Prevalence and Incidence of Type 2 Diabetes and Prediabetes

Diabetes is a common condition in the United States and worldwide, associated with multiple complications and early mortality that result in costly use of health resources and lost productivity. This chapter reviews the prevalence and incidence of type 2 diabetes in terms of diagnosed and undiagnosed diabetes, as well as prediabetes. Variations in estimates are illustrated by age, sex, race/ethnicity, and over time. Data come primarily from analyses of two national health surveys: the National Health Interview Surveys (NHIS) 2011–2015, which include only an interview; and the National Health and Nutrition Examination Surveys (NHANES) 2011–2014, which include an interview and blood draw to detect undiagnosed diabetes by glycosylated hemoglobin (A1c), fasting plasma glucose (FPG), and/or 2-hour plasma glucose (2-hour PG) from an oral glucose tolerance test. While these data do not distinguish type 1 from type 2 diabetes, an estimated 90%–95% are from persons with type 2 diabetes. Data from the literature are used to describe type 2 diabetes in adolescents, Hispanic and Asian subgroups, and American Indians. Crude overall prevalence of diagnosed diabetes based on the NHIS 2011–2015 was 9.5% in adults age ≥20 years, translating to 21.8 million in the U.S. civilian noninstitutionalized population. Prevalence increased with age, ranging from 0.5% in youth age 12–19 years to about 20% in those age ≥65 years. Age-standardized prevalence was somewhat higher in adult men than women. Age- and sex-standardized prevalence was highest in non-Hispanic American Indian/Alaska Native adults (19.1%) and lowest in non-Hispanic whites (8.2%), with prevalences between these in non-Hispanic blacks, all Hispanics, and non-Hispanic Asians. Variability in prevalence was found across Hispanic and Asian subgroups. Prevalence of validated type 2 diabetes in adolescents age 10–19 years based on the SEARCH for Diabetes in Youth Study was 0.46 per 1,000 in 2009, which varied by age, sex, and race/ethnicity. Crude overall prevalence of undiagnosed diabetes in adults ≥20 years based on the NHANES 2011–2014 was 2.9% as detected by A1c/FPG; and when combined with diagnosed diabetes (9.6%), total diabetes prevalence was 12.5% or 28.2 million in the U.S. civilian noninstitutionalized population. Undiagnosed diabetes of 5.0% by A1c/FPG/2-hour PG resulted in total diabetes of 14.6% or 33.0 million. Prevalence of undiagnosed and total diabetes rose with age. The percent of total diabetes that was undiagnosed was highest (33.4%–41.5%) at age 20–44 years. Standardized prevalence of undiagnosed diabetes and total diabetes tended to be higher in men than women, as was the percent of total diabetes that was undiagnosed. Standardized prevalence of undiagnosed diabetes, total diabetes, and the percent of total diabetes that was undiagnosed were highest in non-Hispanic Asians and lowest in non-Hispanic whites, with prevalences for non-Hispanic blacks, all Hispanics, and Mexican Americans in between. Crude overall incidence of diagnosed diabetes based on the NHIS 2012 was 7.4 per 1,000 adults age 20–79 years. Incidence increased to age 65–74 years and then declined. It was higher in women than men, highest in Hispanics, followed by non-Hispanic blacks, and lowest in non-Hispanic whites. Over time, crude prevalence of diagnosed diabetes among all ages based on the NHIS has risen from 0.93% in 1958 to 7.40% in 2015. In adults age 20–74 years during 1980–2012, both age-adjusted prevalence and incidence rose particularly fast during 1990–2008, but may be leveling off or decreasing since 2008. Other data sources have corroborated this finding. An analysis of the NHANES during 1988–2012 found standardized prevalence of total diabetes increased across all subgroups of the U.S. population, due to an increase in diagnosed diabetes, while undiagnosed diabetes remained relatively constant. Both prevalence and incidence of type 2 diabetes in adolescents based on SEARCH have continued to increase significantly since the early 2000s across all age, sex, and race/ethnicity groups. Crude overall prevalence of prediabetes in adults age ≥20 years based on the NHANES 2011–2014 was 34.4% (77.9 million) by A1c/FPG and 36.9% (83.6 million) by A1c/FPG/2-hour PG. Prevalence of prediabetes rose with age. Standardized prevalence was significantly higher in men than women; and prevalences were higher in non-Hispanic blacks, all Hispanics, and Mexican Americans compared to non-Hispanic whites and non-Hispanic Asians. Prediabetes prevalence was fairly constant during 1999–2006, but significantly increased during 2007–2010. Diabetes remains a very prevalent condition, especially in American Indians, non-Hispanic blacks, and Hispanic groups. The long-term trend showing a persistent rise in occurrence, though a slowing in more recent years, needs continued surveillance. The fact that one-quarter to one-third of diabetes is undiagnosed and that another third of the total population has prediabetes emphasizes the importance of sustained monitoring and improvements in health care delivery.