Given that people with high blood pressure (hypertension) are far more likely than others to die prematurely of heart disease and stroke, you might think that low blood pressure would be a good thing. However, abnormally low blood pressure, also called hypotension, can cause problems as well.

At the most basic level, hypotension can cause dizziness or blurry vision, which may increase the risk of falling or contribute to accidents. In more serious cases, it reduces the blood flow to the brain and other vital organs. This decreases the amount of oxygen and nutrients being delivered to these organs and impairs their ability to carry out normal functions. Hypotension may also indicate a more serious underlying health condition.

As blood travels throughout your body, it presses against the walls of your blood vessels, just like water in a hose or air in a tire. This is called blood pressure. When your heart beats (contracts), squeezing blood out and pumping it into your arteries, blood pressure peaks. This is called your systolic pressure. Between heartbeats, when your heart relaxes and blood flows back into it, your blood pressure is lower. This is your diastolic pressure.

A blood pressure reading measures these two pressures and expresses them as two numbers, your systolic pressure over your diastolic pressure. Normal blood pressure for adults is lower than 120/80 mm Hg (mm Hg means "millimetres of mercury," referring to a pressure-measuring device similar to a thermometer).

Blood pressure changes throughout the day and varies from person to person. Various factors affect blood pressure, including your body position, breathing rhythm, stress level, physical activity, medications, what you eat or drink, and the time of the day (blood pressure is usually lowest at night when you sleep and rises when you wake up). In healthy individuals, your body responds and adapts to these changes to keep your blood pressure within a normal range. This ensures that vital organs, such as your brain and kidneys, receive a constant blood flow and nutrient supply.

When the systolic pressure drops below 90 mm Hg and the diastolic pressure falls below 60 mm Hg, this is categorized as low blood pressure. Some people may have low pressure all the time and this may be normal for them. If they do not experience any other signs or symptoms, medical treatment may not be necessary for them. Low blood pressure becomes a concern when it is accompanied by noticeable symptoms, such as dizziness, fainting and, in severe cases, shock. When this occurs, people should seek medical attention to determine if an underlying condition may be responsible for their hypotension.

Hypotension occurs when the body is unable to maintain blood pressure within a healthy range. Hypotension can be caused by a variety of factors and can affect people of all ages. However, there are certain types of hypotension that are more likely to affect certain age groups than others.

Orthostatic hypotension occurs when there is a sudden drop in blood pressure when a person stands up from a sitting or lying down position. This more commonly affects older adults.

Neurally mediated hypotension (NMH) results when a person has been standing for a long period of time or after having an unpleasant or upsetting experience. This is commonly referred to as fainting. Young children are more likely than adults to experience this form of hypotension, and will often outgrow NMH or a tendency to faint easily.

Low blood pressure can occur for some people after eating. This is called postprandial hypotension.

Other factors may cause low blood pressure:

• dehydration: When the body fluids are being lost at a rate faster than they can be replaced, a person's blood pressure may fall. Dehydration may be caused by vomiting, fever, severe diarrhea, or strenuous exercise.
• certain medical conditions:
• thyroid disorders
• Addison's disease
• hypoglycemia (low blood sugar levels)
• heart problems (e.g., heart attack, heart failure, valvular heart disease, a very low heart rate, an abnormal heart rhythm)
• nervous system disorders (e.g., Parkinson's disease) – may affect the communication between your brain and the rhythmic pumping of your heart
• vitamin B12 deficiency, or anemia
• medications: Certain medications used to treat high blood pressure, angina, Parkinson's disease, or depression increase the risk of developing hypotension.
• pregnancy: A woman's circulatory system changes while she is pregnant. Blood vessels expand slightly, decreasing blood pressure. These changes usually go away after delivery.
• shock: The most severe form of hypotension is shock. This occurs when blood pressure drops to dangerously low levels, seriously impairing adequate blood flow to vital organs, such as the brain and kidneys. Shock can be caused by major blood loss (e.g., caused by external or internal bleeding), severe infections, burns, or allergic reactions.

In certain instances, people may experience low blood pressure but otherwise feel fine. Hypotension becomes a concern when it is accompanied by one or more of the following symptoms:

• blurry vision
• cold, clammy, pale skin
• confusion
• dizziness
• fainting
• fast breathing
• fatigue
• inability to concentrate
• lightheadedness
• nausea
• rapid heartbeat
• sleepiness
• weakness

In the case of shock, a person may at first experience any of the above signs or symptoms. If you notice signs of shock, such as cold and clammy skin, very rapid breathing, a bluish skin tone, or a weak and rapid pulse in yourself or someone else, call 9-1-1. Without immediate medical attention, a person may become unconscious.

Low blood pressure is diagnosed by a doctor when they check your blood pressure with a sphygmomanometer. For people who experience low blood pressure without other symptoms, it may only require regular monitoring by a doctor during routine exams, and medical treatment may not be necessary. If certain signs suggest an underlying condition, your doctor may recommend one or more of the following tests to diagnose a cause for your hypotension:

• blood tests – will provide information about a person's overall health
• electrocardiogram (ECG) – measures the heart's electrical activity and helps to identify potential problems affecting blood supply and oxygen delivery to the heart
• echocardiogram – provides information about the size, shape, and functioning of the heart
• stress test – examines your heart's ability to function when it is stressed by physical exercise or with medication that simulates the effect of exercise on the heart
• tilt table test – usually recommended if your doctor suspects you might have orthostatic hypotension or NMH (During this diagnostic test, a person lies on a table and then the table is tilted to raise the upper part of their body. This simulates the change in position from sitting or lying down to standing up. People with orthostatic hypotension or NMH may feel dizzy, lightheaded, or even faint when their position changes.)
• endocrine test – measures the levels of hormones in the blood to examine how an endocrine gland is functioning. This test will help your doctor identify if your hypotension is caused by endocrine problems, such as diabetes, thyroid disease, or Addison’s disease.

Depending on the cause(s) for your low blood pressure, certain lifestyle modifications or medications might help prevent and reduce your symptoms. If there is an underlying medical condition, managing the medical condition will resolve the low blood pressure.

There are a few lifestyle changes that can help with low blood pressure:

• Drink 6 to 8 glasses of water each day, unless you've been advised to limit your fluid intake. Limit your alcohol intake. Even in moderation, alcohol can cause dehydration.
• Avoid taking very hot baths or showers.
• Wear compression stockings to prevent blood from pooling in your lower limbs and help improve blood flow throughout your body.
• Change body positions slowly. Take your time when standing up.
• Increasing your salt intake can help with low blood pressure. But excessive salt intake can lead to an unhealthy increase in blood pressure. These dietary changes should only be made if recommended by your doctor.
• Your doctor may recommend changes to your medications if they are the cause for your hypotension. Fludrocortisone* and midodrine are two medications that your doctor may prescribe in special circumstances to help control low blood pressure.
• In the case of shock, seek emergency medical treatment immediately. Shock is life-threatening and needs to be treated by medical personnel.