About 90% to 95% of hypertension cases, called primary, or essential hypertension, have no known cause.
Primary hypertension may be influenced by factors such as genetic makeup, weight, or salt intake. Research is underway to learn more about the role that genes play in hypertension, as well as to explore the association between hypertension and factors such as obesity, low birth weight, and low levels of nitric oxide.
Nitric oxide is a molecule that affects the smooth muscle cells that line blood vessels. People with low levels of nitric oxide have been found to have high blood pressure; especially African-Americans with low levels of the molecule.
The term "secondary hypertension" refers to high blood pressure with recognizable causes, which are usually treatable or reversible.
Medical conditions
A number of medical conditions can cause secondary hypertension:
Kidney disease -- the kidneys control how much fluid and sodium are retained in the body and how much are excreted in the urine. Damage to the kidneys, therefore, can upset the balance of fluid and sodium -- which can lead to high blood pressure. Kidney disease is the number one cause of secondary hypertension, particularly in older people.
Sleep apnea -- this is a disorder in which breathing halts briefly but repeatedly during sleep. Most people with sleep apnea snore and many are overweight (excess body fat puts an extra burden on the airways). Even mild sleep apnea is associated with high blood pressure, whether overweight or not. Sleeping with a device known as nasal continuous positive airway pressure is the treatment for this condition. As the sleep apnea improves, blood pressure tends to improve as well.
There are also several disorders of the adrenal glands that can cause high blood pressure. The adrenal glands are two small organs that sit above the kidneys and produce several important hormones.
Hyperaldosteronism -- this condition results in excessive amounts of aldosterone, a hormone that helps balance fluid and sodium in the body. It can occur from enlargement of both adrenal glands or a tumor in one of the adrenal glands.
Cushing syndrome -- this is caused by excessive amounts of a steroid hormone called cortisol, produced in the cortex of the adrenal glands. This can be caused by a tumor in the adrenal glands, a tumor in the pituitary gland in the brain, or a cortisol-secreting tumor anywhere else in the body (ectopic Cushing syndrome).
Pheochromocytoma -- in this condition, the adrenal glands produce too much of the hormones that control heart rate and constriction in blood vessels (including the hormone adrenalin). This raises blood pressure. The condition is caused by a tumor in the adrenal medulla -- the center portion of the adrenal gland.
Medications
Certain prescription and over-the-counter drugs can cause temporary high blood pressure, such as:
Corticosteroids -- such as prednisone and prednisolone; long-term use can lead to Cushing syndrome.
Nonsteroidal anti-inflammatory drugs (NSAIDs) -- long-term use may injure the kidney and is an important cause of secondary hypertension in the elderly. Such drugs include ibuprofen (Advil, Motrin), naproxen (Anaprox, Naprosyn, Aleve), and many others.
Cold medicines -- those containing pseudoephedrine increase blood pressure in people with high blood pressure, although they appear to pose no danger for those with normal blood pressure.
Birth control pills -- increase the risk for high blood pressure, particularly in women who are over 35, overweight, smokers, or some combination. Stopping birth control pills nearly always reduces blood pressure within 6 months.
Alcohol, coffee, and cigarettes
Alcohol -- An estimated 10% of high blood pressure cases are caused by alcohol abuse (i.e., three alcoholic drinks a day or more, with heavier drinkers having higher pressure). In one study, binge-drinkers had even higher blood pressure than people who drank regularly. Moderate drinking (one or two drinks a day) may have benefits for the heart and may even protect against some types of stroke. Specifically, red wine may benefit blood pressure. (Red grape juice may have the same advantages.) Despite these benefits, it is critical for people who can't drink moderately to abstain from alcohol.
Smoking -- Smoking is a major contributor to high blood pressure.
Caffeine -- Caffeine causes a temporary increase in blood pressure, which is considered harmless in people with normal blood pressure. However, a high intake of coffee may be harmful in people with high blood pressure. Coffee also increases the body's elimination of calcium, which may negatively affect blood pressure. (Anyone who drinks coffee should maintain an adequate calcium intake.)
Other causes
Temporary high blood pressure can result from a number of other conditions or substances, including:
Stress
Intense workouts (such as snow shoveling, jogging, speed walking, tennis, heavy lifting, heavy gardening)
In adults, exposure to low levels of lead (more studies are needed)
Long-term consumption of large amounts of the herb licorice
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