged 1 year older when they were interviewed than when they received the diagnosis were counted as incident cases (Age at interview -- Age at diagnosis = 1 year). Both the values for age at interview and age at diagnosis were rounded to the nearest year; therefore, among respondents with a difference of 1 year (Age at interview -- Age at diagnosis = 1 year), the actual duration with diagnosed diabetes was in the interval (0, 2). Durations were assumed to be spread uniformly over the interval (0, 2), and half were assumed to be within 1 year of diagnosis. Prevalence (cases of diabetes of any duration per 100 population) was calculated for adults aged ≥18 years. Incidence (cases of diabetes ≤1 year's duration per 1,000 population) was calculated for adults aged 18--79 years.

Analyses were performed to assess disparities between groups, defined by age, sex, race/ethnicity, socioeconomic position (measured as educational attainment and poverty to income ratio [PIR]) (7), disability status, and U.S. Census region. Persons with a disability were adults with either a functional limitation from any condition or a health problem that required use of special equipment (8). In each disparity domain (i.e., classifying variable), the group with the lowest stable estimate (i.e., relative standard error <30%) of diabetes prevalence or incidence was chosen as the referent category; for racial/ethnic disparities, white men and white women, the largest groups, were selected as the referent category (9,10). Absolute difference was calculated by subtracting the value in the referent category from each category of the classifying variable. Relative difference (percentage difference) was calculated by dividing the absolute difference by the value in the referent category. For example, with women as the referent category, the relative difference in prevalence between men and women is the absolute difference divided by the value for women with the fraction expressed as a percentage. To assess whether disparities changed with time, the difference between group relative differences that were significant in the 2008 and 2004 data were calculated (9,10). Statistically significant increases and decreases in relative difference from 2004 to 2008 were interpreted as increases and decreases in disparity over time, respectively. In all analyses, data were weighted to provide estimates representative of the U.S. population. Estimates were age adjusted to the U.S. 2000 Census population (11). The z statistic and a two-tailed test with Bonferroni correction were used to test for statistical significance of absolute differences and the change in relative difference between 2004 and 2008. Differences were considered statistically significant at p<0.05.

Substantial racial/ethnic disparities were identified between the 2008 age-standardized prevalence of medically diagnosed diabetes for each nonwhite group and for whites (Table 1). Overall and for either sex, absolute differences were statistically significant (p<0.05) for blacks and Hispanics but not for Asians. Substantial socioeconomic disparities also were identified in the age-standardized prevalence of diagnosed diabetes. Statistically significant absolute differences increased with decreasing levels of education attained and levels of PIR; the greatest disparities were experienced by the groups who had the lowest level of education, were living below the federal poverty level, or both. Statistically significant differences in prevalence of diagnosed diabetes were also found, according to disability status, age, and U.S. Census region (i.e., the South in 2008). The absolute age-specific differences increased with age, reflecting the expected age-related increase in diabetes risk (1,12). The significant absolute difference in age-standardized prevalence of diagnosed diabetes between the groups with and without disability might reflect the association between diabetes and disability (13). The geographic disparity observed for the South is consistent with recent reports of geospatial variation in the prevalence of diagnosed diabetes (14). All relative disparities in prevalence demonstrated similar patterns.

Changes across time occurred in the racial/ethnic, age, and education disparities in the age-standardized prevalence of diagnosed diabetes observed for 2008 and 2004 (Table 1). Relative differences in the aged-standardized prevalence of diagnosed diabetes among Hispanic and black women were significantly lower during 2008 than 2004. No significant change occurred among men or among both sexes combined. The relative difference between the age-specific prevalence of diagnosed diabetes for the referent category (18--44 years) and each of the age groups (45--64, 65--74, and ≥75 years) was significantly lower during 2008 than 2004. However, the relative differences between the age-standardized prevalence of diagnosed diabetes among persons who had a high school education or less and the referent category (more than high school) were significantly higher during 2008 than 2004.

For 2008, statistically significant socioeconomic, age, and disability disparities were identified in the age-standardized incidence of diagnosed diabetes (Table 2). Absolute differences between the incidence rates of diagnosed diabetes in the groups with a high school education or less and the rate in the referent category (more than high school) were significant. Absolute differences between the incidence rates of diagnosed diabetes among the poor, near-poor, and middle income PIR categories and the incidence rate in the referent category (high income, PIR ≥4.0) were also significantly different. In addition, the absolute disparities in the age-standardized incidence rate of diagnosed diabetes increased progressively with decreasing levels of education and PIR; these disparities increased to >100% for the groups who did not complete high school or who lived below the federal poverty level (PIR < 1.0). The absolute disparities between the age-standardized incidence rates of diagnosed diabetes for adults aged 45--64 and 65--79 years and the rate among those aged 18--44 years were significant and increased with age, reflecting the age-related increased risk for diabetes (1,6). Finally, the incidence rate of diagnosed diabetes among the group with disabilities was significantly different from the rate in the group without disabilities. The relative disparities in incidence rates demonstrated similar patterning.

Socioeconomic, age, and disability disparities in the incidence rate of diagnosed diabetes increased from 2004 to 2008 (Table 2). The relative disparities in the age-standardized incidence rates of diagnosed diabetes among the groups who had a high school education or less increased more than twofold and threefold, respectively, from 2004 to 2008 (p<0.05 for both groups). The change was less consistent for the groups by income. The relative disparities for the lowest income group (PIR < 1.0) were not significantly different; however, relative disparities among the near-poor and middle income groups were more than threefold higher during 2008 than 2004 (p<0.05 for both groups). In 2008, the relative disparity for the group with disabilities was approximately twice the relative disparity during 2004 (p<0.05).

The findings in this report are subject to at least two limitations. First, all data are self-reported and therefore subject to recall and social desirability bias. However, self-reported diabetes data have been reported to have high reliability (15,16). Second, differences were not assessed for total prevalence of diabetes (i.e., diagnosed and undiagnosed); therefore, the findings might underestimate the extent of the disparities in prevalence and incidence among the U.S. population. The percentage of persons with undiagnosed diabetes is estimated to range from 24% to 40% of the total prevalence of diabetes (11,17). However, the racial/ethnic, socioeconomic, geographic, disability, and change over time of the disparities in prevalence and incidence of medically diagnosed diabetes are consistent with reports on diabetes risk among U.S. adults (1,4--6,12,13).

Marked sociodemographic disparities in prevalence and incidence of diagnosed diabetes exist among U.S. adults. Moreover, no evidence indicates that racial/ethnic disparities in prevalence and incidence of diagnosed diabetes decreased from 2004 to 2008, although socioeconomic disparities worsened during the same interval. Health promotion and risk-reduction efforts have been focused primarily on racial/ethnic minority groups identified as groups at high risk for diabetes. The findings in this report demonstrate that, despite these efforts, decreases in racial/ethnic disparities have been substantially limited. Increased awareness about the risk for diabetes among adults with low levels of income and educational attainment and those with disabilities might help decrease disparities. Interventions designed specifically for these groups might increase the effectiveness of efforts to reduce disparities in diabetes risk.

References

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