Staying attuned to blood pressure

Blood pressure — especially that top number — should get more of our attention.

Maybe your blood pressure has been normal for as long as you can remember, but that doesn't mean you should let it slip beneath your health radar. The older we get, the greater our chances of developing high blood pressure (also known as hypertension). Even if you don't have high blood pressure by age 55, your chances of developing it eventually are 90%. According to a report from the government's Agency for Healthcare Research and Quality, more than 25 million women, most over age 45, were treated for high blood pressure in 2006. That makes it the most common condition for which women seek treatment.

Uncontrolled hypertension can damage the lining of the arteries, increasing the risk of cardiovascular disease (in particular, heart disease and stroke), which is the leading cause of death among women in the United States. High blood pressure can also impair vision, cause kidney failure, and contribute to dementia. Yet its symptoms are subtle and largely unnoticeable until it has caused considerable damage.

Clinicians once assumed that high blood pressure was a normal part of aging and rarely treated it in older people. But now, several large clinical trials have shown that in people ages 60 and over (including those over the age of 80), treatment reduces the incidence of strokes and other cardiovascular events. Fortunately, there are many ways to prevent or control high blood pressure.

The two numbers in a blood pressure reading represent the peak pressure reached in the heart's pumping cycle (the systolic pressure, the top number) and the lowest pressure during the resting phase of the cycle (the diastolic pressure, the bottom number). The result is measured in millimeters of mercury (mm Hg), and expressed as systolic over diastolic — for example, 110/80 mm Hg. You have high blood pressure if your systolic pressure is 140 or above or your diastolic pressure is 90 or above, or both. Blood pressure naturally rises and falls throughout the day, so a single reading doesn't tell you much. What matters is the pattern over time. High blood pressure is diagnosed only if your clinician finds a consistently elevated level over several months.

Systolic and diastolic blood pressures tend to rise and fall together, especially in young and middle-aged adults, but diastolic pressure fluctuates less, and for that reason, clinicians used to focus on the diastolic reading. But since the 1990s, research has highlighted the importance of systolic pressure, especially in older adults.

In 2003, the Joint National Committee on Prevention, Detection, Evaluation, and Treatment of High Blood Pressure stated unequivocally that in people over age 50, an elevated systolic reading (140 mm Hg or higher) is a much more significant risk factor for cardiovascular disease than an elevated diastolic reading. Its conclusion was based on a large body of evidence. The Framingham Heart Study, for example, showed that systolic blood pressure alone identified 91% of people who needed treatment, while diastolic pressure identified only 22% of those needing treatment. Other research has demonstrated that treating high systolic pressure cuts the risk of stroke in people ages 60 and over, even when diastolic pressure is normal.

In 2008, three hypertension experts writing in The Lancet proposed that the systolic reading be the only blood pressure measurement used in tracking and diagnosing hypertension in people over age 50. That proposal requires more research, but there's no question that systolic pressure should be front and center at midlife and beyond. By age 60, high blood pressure affects one out of every two people, and most have isolated systolic hypertension — a systolic pressure of 140 or above with a normal (under 90) diastolic pressure. (See the graph, "Age and isolated systolic hypertension.") Fortunately, that condition is treated like other forms of hypertension, with lifestyle changes and sometimes medications. If you have no complicating health problems, the goal is to reduce blood pressure to under 140/90 mm Hg. If you have diabetes or kidney disease, the target is under 130/80 mm Hg. However, diastolic pressure should not go below 60 mm Hg (or below 65 mm Hg in the very old or people with coronary artery disease).

Why isolated systolic hypertension?

Certain medical conditions can cause or contribute to isolated systolic hypertension. These include anemia, an overactive thyroid or adrenal gland, a malfunctioning aortic valve, kidney disease, and even obstructive sleep apnea. But usually it results from age-related stiffening of the large arteries.

Blood pressure reflects both the amount of blood the heart pumps out every minute (cardiac output) and the pressure the walls of the arteries exert on the flowing blood (arterial resistance). A healthy artery can expand as blood surges through it and return to its original shape when the blood flow ebbs. As we age, our arteries tend to lose their elasticity and therefore their capacity to accommodate surges of blood.

