Just a few decades ago, doctors thought a blood pressure reading of 160/95 millimeters of mercury (mm Hg) was an acceptable target rate. Today, those numbers are regarded as dangerously high, and blood pressure lower than 120/80 is considered optimal for good health.
The ongoing downward revision of blood pressure standards had led some people to assume that just as you can't be too thin or too rich, your blood pressure can't be too low. But that's not always the case.
Many people who have low blood pressure (hypotension) are healthy and have no signs or symptoms related to lower than normal readings. But for others, low blood pressure can cause dizziness and fainting or indicate serious heart, neurological disorders. Severely low blood pressure can deprive the brain and other vital organs of oxygen and nutrients, leading to shock, a life-threatening condition.
Signs and Symptoms (Warning Sign)
Some people with low blood pressure are in peak physical condition with strong cardiovascular systems and a reduced risk of heart attack and stroke. For these people, low blood pressure, rather than being a cause for concern, is a cause for celebration.
But low blood pressure can also signal an underlying problem, especially when it drops suddenly or is accompanied by signs and symptoms such as:
- Dizziness or lightheadedness
- Fainting (syncope)
- Lack of concentration
- Blurred vision
- Cold, clammy, pale skin
- Rapid, shallow breathing
The heart is the prime mover of the circulatory system; with each beat it launches your blood on a journey through 60,000 miles of arteries, veins and capillaries, ultimately circulating about 2,000 gallons of blood each day. Blood pressure is a measurement of the pressure in your arteries during the active and resting phases of each heartbeat. Here's what the numbers mean:
Systolic pressure. The first number in a blood pressure reading, this is the amount of pressure your heart generates when pumping blood through your arteries to the rest of your body.
Diastolic pressure. The second number in a blood pressure reading, this refers to the amount of pressure in your arteries when your heart is at rest between beats
Although you can get an accurate blood pressure reading at any given time, blood pressure isn't static. It can vary considerably in a short amount of time — sometimes from one heartbeat to the next, depending on your body position, breathing rhythm, stress level, physical condition, the medications you take, what you eat and drink, and even the time of day. Blood pressure is usually lowest at night and rises sharply on waking.
Blood Pressure: How low can you go?
Current guidelines identify normal blood pressure as lower than 120/80 — many experts think 115/75 is optimal. Higher readings indicate increasingly serious risks of cardiovascular disease. Even blood pressures formerly considered healthy — 120 to 139 systolic and 80 to 89 diastolic — are now believed to increase the risks. Low blood pressure, on the other hand, is much harder to quantify.
Some experts define low blood pressure as readings lower than 90 systolic or 60 diastolic — you need have only one number in the low range for your blood pressure to be considered lower than normal. In other words, if your systolic pressure is a perfect 115, but your diastolic pressure is 50, you're considered to have lower than normal pressure.
Yet this can be misleading because what constitutes low blood pressure is highly relative, varying considerably from one person to another. For that reason, doctors often consider chronically low blood pressure too low only if it causes noticeable signs and symptoms.
On the other hand, a sudden fall in blood pressure can be dangerous. A change of just 20 mm Hg — a drop from 130 systolic to 110 systolic, for example — can cause dizziness and fainting when the brain fails to receive an adequate supply of blood. And precipitous plunges, especially those caused by uncontrolled bleeding, severe infections or allergic reactions can, be life-threatening.
How low blood pressure gets that way
Low blood pressure can be a boon when it results from a healthy lifestyle. Athletes and people who exercise regularly, for example, tend to have lower blood pressure than do people who aren't as fit. So, in general, do nonsmokers and people who eat well and maintain a normal weight.
But in some instances, low blood pressure can be a sign of serious, even life-threatening disorders. And although the reason for lower than normal blood pressure isn't always clear, doctors know that the following factors can cause or contribute to low and sometimes to dangerously low readings:
Pregnancy. Because a woman's circulatory system expands rapidly during pregnancy, blood pressure is likely to drop. In fact, during the first 24 weeks of pregnancy, systolic pressure commonly drops by five to 10 points and diastolic pressure by as much as 10 to 15 points.
Medications. A number of drugs can cause low blood pressure, drugs that treat hypertension; heart medications, drugs for Parkinson's disease, Viagra, narcotics, and alcohol. Other prescription and over-the-counter medications may cause low blood pressure when taken in combination with high blood pressure drugs.
Heart problems. Among the heart conditions that can lead to low blood pressure are an extremely low heart rate (bradycardia), problems with heart valves, heart attack and heart failure. These are conditions in which your heart may not be able to circulate enough blood to meet your body's needs.
Endocrine problems. These include an underactive or overactive thyroid (hypothyroidism and hyperthyroidism), adrenal insufficiency (Addison's disease) low blood sugar and in some cases, diabetes.
