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Body Mass Index (BMI)
The body mass index (BMI) or Quetelet Index is a statistical measure of the weight of a person scaled according to height. It is used as a simple means of classifying inactive individuals of an average body composition according to their body fat content. As a rough guideline for adults a BMI of less than 20 implies underweight, over 25 is overweight, and over 30 is obese. It is calculated by taking the weight of the individual in kilograms and dividing by the square of the height in metres. It was originally developed between 1830 and 1850 by the Belgian polymath, Adolphe Quetelet during the course of developing "social physics". The BMI is a controversial measurement as it is not intended to make a medical diagnosis, but instead to broadly categorise populations for purely statistical purposes, and its accuracy in relation to actual individual body fat composition can be distorted by such factors as fitness level, muscle mass, bone structure, and ethnicity.
The index is calculated from an individual’s weight and height as
This is the body weight of the individual scaled according to the square of the height. In physiology the word “weight” means the same as "mass”. The reason height is squared rather than cubed or raised to some other power is simply that, taken over people of different height, the resulting index correlates reasonably well with degree of underweight or overweight. No law of physics or physiological growth is implied.
Generally, a BMI chart displays calculated BMI as a function of weight (horizontal axis) and height (vertical axis) using “contour lines” for different values of BMI or colors for different BMI categories.
A frequent use of the BMI is to assess how much an individual's body weight departs from what is normal or desirable for a person of his or her height. The weight excess or deficiency may, in part, be accounted for by body fat (adipose tissue) although other factors such as muscularity also affect BMI (see discussion below and overweight).
Human bodies rank along the index from around 15 (near starvation) to over 40 (morbidly obese). This statistical spread is usually described using categories: eg, severe underweight, underweight, optimum weight, pre-obese (or overweight), obese, morbidly obese. The exact index values used to determine weight categories vary from authority to authority, but in general a BMI less than 18.5 is underweight and may indicate malnutrition, an eating disorder, or other health problems, while a BMI greater than 25 is overweight and above 30 is considered obese. These range boundaries apply to adults over 20 years of age. For example, if a person is two meters tall and weights two hundred kilograms, then he would have a BMI of 50. See picture on the right.
In patients with diabetes mellitus or kidney disease studies have shown that blood pressure over 130/80 mmHg should be considered a risk factor and may warrant treatment.
Etiology
Essential hypertension
Cerebrovascular accident (CVAs or strokes)
Myocardial infarction (heart attack)
Hypertensive cardiomyopathy (heart failure due to chronically high blood pressure)
Hypertensive retinopathy - damage to the retina
Hypertensive nephropathy - chronic renal failure due to chronically high blood pressure
Source: Wikipedia
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