Diabetes Prevalence Rose Substantially in 20 Years

Larry Hand

April 15, 2014

The prevalence of diabetes in the United States has increased substantially over the course of the last 2 decades, paralleling an increase in the prevalence of obesity, according to a study published online April 14 in the Annals of Internal Medicine.

The new evidence suggests, however, that the proportion of undiagnosed diabetes cases is far less than the widely held belief of 50%.

Elizabeth Selvin, PhD, MPH, from the Welch Center for Prevention, Epidemiology and Clinical Research, Johns Hopkins Bloomberg School of Public Health, Baltimore, Maryland, and colleagues analyzed data from the National Health and Nutrition Examination Survey from 1988 to 1994 and 1999 to 2010.

For analyses of undiagnosed diabetes and prediabetes, the researchers limited their study population to 43,439 individuals who attended clinical examination, were aged 20 years or older, were not missing hemoglobin A1C (HbA1C) level measurements, and were not pregnant (15,578 for 1988 - 1994, 12,726 for 1999 - 2004, and 15,135 for 2005 - 2010).

For analyses of diagnosed diabetes, the researchers further limited the population to 19,784 participants who attended morning fasting sessions and had glucose measurements (7385 for 1988 - 1994, 5680 for 1999 - 2004, and 6719 for 2005 - 2010).

Calibration Methods

The researchers calibrated undiagnosed diabetes based on HbA1C levels of 6.5% or higher and prediabetes based on HbA1C levels between 5.7% and 6.4%. They calibrated physician-diagnosed diabetes based on HbA1C levels of lower 7.0% or lower than 8.0%. For the fasting subsample, they included fasting glucose levels of 7.0 mmol/L or higher for undiagnosed diabetes and 5.6 to 6.9 mmol/L for prediabetes.

They calibrated total confirmed diabetes cases (self-reported diabetes or diagnostic levels for both fasting glucose and calibrated HbA1c) as either diagnosed diabetes or individuals who had both fasting glucose levels of 7.0 mmol/L or higher and HbA1C levels of 6.5% or higher, which, the researchers write, approximates most clinical cases.

They found that among individuals without diabetes, mean calibrated HbA1C levels amounted to 5.25% for 1988 to 2004, 5.35% for 1999 to 2004, and 5.36% for 2005 to 2010 (P < 0.001). The trend was stable for a subgroup of young, healthy individuals, at 5.1%.

The prevalence of obesity, however, among persons without diagnosed diabetes increased from 21.2% in 1988 to 1994 to 32.4% in 2005 to 2010, and the mean body mass index increased significantly during the entire period (P < .001). Trends were similar for persons with diabetes, with the exception of obesity prevalence being "much greater in all periods," the researchers write.

When the researchers calculated the prediabetes prevalence using HbA1C levels alone, the prevalence rose from 5.8% to 11.9% to 12.4% during the 3 periods. When their calculations included fasting glucose levels, the prevalence rose from 25.2% to 26.3% to 28.7%, respectively.

Confirmed Diabetes

The authors found that the prevalence of total confirmed diabetes increased from 6.2% in 1988 to 1994 to 8.8% in 1999 to 2004 to 9.9% in 2005 to 2010. When they included fasting glucose levels in their analysis, the trend was similar, but at higher rates, going from 7.3% to 9.4% to 10.9%, respectively.

For all periods, when fasting glucose levels were included, the prevalence of undiagnosed diabetes was 60% to 180% greater than when HbA1c levels alone were considered.

"One of the novel aspects of this study is that we confirmed the undiagnosed cases based on the glucose with a second test called the hemoglobin A1C. That gives us more accurate estimates of the true burden of diabetes in the population," Dr. Selvin told Medscape Medical News. "In clinical practice, a physician would always confirm an elevation of either glucose or hemoglobin A1C with a second test."

Lesser Proportion Undiagnosed

The researchers used logistic regression to calculate trends, adjusting for demographic characteristics, body mass index, and waist circumference, and found disparities among ethnic groups. They found that total diabetes prevalence was almost twice as high in non-Hispanic blacks as whites (15.4% vs 8.6%) and was greater in Mexican-Americans than in whites (11.6% vs 8.6%).

Overall, the prevalence of diagnosed diabetes rose from 5.5% to 7.7% to 9.3% for the 3 periods, representing about 21 million US adults with confirmed diabetes, the researchers write.

They found, however, that the prevalence of undiagnosed diabetes defined by either HbA1C or fasting glucose remained fairly stable, at 0.9% to 1.3% to 1.0%, respectively, amounting to 11% of all cases in 2005 compared with 16% in 1994.

"What we found is that the prevalence of diabetes has increased dramatically over the past 2 decades, but the proportion of the total...cases that are undiagnosed has actually decreased," Dr. Selvin told Medscape Medical News. "Currently, most cases of diabetes are diagnosed, and...only 11% of cases in this country are undiagnosed."

She continued, "What that really suggests is that we're doing a good job with screening and diagnosis. That counters statements that have been out there in the literature that suggest that as many as half the cases of diabetes in the US are undiagnosed."

New Treatments, Greater Awareness Have Helped

In an accompanying editorial, Roeland J.W. Middelbeek, MD, and Martin J. Abrahamson, MD, from Joslin Diabetes Center and Harvard Medical School in Boston, Massachusetts, write that new pharmaceutical treatments for type 2 diabetes, greater awareness of diagnosis severity, and better diagnostics have likely contributed to improvements in overall glycemic control in diabetics during the last 2 decades.

"The alarming increase in obesity and diabetes rates not only shifts the focus on further improving diabetes treatment but underscores the ongoing need to prevent type 2 diabetes," they write.

"Indeed, the public and private sectors need to work closely together to tackle this immense problem," they continue. "Such collaboration may be the only way to prevent further increases in the prevalence of obesity and diabetes in the next decades and reduce the human and health care costs associated with these conditions."

Dr. Selvin sums it up this way: "Even despite the bad news and the growing need to recognize the seriousness of the epidemic of diabetes in the United States, this surely suggests we're doing better with screening and diagnosis overall. We're getting people diagnosed earlier, and our screening programs are working, and that's good news because diabetes puts people at high risk for heart attack, stroke, blindness, kidney disease, and amputation, and if we can prevent diabetes and identify diabetes cases early, then we can prevent those major complications."

This research was supported by grants from the National Institute of Diabetes and Digestive and Kidney Diseases; the National Heart, Lung and Blood Institute; and the Intramural Program of the National Institutes of Health. The authors have disclosed no other relevant financial relationships. Dr. Abrahamson has reported receiving fees for serving on advisory boards of 3 pharmaceutical companies and WebMD Health Services.

Ann Intern Med. Published online April 14, 2014. Abstract


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