Diabetes — United States, 2006 and 2010

Gloria L. Beckles, MD

Chiu-Fang Chou, DrPH

Division of Diabetes Translation, National Center for Chronic Disease Prevention and Health Promotion

Corresponding author: Gloria L. Beckles, Division of Diabetes Translation, National Center for Chronic Disease Prevention and Health Promotion, CDC. Telephone: 770-488-1272; E-mail: glb4@cdc.gov.

Introduction

In 2011, an estimated 26 million persons aged ≥20 years (11.3% of the U.S. population) had diabetes (1). 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 (2–5).

This analysis and discussion of diabetes is part of the second CDC Health Disparities and Inequalities Report (CHDIR). The 2011 CHDIR (6) was the first CDC report to assess disparities across a wide range of diseases, behavioral risk factors, environmental exposures, social determinants, and health-care access. The 2011 CHDIR report discussed the magnitude and patterning of absolute and relative measures of disparity in the prevalence and incidence rate of medically diagnosed diabetes during 2004 and 2008 and identified marked disparities in terms of race/ethnicity, socioeconomic status, disability status, and geography (7). The topic presented in this report is based on criteria that are described in the 2013 CHDIR Introduction (8). This report updates information on disparities in prevalence and incidence rates of diagnosed diabetes presented in the 2011 CHDIR. The purposes of this report are to discuss and raise awareness about group differences in the level of diagnosed diabetes and to prompt actions to reduce these disparities.

Methods

To monitor progress toward eliminating health disparities in the prevalence and incidence rate of medically diagnosed diabetes, CDC used data from the 2006 and 2010 National Health Interview Survey (NHIS). NHIS is an ongoing, cross-sectional, in-person household interview survey of a probability sample of the civilian, noninstitutionalized U.S. population. Household interviews were completed for 75,716 persons in 2006 and 89,976 persons in 2010, with response rates of 87.3% and 79.5%, respectively (9,10).

The methods used to assess prevalence and incidence rates of medically diagnosed diabetes have been described previously (7). Analyses were repeated to assess disparities in each year and changes in disparity over time (11), according to the selected characteristics of age, sex, race/ethnicity, socioeconomic status,* geographic region as defined by the U.S. Census Bureau,† and disability status. Because of the association between place of birth and diabetes, the data also were examined by place of birth, defined as U.S.-born or not U.S.-born§ (12,13).

Prevalence (cases of diabetes of any duration per 100 population) was calculated for adults aged ≥18 years. Incidence rate (cases of diabetes ≤1 year's duration per 1,000 population) was calculated for adults aged 18–79 years. Estimates were standardized by the direct method to the age distribution of the U.S. 2000 Census adult population (14). Age-specific estimates were not age-standardized. CDC used software to account for the complex sample design of NHIS and to produce point estimates, standard errors, and 95% confidence intervals (CIs).

Disparities were measured as the deviations from a referent category incidence rate or prevalence. Absolute difference was measured as the simple difference between a population subgroup estimate and the estimate for its respective reference group. The relative difference, a percentage, was calculated by dividing the difference by the value in the referent category and multiplying by 100. To assess change in disparities over time, CDC calculated change in relative difference by subtracting the relative difference in the ending time period from the relative difference for the beginning period. To test for the statistical significance of the observed absolute and relative differences, CDC used the z statistic and a 2-tailed test at p<0.05 with Bonferroni correction for multiple comparisons; 95% CIs were calculated. Statistically significant increases and decreases in relative differences from 2009 to 2011 were interpreted as increases and decreases in disparity, respectively. Estimates with relative standard error ≥30% were not reported.

Results

Racial/ethnic and socioeconomic disparities were identified in the age-standardized prevalence and incidence rate of medically diagnosed diabetes in 2006 and 2010 (Tables 1 and 2). In both years, overall, and for both males and females, significant absolute differences for race and ethnicity were present between non-Hispanic whites and non-Hispanic blacks or Hispanics (p<0.05 for all comparisons). The only significant temporal decline in disparity was found for age-standardized prevalence of diagnosed diabetes among non-Hispanic black females (change: -23.3 percentage points; p<0.05). Temporal increases in disparities from 2006 to 2010 were identified for prevalence of diagnosed diabetes among Hispanics, with increases greater among Hispanic females (change: 34.6 percentage points; p<0.05) than among Hispanic males (change: 11.6 percentage points; p<0.05). Temporal increases in disparities in incidence rates were greater among Hispanics (change: 79.0 percentage points; p<0.05) than among non-Hispanic blacks (change: 12.6 percentage points; p<0.05).

