Prediabetes describes blood glucose levels that are above normal but lower than those required for a diagnosis of overt diabetes. In the prediabetes that leads to type 2 diabetes, the body becomes resistant to insulin’s actions and with time the pancreatic islets do not produce enough insulin to compensate, leading to elevated blood glucose levels.4 The primary risk associated with prediabetes is the possible progression to type 2 diabetes. The concept of prediabetes emphasizes that type 2 diabetes is potentially preventable at this stage.23 Without intervention, however, prediabetes usually progresses to overt type 2 diabetes within 10 years of diagnosis. In a 1994-2003 study of HMO members with at least two elevated fasting plasma glucose tests (100-125 mg/dL) but no prior history of diabetes, a higher impaired fasting glucose indicated a higher risk of developing type 2 diabetes. In the study, 8.1% of subjects with fasting glucose of 100–109 mg/DL and 24.3% of those in the higher range (110–125 mg/dL) developed diabetes. A steeper rate of increasing fasting glucose; higher BMI, blood pressure, and triglycerides; and lower HDL cholesterol predicted diabetes development. 24
Numerous sources have published prevalence data for prediabetes, with estimates ranging from a low of 5.8% to a high of 35% among adults 20 years and older (Table 12). Reported prevalence varies depending on the criteria used to define prediabetes.
|NHANES 1988-1994 and 1999-2010||US adults, age 20 + years||Calibrated A1C, 5.7%–6.4%||5.8%–12.4%||Selvin et al. 20144|
|Fasting glucose, 5.6-6.9 mmol/L||25.2%-28.7%|
|IDF Diabetes Atlas (2013)||Adults in North America and the Caribbean region, age 20-79 years||Impaired glucose tolerance (100–125 mg/dL)||13.2%||International Diabetes Federation. 201325|
|2009-2012 NHANES||US adults, age 20+ years||Impaired glucose tolerance (100-125 mg/dL) or A1c, 5.7%–6.4%||37%||Centers for Disease Control and Prevention. 20143|
Abbreviations: A1C, Hemoglobin A1c; IDF, International Diabetes Federation; NHANES, National Health and Nutrition Examination Survey
Prediabetes prevalence has increased over the last few decades. Comparison of NHANES data from 1988–1994 and 1999–2010 showed that the prevalence of prediabetes increased from 5.8% to 12.4% over the two time periods.4 Without intervention, it is estimated that 15% to 30% of people with prediabetes will develop type 2 diabetes within five years.26
An evaluation of 2005 to 2008 NHANES data found similar prevalence for non-Hispanic whites (35%), non-Hispanic blacks (35%) and Mexican Americans (36%).27 Using NHANES data from 2010, another study reported gender differences by ethnicity: prevalence was consistent across ethnic groups among females, but lower among non-Hispanic black males compared to non-Hispanic white or Mexican American males. These results are summarized in Table 13.
Source: Go et al. 201428
A review of 26 prospective cohort studies that include data on prediabetes and mortality found that the risk of all-cause and cardiovascular mortality was increased in people with prediabetes defined as impaired fasting glucose (IFG) of 110–125 mg/dL or with impaired glucose tolerance (IGT) or combined IFG 110 and/or IGT. 29
An examination of 832 deaths among a cohort of 17,044 participants with prediabetes found that normal-weight individuals with low cardiorespiratory fitness levels had a higher risk of all-cause mortality than those who were normal weight and fit.30
Preventing the progression of prediabetes to type 2 diabetes has been identified as a strategy to address the growing prevalence of diabetes. According to a 2006 study published by the CDC, most adult prediabetes patients who are aware of their condition try to adopt lifestyle changes to reduce their risk of progression. In a study that used data from the National Health Interview Survey (NHIS), 68% of patients with self-reported prediabetes said that during the previous year they had been trying to lose or control their weight, 60% had reduced dietary fat and/or calories, and 55% had increased physical activity. Despite the importance of risk reduction, 24% reported not engaging in any lifestyle changes.31
The landmark Diabetes Prevention Program (DPP)32 further demonstrated the efficacy of weight loss, dietary modification and exercise for preventing or delaying the onset of diabetes in individuals with prediabetes. Patients in this study who were randomized to lifestyle treatment lost an average of 15 pounds and reduced their risk of developing type 2 diabetes by 58% over 3 years. The efficacy of the common first-line oral agent metformin was also established in the DPP study, where the risk of progression to diabetes was 31% lower in subjects randomized to the drug as compared to those given placebo. Metformin is only effective for as long as it is taken.
Beyond the DPP, additional studies have identified interventions that are effective in the treatment of prediabetes, toward preventing or delaying progression to type 2 diabetes. The effectiveness of lifestyle interventions in preventing type 2 diabetes, as found in the DPP, has been corroborated by international studies such as the Finnish Diabetes Prevention Study33 and the Da Qing IGT and Diabetes Study34. Pharmacotherapies have also been tested as adjuncts to lifestyle modification for diabetes prevention. For example, the STOP-NIDDM trial showed that acarbose can delay development of type 2 diabetes when compared to placebo.35 In Hispanic females with a history of gestational diabetes and high-risk for type 2 diabetes, troglitazone (an insulin-sensitizing drug) delayed or prevented its onset.36