Increasing body weight, long associated with increasing blood pressure, is now recognized as an independent risk factor for cardiovascular disease (CVD) and is strongly associated with other risk factors. In June of 1998, the American Heart Association added obesity to its list of major cardiovascular risk factors.
An estimated 55% of U.S. adults are overweight or obese. Overweight individuals have a threefold increased risk for the development of hypertension compared with lean individuals. Obesity is one of the most common factors responsible for hypertension, with hypertension among the obese approaching 50%. The National Institute of Health National Heart, Lung & Blood Institute (NHLBI) guidelines for the treatment of overweight and obese adults recommend weight-reduction strategies that include both nonpharmacologic and pharmacologic treatments. This article reviews the mechanisms that link obesity with hypertension and describes changes that may occur in these mechanisms and in blood pressure levels when weight loss is used to treat hypertension.
OBESITY: AN EPIDEMIC
The increasing prevalence of obesity in the industrialized world is an alarming epidemic. In a recent Centers for Disease Control & Prevention press release, Atlanta director Dr. Jeffrey P Koplan commented that the obesity epidemic "should be taken as seriously as an infectious disease epidemic." Despite the goal to decrease the prevalence of obesity in the United States to less than 20% by the year 2000 (Healthy People 2000, National Health Promotion & Disease Prevention objectives), recent studies have estimated that 54.9% of the U.S. population 20 years of age and older are overweight or obese. This represents an 8% increase in the last 10 years.
The increase in obesity is seen in all racial/ethnic, gender, and age groups. According to National Health & Nutrition Examination Survey (NHANES) data, an estimated 60.6% of white men and 56.7% of African American men are overweight or obese, while 47% of white women and 65.9% of African American women are overweight or obese.
The nature of health risks related to overweight and obesity is similar in all populations, even though the specific level of risk associated with a given level of overweight or obesity may vary with race/ethnicity, age, gender, and societal conditions. Morbidity for a number of health conditions increases as body mass index (BMI) increases (above a BMI of 20), as illustrated in Figure 1.
The recent publication of the Clinical Guidelines on the Identification, Evaluation, and Treatment of Overweight and Obesity in Adults by the NHLBI demonstrates a commitment to the management of obesity as a chronic disease and as a public health problem. Methods for clinical assessment and classification of overweight and obesity are listed in Tables 1 and 2. Table 3 illustrates the estimated BMI based on height and weight taken in nonmetric measures.
BMI is recommended as a practical approach for assessment of total body fat for the majority of patients. Limitations of BMI as a measure of total body fat include overestimates of body fat in persons who are very muscular and underestimates of body fat in persons who have lost muscle mass. Waist circumference, waist-tohip ratio, and skinfold thickness are additional measures used to estimate body fat. BMI, however, remains the most clinically useful measure.
ASSOCIATION BETWEEN OBESITY AND HYPERTENSION
Epidemiologic studies clearly demonstrate a correlation between body weight and blood pressure in obese populations as well as in lean populations. The relationship between body mass
and diastolic blood pressure is shown in Figure 1. Not only are obesity and hypertension related, but there is also a close relationship between the continuous variables of BMI and blood pressure. Excess adiposity in a visceral or android distribution, as opposed to a peripheral (gynoid) distribution, poses a greater risk for the development of hypertension. …