Nearly 50 million Americans have high blood pressure.

Older women are particularly likely to develop high blood pressure. More than half of all women over age 60 have it.

Others who are at a high risk of developing it are African Americans, the overweight, those with a family history of high blood pressure, and those with a high-normal blood pressure.

What is high blood pressure?

Blood is pumped by the heart through vessels to bring oxygen and nutrients to the body. Blood pressure is the force of the blood against the vessel walls. The more the pressure, the harder the heart is working.

Blood pressure often goes up and down during the day. When it goes up and stays high, then it is high blood pressure. The medical term is hypertension.

An easy test measures blood pressure. It uses an inflatable cuff around an arm. If the pressure is high, the test will be repeated on several days to get an accurate reading. You probably have had such a test on a visit to your doctor.

The test gives two numbers: The systolic pressure is the pressure of blood in the vessels as the heart beats. The diastolic pressure is the pressure of the blood between heartbeats. The numbers are usually written like a fraction with the systolic above or to the left. An example is 120/80 mm Hg (millimeters of mercury), a normal adult blood pressure.

Both numbers count. Your blood pressure is high if the systolic pressure is 140 or above, or the diastolic pressure is 90 or above, or both are high.

If you do not know your blood pressure, you should have it taken. Those with high blood pressure often do not feel sick. In fact, high blood pressure is often called "the silent killer," because it may cause no symptoms for a long time. But untreated, it can damage the kidneys and raise the chance of stroke, heart attack, or other cardiovascular ("heart and vessels") problems. It causes three of every five cases of heart failure in women. ("Heart failure" is a severe condition in which the heart cannot adequately supply the body with blood.)

Women who have both diabetes and high blood pressure are at an even higher risk of stroke and heart and kidney problems than those who have only high blood pressure.

You may be surprised to learn that many women take blood pressure drugs but still have high blood pressure. This is especially true for older women.

Why? There are various causes. Some women may not take their drugs as prescribed--in the right amount and at the right times. For others, a drug may not lower blood pressure enough. To prevent stroke, heart attack, or heart failure, blood pressure must be controlled to below 140/90.

So make sure you're in control of your high blood pressure. Talk with your doctor. Ask about your blood pressure level. If it is too high, ask about adjusting your drug and making lifestyle changes that will bring your blood pressure to below 140/90.

Key: = means equal to or more than

*These categories for those 18 and older are from the National High Blood Pressure Education Program. The categories are for those not on a high blood pressure drug and with no short-term serious illness.

**If your systolic and diastolic pressures fall into different categories, your overall status is the higher category.