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Prehypertension is an American medical classification for cases where a person's blood pressure is elevated above normal, but not to the level considered hypertension (high blood pressure). Prehypertension is blood pressure readings with a systolic pressure from 120 to 139 mm Hg or a diastolic pressure from 80 to 89 mm Hg. Readings greater than or equal to 140/90 mm Hg are considered hypertension. Classification of blood pressure is based upon two or more readings at two or more separate occasions separated by at least one week. The seventh report of the Joint National Committee (JNC 7) proposed the new labeling for elevated blood pressure values below 140/90 to more accurately communicate the tendency of blood pressure to rise with age.
Data from the 1999 and 2000 National Health and Nutrition Examination Survey (NHANES III) estimated that the prevalence of prehypertension among adults in the United States was approximately 31 percent. The prevalence was higher among men than women (39 and 23 percent, respectively).
Elevated blood pressure develops gradually over many years usually without a specific identifiable cause. However, possible medical causes, such as medications, kidney disease, adrenal problems or thyroid problems, must first be excluded. High blood pressure that develops over time without a specific cause is considered benign or essential hypertension. Blood pressure also tends to increase as a person ages.
A primary risk factor for prehypertension is being overweight. Other risk factors include a family history of hypertension, a sedentary lifestyle, eating high sodium foods, smoking, and excessive alcohol intake. Blood pressure levels appear to be familial, but there is no clear genetic pattern.
Prehypertension is often asymptomatic (without symptoms) at the time of diagnosis. Only extremely elevated blood pressure (malignant hypertension) can, in rare cases, cause headaches, visual changes, fatigue, or dizziness, but these are nonspecific symptoms which can occur with many other conditions. Thus, blood pressures above normal can go undiagnosed for a long period of time.
The extent to which prehypertension constitutes a serious health concern remains controversial. Several long-term studies have suggested no significant increase in all-cause mortality over long periods of time for individuals falling within the prehypertensive range. Many studies further indicate a J-shaped relationship between blood pressure and mortality, whereby both very high and very low levels are associated with notable increases in mortality On the other hand, the National Heart, Lung and Blood Institute suggests that people with prehypertension are at a higher risk for developing hypertension, or high blood pressure, compared to people with normal blood pressure.
According to some studies, prehypertension can increase the risk for heart attacks, strokes, congestive heart failure, and renal failure. One study found that a prehypertensive person is more than three times more likely to have a heart attack and 1.7 times more likely to have heart disease than a person with normal blood pressure. A meta-analysis concluded that prehypertension increases the risk of stroke, and that even low-range prehypertension significantly increases stroke risk.
To lower the risk of prehypertension progressing to hypertension, modification of lifestyle or behaviors is necessary.
A low-fat, low-sodium, high potassium diet (e.g. DASH diet) is recommended, along with increasing physical activity to at least thirty minutes a day most days of the week, quitting smoking, reducing alcohol consumption, and maintaining a healthy weight.
Some research indicates that the link between low-fat, low-sodium diets may have little to no effect on treating hypertension, particularly in cases of diabetics. There are also links to high-carbohydrate diets heavy in refined carbohydrates (sugar, corn syrup, white flour) as potential sources for increases in blood pressure. Recent research has found that low carbohydrate diets can lower weight and blood pressure in manners similar to medications.
Foods rich in potassium include orange juice, potatoes, bananas, avocados, cantaloupes, tomatoes, broccoli, soybeans, brown rice, garlic and apricots, although it is also abundant in most fruits, vegetables and meats.
Several studies have found that hibiscus tea has a substantial antihypertensive effect attributable to the flower's ACE-inhibiting anthocyanin content, and possibly to a diuretic effect. One study found that hibiscus conferred an antihypertensive effect comparable to 50 mg./day of the drug captopril.
Careful monitoring for signs of end-organ damage or progression to hypertension is an important part of the follow-up of patients with prehypertension. Any change in blood pressure classification should be confirmed on at least one subsequent visit.
The major indication for pharmacologic antihypertensive therapy is progression to hypertension. The threshold is lower in patients with diabetes, chronic renal failure, or cardiovascular disease. The target blood pressure for these conditions is currently less than 120/80 mm Hg.
Home monitoring of blood pressure can be used to monitor and track prehypertensive patients. This can help to raise the awareness of the patient and their doctor if their blood pressure levels rise to hypertensive levels. Home monitoring can help to avoid white coat hypertension which results in blood pressure levels being elevated due to the presence of a doctor or physician in a ‘white coat’. Monitoring at home or work at regular times each day helps diagnose a patient with prehypertension or hypertension.
The American Heart Association website says, "You may have what's called 'white coat hypertension'; that means your blood pressure goes up when you're at the doctor's office. Monitoring at home will help you measure your true blood pressure and can provide your doctor with a log of blood pressure measurements over time. This is helpful in diagnosing and preventing potential health problems."
People using home blood pressure monitoring devices are increasingly also using blood pressure charting software. These charting methods provide print outs for the patient's physician and reminders to check blood pressure.