Blood pressure is the measure of the force of blood pushing against blood vessel walls. The heart pumps blood into the arteries (blood vessels), which carry the blood throughout the body. High blood pressure, also called hypertension, is dangerous because it makes the heart work harder to pump blood to the body and contributes to hardening of the arteries, or atherosclerosis, and to the development of heart failure.
What Is "Normal" Blood Pressure?
A blood pressure reading has a top number (systolic) and bottom number (diastolic). The ranges are:
Normal: Less than 120 over 80 (120/80)
Prehypertension: 120-139 over 80-89
Stage 1 high blood pressure: 140-159 over 90-99
Stage 2 high blood pressure: 160 and above over 100 and above
People whose blood pressure is above the normal range should consult their doctor about steps to take to lower it.
What Causes High Blood Pressure?
The exact causes of high blood pressure are not known, but several factors and conditions may play a role in its development, including:
Being overweight or obese
Lack of physical activity
Too much salt in the diet
Too much alcohol consumption (more than 1 to 2 drinks per day)
Family history of high blood pressure
Chronic kidney disease
Adrenal and thyroid disorders
In as many as 95% of reported high blood pressure cases in the U.S., the underlying cause cannot be determined. This type of high blood pressure is called essential hypertension.
Though essential hypertension remains somewhat mysterious, it has been linked to certain risk factors. High blood pressure tends to run in families and is more likely to affect men than women. Age and race also play a role. In the United States, blacks are twice as likely as whites to have high blood pressure, although the gap begins to narrow around age 44. After age 65, black women have the highest incidence of high blood pressure.
Essential hypertension is also greatly influenced by diet and lifestyle. The link between salt and high blood pressure is especially compelling. People living on the northern islands of Japan eat more salt per capita than anyone else in the world and have the highest incidence of essential hypertension. By contrast, people who add no salt to their food show virtually no traces of essential hypertension.
The majority of all people with high blood pressure are "salt sensitive," meaning that anything more than the minimal bodily need for salt is too much for them and increases their blood pressure. Other factors that can raise the risk of having essential hypertension include obesity; diabetes; stress; insufficient intake of potassium, calcium, and magnesium; lack of physical activity; and chronic alcohol consumption.
When a direct cause for high blood pressure can be identified, the condition is described as secondary hypertension. Among the known causes of secondary hypertension, kidney disease ranks highest. Hypertension can also be triggered by tumors or other abnormalities that cause the adrenal glands (small glands that sit atop the kidneys) to secrete excess amounts of the hormones that elevate blood pressure. Birth control pills -- specifically those containing estrogen -- and pregnancy can boost blood pressure, as can medications that constrict blood vessels.