Blood pressure is the force of blood against the walls of arteries. This pressure is known as systolic (when the heart beats) and diastolic pressure (when the heart is at rest).

It's measured in millimeters of mercury (mm Hg). The measurement is written with the systolic number on top and the diastolic number on the bottom i.e. for example a systolic blood pressure of 120 and a diastolic blood pressure of 80 is written as 120/80 mm Hg (millimeters of mercury) and is expressed verbally as "120 over 80".

High blood pressure increases your risk of coronary heart disease (that may lead to a heart attack) and strokes. High blood pressure (or hypertension) is defined in an adult as a blood pressure greater than or equal to 140 mm Hg systolic pressure or greater than or equal to 90 mm Hg diastolic pressure.


High blood pressure can occur in both adults and children. However adults over the age of 35 years are more likely to have this condition. High blood pressure is more common in middle aged and elderly people, especially those who are overweight, or drink heavily.

Women who take oral contraceptive pills are also more likely to have high blood pressure. Similarly people with diabetes mellitus or kidney disease are more prone to hypertension.

Why does blood pressure become high?

Many people have high blood pressure for years without knowing it, since there are no symptoms of high blood pressure. When high blood pressure is left uncontrolled, it can lead to severe problems like a stroke, heart attack, heart failure or kidney failure. The only way you know if your blood pressure is under control is to have it regularly checked.

In most cases the cause of hypertension is not known. High blood pressure usually is incurable, however, in most cases it can be easily controlled, helping to prevent strokes, heart attacks etc.
How high blood pressure affects your body?
High blood pressure affects different parts of the body in different ways.

• Brain: The most important risk factor for stroke is Hypertension. A very high level of blood pressure can break a weakened blood vessel. This broken vessel then bleeds in the brain causing a stroke. On the other hand if a blood clot blocks a narrowed artery (narrowed due to high blood pressure), it can also cause a stroke.

• Arteries: Arteries especially those in the heart, brain, and kidneys get hard, with the passage of time as people get older. High blood pressure is associated with these "stiffer" arteries. This, in turn, means the heart and kidneys must work harder.

• Kidneys: The function of the kidneys is to filter and rid the body of waste. Over a period of time, high blood pressure narrows and thickens the blood vessels in the kidneys. This makes it more difficult for the kidneys to filter fluid, and so a build-up of waste products in the blood may occur. This may in rare cases cause kidney failure.

• Heart: High blood pressure is one of the major risk factors for a heart attack. The arteries on the outside of the heart bring oxygen-carrying blood to the heart muscle. If the heart cannot get enough oxygen, chest pain can occur. If the flow of blood is blocked, a heart attack results. In a heart attack a small area of the muscle in the heart dies due to lack of oxygen.

• Eyes: High blood pressure can eventually cause blood vessels in the eye to burst or bleed. Vision may become blurred and eventually this can result in blindness.

Written by Medpages Editorial Team
Last Editorial Review: 25/1/2010