Body mass index (BMI) is a standardized measure that renders body mass in relation to height. It allows for the classification of an individual as underweight, normal, overweight, or one of the varying degrees of obese. In the general population, the risk of Type 2 diabetes mellitus (T2DM) increases with increasing BMI. According to "Greenspan's Basic and Clinical Endocrinology," in individuals 55 years or younger, a BMI above 40 increases the risk of developing T2DM to as much as 18 times that of a normal weight individual. A BMI in the range of 25 to 30 increases the prevalence of T2DM three to fourfold in those 55-years-old or younger.
BMI Features
The BMI is calculated by dividing the weight in kilograms by the square of the height in meters (the units are kg/m2). BMI classifications are as follows:
A BMI less than 18.5 is classified as underweight, 18.5 to 25 is considered normal, greater than 25 and up to 30 is classified as overweight, greater than 30 and up to 35 is obese, greater than 35 and up to 40 is classified as very obese, and greater than 40 is extremely obese.
The BMI does not differentiate between increases in muscle mass and increases in fat mass. Thus, individuals with a muscular build may not be properly classified.
Pathophysiology of T2DM
T2DM is a disease characterized by insulin resistance and resultant hyperglycemia. There are two defects that are responsible for the metabolic perturbations that characterize T2DM: 1) insulin resistance in tissues, specifically muscle and fat tissues 2) inadequate secretion of insulin from the pancreas. In a normal state, insulin allows body tissues to uptake glucose for energy metabolism. In a state of insulin resistance, the tissues are unable to utilize glucose causing it to accumulate to the point of excess (hyperglycemia).
Insulin resistance is a key factor in the link between obesity and T2DM. Fat tissue is a primary mediator of insulin resistance. Though the mechanism by which fat tissue contributes to insulin resistance has not been completely established, it is understood that central fat (in the abdominal region) is the most important contributor to insulin resistance. According to the World Health Organization, 90 percent of T2DM patients are obese. However, consideration must also be given to the fact that although most obese individuals are insulin resistant, many do not develop T2DM. This gives strength to the idea that there is also a genetic predisposition for developing T2DM.
Additional Risk Factors
Though increased BMI is an important risk factor for developing T2DM, there are other risk factors that should be considered such as pre-diabetes, which is defined as having an impaired fasting glucose (IFG) or an impaired glucose tolerance (IGT); prior gestational diabetes or giving birth to infant greater than 9 lbs.; hypertension, which is defined as a blood pressure 140/90 mmHg or higher; dyslipidemia, which is defined as an HDL cholesterol less than 35 mg/dL and/or triglycerides greater than 250 mg/dL; lack of regular physical activity; high-fat, high-calorie, simple carbohydrate diet; central (abdominal) obesity; low birth weight and low socioeconomic status.
Weight Reduction and T2DM
According to "Greenspan's Basic and Clinical Endocrinology," therapy for T2DM is directed toward adequate weight reduction as this can often reverse the disease by increasing insulin sensitivity. Thus, the American Diabetic Association recommendations are made for healthy diet choices and increased physical activity.
Symptoms
According to the American Diabetes Association, the classic symptoms of T2DM are increased urination, thirst, recurrent blurred vision, numbness and tingling in extremities and fatigue. However, the symptoms may often develop slowly and silently, particularly in obese patients. Thus, diabetes may be detected only after glucose is detected in the urine or abnormally high glucose is detected in the blood during routine laboratory studies. Repeated skin infections are also common. Vaginal or urinary tract infections are frequently the first presentation of women with Type 2 diabetes.
References
- "Greenspan's Basic and Clinical Endocrinology;"; David G. Gardner MD,MS, Dolores Shoback MD; 2007
- "DeGowin's Diagnostic Examination, 9e, Chapter 4;" Richard F. LeBlond MD, Donald D. Brown MD, Richard L. DeGowin MD; 2009
- World Health Organization: Global strategy on diet, physical activity and health
- "Tintalli's Emergency Medicine;" Micheal D. Rush MD, Sonia Winslett MD, Kimberly D. Wisdom MD; 2004
- American Diabetes Association: Symptoms
Member Comments