Overview
Low blood pressure might seem desirable, and for some people, it causes no problems. However, for many people, abnormally low blood pressure (hypotension) can cause dizziness and fainting. In severe cases, low blood pressure can be life-threatening.
A blood pressure reading lower than 90 millimeters of mercury (mm Hg) for the top number (systolic) or 60 mm Hg for the bottom number (diastolic) is generally considered low blood pressure.
The causes of low blood pressure can range from dehydration to serious medical or surgical disorders. It's important to find out what's causing your low blood pressure so that it can be treated.
Symptoms
For some people, low blood pressure signals an underlying problem, especially when it drops suddenly or is accompanied by signs and symptoms such as:
- Dizziness or lightheadedness
- Fainting (syncope)
- Blurred vision
- Nausea
- Fatigue
- Lack of concentration
Causes
Blood pressure is a measurement of the pressure in your arteries during the active and resting phases of each heartbeat.
- Systolic pressure. The top number in a blood pressure reading is the amount of pressure your heart generates when pumping blood through your arteries to the rest of your body.
- Diastolic pressure. The bottom number in a blood pressure reading refers to the amount of pressure in your arteries when your heart is at rest between beats.
Current guidelines identify normal blood pressure as lower than 120/80 mm Hg
Conditions that can cause low blood pressure
- Pregnancy. Because the circulatory system expands rapidly during pregnancy, blood pressure is likely to drop. This is normal, and blood pressure usually returns to your pre-pregnancy level after you've given birth.
- Heart problems. Some heart conditions that can lead to low blood pressure include extremely low heart rate (bradycardia), heart valve problems, heart attack and heart failure.
- Endocrine problems. Thyroid conditions such as parathyroid disease, adrenal insufficiency (Addison's disease), low blood sugar (hypoglycemia) and, in some cases, diabetes can trigger low blood pressure.
- Dehydration. When your body loses more water than it takes in, it can cause weakness, dizziness and fatigue. Fever, vomiting, severe diarrhea, overuse of diuretics and strenuous exercise can lead to dehydration.
- Blood loss. Losing a lot of blood, such as from a major injury or internal bleeding, reduces the amount of blood in your body, leading to a severe drop in blood pressure.
- Severe infection (septicemia). When an infection in the body enters the bloodstream, it can lead to a life-threatening drop in blood pressure called septic shock.
- Severe allergic reaction (anaphylaxis). Common triggers of this severe and potentially life-threatening reaction include foods, certain medications, insect venoms and latex. Anaphylaxis can cause breathing problems, hives, itching, a swollen throat and a dangerous drop in blood pressure.
- Lack of nutrients in your diet. A lack of the vitamins B-12 and folate can keep your body from producing enough red blood cells (anemia), causing low blood pressure.
Types of low blood pressure
- Low blood pressure on standing up (orthostatic, or postural, hypotension). This is a sudden drop in blood pressure when you stand up from a sitting position or after lying down.
- Low blood pressure after eating (postprandial hypotension). This sudden drop in blood pressure after eating affects mostly older adults.
- Low blood pressure from faulty brain signals (neurally mediated hypotension). This disorder, which causes a blood pressure drop after standing for long periods, mostly affects young adults and children. It seems to occur because of a miscommunication between the heart and the brain.
- Low blood pressure due to nervous system damage (multiple system atrophy with orthostatic hypotension). Also called Shy-Drager syndrome, this rare disorder causes progressive damage to the autonomic nervous system, which controls involuntary functions such as blood pressure, heart rate, breathing and digestion. It's associated with having very high blood pressure while lying down.
when to sea a doctor
If you have indications of shock, seek emergency medical help.
If you have consistently low blood pressure readings but feel fine, your doctor is likely just to monitor you during routine exams.
Even occasional dizziness or lightheadedness may be a relatively minor problem — the result of mild dehydration from too much time in the sun or a hot tub, for example. Still, it's important to see your doctor if you have signs or symptoms of hypotension because they can point to more-serious problems. It can be helpful to keep a record of your symptoms, when they occur and what you're doing at the time.