What Causes High Blood Pressure?

In 90 to 95 percent of people with high blood pressure, doctors do not know what causes it. High blood pressure with an unknown cause is called essential, or primary, hypertension.

Sometimes, an underlying disease or other condition is found to be the cause of the high blood pressure. This type, called secondary hypertension, only occurs in 5 to 10 percent of people with hypertension.

• High blood pressure with no known cause (essential hypertension)

• High blood pressure for which there is a cause (secondary hypertension)

• Potential causes of high blood pressure

High Blood Pressure With No Known Cause (Essential Hypertension)

Essential hypertension is the term used when no cause can be found for the high blood pressure. Most people with high blood pressure have essential hypertension.

Researchers do know that essential hypertension tends to cluster in families, so heredity is thought to play a strong role. For example, siblings of people with high blood pressure are more likely to have high blood pressure than the general population. Essential hypertension is more common in some racial and ethnic groups, which also suggests a genetic basis.

Family members may also share environment and lifestyle habits associated with an increased risk of essential hypertension.

High Blood Pressure For Which There Is A Cause (Secondary Hypertension)

While most people with high blood pressure cannot attribute it to a specific cause, the other 5 to 10 percent of people with high blood pressure have an underlying condition that causes it.

In a few cases, high blood pressure can be attributed to a specific cause. This form of high blood pressure is called secondary hypertension, because it is secondary to something else.

In these people, treating the underlying cause can often control the high blood pressure.

Causes of secondary hypertension include:

• Renal (kidney) disorders, such as:
  • Renal vascular disease - A disease involving the kidneys' blood vessels

  • Renal parenchymal disease - A variety of diseases involving kidney tissue

• Endocrine disorders, such as:
  • Hyperaldosteronism - A clinical syndrome caused by excessive secretion of aldosterone, a hormone that influences body sodium and potassium levels

  • Cushing's syndrome - A group of symptoms caused by high levels of the steroid hormone cortisol.

  • Adrenal gland tumors

  • Hyperthyroidism - A condition encompassing several specific diseases of the thyroid gland in which secretion of thyroid hormone is unusually increased.

    For further information about hyperthyroidism, see Hyperthyroidism.

  • Hyperparathyroidism - A condition caused by excessive secretion of parathyroid hormone, due to disease of the parathyroid glands or chronic low serum calcium levels. This hormone plays a most important role in controlling calcium levels in the body.

• Neurological conditions, such as:
  • Increased pressure inside the space within the skull occupied by the brain

  • Lead poisoning - A sudden or ongoing intoxication with lead or its salts, which may cause stomach upset, constipation, abdominal pain, and/or neurological problems

  • Quadriplegia - The paralysis or loss of voluntary movement of all four limbs

• Drugs and chemicals, including:
  • Oral contraceptives (birth control pills)

  • Corticosteroids

  • Appetite suppressants

  • Antidepressants

  • Nonsteroidal anti-inflammatory agents (such as Advil or Motrin)

  • Nasal decongestants

  • Cocaine

• Miscellaneous causes, including:
  • Pregnancy - Hypertension can develop during pregnancy. If the high blood pressure is sudden and severe, the condition is called pre-eclampsia and can endanger both mother and child.

  • Coarctation of the aorta - Constriction or narrowing of the aorta, the large artery arising from the base of the left ventricle

  • Excessive licorice consumption - Licorice contains substances known to raise blood pressure, although the exact amount a person would have to consume to have an effect on blood pressure is not fully researched.

Potential Causes Of High Blood Pressure

Researchers are studying conditions that may cause hypertension. The list of potential causes includes:

• Genetic abnormalities of the renin-angiotensin-aldosterone system - Researchers are studying genes that control a group of hormones called the renin-angiotensin-aldosterone system (RAAS). The RAAS is a critical player in blood pressure control. It regulates blood volume, blood vessel contraction, sodium and water balance, and the development of cells in the heart.

  Abnormalities of this system, which can be genetic, may lead to hypertension by causing an increase in:

  • Blood volume (by causing the kidneys to retain too much water and sodium), and/or

  • Peripheral resistance (by causing blood vessels to narrow)

• Genetic abnormalities of the "fight or flight" system, called the sympathetic nervous system - Excessive activity of the sympathetic nervous system can increase blood pressure by increasing heart rate, the force of the heart's contractions, and/or resistance to blood flow.

• Insulin resistance - Insulin is a hormone secreted by the pancreas that acts as the "key" that allows sugar and other nutrients to move from the blood into cells. Insulin resistance refers to a state in which cells are resistant to the effects of insulin. Insulin resistance in skeletal muscle cells causes them to take up less sugar from the blood, leading to high blood sugar levels and eventually, type 2 diabetes, which is linked to high blood pressure.

• Sodium retention in the urine - Usually, the kidneys respond to high blood pressure by excreting sodium in the urine. If this normal mechanism of regulating blood pressure is lost, persistent hypertension can result.

• Resetting of baroreceptors - Large blood vessels contain pressure detectors called baroreceptors, which signal the brain when blood pressure gets too high or too low. These baroreceptors may be "reset" so that higher blood pressures are required before the body recognizes increased blood pressure and acts to lower it.

• Arterial stiffening - Stiffening of the large arteries has been associated with all forms of hypertension. As a blood vessel loses its ability to stretch and to hold fluid, blood pressure increases.

• Blood vessel thickening - Stress, hormones, and genetic defects that cause smooth muscle cells in the walls of smaller arteries to constrict or grow are also being studied. These factors can cause smooth muscle cells in the arteries to increase in size and number, leading to thicker vessel walls and narrowing vessels.

• Deficiencies in vasodilators - A variety of substances in the body cause vessels to dilate, making it easier for blood to flow and reducing blood pressure. Deficiencies in some of these substances have been linked to hypertension.