What Is Blood Pressure--And What Happens When It is High?

Blood is carried from the heart to all of your body's tissue and organs in vessels called arteries. Blood pressure is the force of the blood pushing against the walls of those arteries. In fact, each time the heart beats (about 60-70 times a minute at rest), it pumps blood out into the arteries. Your blood pressure is at its greatest when the heart contracts and is pumping the blood. This is called systolic pressure. When the heart is at rest, in between beats, your blood pressure falls. This is the diastolic pressure.

Blood pressure is always given as these two numbers, systolic and diastolic pressures. Both are important. Usually they are written one above or before the other, such as 120/80 mm Hg (millimeters of mercury), with the top number the systolic, and the bottom the diastolic.

Different actions make your blood pressure go up or down. For example, if you run for a bus, your blood pressure goes up. When you sleep at night, your blood pressure goes down. These changes in blood pressure are normal.

Some people have blood pressure that stays up all or most of the time. Their blood pushes against the walls of their arteries with higher-than-normal force. If untreated this can lead to serious medical problems such as:

Arteriosclerosis ("hardening of the arteries"). High blood pressure harms the arteries by making them thick and stiff. This speeds the buildup of cholesterol and fats in the blood vessels like rust in a pipe, which prevents the blood from flowing through the body. In time it can lead to a heart attack or stroke.

Heart Attack. Blood carries oxygen to the body. When the arteries that bring blood to the heart muscle become blocked, the heart cannot get enough oxygen. Reduced blood flow can cause chest pain (angina). Eventually, the flow may be stopped completely, causing a heart attack.

Enlarged Heart. High blood pressure causes the heart to work harder. Over time, this causes the heart to thicken and stretch. Eventually the heart fails to function normally causing fluids to back up into the lungs. Controlling high blood pressure can prevent this from happening.

Kidney Damage. The kidney acts as a filter to rid the body of wastes. Over a number of years, high blood pressure can narrow and thicken the blood vessels of the kidney. The kidney filters less fluid and waste builds up in the blood. The kidneys may fail altogether. When this happens, medical treatment (dialysis) or a kidney transplant may be needed.

Stroke. High blood pressure can harm the arteries, causing them to narrow faster. So, less blood can get to the brain. If a blood clot blocks one of the narrowed arteries, a stroke (thrombotic stroke) may occur. A stroke can also occur when very high pressure causes a break in a weakened blood vessel in the brain (hemorrhagic stroke).

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Who's Likely To Develop High Blood Pressure?

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 African-Americans than in Caucasians.

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 age 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.

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 (obesity). Eleven 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.

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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 released from the cuff. The sound of your blood rushing through an artery is 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. As more air is released from the cuff, the last sound heard is the diastolic blood pressure. It represents the lowest pressure that remains within the artery when the heart is at rest.

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What Do the Numbers Mean?

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." See the table below which shows categories for blood pressure levels in adults.

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.

CATEGORIES FOR BLOOD PRESSURE LEVELS IN ADULTS*

(Age 18 Years and Older)
Blood Pressure Level (mm Hg)

      Category                                              Systolic               Diastolic
      Normal                                                   <130                       <85
      High Normal                                         130-139                   85-89
      High Blood Pressure
        Stage 1                                               140-159                   90-99
        Stage 2                                               160-179                 100-109
        Stage 3                                                 >180                       >110

*For those not taking medicine for high blood pressure and not having a short-term, serious illness. These categories are from the National High Blood Pressure Education Program.

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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.

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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:

1) Maintain a healthy weight, lose weight if you are overweight,
2) Be more physically active,
3) Choose foods lower in salt and sodium, and
4) 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:

1) 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 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.

Here's a good tip to help you control or change your eating habits: keep track of what you eat, when you eat, and why, by writing it down. Note whether you snack on high fat foods in front of the television, or if you skip breakfast and then eat a large lunch. Once you see your habits, you can set goals for yourself: cut back on TV snacks and, when you do snack, have fresh fruit, unsalted air-popped popcorn, or unsalted pretzels. If there's no time for breakfast at home, take a low fat muffin, bagel (skip the cream cheese), or cereal with you to eat at work. Changing your behavior will help you change your weight for the better.

2) 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 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. So you can fit physical activity into your daily routine in small but important ways.