Dehydration. Fever, vomiting, severe diarrhea, and strenuous exercise can all lead to dehydration, a potentially serious condition in which your body loses more water than you take in. Even mild dehydration, a loss of as little as 1 percent to 2 percent of body weight, can cause weakness, dizziness and fatigue. Far more serious is hypovolemic shock, a life-threatening complication of dehydration. It occurs when low blood volume causes a sudden drop in blood pressure and a corresponding reduction in the amount of oxygen reaching your tissues. If untreated,
When to seek medical advice
In many instances, low blood pressure isn't serious. If you have consistently low readings but feel fine, your doctor is likely to monitor you during routine exams. Even occasional dizziness or lightheadedness may be relatively minor — the result of mild dehydration, low blood sugar or too much time in the sun or a hot tub, for example. In these situations, it's not a matter so much of how far, but of how quickly, your blood pressure drops. Still, it's important to see your doctor if you experience any signs or symptoms of hypotension because they sometimes can point to more serious problems. It can be helpful to keep a record of your symptoms, when they occur and what you were doing at the time.
The goal in evaluating low blood pressure is to find the underlying cause. This helps determine the correct treatment and identify any heart, neurological problems that may be responsible for lower than normal readings. To help reach a diagnosis, your doctor may recommend one or more of the following:
Blood tests. These can provide a certain amount of information about your overall health as well as whether you have hypoglycemia or anemia, both of which can cause lower than normal blood pressure.
Electrocardiogram (ECG, EKG). This noninvasive test, which can be performed in your doctor's office, detects irregularities in your heart rhythm, structural abnormalities in your heart, and problems with the supply of blood and oxygen to your heart muscle. It can also tell if you're having a heart attack or if you've had a heart attack in the past. Sometimes you may be asked to wear a 24-hour Holter monitor to record your heart's electrical activity as you go about your daily routine.
Echocardiogram. Using the same technology that allows you to view a fetus in the womb, an echocardiogram produces images of your heart that may show abnormalities in your heart muscle or valves.
Valsalva maneuver. This noninvasive test checks the functioning of your autonomic nervous system by analyzing your heart rate and blood pressure after several cycles of a type of deep breathing: You take a deep breath and then force the air out through a closed mouth, as if you were trying to blow up a stiff balloon.
Tilt-table test. If you have postural or neurally mediated hypotension, your doctor may suggest a tilt-table test, which evaluates how your body reacts to changes in position. During the test, you lie on a table that's tilted to raise the upper part of your body, which simulates the movement from a prone to a standing position.
Even moderate postural, postprandial or neurally mediated hypotension can seriously affect quality of life, leading not only to dizziness and weakness but also to fainting and a risk of injury from falls. And severely low blood pressure from any cause can deprive your body of enough oxygen to carry out its normal functions, leading to damage to your heart and brain.
In addition, chronic low blood pressure may increase the risk of Alzheimer's-type dementia in some older adults. A diastolic pressure lower than 70 over a long period of time is most closely associated with dementia, and for every 10-point drop in pressure, the likelihood of dementia may increase by as much as 20 percent.
For years, researchers debated whether the low blood pressure often seen in people with Alzheimer's was a consequence or a cause of the disease. Current research seems to indicate that it's both, although in younger people, lower blood pressure is usually associated with a reduced risk of dementia.
Scientists speculate that age-related changes in cardiovascular function may explain the difference. Because older adults are more likely to have blocked arteries than younger people are, their blood pressure may need to be higher to maintain adequate blood flow to the brain.
Low blood pressure that doesn't cause signs or symptoms rarely requires treatment. In symptomatic cases, the appropriate therapy depends on the underlying cause, and doctors usually try to address the primary health problem — dehydration, heart failure, diabetes or hypothyroidism, for example — rather than low blood pressure itself. When hypotension is drug-induced, treatment usually involves changing the dose of the medication or stopping it entirely.
If it's not clear what's causing hypotension or no effective treatment exists, the goal is to raise your blood pressure and reduce signs and symptoms. Depending on your age, health status and the type of hypotension you have, this may be accomplished in several ways:
- Increased salt intake. Experts usually recommend limiting the amount of salt in your diet because sodium can raise blood pressure, sometimes dramatically. But for people with low blood pressure, that can be a good thing. Still, it's not quite as simple as dousing your salads with salt, Because excess sodium can lead to heart failure, especially in older adults, it's important to check with your doctor before upping your salt intake.
- Increased water. Although nearly everyone can benefit from drinking more water, this is especially true of people with low blood pressure. Fluids increase blood volume and help prevent dehydration, both of which are important in treating hypotension.
- Compression stockings. The same elastic stockings and leotards commonly used to relieve the pain, swelling, and blood stagnation of varicose veins may help reduce the pooling of blood in your legs.
- Medications. Doctors have used the drug to raise blood pressure levels in people.