Essential hypertension refers to abnormally high blood pressure without known cause. In adults it is arbitrarily defined as a systolic pressure equal to or greater than 160 mmHg (21.3 kPa) and/or a diastolic pressure (fifth phase) equal to or greater than 95 mmHg (12.7 kPa). Normal blood pressure is 120 mmHg. Over time this can cause major complications such as heart attack, hardening of the arteries, stroke, kidney failure, and congestive heart failure. How much time is required for damage to occur depends largely on how high the blood pressure is. The higher the pressure, the sooner complications will develop unless the blood pressure is treated. Additional factors that may hasten problems caused by high blood pressure include smoking, diabetes, and high cholesterol, age (more frequent in those over 40); heredity; obesity; high salt intake; high alcohol intake; psychological and social conditions (such as stress or low income); and renal disease.
The evidence that psychological factors play a primary role in human essential hypertension is inconclusive, but there is overwhelming clinical and experimental evidence that renal disease in man and a variety of experimental procedures in animals that affect renal function are associated with or induce hypertension. The mechanism by which the blood pressure-obesity correlation arises is unknown. Possible mechanisms include increased sodium intake and retention, increased tubular reabsorption of sodium due to increased insulin levels, increased oestrogen levels, disproportion between body mass and renal size, disproportion between increased blood volume and vascular capacity, and increased sympathetic nerve activity due to increased energy consumption.
More than 95% of all high blood pressure is essential hypertension.
50 million Americans, or 20% of the population, have high blood pressure. One in four are adults and more than 31% are unaware of their condition. Since 1970, therapies for hypertension have greatly reduced the rates of death from stroke and coronary heart disease. There has however been a rise recently in diseases due to chronic high blood pressure: severe kidney disease, heart failure, and stroke; and the death rate due to coronary heart disease has stabilized.
Contributing factors may be a rise in obesity and growing complacency about hypertension. Patients have stopped their therapies because of undesirable side effects, such as decreased sexual drive and fatigue. There has been little effective communication to the public about the risks recently as well.
In 1994 68% of Americans with the disease were aware that they had it; 54% were taking treatment for it; and 27% had it under adequate control. These rates are 2 to 5% lower than 3 years previously.