Trends in the prevalence and ratio of diagnosed to undiagnosed diabetes according to obesity levels in the U.S.

OBJECTIVE To examine trends in the prevalence of diagnosed and undiagnosed diabetes and the proportion of total cases previously diagnosed, according to obesity status in the U.S. over the past 40 years. RESEARCH DESIGN AND METHODS We assembled data from five consecutive cross-sectional national surveys: National Health Examination Survey I (1960-1962), National Health and Nutrition Examination Survey (NHANES) I (1971-1974), NHANES II (1976-1980), NHANES III (1988-1994), and NHANES 1999-2000. Diagnosed diabetes was ascertained, and height and weight were measured in adults aged 20-74 years in all surveys. In NHANES II, NHANES III, and NHANES 1999-2000, a fasting glucose level > or =126 mg/dl was used to identify cases among individuals not reporting diabetes. Design-based analyses and Bayesian models estimate the probability that prevalence of diabetes increased within four BMI groups (<25, 25-29, 30-34, and > or =35 kg/m2). RESULTS In the U.S. population aged 20-74 years between 1976-1980 and 1999-2000, significant increases in the prevalence of diagnosed diabetes (3.3-5.8%, probability >99.9%) were accompanied by nonsignificant increases in undiagnosed diabetes (2.0-2.4%, 66.6%). This resulted in an increase in total diabetes (5.3-8.2%, >99.9%) and a modest nonsignificant increase in the proportion of cases that were diagnosed (62-70%, 62.4%). However, these trends varied considerably by BMI level. In individuals with BMI > or =35 kg/m2, diagnosed diabetes increased markedly (from 4.9% in 1960, to 8.6% during 1976-1980, to 15.1% in 1999-2000; probability >99.9%), whereas undiagnosed diabetes declined considerably (12.5% during 1976-1980 to 3.2% in 1999-2000, probability of increase 4.5%) Therefore, the proportion of total diabetes cases that were diagnosed increased from 41 to 83% (probability 99.9%) among individuals with BMI > or =35 kg/m2. By comparison, changes in prevalence within BMI strata <35 kg/m2 were modest and there was no increase in the percent of total cases that were diagnosed. CONCLUSIONS National surveys over the last several decades have found large increases in diagnosed diabetes, particularly in overweight and obese individuals, but this has been accompanied by large decreases in undiagnosed diabetes only among individuals with BMI > or =35 kg/m2. This suggests that improvements in diabetes awareness and detection are most prominent among this subgroup.