In 2006 and 2010, the groups with the lowest levels of education and income continued to experience the greatest socioeconomic disparity in age-standardized prevalence and incidence rate of diagnosed diabetes (Tables 1 and 2). Among these disadvantaged groups, no significant change in the relative difference in prevalence occurred from 2006 to 2010, but the disparity in the incidence rate worsened over time. In addition, a significant decline in disparity in the prevalence and incidence of diagnosed diabetes occurred among persons with a high school education (p<0.05 for both comparisons). From 2006 to 2010, age disparities in the age-standardized prevalence and age-standardized incidence rate of diagnosed diabetes worsened, and no significant change occurred in the geographic and disability disparities in age-standardized prevalence. However, for the age-standardized incidence rate, disparities between the Northeast and each of the other U.S. Census Bureau regions worsened significantly while disability disparities improved (Table 2). No significant disparities between U.S.-born and not U.S.-born persons were identified in the total population or in any racial/ethnic population.

Discussion

From 2006 to 2010, a decline occurred in the disparity between the prevalence of diagnosed diabetes among non-Hispanic black women and that among white women; among men, no evidence of a decline in racial/ethnic disparities in diagnosed diabetes was identified. In addition, during the survey years, socioeconomic disparities in the incidence of diagnosed diabetes worsened among the groups with the lowest level of education and income.

Although racial/ethnic and socioeconomic disparities in the prevalence and incidence rate of diagnosed diabetes persist in the U.S. adult population, some improvements occurred from 2006 to 2010. Significant improvements were noted for prevalence of diagnosed diabetes among non-Hispanic black women compared with non-Hispanic white women, among those with a high school diploma or some college compared with those with a college degree or higher, and among the poor (IPR <1.0 federal poverty level [FPL]) and middle income (IPR 2.0–2.9 FPL) groups compared with persons whose incomes were high (IPR ≥4.0 FPL). A significant improvement also occurred in the disparity in the diabetes incidence rate by disability status.

Although improvements are noted for disparities in prevalence of diagnosed diabetes, the annual incidence of diagnosed diabetes among the U.S. population is increasing (2,4), and mortality is declining among age, racial/ethnic, socioeconomic, and disabled subgroups in the adult diabetic population (15,16). If these circumstances continue, then the prevalence of diabetes among the U.S. population is projected to increase to as high as 33% by 2050 (15), posing major challenges for U.S. public health. Diabetes is the principal cause of kidney failure, nontraumatic lower extremity amputation, and new cases of blindness, and it is a major cause of cardiovascular disease among U.S. adults (1). The economic costs of diagnosed diabetes reflect the substantial burden imposed on the U.S. society (18). Between 2007 and 2012, the total estimated annual cost increased by 41% (in 2007 dollars) to $245 billion, including $69 billion in reduced productivity (18). Medical expenditure among persons with diabetes is two to three times that of persons without diabetes, and the largest component (43%) of total medical expenditures attributed to diagnosed diabetes is hospital inpatient care.

Limitations

The findings presented 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 (18,19). 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 (1,20). However, the racial/ethnic, socioeconomic, geographic, disability, and change over time of the disparities in prevalence and incidence of medically diagnosed diabetes provided in this report are consistent with data provided in previously published reports on diabetes risk among U.S. adults (2–5,12,20,21).

Conclusion

Obesity and lack of physical activity are major risk factors for diabetes (22,23). The Community Preventive Task Force has recommended several effective evidence-based interventions that communities, policy makers, and public health authorities can use to delay or prevent onset of diabetes by reducing obesity and increasing physical activity. Strategies to increase physical activity and physical fitness include communitywide campaigns, school-based physical education, and creation of or enhanced access to places for physical activity (22). Interventions to prevent or control obesity include behavior interventions to reduce screen time, multicomponent counseling intended to reduce weight and maintain weight loss, and worksite programs intended to reduce weight among employees by improving diet and physical activity (23). The CDC-led National Diabetes Prevention Program (24) is designed to bring to communities strategies for adopting evidence-based lifestyle changes known to prevent or delay the onset of type 2 diabetes among adults at high risk for diabetes, including modest weight loss, increased physical activity, and reduced fat and calorie intake. Widespread implementation of these and similar interventions to prevent obesity and promote physical activity might reduce future incidence and prevalence of diabetes and reduce disparities in diabetes risk.

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