What is hypertension (high blood pressure)?
Blood pressure is the force exerted by the blood against the walls of blood vessels, and the magnitude of this force depends on the cardiac output and the resistance of the blood vessels.
The blood flowing inside vessels exerts a force against the walls – this is blood pressure.
More information on the biology and physics of normal blood pressure is available, along with details of how blood pressure is measured, what normal measurements look like, and how they change with age and exercise.
Hypertension is defined as having a blood pressure higher than 140 over 90 mmHg, with a consensus across medical guidelines.1,5
This means the systolic reading (the pressure as the heart pumps blood around the body) is over 140 mmHg (millimeters of mercury) and/or the diastolic reading (as the heart relaxes and refills with blood) is over 90 mmHg.
This threshold has been set to define hypertension for clinical convenience as patients experience benefits once they bring their blood pressure below this level.6
However, medical experts consider high blood pressure as having a continuous relationship to cardiovascular health.1,6They believe that, to a point, the lower the blood pressure the better (down to levels of 115-110 mmHg systolic, and 75-70 mmHg diastolic).1
They believe that, to a point (down to levels of 115-110 mmHg systolic, and 75-70 mmHg diastolic) the lower the blood pressure the better.1
This view has led the American Heart Association (AHA), for example, to define the following ranges of blood pressure (in mmHg):
- Normal blood pressure is below 120 systolic and below 80 diastolic
- Prehypertension is 120-139 systolic or 80-89 diastolic
- Stage 1 high blood pressure (hypertension) is 140-159 systolic or 90-99 diastolic
- Stage 2 high blood pressure (hypertension) is 160 or higher systolic or 100 or higher diastolic
- Hypertensive crisis (a medical emergency) is when blood pressure is above 180 systolic or above 110 diastolic.
Causes of hypertension
As acute stress, intense exercise and other factors can briefly elevate blood pressure even in people whose blood pressure is normal, a diagnosis of hypertension requires several readings showing high blood pressure over time. 7
Having high blood pressure for a short amount of time is a normal physiological response to many situations. However, a systolic reading of 180 mmHg or higher OR a diastolic reading of 110 mmHG or higher could be a sign of a hypertensive crisis that warrants immediate medical attention.
Anyone who gets such a reading when testing their own blood pressure should wait a couple of minutes and repeat the test. If the reading remains at that level or increases, seek emergency medical treatment (call an ambulance or have someone drive you to the hospital immediately.
Blood pressure does vary throughout the day, lowering during sleep and rising on awakening. It also rises in response to excitement, anxiety and physical activity.7
Blood pressure also increases steadily with age as arteries become stiffer and narrower due to plaque build-up. Vascular and heart disease also contribute to rising blood pressure in older adults, and a high systolic reading is a major risk factor for cardiovascular disease in adults over 50 years old.
The disease burden of high blood pressure is a growing problem worldwide, in part because of a rapidly aging population. Other key contributors include lifestyle factors, such as:1
- Physical inactivity
- A salt-rich diet associated with processed and fatty foods
- Alcohol and tobacco use.
Certain diseases and medications (as described below) can cause high blood pressure, and there are a number of general risk factors for hypertension, including:7
Obesity is a risk factor for high blood pressure and other cardiovascular conditions.
- Age – everyone is at greater risk of high blood pressure as they get older. Prevalence of hypertension is higher in people over 60 years of age
- Race – African-American adults are at higher risk than white or Hispanic American adults
- Size – being overweight or obese is a key risk factor for hypertension
- Sex – males and females have different risk profiles. While lifetime risk is the same for everybody, men are more prone to hypertension at a younger age and women have a higher rate of hypertension at older ages
- Lifestyle – greater intake of dietary salt, excessive alcohol, low dietary potassium, and physical inactivity all contribute to an increased risk of hypertension.