Age-related changes, some at the cellular level, also promote the accumulation of fatty deposits (plaque) on the inside of the arterial walls. These changes contribute to the artery-clogging process known as atherosclerosis (hardening of the arteries). Plaque accumulation reduces arterial resiliency and stimulates other processes that further arterial thickening and rigidity. The less flexible the arteries, the greater the arterial resistance — and the harder the heart has to work to pump blood.

As artery walls stiffen, diastolic blood pressure tends to drop, while systolic pressure rises. Diastolic pressure usually levels off or falls off after age 50, but systolic pressure continues to increase throughout life.

What's gender got to do with it?

Up to about age 55, women have a lower incidence of hypertension than men do, but after that, our blood pressure tends to rise more sharply than men's — especially systolic pressure. Hormones may be part of the story. There is some evidence that estrogen protects women against hypertension. Animal studies suggest that it prevents arterial stiffening and vulnerability to atherosclerosis, though that hasn't been proven in humans.

Still, it's unclear how menopause and the resulting decline in estrogen affect blood pressure. Longitudinal studies (those that follow health changes over time) haven't shown an increase in blood pressure during the menopausal transition. Other research suggests that even after adjusting for factors such as age and weight, postmenopausal women are twice as likely as premenopausal women to have high blood pressure. In the Third National Health and Nutrition Examination Survey, the rise in systolic blood pressure was steeper in postmenopausal women, up to age 60. So at least some of the increase in blood pressure (mainly systolic) could be related to menopause. But it's important to remember that many other factors are in play as well.

What to do

If you have isolated systolic hypertension, your clinician should run tests to rule out anemia and other medical conditions. She or he will also evaluate your cardiac risk factors, including body mass index and cholesterol levels, and check for hypertension-related damage to the eyes or kidneys.

The next step is to adopt healthier habits — the cornerstone of prevention and treatment. That means losing excess weight, getting regular exercise (which can also help you lose weight), not smoking (and making sure you avoid others' smoke), reducing sodium (salt) intake, and eating plenty of fruits, vegetables, and whole grains. To get an idea of the impact these changes can have on systolic blood pressure, see the chart, "Effects of lifestyle changes on systolic blood pressure." Regular exercise is especially effective. It increases the heart's pumping capacity in several ways and also improves vessel elasticity and function.

If you don't have diabetes or any damage to your heart, brain, kidneys, or eyes, lifestyle changes alone may be enough to bring high blood pressure down to normal.

If lifestyle changes alone don't get your systolic pressure under control, an antihypertensive drug should be added. There are many kinds of blood pressure medications, and which one is appropriate for you will depend on your particular situation. If you have relatively mild hypertension and no complicating health problems, guidelines suggest starting with a thiazide diuretic (a "water pill"), which works in the kidneys to flush excess water and sodium from the body. If you have heart disease or diabetes, your clinician may recommend an angiotensin-converting enzyme (ACE) inhibitor or calcium-channel blocker — both of which reduce blood pressure by relaxing blood vessels. Because different kinds of drugs work in different ways, you may need to take two or more. Also, the same drug may have different side effects in different people. (For a more detailed list of high blood pressure medications, how they work, and their side effects, go to /womenextra.)

Once you've been diagnosed with hypertension, you should keep track of your blood pressure with a home monitoring device. You can buy one at a drugstore or medical specialty shop or on the Internet for as little as $50. The best type of home blood pressure monitor is oscillometric — that is, it doesn't require a stethoscope — and works with a cuff that fits on the upper arm. (Wrist and finger models are not recommended.) Bring the monitor to your clinician's office to check its accuracy and your technique.

To learn more about how to monitor your blood pressure at home, go to /womenextra. You can also watch a video demonstration at health.harvard.edu/128. For a downloadable blood pressure–tracking chart and other helpful tools, visit the American Heart Association's High Blood Pressure Web page at www.americanheart.org/HBP.