High blood pressure, also called hypertension, is a risk factor for heart and kidney diseases and stroke. This means that having high blood pressure increases your chance of getting heart or kidney disease, or of having a stroke. This is serious business: Heart disease is the No. 1 killer in the United States, and stroke is the third most common cause of death.

Also in this article: What Is Blood Pressure, and What Happens When It Is High? Who's Likely to Develop High Blood Pressure? How Is Blood Pressure Checked? What Do the Numbers Mean? What Causes High Blood Pressure? How Can You Prevent High Blood Pressure? What Else Might Prevent High Blood Pressure?

About one in every four American adults has high blood pressure. High blood pressure is especially dangerous because it often gives no warning signs or symptoms. Fortunately, though, you can find out if you have high blood pressure by having your blood pressure checked regularly. If it is high, you can take steps to lower it. Just as important, if your blood pressure is normal, you can learn how to keep it from becoming high.

Anyone can develop high blood pressure, but some people are more likely to develop it than others. For example, high blood pressure is more common - it develops earlier and is more severe - in black people than in white people.

In the early and middle adult years, men have high blood pressure more often than women. But as men and women age, the reverse is true. More women after menopause have high blood pressure than men of the same age. And the number of both men and women with high blood pressure increases rapidly in older age groups. More than half of all Americans over 65 have high blood pressure. And older African American women who live in the Southeast are more likely to have high blood pressure than those in other regions of the United States.

In fact, the Southeastern states have some of the highest rates of death from stroke. High blood pressure is the key risk factor for stroke. Other risk factors include cigarette smoking and overweight. These 11 states - Alabama, Arkansas, Georgia, Indiana, Kentucky, Louisiana, Mississippi, North Carolina, South Carolina, Tennessee and Virginia - have such high rates of stroke among persons of all races and in both sexes that they are called the "Stroke Belt States."

Finally, heredity can make some families more likely than others to get high blood pressure. If your parents or grandparents had high blood pressure, your risk may be increased. While it is mainly a disease of adults, high blood pressure can occur in children as well. Even if everyone is healthy, be sure you and your family get your blood pressure checked. Remember, high blood pressure has no signs or symptoms.

How Is Blood Pressure Checked?

Having your blood pressure checked is quick, easy and painless. Your blood pressure is measured with an instrument called a sphygmomanometer (sfig-mo-ma-nom-e-ter).

It works like this: A blood pressure cuff is wrapped around your upper arm and inflated to stop the blood flow in your artery for a few seconds. A valve is opened and air is then released from the cuff and the sounds of your blood rushing through an artery are heard through a stethoscope. The first sound heard and registered on the gauge or mercury column is called the systolic blood pressure. It represents the maximum pressure in the artery produced as the heart contracts and the blood begins to flow. The last sound heard as more air is released from the cuff is the diastolic blood pressure. It represents the lowest pressure that remains within the artery when the heart is at rest.

Blood pressure is always expressed in two numbers that represent the systolic and diastolic pressures. These numbers are measurements of millimeters (mm) of mercury (Hg). The measurement is written one above or before the other, with the systolic number on the top and the diastolic number on the bottom. For example, a blood pressure measurement of 120/80 mm Hg is expressed verbally as "120 over 80."

If your blood pressure is less than 140/90 mm Hg, it is considered normal. However, a blood pressure below 120/80 mm Hg is even better for your heart and blood vessels. People use to think that low blood pressure (for example, 105/65 mm Hg in an adult) was unhealthy. Except for rare cases, this is not true. High blood pressure or "hypertension" is classified by stages and is more serious as the numbers get higher.

What Causes High Blood Pressure?

For most people, there is no single known cause of high blood pressure. This type of high blood pressure is called "primary" or "essential" hypertension. This type of blood pressure can't be cured, although in most cases it can be controlled. That's why it's so important for everyone to take steps to reduce their chances of developing high blood pressure.

In a few people, high blood pressure can be traced to a known cause like tumors of the adrenal gland, chronic kidney disease, hormone abnormalities, use of birth control pills or pregnancy. This is called "secondary hypertension." Secondary hypertension is usually cured if its cause passes or is corrected.

How Can You Prevent High Blood Pressure?

Everyone -- regardless of race, age, sex, or heredity -- can help lower their chance of developing high blood pressure. Here's how:

• Maintain a healthy weight; lose weight if you are overweight.
• Be more physically active.
• Choose foods lower in salt and sodium.
• If you drink alcoholic beverages, do so in moderation.

These rules are also recommended for treating high blood pressure, although medicine is often added as part of the treatment. It is far better to keep your blood pressure from getting high in the first place.

Another important measure for your health is to not smoke: While cigarette smoking is not directly related to high blood pressure, it increases your risk of heart attack and stroke.

Let's look more closely at the four rules to prevent high blood pressure and for keeping a healthy heart:

Maintain a healthy weight; lose weight if you are overweight.

As your body weight increases, your blood pressure rises. In fact, being overweight can make you two to six times more likely to develop high blood pressure than if you are at your desirable weight. Keeping your weight in the desirable range is not only important to prevent high blood pressure but also for your overall health and well being.

