Low Blood Pressure — the Unknown Threat?

Low blood pressure gets much less attention than high blood pressure, and for good reason: for most people it is harmless, and a naturally low reading even goes with a lower risk of heart attack and stroke. But in some situations a low or falling blood pressure is a real problem, especially sudden drops, low readings in older adults and low blood pressure that causes falls.

Usually not a disease

Many healthy people, often young, slim women and athletes, have readings around 100/60 or even lower all their lives. If you feel well, this is not a condition that needs treatment. Attitudes differ between countries: in some parts of Europe, "low blood pressure" is commonly diagnosed and treated, while doctors in the US and UK generally see it as a problem only when it causes symptoms. The evidence supports the second view.

A systolic value below 90 or a diastolic value below 60 is called hypotension; below 80 or 50 it is clearly low, and below 70 or 40 very low — see how low is too low. For causes and everyday tips, see low blood pressure (hypotension).

When low blood pressure becomes a threat

Sudden drops

A sudden fall in blood pressure, compared with your usual values, is more worrying than a constantly low reading. It can be caused by blood loss (including hidden bleeding in the stomach or bowel), severe dehydration, a serious infection (sepsis), a severe allergic reaction, a heart attack or a heart rhythm problem.

Orthostatic hypotension

This is a drop of at least 20 mmHg systolic or 10 mmHg diastolic within three minutes of standing up. It causes dizziness, blurred vision or fainting when getting up. It becomes more common with age and is often caused by medications (blood pressure drugs, diuretics, some antidepressants and prostate medicines), dehydration, diabetes with nerve damage or Parkinson's disease. People with high blood pressure can have it too: their blood pressure is high when sitting but drops on standing.

Falls in older adults

In older people, dizziness from a drop in blood pressure is an important cause of falls, fractures and loss of independence. If an older person falls or nearly faints, blood pressure should be measured lying down and after standing, and medications reviewed. Sometimes blood pressure treatment needs to be reduced; this should always be done by the doctor, not by stopping tablets.

Postprandial hypotension

Some people, mainly older adults and those with Parkinson's disease or diabetes, experience a significant drop in blood pressure within about two hours after eating, as blood flows to the gut. It can cause dizziness, falls and fainting after meals. Helpful measures:

• eat smaller, more frequent meals
• limit fast-acting carbohydrates such as white bread, sweets and sugary drinks
• drink a glass of water before eating
• avoid alcohol with meals
• sit or lie down for a while after eating rather than walking right away

Fainting with warning signs

Fainting during exercise, fainting while lying down, fainting with palpitations or chest pain, or fainting in someone with heart disease can point to a heart problem and needs prompt medical assessment.

What to do

• If you have low readings and feel well: no action needed.
• If you get dizzy on standing: get up slowly, drink enough fluid and talk to your doctor.
• If you take blood pressure medication and feel faint: measure your blood pressure and contact your doctor; do not stop the medication on your own.
• If you notice a sudden drop or new symptoms: see a doctor promptly, or call for emergency help if there are signs of shock.

To get reliable values, see measuring blood pressure correctly. For the healthy range, see ideal blood pressure.