More vigorous exercise has added benefits. It helps improve the fitness of the heart and lungs. That in turn protects you more against heart disease. Activities like swimming, brisk walking, running, and jumping rope are called "aerobic." This means that the body uses oxygen to make the energy it needs for the activity. Aerobic activities can condition your heart and lungs if done at the right intensity for at least 30 minutes, three to four times a week. But if you don't have 30 minutes for a break, try to find two 15-minute periods or even three 10-minute periods. Try to do some type of aerobic activity in the course of a week.

Most people don't need to see a doctor before they start exercising, since a gradual, sensible exercise program has few health risks. But if you have a health problem like high blood pressure; if you have pains or pressure in the chest or shoulder area; if you tend to feel dizzy or faint; if you get very breathless after a mild workout; or are middle-age or older and have not been active, and you are planning a vigorous exercise program, you should check with your doctor first. Otherwise, get out, get active, and get fit--and help prevent high blood pressure. The sample walking program at the end of this fact sheet can help you get started.

3) 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 helps to lower blood pressure. Some people like 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, 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.

You can teach your taste buds to enjoy less salty foods. Here are a few tips:

Check food labels for the amount of sodium in foods. Choose those lower in sodium most of the time. Look for products that say "sodium free," "very low sodium," "low sodium," "light in sodium," "reduced or less sodium," or "unsalted," especially on cans, boxes, bottles, and bags.

Buy fresh, plain frozen, or canned with "no salt added " vegetables. Use fresh poultry, fish and lean meat, rather than canned or processed types.Use herbs, spices, and salt-free seasoning blends in cooking and at the table instead of salt. Cook rice, pasta, and hot cereals without salt. Cut back on instant or flavored rice, pasta, and cereal mixes because they usually have added salt. Choose "convenience" foods that are lower in sodium. Cut back on frozen dinners, mixed dishes like pizza, packaged mixes, canned soups or broths, and salad dressings which often have a lot of sodium.When available, buy low-or reduced-sodium, or "no-salt-added" versions of foods.

4) 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 2 drinks a day. The "Dietary Guidelines for Americans" recommend that for overall health, women should limit their alcohol to no more than 1 drink a day.

You may have heard that some alcohol is good for your heart health. Some news reports suggest that people who consume a drink or two a day have lower blood pressure and live longer than those who consume excessive amounts of alcohol. Others note that wine raises the "good" blood cholesterol that prevents the build up of fats in the arteries. While these news stories may be correct, they don't tell the whole story: too much alcohol contributes to a host of other health problems, such as motor vehicle accidents, diseases of the liver and pancreas, damage to the brain and heart, an increased risk of many cancers, and fetal alcohol syndrome. Alcohol is also high in calories. So you should limit how much you drink.

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What Else Might Prevent High Blood Pressure?

Other things also may help prevent blood pressure. Here's a roundup of what's being said about them--and whether it's true or false.

Dietary Supplements--Potassium, Calcium, Magnesium, Fish Oils.

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--800 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, 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.

Other Factors--Fats, Carbohydrates, and Protein.

Varying the amount and type of fats, carbohydrates, and protein in the diet has little, if any, effect on blood pressure. But for overall heart health, it is crucial to limit the amount of fat in your diet, especially the saturated fat found in foods like fatty meats and whole milk dairy foods. Saturated fats raise your blood cholesterol level, and a high blood cholesterol level is another risk factor for heart disease. Foods high in fat are also high in calories.

Remember, foods high in complex carbohydrates (starch and fiber) are low in fat and calories--so eating these foods in moderate amounts instead of high fat foods can help you to lose weight if you are overweight or prevent you from gaining weight.

Caffeine. The caffeine in drinks like coffee, tea, and sodas may cause blood pressure to go up, but only temporarily. In a short time your blood pressure will go back down. Unless you are sensitive to caffeine and your blood pressure does not go down, you do not have to limit caffeine to prevent developing high blood pressure.

Garlic or Onions. Increased amount of garlic and onions have not been found to affect blood pressure. Of course, they are tasty substitutes for salty seasonings and can be used often.

Stress Management. Stress can make blood pressure go up for a while and over time may contribute to the cause of high blood pressure. So it's natural to think that stress management techniques like biofeedback, meditation, and relaxation would help prevent high blood pressure. This does not seem to be the case: the few studies that have looked at this have not shown that stress management helps to prevent high blood pressure. Of course, stress management techniques are helpful if they help you feel better or stick to a weight-loss and/or exercise program.

SOURCE: Exercise and Your Heart, National Heart, Lung, and Blood Institute and the American Heart Association, NIH Publication No. 93-1677.

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