Epidemiology and Classification of Diabetes Mellitus

Diabetes can be classified into these four general categories: 1) Type 1 diabetes, which is due to β-cell destruction and usually leads to a complete lack of insulin, 2) Type 2 diabetes (the most common form of diabetes mellitus), which is due to a progressive defect in insulin secretion as well as cellular insulin resistance, 3) Gestational diabetes, which is typically diagnosed during the 2nd or 3rd trimester of pregnancy and resolves after birth, and 4) diabetes due to other systemic diseases and conditions (e.g., monogenic diabetes syndromes, diseases of the endocrine pancreas, and drug or chemical induced diabetes).3 Additionally, some individuals have glucose levels that do not meet the criteria for diabetes, but are elevated compared to normal levels. The conditions may be labeled “prediabetes,” which includes both impaired fasting glucose (IFG) and impaired glucose tolerance (ITG).3 These individuals may have elevated blood glucose only in specific circumstances. IFG, ITG, and gestational diabetes are strong predictors for future development of Type 2 diabetes mellitus, and IGT is a significant predictor for myocardial infarction and stroke.12,13

Diagnosis of diabetes mellitus in adults can be based on 2 different lab tests. Plasma glucose, which may be tested either fasting or 2 hours after a 75g oral glucose tolerance test (Table 1), shows current glycemic control.14,15 The use of glycated hemoglobin, or HbA1c, in clinical treatment of patients with diabetes allows the practitioner to estimate the average glucose level over the 30-90 day period preceding the test. It does not account for short-term fluctuations in plasma glucose, but may allow for an overall assessment of glycemic control (Table 2).16 An additional advantage of HbA1c testing includes convenience, with no fasting required. The utility of HbA1c levels for diagnosis may be limited to adult populations; it is unclear whether similar benchmarks should be applied to children and adolescent popualtions for diagnosis purposes. Treatment goals for patients with diabetes range from 6.5-7% for HbA1c levels, and the ADA recommends physician intervention in diabetes management to improve glycemic control when HbA1c reaches 8%.3 The American Diabetes Association (ADA) recommends testing overweight or obese adults who have one or more risk factors for diabetes and all overweight and obese patients 45 years of age and older yearly to identify diabetes and prediabetes diagnoses.3

Table 1. Diagnostic Criteria for Diabetes Mellitus, IGT, and IFG.3
Fasting plasma glucose (mg/dl)<100≥126 100-125
Casual plasma glucose (mg/dl) ≥ 200 plus symptoms of diabetes  
2-hour postload glucose (OGTT)<140≥ 200140-199 
Table 2. Correlation between HbA1c Levels and Mean Plasma Glucose Levels.16
HbA1c (%)Mean Plasma Glucose (mg/dl)

Diabetes is a large and growing health problem in the United States. In 2012, 29.1 million people or 9.3% of the U.S. population, was estimated to have diabetes.4 Of these individuals, approximately 21 million have been diagnosed and 8.1 million, or 27.8% of patients with diabetes, remain undiagnosed.4 Put another way, more than 1 out of 4 Americans who has Diabetes Mellitus are undiagnosed. Additionally, nearly 37% of U.S. adults aged 20 years and older and 51% of those aged 65 years and older had prediabetes.4 Diabetes is currently the seventh leading cause of death in the U.S. In addition to the direct effects of diabetes, it is also a risk factor for many other diseases which can also lead to death Complications associated with diabetes include: hypertension, hypercholesterolemia, cardiovascular disease and stroke, ophthalmic complications, kidney disease, macrovascular disease leading to amputations, neuropathy, non-alcoholic fatty liver disease, periodontal disease, hearing loss, erectile dysfunction, complications during pregnancy and others.4 Obesity and diabetes prevalence trends have followed a similar pattern over the past 20 years, and it is likely that both diseases will continue to become more prevalent over time (Figure 1). Given the high prevalence of diabetes and the overlap of risk indicators between diabetes and periodontal disease, it is critical dental care providers are aware of the interactions and able to adequately counsel patients and customize treatment protocols.

Figure 1. Diabetes and obesity rates in the United States from 1994 to 2014.93
Maps showing Obesity and Diabetes rates in the US