It's not just how much you weigh that's important; it also matters where your body stores extra fat. Your shape is inherited from your parents just like the color of your eyes or hair. Some people tend to gain weight around their belly; others, around the hips and thighs. "Apple-shaped" people who have a pot belly (that is, extra fat at the waist) appear to have higher health risks than "pear-shaped" people with heavy hips and thighs.

No matter where the extra weight is, you can reduce your risk of high blood pressure by losing weight. Even small amounts of weight loss can make a big difference in helping to prevent high blood pressure. Losing weight, if you are overweight and already have high blood pressure, can also help lower your pressure.

To lose weight, you need to eat fewer calories than you burn. But don't go on a crash diet to see how quickly you can lose those pounds. The healthiest and longest-lasting weight loss happens when you do it slowly, losing 1/2 to 1 pound a week. By cutting back by 500 calories a day by eating less and being more physically active, you can lose about 1 pound (which equals 3,500 calories) in a week.

Losing weight and keeping it off involves a new way of eating and increasing physical activity for life. Here's how to eat and get on your way to a lower weight:

Choose foods low in calories and fat. Naturally, choosing low-calorie foods cuts calories. But did you know that choosing foods low in fat also cuts calories? Fat is a concentrated source of calories, so eating fewer fatty foods will reduce calorie intake. Some examples of fatty foods to cut down on are: butter, margarine, regular salad dressings, fatty meats, skin of poultry, whole milk dairy foods like cheese, fried foods, and many cookies, cakes, pastries and snacks.

Limit serving sizes. To lose weight, it's not just the type of foods you eat that's important, but also the amount . To take in fewer calories, you need to limit your portion sizes. Try especially to take smaller helpings of high calorie foods like high fat meats and cheeses. And try not to go back for seconds.

Be more physically active.

Besides losing weight, there are other reasons to be more active: being physically active can reduce your risk for heart disease, help lower your total cholesterol level and raise HDL-cholesterol (the "good" cholesterol that does not build up in the arteries), and help lower high blood pressure. And people who are physically active have a lower risk of getting high blood pressure - 20 percent to 50 percent lower -- than people who are not active. You don't have to be a marathon runner to benefit from physical activity. Even light activities, if done daily, can help lower your risk of heart disease. These include:

• Using the stairs instead of the elevator.
• Getting off the bus one or two stops early and walk the rest of the way.
• Parking farther away from the store or office.
• Riding a bike.
• Working in the yard or garden.
• Dancing.

More vigorous exercise has added benefits. It helps improve the fitness of the heart and lungs. And that in turn protects you more against heart disease.

Choose foods lower in salt and sodium.

Americans eat more salt (sodium chloride) and other forms of sodium than they need. And guess what? They also have higher rates of high blood pressure than people in other countries who eat less salt.

Often, if people with high blood pressure cut back on salt and sodium, their blood pressure falls. Cutting back on salt and sodium also prevents blood pressure from rising. Some people, such as African Americans and the elderly, are more affected by sodium than others. Since there's really no practical way to predict exactly who will be affected by sodium, it makes sense to limit intake of salt and sodium to help prevent high blood pressure.

All Americans, especially people with high blood pressure, should eat no more than about 6 grams of salt a day, which equals about 2,400 milligrams of sodium. That's about 1 teaspoon of table salt. But remember to keep track of all salt eaten -- including that in processed foods and added during cooking or at the table. Americans eat 4,000 to 6,000 milligrams of sodium a day, so most people need to cut back on salt and sodium.

If you drink alcoholic beverages, do so in moderation.

Drinking too much alcohol can raise your blood pressure. It may also lead to the development of high blood pressure. So to help prevent high blood pressure, if you drink alcohol, limit how much you drink to no more than two drinks a day. The "Dietary Guidelines for Americans" recommend that for overall health, women should limit their alcohol to no more than one drink a day.

This is what counts as a drink:

• 1-1/2 ounces of 80-proof or 1 ounce of 100-proof whiskey
• 5 ounces of wine
• 12 ounces of beer (regular or light)

Other things also may help prevent blood pressure. Here's a roundup of what's being said about them:

Potassium: Eating foods rich in potassium will help protect some people from developing high blood pressure. You probably can get enough potassium from your diet, so a supplement isn't necessary. Many fruits, vegetables, dairy foods, and fish are good sources of potassium.

Calcium: Populations with low calcium intakes have high rates of high blood pressure. However, it has not been proven that taking calcium tablets will prevent high blood pressure. But it is important to be sure to get at least the recommended amount of calcium - 1,000 milligrams per day for adults (pregnant and breastfeeding women need more) -- from the foods you eat. Dairy foods like low fat selections of milk, yogurt, and cheese are good sources of calcium. Low-fat and nonfat dairy products have even more calcium than the high fat types.

Magnesium: A diet low in magnesium may make your blood pressure rise. But doctors don't recommend taking extra magnesium to help prevent high blood pressure -- the amount you get in a healthy diet is enough. Magnesium is found in whole grains, green leafy vegetables, nuts, seeds, and dry peas and beans.

Fish oils: A type of fat called omega-3 fatty acids is found in fatty fish like mackerel and salmon. Large amounts of fish oils may help reduce high blood pressure, but their role in prevention is unclear. But taking fish oil pills is not recommended because high doses can cause unpleasant side effects. The pills are also high in fat and calories. Of course, most fish if not fried or made with added fat are low in saturated fat and calories and can be eaten often.