Why is high blood pressure harmful?

Elevated blood pressure indicates that the heart is working harder than normal, putting both the heart and the arteries under a greater strain. This may contribute to heart attacks, strokes, kidney failure, damage to the eyes and atherosclerosis. If high blood pressure isn't treated, the heart may have to work progressively harder to pump enough blood and oxygen to the body's organs and tissues to meet their needs.

When the heart is forced to work harder than normal for an extended time, it tends to enlarge. A slightly enlarged heart may function well, but one that's significantly enlarged has a hard time meeting the demands put on it.

Arteries and arterioles also suffer the effects of elevated blood pressure. Over time they become scarred, hardened and less elastic. This may occur as people age, but elevated blood pressure speeds this process, probably because hypertension accelerates atherosclerosis.

Arterial damage is bad because hardened or narrowed arteries may be unable to supply the amount of blood the body's organs need. And if the body's organs don't get enough oxygen and nutrients, they can't function properly. There's also the risk that a blood clot may lodge in an artery narrowed by atherosclerosis, depriving part of the body of its normal blood supply. The heart, brain and kidneys are particularly susceptible to damage by high blood pressure.

What causes high blood pressure?

In 90-95 percent of the cases of high blood pressure, the cause is unknown. This type of high blood pressure is called essential hypertension. Fortunately, even though scientists don't fully understand the causes of high blood pressure, they have developed drugs that are effective over the long term in treating this disease.

In the remaining cases, high blood pressure is a symptom of a recognizable underlying problem such as a kidney abnormality, tumor of the adrenal gland or congenital defect of the aorta. When the root cause is corrected, blood pressure usually returns to normal. This type of high blood pressure is called secondary hypertension.